horizontal oil well drilling technology
TRANSCRIPT
Suer, Canal UniversitltFaculty of Petroletm & Mining Eng.
P etro leum Engineering D ept.
HonrzoNTAL OnWprrDTIuNG TBcmxoLoGY
Dr. Mohamed Shehata Farahat
(2000)
Suen Canal University
Faculty of Petroleum & Mining Eng.
Petroleurn Engineering Dept.
HOruZONTTAL On WpLLDTLLII{G TpcHNoLoGY
Dr. Mohamed Shehata Farahat
(2000)
CoNrsNrs
SELECTIoN AND REAsoNs FoRDRILLINGHORIZONTAL WELLST AND DRATNHOLES
l.l Seleclion of horizontal wells and drainholes
1.2 Reasons for Drilling Horizontal Well and Drainholes
1.3 Main Aoolications of Hoizontal llells and Drainholes1,3.1 Thin Formatious1.3.2. Verticsl Natumlly Fractured Fornrations1,3.3 Lotv Perm eability Formations1.3.4 Heterogeneous Reservob or Formstions1.3.5 Applicttion in Resemoits rriflt Botton Water or
with o Gas Cap1,3.6 Advantages of Horizontal lVells in Offshore
Applications1.3.7 Heavy Oil Applications1.3.8 Sand Production
Typns oF HoRTzoNTAL WELLS ANDD r proRnnt Dnrr,r,rNc TncnNrquns
Usno
2.1 Utru-shott Turnins Radius2.1.1 System Processes a,td Equipment for Multiplc
Radisk
2.2 Short Tarnins Radius
2. 3 Medium-Turning Radias
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2.i.1 Dil!fins rttt Mulinn-Rutlius Dtilling2.3.2 Metliunt-Rsdius Dri!!iug MoJors an{ SlsteuLs-2.3,3 HigbMedium and Lott-Soeed Drilling2. 3.4 Medium-Radius-Ho rizo trtttl lltell S ectio ns
2.3,4. I Vertical Section2.3.4.2 Curved Sectiau2.3.4,2 Horizoutsl Section
2.4 Lottg-Radius Horizontgl lyell2.4,1 Vertical Section2.4.2 Cumed (Turning) Section2.4.3 H orizoutal Section
Pt,nNNtNc or lloRrzoNTAL WnLl,sAND DRAINHOI,ES G NOUNTRY
j. Geontetrv of Horizontsl WelI or Drainhole3.1 lf ell Diameter3'2 VplLltpllle
3.2.1 Fktt wells3. 2.2 I) n tlulatiug wells
3.2,j Llpt'ard inclined uells3.2.4 Dou,nward ittclined wells3.2.5 Multilet el t'ells3.2.6 Multi brtuch3.2.7 Grsvit! drsinage wells3.2.8 Complex well shryes
3. 3 D esistlEqip ntal-lysll f&i949!!
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Dmrlrxcl PRosr-svs Assocnrso wttHHoRtzoNteL
WBU- DzuLLING aNo THBTRREMEDY
4.1 DeliNery Weisht to the Bit
4.2 Reducing Torque and Drsg Forces
a3 Epls_ekutus ale ftliag;4e
4.4 Protectian of lyater Sensilive Shales
4. 5 Direclional Control4,5.I C lassifrcation of hotto,n-4.5.2 Measurfug it'.slrune ls4,5,2,1 Steering tool4. 5, 2, 2 M essurcntent-while tuillittg (Mll/D)4.5.2.3 Geosteering, Equipnrcnt and Irrstrume tfltiort
DRILLSTRING DESIGN 72
HonrzoNrat, WELL ConrplnrroNTncnNreuns
6.1 Comoletion Technolosict :fu-U!X4:[!!!41-LglL!sH o rizontal Radial B ore lrc le
6.2 Conpletion Oltion for Short-Rtttlius, Mediam-Radius,ond l-ong-Radius of Horizotrtsl ly'elk Draiflholg;-
6.2,1 Open hole cotn elion
54
57
58
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606l6l626268
89
94
IIIIjiII
| l l
95
Poge #6.2.2 Tail completion and slotted liner completiott 95
AppucarIoNoF COILED TueINc TNHoRIZoNTAL DRILLING
AND MULTI-LATERAT, CASB STUOII]S ANDHlsroRms
7.1 Coiled Tubins Drilli,tg
7. 2 M&LUels I Ci?,ts]J:t lldtet7,2.1 Case 17.2.2 Case 27.2.3 Case 37.2,4 Csse 4
7.3 Multilatersl Case Histot! Case 1
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SELECTION AND REASONS FORDRILLING TIORIZONTAL WELLS.
AND DRAINHOLES
:
1.1 Selection o-f horizofial u,ells arul drainltoles:
l lorizontal wells are ofgrcat intelest to thc petrolcutn indttstry today becattsc
they proviclc an attractivc nrcans for improving both plodtrction ratc and
rccovery efficiency. 'l'hese are due to that horizontal wellsprovide a latger
area of contact witl l t lrc lcscrvoif than do vcttical; wclls ancl, ir l addition, thcy
provide a means for the latetal t lansPodation of f lt l id. Thus, the horizorrtal
wells can be dril led as new u,ells or ho zontal sidctracks, dri l led to revitalrze
ttrc pcrformance of exiting vertical wclls that are callcd drainholes l l lc past
fcw years havc seen great improvement in dri l l ing technology. Dcvelopments
suclr as tlre use of bent, downhole dri l l ing rnotors, top drive l igs, and MWD
(measurcment whilc dLil l ing) or advanccd N4WD callcd gcoslecring tcchnique,
togcther with stccrable drill systcms have grcatly rcduced costs. Recent
horizontal wclls havc cost no mora pcr lnctct ofrvcll t l t i l lcd lhltn conlpatablc
conventional wells. Thus, great advances have also bcen in nlcthods lor
drilJing short-radius drainholes ftom crisling vel1ical wcl1s.
The construction and placing ofhorizontal wells has become rautine Usually
it is no longer speculative as to whether horizontal rvells can be drilled- Tn
most cases no|, the choicc is not whethcr one can dli l l horizontally, but
whethcl on should.
l),-. M.S. Farrhat
CIl- I IIo urtutl lrt s D'lllinA
Grcat advancos in the technology of dri l l ing and locating horizontal wellscontinue to be made. Today much attention is being paid to thc problems ofre-entering existing vertical wells using smaller diameter, mcdium-radius and
short-radius equipment. These improvements will allow a much largerproportion of existing conventional wells to have their live extended by re-completion with long, hofizontal drianholcs. 1 hc provision of M WD tools that
will opemte in smaller diameter holes is a particularly active area. Thorc arcdevelopmcnt, too, in logging tools. Tools arc now available that can beopcrated while dri l l ing to providc irlfornratiotr about lhc rcscrvoir beingencountored. Locating the logging sensors closer to the dril l bit to allow anore timely evaluation of the bit position and o f the rock bcing penctrated isanother area of active dcvclopment.
Thus, drilling a horizortal well to exploit a reservoir usually involves several
important questions. Thcse questions are as lollows:
1. Whcrc should the well be located?2. lr what direction should thc well bc dril lcd?3. Whcrc should thc kick-offpoint (KOI') to horizontll bc?4. IIow long should the horizontal section be?5, ls it neccssary to stirnulatc thc wcll?
The answer of these questions require gathering information about thereservoit and the conditions existing in thc arca. I[o[izontal well should not bedrilled in all cases, cateful study of tcchnicnl feasibility and economicalpotcntial of holizontal dril l ing is needed beforc its application. For theselcasors, accuratc resewoir ard adjust rvcll data should bc collected.
Therefore, the horizontal wells are corsidered feasible primarily in thefollowing areas:
l. Thin permeable formation.2. Vertical naturally-fractured formation.3. Low permeability fomation.4. Formation with sand production.
5. Fomation with water coning.6.FoImation with gas coning.
D,: Nl.S. Frrahrt
AL I ottzo,tk lllrtts Drtltl t! 3
7.Offshore applications.8. t lcavy oi l appl icat ions.9. Fonnation access blowouts.
1.2 Reasons for Drillitts Horizontal Well and Drsinlrcles
' l hclc arc scvcml tcnsorrs lo t l l i l l a l rol izorr lul wcl l nr l l rcr t l r iur a vct l ical wcl l .'l 'hcsc rcasons are:
l. Increasing oil productivity.2. Connecting veltical naturally fractures.3. Producing from low-pe rmeability reser.roits.4. Staying away fi-om oil-gas and oil-water contacts.5. Injecting stream (thcrrral oil rccovery).6. Controlling sand production.7. I'r'oducing thin hydrocarbons reservoirs.8. lncreasing injccl iv i ty.9. l'roducing gas liorn coal scanls and proving bcttcr swccp cfficicncy.l0.lncreasing the retum on the investment (ROl).
Sornctimes, the cost of a drilling a horizontal well is more than that ofavcrt ical wcl l and complet iorr costs arc usual ly h ighcr ' . l lowcvcr, nto lc o i lwould be ultiuratcly rccovered by thc horizontal wcll.
'[hus, horizontal wcll is
justified in view ol'quicker return on well investment.
Horizontal wells and drainhole can be mainly applied for the followingcircumstance or pay zollcs (reservoir-s) chalactcristics, namcly:
l. Thin permeable fornrations.
2. Verlical naturally fractured lonnations.
3. Low pelmeability l'ornrations.
4. Formzrtion with sand production and coning problems.
1,3 Mgitr A licntions of Hori ntal ,Y'ells a,td Drainltoles
Iha izintal llitlk Dj iIIi
1.3.1 Thin Formstions
When consideriirg thjn fonnation for homogeneous fcrnration, it shoulcl avoiddti l l ing a horizontal well into this fonration thickcr than 200 ft. however, t lr ismaximum pay zone thjcloress does not hold tnrc for formatiolls withhelerogeteous fonnation or fotmaljon with verlical naturally fractures, asshown in Figure 1.1and Fig. 1.2.
Thlrr producli lg zonos
Wa le r con lng p rob lems cas con lng .p rob lems '
Other app l l ca( ions : f leavy c rude, con l scams,fo rmal ion access , b lowouts .
Fig. 1.1 A4oin applicotiotts ofhorizottttl trll,r.
INTERSECTION OF VERTICAL FRACTUR€SBY I.JORIZONTAL WELL
Fig. 1.2.
, / . M .S . F r r xh r i
C . I llorizofttdl lYc4s Dtiqi!ry 5
' lhus, the productivity index (PI) for a lroriT-ontal rveilreflects the increases
arca ofcontact ofthc well with the reservoir. 'l'ypically, the Pl for a horizontal
well maybe increased by a factor of4 compared to a vertical well pcnctrating
the same reseloir, although enhancement by a factor of l0 or more may beaclrievable in certain circunrstance, as shown in Figure 1.2.
1.3.2. Vet'tic Natt,trallv Fr'flct.rred Forut ions
A horizontal well provide a means of communicating with natural verticalfractures, e. g., a high fractured l imestone. lfthe well is oriented to intcrcst
thcsc fractures the productivity index can be substantially increascd cvcn rvhcn
thc lrac(ure density is low. Unfottrnatcly, this can also accclcratc thc
movement ofgas or water to reach the wellbore.
l. 3. 3 Low Pernrcabilitv Fornntio tts
One qucstion is often asked by the opcratol tlrat is how low should thcpcrnrcabil i ly be in a horrrogcnous fornration bcforc consi<icring clri l l ing alroriz-ontal wcll?. Gigcr detcrnrincd the anrount ofoil that could bc lno(luccdundcr the same conditions for lrorizontal n'ell and veltical well using tlre same
lromogcncous reservoir for valious rcscrvoir pcrmcabil it ics. Thc tesults ofhis
study are prcsented ln Figuic 1.3. This figulc shows thrt thc honrogcncous
fomration witlr rssetvoi| pcrnrcabil it ics grcatcr than 10 md should not be
considclcd fol a horizorltal wcll conrplction. For I00 nrd thc sanrc oil volume
rvould be produced after about 200 days from either types ofwells. Even
during the first 200 days, thcrc is l i tt lc cliffcrcncc in thc anrount produccd frotn
a horizontal well versus a veflical well because formation is not homogeneous.
However, thc productivity, obtained by dril l ing a holizontal well partially
depends on the magnitude of thc vertical pelmeabil ity and the length ofthe
drainhole. Where the ratio ofvertical permeability to holizontal permeability
is high a horizontal well may prcduce more cost effcctively than a vertical
well.
Dr. M.S. Ih ' r lat
CII. I lln,ito d lITtts Dti i"p
PEBMEN BILITY EFFECT
75lronizoNl t wErtvlnt l :At. wn.t
Irig. I -.1 Penrcdbili0 effcc|.
Heterose Rese ir or Fo,'ntsti
A l r . l i zo r r l , I rvc l l r r r r ry 1 r . .v i r l c r r r r r r r r r l x r , r ' r r r r ' r r r r ( r r11es r ' r rc r r r r .sc r r ' i r .hclcrogencity exisls in thc horizonlal planc. A horizonlal lvcllborc irr lhclescrvoir provides potential for far more information about the reservoir thalrwould nornrally bc availnblc. As logging and conrplclion tcchrrirlucs bccornomore sophisticated, this aspect of horizontal wells is l ikely to be usecladvantage.
Frotn a prodrrction viewpoint, a horizontal well in an irregular rcservoir nrayprovide a mcans ofaccessing isolated productive zoncs which nright other.wiscbe missed. Furthermore, in beterogeneous reservoirs, the influence of thehctclogcneous along thc wcllbolc is r.ctlucccl lry thc cornpositc 0or,v gcon]clry,so thrt production rltcs arc gclrcrl l ly cnhlnccd in lhcsc cit.crrnrs{anccs.
L3.5 Application in Reselyl|I tl'ith BottQn lyqlqor with n Gns Cor2
In nrany cascs,
rosclvoil is thc
lhc tnos l in tpor l ln l l i r c lo r l in r i t ing lhc p loc l r rc t ion o fo i l f ionrtcndcncy lbl rvtrtcl l ionr atr urrclcrlyi lg acluit lr., or- gas l iorl
n
1]r. M.S. l , :rr, 'hxt
Ctl- I lloti. ti l lYdts Dti ing 7
gas cilp, to bc dlawn vcr(ici i l ly to thc prod(rction wcll. l lor.izontal wcllscanhave substantial advantages in such lcsctvoirs. The conventional rvay ofreducing thc effect of coning is to complete the vertical well over a linritcdvcrlicnl distaDce to tnaxinlizc thc stand off front lhc watcr or gas cap, as thccasc may bc.
Because of its extended contact with the reservoir, a lrorizontal wcll usuallyhas lcss pressure drawdown for a givcn production ratc ihan docs a vcrtici l lwcll. This reduced drawdown lessens the tendency fot thc coning ofwater orgas with the produced oil. Thus, for example, horizontal wells may beoperated at ths santc lates as aonventional wells but rvith less-sometimes muchless-coning, i.e., witlr bctter water-oil ratios or gas-oil ratios or both, in somecase, productiol without coniDg nray be economic using horizontal wclls,whcrc it would be plohibitively slow with conventional wells. In situationswhere the jlitial rate for production without fiee gas coning would beimpractical \a,ith vcrtical wells, it may be possible with horizontal wells toaclrieve economic production by gravity drainagc wilh onJy a small ratc ofgasinjcction to maintain gas cap plessure.
Even if oporation below thc critical rate for coning is impractical bccausc ofeconomics, thero can still be a large advantage for horizontal welis. Thissituation is conlmon when viscous, conveutioual heavy oils ale produced lronrabovc a watcr layer. When the high oil viscosity and thelow diffcr.encc intlcnsity between the oil and waler makcs coning, or more concctly fingcrrng,occLu cven at vcty low productiolr ratcs. [n thcse cascs, thc volume ofoi] thnlis produccd is approximatcly proportional to thc volurne swept by thc wateffinger. As is shown in Figure 1.4, horizontal rvells havc an advantage ovcrvcrlical wells here because the figure (really a crest shaped liked the roofofahouse along the length ol-the horizontal well) has a much lar.ger volume andthis lalger crcst displaces a nruch larger volurue ofoil.
Dr. M.S. I : rrahrt
LI1. I Ilotito rl ll'clls Dtilti g
@A CohparLon_or.a $dcr .rre Leto* , v.r cat Udt ent, - (, e.t
treror, s.ciion ora fizontat iveu
VEBTICAL WELL WITIIRISING CONE
HORIZONTAL WELL WI'rHRISING CREST
Fis. 1.4.
1. 3. 6 Atlttantages o.f Horizontnl rySAtjlt O:fit!!!!!,4tU,lk!l!!!j
Many horizontal welis have been drilled from offshore platforms. Such wellsoflct savings in Plalfolrl rursls i l nrkii l ion lo l l t( ' i t{ l! i l l l i t [,r.t i ftr lrrrl orrslrrtr,,Fot example, one operator statcs that the cost ofhis North Sea platforrns isapprox imatc ly $ 6 mi l l ion per . rvc l l s lo t . [ Js ing hor izon la l rvc l l s , lhcsanrcnunrbcr of well slots on a platfonrr can proclucc sincc cach horizonlal wcll isnote productive than each convcntional wcll. I\rr.thcrntorc, since ollbhorewells are nolmally highly dcviatcd in any casc thccxlla cost lbr horizontaldli l l ing can be relatively srralJ.
7,'\
/ ) r ' . l \ { .S. Farrh^t
a:lL t Ilotitotthtt tl'! rDti it|')
Commcrcial ofl 'shore horizontal rvell projects in various alea includingthe
ArI i i l l ic, l lrc Nor th Scn il | |( l ( lrc . l irvn Scas urc tlosclihc(l i l l l l lc l i lclr(lrrc.
1,3.7 IIeu_y Oil Annlicttions
Probably thc most prospective arca for using horizontal wells lies in the field
of heavy oil recovery, particularly thcmral recovery using strcarn. For
exanrplc, tlre bitunren deposits is Canada, which arc intpossiblc to rccover
economically by corlvcntional methods, have a volttnre of oil in placc
approximately equal to that of all the known couvcntional crudc oil tn thcworld. One approaclr uscd to rccovcl thcsc rcsourccs is operr pit nrining.l l o rvcvcr ' , th is i s l i r r r i l c r l k r lhcsnr i r l l l i ac l io r t o f l l l c A t l r i r l ) rsc i t r -csc tvo i r tha t i s
close to the surfacc and thc approaclr involves handling vast qurnti i ics of
natclial. In situ lhclmal lccovcty is trolc gcnclally tp;tl icablc, cltcrtpcr a<l lcss
danragirrg crvirorrntcntally.
lhcrnral rccovcry nortnally lequircs closcwcll spacings. Iypical pr.ojccts lravc
a spacirrg ol '2.5 to 5 acfcs pcr woll and. in mary cascs, thcsc arc Ialtcl in f i l led
lo i r r rp lovc lccovcry . S l tc i t tn l l t x p to jcc ls i r r ( a l i l i r r t r ia w i {h sp i tc i t rgs as low
as 5/8 acfc arc bcing opcratcd. In such oifcunrsta|]ccs, a sirtglc hofizorltt l
wclls. This may bccome otrc ofthc most inrportant applicalions ofhorizontal
wclls. I he succcssful opelations of f icld pilot in Cold [,akc. thc l, loydrninstct'
arca and in Athabasca using horizontal rvclls an<l strcants-assistctl gtavity
drainagc (SAGD) are discusscd in thc l itcralurc. A t)l l l icularly ir lrportarrt
featule of t lrc usc ofhorizontal wclls fol strcanr rccovcry is t lrat it is possible
to operate and obtain high rccovcries with l itt lc strcanl production, i. c., with
litt lc sllcarns bypassing try crcsti l lg. with horizon{ul rvclls, it is possiblc to
prodrce econornictrl ly bclow thc crit ical ratc for strcanr by pass; with vclt ical
wclls, s(r'carr I loo<ling is itrrpractical wilhout thc bypass ofs{rcanr cxccpt on
very loso spaclngs.
1.J.8 Sanl Production
At higlrer drawdown-pressure, sand production is a common problem,
espccialJy the production from uncorrsolidated and firc grained sand. Sand
D/. iV.S. Frrahat
CI. I llo,izont.tl llcls Drillirrs l0
crodes and plugs the equipmcnt and rcstrictiog thc flow rates. Scrccns andgravel placing limit sand entry into thc rvcllborc and in somc cases rcducesproductions rates, less pressure drawdown eliminates the necd for screen andgravcl placing and allorvs higlrcr production ratcs frorlr drainholc or horizontal
wcll.
ti.r. , t
D/ Nl.S. Fxr.hxl
CII. II Dti i'tg Tcchttiques l l
c[AP'ftrR lt
TypES OF HoRIZoNTAL WELLs Ar'ln DlnrnnsNrDRrr,r,rNG TpcuntQu Ps Ussu
The choice of drilling me0thod depends upon drilling cost, well spacing and
the mcchanical condition ofa verlical wellbore is existing Also, the rcsctvoir
consideratiols are also important in sclecting the drilling method. During thc
last decade, the incrcmental cost ofdrilling horizontal wells and drainholes,
over a vcrlical well cost, has come down considerably. But today oil industry
grains tnore experiencc and rtses newcr dri l l ing lechnologics, in tum the cost
of dri l l ing horizontal wclls nray be furthcr reduced. Accorclingly, thc practical
holizontal drilling methods can be classified into four broad categories as
shown in Figure 2.1, depending upon thc turning radius rcquircd to turn fionr a
vertical to a horizontal direction. Also, the use ofa top-clrivc dt.i l l ing sysfenr
(TDS) is essential to the successful implementation ofa horizontal dri l l ing
program fol: deeper wells; larger wellborcs; ouler-rorv wells (olfshore
platforrns); Gumbo or bentonitic hole sectious whcn dril led with water base
mud; whcre simultaneous high torque and tension is requiled to be applicd
dril lstring. A discussion ofvarious dli l l ing methods are given below for caclr
types ofhorizontal well and drainhole.
2.1 Ultra-short Turning Ra irls
Ultra-shor1 turn-radius horizontal lroles, sometinres called drainhole. Inthis
mothod, it uti l ized waterjef to dri l l 100-200 ft long drainholcs with a tulrrirrg
radius of 1 to 2 ft. these arc dri l led in ptcviously cascd often mrrll iplc
horizontal laterals are drilled lrom the same wcllbore, as shown in Iiigure 2.2.
It is repofied that, sidetmcking may be done with a whipslock deviating tool
with a curwed guide. Also, a long slender stcel tubc fits inside the dril lpipe into
the top of the whipstock guide, as shown in Figurc 2.2. Tbe upper end ofthe
tube has a pressurc seal to contain pressule and divert drilling flrrid through
the tube. Thejet nozzle fits on the iower erd ofthc tubc.' l 'hus, dti l l ing rate is
controlled with a letaining cable connccted to tlre top ofthe tubc as shown in
D,: M.S. Fnrahat
CH.ll D lli E T..huiques t2
Figure 2.2. The hole is prepared first by plugging the lowcr required andremoving a scction of casing by nril l ing the section is undcr-reamed toincrease the hole diamctet, i.e. the proccss involt,es urdcr-reaming thc verticalwcllbore and then dril i ing severai radials fionr the under-rearned zone.Howevcr, t lte length of the s€ction and diameter oftl ieunder lcamed holebasccl upon thc specification of deviating tool. A spccial packer is placed inthc casing with a curved guide bclow thc milled section. Ihe whipstocktlcvitt irg tool is conncctcd to thc cl. i l lpipc rntl usscrlbly turr irrlu l lrc lrolopositioned at the kicl(-off point. ' l 'he
whipstock is oriented and setontnepacker. Then, t lre slender tubc is lowered with the rctaining cablc..l.he rnudpurnp is stattccl and circulatiotr bcgins downs thc dri l lpipc tlrrough slcnclcrtube and ort thejet nozzlcs. I lydtaulic nrud pressure against the ptcssure scalon lhc tol) oflhc tubc forccs it downward. I ltc t l l l)c t)asscs througlj thc cur.vcdguidcs ol lhc r,vhipstock. ' l
hcsc turn thc tul)c through 90 anglc l irrrrr vcltrcalto horizolttal. A strcam ofhigll prcssurc rrrucl l ionr thcjcl rrozzlcs ctorlcs thelor.nralion and dril ls thc lrolc horizontally whcn thc horizonlal sccliorr is <lri l lcclby this rnanner, thc tLrbc is pullcd blck into thc pipc with tlrc rctaining cablc.A lso , lhc add i t iona l ho l i zon ta l ho lc rn r ry bc r l r i l l c i l l i .o ru thc s r rn rc rvc l lborc r ryturning thc whipstock in anothcr rl ircctiorr (irs shorvrr in Irigurcs 2.-j antl 2.4)n( l l cpc i l l i l l g (hc p roccc lu fc . l l r r rs , l r ig . 2 ._ l l r t r l l ; i g . 2 .4 s lx )w l lwo
anangcments of multiple r.adials in nrul(iplc laycrs. 't.hc chr.rice ofradial
lcnglh, nunrbcr of radials, and radial array is a function of thc r.cscrvoirpfopottios. lhcsc pl.oportics arc: rcscr.voiI l lr iokrrcss, vcrLiclrl arrd lroriz0rrlulpermcabil it ies, oil plopertics, wcll spacing, outcr-bountlary lcscr.voir prcssure,gravily dlnilugc, t l)crnti l l non-ll lcfnti l l proccsscs, arrrl l tr.csclcc ol. irrrpcrnrclblol ) r r l ings w i l l l i n l l t c rcsc lvo i r . . l l o rvcvc t , l l r c c l ro icc o l . rx l i l t l l e lg l l r n lx lal-rangcncnt gcnerally is unique to each rescryoir.
2.1.1 Slstent Prccesses !t4!! E41liltmenUat lvutliple Rsdj!ils
Thc basic rrltrn-short radius radial systern (( tRRS) uscs an crcclablc whinstocklowered downhole by 4.5 in. workilg into an urrrlcrLcarrcd cavity orhydraulicafly siotted opening of 22 in. dianclcr. Thc whipstock (Fig. 2.2) isdesigncd for use in a 7-in. casing. 1'he dr.i l lsh.ing nraybcprovitlcd firmacoiled tubing rig or it may be fabricatcd on sitc fron 30 to 40 fr rubing.ioirts.
Dr-. M.S. Farahltt
CIL II Dti i,l4 lcchltiqrcs I J
A./ i i ,. '1l "r'r i o"
\ ' r - l100 - 300 ll -:- |
A{i
Ali"
.fi' T-
Fig. 2.2 URRS.
r.soo _ 3.ooo rt + |
2,OOO S,OOO rr --- :'I
Molion Controuer
O.ill String
Working Str ing
High Pr€ssur€,R€movabl€ S€al
=-:- - und€rream€d zon€
Dri l l Sk i i lq
"t')'*,1+
Fig. 2.1.
D/. M.S. Fnrahat
Fadia l Bor€ Hole
Cll, Dt lhtU ll'dt,tltlurN t4R.dlal Compl.tlon gyit.n
PERSPECTIVE
Fig. 2.1 URRS.
16!Ftrr=ll11'11lr''"'"'' '1,,,'l!Orl1[: rr" .rL,r l s-a l : l
i l l , "" ' ' ' ' l l l ll l - l l t - - . - - , r l l l- r t 1|=l l l | - 'Sectlon A
PaY |.utto
Fig, 2.4. Multiple-rodiol cotnpletion.
,l),r M.S. Frrnh:ra
A lry<lrnul ic dri l l hcad is wcldcd to thc nosc of thc f irst. ioint of l t l rc dri l lstr ing
(radial tubc). I f thc dri l lstr ing is labricatccl on sitc, sttbsccltront 30 to 40 ft joints
of drillstring are welded by automatic computer-controlled welding on the fig
floor to form the drillstring. A hydraulic motion controller that regulates rate
of pcnctrat ion is welded to i ts tai l .
As thc dri l lstr ing is fabl icatcd, i t is lowcrcd insidc thc vcrt ical 4.5 in. rvofking
The nosc (dri l l head) of the dri l lstr ing enters a high-pressure removable scal at
tho top of the whipstock. ' l - l re scal providcs thc bottom closurc of thc
workstr ing. I lence, the 1.25 in. dri l lst l ing is ful ly continucd within the 4.5 in.
workstring at the outset of drillstring as shown in Figure 2.2.
A wireline as attached to the tail of thc drillstring runs to thc surface within the
workstring and passes through thc top closure of the workstting.'llrus' a long
sealed chanrber containing the 1.25 in. dri l lstr ing and i ts connccting cablc is
crcatcd by thc 4.5 in. vcr-t ical workstr ing.
Watci drilling fluid at 8000 to 10000 psi is pumped into the long vertical
workstring at the surface with a conventional fi'acture punrp. The drilling fluid
is then pumped down the wotkstling rvhcre it entcrs tlrc dlillstring. The
internal water pressure of the dtilling systetrr propels the dlillstr-ing tlrrotrgh thc
Irigh-prcssure bottom scal and through the bending ancl confining slidcs and
rol lers of the whipstock. Travcrsing the 12-in radius and 90
whipstock, the dri l l hcad entcrs the fornration horizontal ly. The dri l lstr ing is
not rotated.
and the whipstock-combhre to propel and to control the motion of the
drillstling into, through, and out of the whipstock, r'csulting in three load
cond i t ions o f thc d r i l l s t r ins .
The first URRS conrponent related to propulsion and control is the drillstring
(radial tube), which is propellcd out of the vertical workstring by the fluid
pressure within the workstring.
/ ) / . l \ 1 .S . l i : r I a l r f l t
It la
IIII
I
CIL II Drillirtg T,
owrate de ter rn inesDri l l Str ing speedControl Or i f ice
Mot ion Control lerDirec t io r t o f Mot io r r
Dri l l Str ing
Vert ical Tubir tg Str ing
Trapped Water
Seals
Flow to Conica l JetPenel ral iorr corr I t'ol v,lt i I e d ri I I i ng.I'ig.
t
;l
ril2.:
b::li,;tl nrir sr,rq srr",r";
Er,- t l o, , r sr ,r , , r Gr,P5, jc5
lsr. i r i i ct l Drr t ' i r , , r ; . ; r , ' , : : r . :
, r r , ' l ' ' l r w l l r r , r ' r \ l r l x , , , l
. r { r c . , j l l , f e l ' J s l k h , 1 , 1
, r , l \ . 1 , , w l i , . . 1 , ' i l i , r i ' l
Fig. 2.6 Stres,ses on drillstring.
Drill Strins [:"_..1t; -d
Hig l r Prossuf€ Soa l
W h i p s t o c k w , l r , t r i l , ! ' r ' , r ' . n r , r !nnl sh4. :s la br , , { r d, id .onrr ' .l l ,c D, , l l Sl , t r ,q
- . - Dr i l l S l r inq l io ' l ' , ' , t l I
Dr i l l St r ing l1 'e , l r ' r r r
/)r'. I\l.S. ltu r:t hnt
The second component is the motion controller (Figure 2.5) on the tail of the
dl i l lstr ing, rvhich acts as a hydraul ic restraint. In csscncc, i t is a piston wit lr
external seals that slide within a special snrooth borehole portion of the
vcrt ical wolkstr ing. ' fhc high-plcsstrrc wettcr pushcs on thc top of tho lnotion
controller, and water is trappcd bctrveen it and the high-prcssure seal at the
bottonr of the workstring. Water can escape only through a central orificc
wit lr in thc corr lrol lcr (Fig. 2.5). t l rc rcstt l ts is a hy<h-atr l ic rc{r:r i tr , or tr t 'akc on
thc forward rnotion of the 1.25 in. dri l lstr ing.
The third URRS component of the propulsion atrd control system is the
whipstock, which bends the drillstring from vertical to horizontal.
Figure 2.6 slrows the loads on the drillstring that results fi'orn propulsion and
rcslraint fbrces. In its passagc into, through, and out of thc wlripstock, thc
dri l lstr: ing is subjected to axial, internal-pressure and bending loads.
From Figurc 2.6, section A of thc dl i l lstt ing (abovc thc higlr prcssure scal), thc
drillstring stresses are below the clastic linrit. In section B, rvhcre tltc
dri l lst l ing is bclow thc high-prcssurc scal and within thc whipstock, thc
drillstring stresses exceed tlre elastic limit and thc drillstring dclbrnrs
p las t ica l l y .
Becausc the drillstring is internally pressurized and is constrained by rollers
and sl ides within t lrc whipstock, i t docs rrot bucklc u,hi lc i t is being bcnt. In
section C, the 1.25 in. dri l lstr ing exists the whipstock horizontal ly. Thcse i t is
undcr only axial and irr tcnra l-pressurc loads. Again, thc strcsses arc bclow thc
c las l i c l in r i t .
The pressure on the water drilling fluid in the system not only propels the
dri l lstr ing, but also dri l ls the horizontal borchole in the formation. ' fo dri l l t l re
fonnation, the water dri l l ing f luid is accclerated through the conical- jet dri l l -
head nozz,le, creating a conical shell of water particles travelling at 800 to 900
fVsec.
Dr". M.S. Farahat
CII. II Drillirtg'I.echniqtcs t8
l t ig. 2. ' l t t shows zl sclrcnlat ic of t l ro corr ical jct. At t l rr : top ol t l rc l i igrrrc 2. ' / t isa standard crrllirnated jet nozzle. The addition of fixed vanes within the nozzlecauses a conical shell of high-velocity water particles to fonl a conical .iet(I ; ig. 2.7b).
' l 'hc sizc of t l tc horiz.orrtal bolcholc is cstabl ishctl by lhc lwist of
thc vattcs, 'uvlr ich irr l t trn cotrtrols, l l rc iutglc oIr l ivclgcncc of t l r t : corrc of wir{cr 'patt iclcs. Fig.2.7c and Fig. 2.7d show vancs l 'or 1wo dif fclcnt conical anglcs.
Fig. 2.7 Cotticul jet nozzle.
Fig. 2.8a slrows water jets resultirrg fronr variorrs deglees 01'vanc tu,ist in l-microsccol ld l lash photoglaphs oI a col l i l t ratod jct and two cl i l lc l .cnt corr ical
iets. The conical angle is not affected by dri l l ing-f lrr id pressure. These conicaljets function at both ambient and clcvatcd back-pressurcs. At highcr back-pressules, cavitation does not appear to be an important cutting rtrechanisrn.
Fig. 2.2 sltows thc basic rvhipstock colt [ igul i t l iorr, a r lorrbly crr lvot l i rrvcl lct lqLrcst ion nrark. Insidc thc IJRRS whipstocl< is a scrics of rol lcr.s anrl sl idcs lhrrtcauses a progressive dcflcct ion ancl bcnding ofthc 1.25 in. dri l l ing as i t nrovcsthtough the w,hipstock.
n) LE CII A D w^r kEn CONTtOUnAItON
tr) COl.llCAl- JET NO77Lf tN SECTTON
n) v^ l {L: r ra[ t , t ao 'coutc^ l . . , r r NozztF
d) vANE USED tN 10" CONTCAL JEr NOZZLE
/)r ' . Nl.S, lr l r-rrhu I
CII. Drilling T rchniqucs l9
The whipstock is held in place by downhole anchor jrws engaging thc rvcll
casing. The anchoring jaw are set by rotating the 4.25 in. vcrtical workstting'
To erect the whipstock, the workstring is raised about I ft by the blocks, the
resulting verlical motion erects the whipstock, he workstring and whipstock
arc lrelcl ercct by a set of hydraul ic cyl inders at thc wcl lhcad that maintain
cotrstant tonsion.
Aftcr each radial placcnrcnt, the stcps or","u"r."d. Thc rvhipstock can thcn bc
cle-erccted, rotated, and re-erected downhole without losing its calibration. A
gyroscope is used to set the whipstock azimuth] for each radial. Thus, nrultiple
radials can be placed at differcnt azimuths downhole without having to trip the
whipskrck back to thc stt t ' lacc bctwccn cach sttcccssivc rarl ial .
After each radial borehole is drilled, a 3D positional survey can be applied
(Fig. 2.8b). The 1.25 in. drillstring can be surveyed to determine its trajectory
with special flexible radius-of-curvature (ROC) survey tools designed to pass
through 12 in (or smaller) bend radius of the drillstring. The ROC survcy tool
was developed to provide both plan (azimuth) and profile (up/down trajcctory)
data.'It is pumped down the workstring and enters and passes through the
drillstring as a wireline tool. The tool (Fig. 2.8b) resernbles an animal
backbone and has long slide wires placed at each quadrant that rnove within
veftebrae attached to a flexible, torque-resistant, wire-cable backbone. The
slicle wires actuate very prccise sensors that measut'e thc nrovetlre nt of eaclr
slide wire separately, translating directly into the curvaturc of the ROC tool.
And, in turn, of thc dri l lstr ing. Within the ROC tool arc an incl inometcr rnd a
roll sensor. All these data are transmitted to the surlace by wireline"l'he
curvature is converted into convctrtional azintuth and inclination by rrpholc
software, providing a 3D printout of both the azimuth and the bore inclination'
However, the drilling method used for ultar-short radius poses the following:
l. turning radius of I to 2 ft.
2. length ofdrainhole of 100 to 200 ft.
3. the first drilling system requires a 48 in. dianreter under-reamed zone
while the improved second system requires 24 in. diarneter zone.
4. the under-reamed zone length varies lrom 6 to l0 ftdepending on the
systcm uti l ized.
/)r. M,S. Faraltat
UI. DrilllngI'r:chuiqres
5. the drainholc diamcter varies 1.5 to 2.5 in. t l t t ts two or trtol 'c dtuilr l tolcs at'o
d ri l lccl.6, fol sarrd control, thc thl irrholcs ntc crorrrplclct l usirrg ci l l rcr slol lcr l l i rrcrs ns
gravel packing.
7. after completing the drainhole, the pipe is several, then ifdesired, a slotted
l incr is l incr is inscrtcd in thc uutlcr-rcarncd zonc, the dircct iotral sttrvcy
tools catt [rc uscd.
8. t l r is nrcthocl has bccn succcssful irr l l rc rrnbonsolidatcd sarrr ls, r t t tr l rccctt l ly
it has bcen used to drill hard rock such as grarrite.
9. a large under-reamed zone may pose difficulties in reservoirs with strong
bottonr watcr drive.
At last thc short-radius dri l l ing mcthod poscs t lrc lbl lowing:
l . l 'he process involves cutt ing a | 5 b 2{) f l lorrg window in t lrc casing of an
existing vertical well and kicking-off the dlainhole through tbe window.
2. A whipstock and curved dri l l ing errtry guide assist f lexible shel l pipes (30
60 ft) or wiggly dri l lcol lars in making a 20 to 40 l t turr ing racl ius. Also,
di lcct ional survcy may lrc usod to locatc dr 'ainlrolc path.
3. ' f ' l rc l tot izonti t l por( ion wi{ lr t , l l /2 kt (r - l l4 in t l i r trrc: l t :r , is rrotrrrrr l ly
completcd eithel openhole or by insert ing a slotted l incr in thc holc. In thccase of unconsolidated sand reservoirs, a wire mesh seven is wrappedaround the liner for sand control. lt is possible to drill several dlainholes atdif lcrcnt clcvations t lrrough a singlc vcrt ical wr: l l .
4. ' l 'he
short turning radius dri l l ing ntcthod has bccn vcry succcssful i l r nrarryfield applications. But the limitation ol this method, is that it does not offer0 sclcct ivc cotl l l ) lct ion option. lrr ot lrcl wotls, i t is rrot possi lr lc {o isolrr lcccrtain prot lucing zorrcs sclcct ivoly. ' l his coulcl causc dif f icult ics in lhcci lscs whclc fr irclrucs intcrsccting lhc drainlrolc f lrc in dircctconrnrun icatiorr with eithcr top gas or bo{toltr watcr.
5, Moreover, milling a widow in thc casing can be very expensive and timeconsuming. I f possible, a prefcncd opl ion is to dri l l a drainholc through anew vertical well with arr open hole section.
6, A 90 ft turning radius drainholc is a succcssful technology. Thistechnology employs a downhole nrud motors and articulatcd drillstring.Also, i t has been succcssful ccrncntccl tho casing irr a curvcd scotion ol '90ft turning radius hole and harrging, the lolntat ion evaluation tools can beuscd.
' l h is t l r i l l i ng toc l r r ro logy cou l t l l r rob lb ly bc uscr l to rh i l l 2 ( ) to 2 ( )0 l l
t r r t r r ing ra r l ius wc l l s by rnor lc l i r rg t l rc < l l i l l s t r . i r rg a r l i cu l l r l i on .
Dr. M.S, Falalrat
CH. II Drilling I'echniques
Fig. 2.8a. Water jets.
c ) 3 O " C o n l c a l J e l n o z r l e a t o . 4 M P 8Separ a lor
Tool Cross-Sect ion
Slide WkeL----
Convgr lo rComputer
To FOC ToollExcitation f-----'/I Sourye J
Electr ical Schemat ic
Pr in ter
1)r. M.S. Farnhat
Fig.2.8b ROC tool.
Cn l l L , r i i ' t ( 7 i lhr iqur \ 22
2.2 Short Turnine Radius
Short-lullr ltoIizorrtal p (ctns Ituvc a tu|1t mdius ol about J0_00 ll, lbr.dri l l i Igfiom cascd holcs. Thc proccss bcgins by sicletrucking, built l irrg angrc, urrudti l l ing thc curved section with a special anglc building rsscnrLrly. l. lrrrs, lol are-entry dri l l ing system to be tcchnically succcssftrl, i t mustbccapablcofdril l ing a consistort raclitrs of ourvaturc arrcl ol dr.i l l irrg cut.vc irr thc rlcsitccldircction, Thcsc lcqrrircnrcnt nlisc lrorrr l lrc lcc<ls;
,To position the end ofthe curve within a prccise dcpth intcrval so that rnclatcral can havcrse lhc fay zonc as dcsircrl.
, lo plircc l ltc Lrtcnll in a dir.cctiorr rl ictatod by wcll spacirrg, dcsilcrJ swccppatterns, or other geological considerations.
,To establish a smooth curve to facil i tatc dr.i l l ing thc latcral an<l corrrplctingthe well.
Sevc[al types of shott-radius curve-dril l ing systcnrs arc comrlcrcinllyavailablc. ' l l ic most conrrnon lypcs uscs a nrurl motor to rotatc a dfi l l bit that lstit lcd bit dri l ls a curvcd patlr, anrl thc rotational oricntation of t lrc ruotorhousing in thc boreholc dctermincs thc dircction ofthc curve. Eithcr.a stcclingtool or a measurement while drilling (MWD) tool is required to kecp themotor housing oriented during dril l ing. The systcm nray be usccl withcotrvcntiorral or workovcr rigs ol witlt coilod- tubing urrits. l. lr is is t lrc rrrostpopular method of drilling a curved borehole, but jt is often too cxpensive tobe economical for re-entcrs in mature ficlds.
Constraincd-rolaty systcfis afc sccon(l cllcgoty oI coltrrrr:r.cially irviri l tr lr lctools. ' lhcy havc a flcxiblc cfi. ivc shrrl i irrsidc nn nr.l icrrl:rtc(l n{)l folNti lghousing. Since originated by Zublirr in 1052, this approirch hns hccn grea yrclincd. A resil icnt curve guidc acts as a sprilg that applics a sidc l i)rcc to rcbit ond forcc thc bit to dr.i l l a curwcd pr{h. ' l hc curvc guitlc inil ially is or.icrrtcdin the desired direction and then rclies on wcllboie fr. iction lo nnrntarnorientation as it advances along the curve. Because of the considerablel'rardwarc required and the associated opcrali l lg procedu[cs, usc oIconstraincd-rotating systclns has dcclined in l lvor of l lrc nrorc rcli irblc rnucl ntotor.systcrlrs.
,r ll.S. I,':tr^hnt
CII. II Dritti"g luhniqucs 23
Rotating-guidcd systems are a third category of short-radius cuwe-drilling
tools. Fig. 2.9 slrows thc downlrole conrponcnts of onc such systcm. ' l 'hcy
include the curve asscmbly, f lexible dri l i collars, and oricntation equipment.
Thc lclativcly short curvc rsscmbly incorpotatcs a flcxiblc.joint lhat is pushcd
to onc sidc of thc holc lo ti l t {hc bit. ' lhc oricntation cqttipnrcnt conrprisc a
standard muleshoc sub for gyro orienting or a nonmagnctic collar and
rnulcslroc strb for magnclic olicnting- I his basic tool corccpt has bcen arotrnd
for decades, but problems rvith angle builds and directional control have
limitcd its conrmercial succcss. I lolvcvcr, thc apPcal of dri l l ing horizontal
wc l l s c l rc lp ly w i th such cqu ip rncr t l c r r ra i r rs .
Fig. 2.10 highiights the evolution of rotary-guided cuwe drilling tools before
1988. Early described a tool in 1934 that used a flcxiblejoint to allow the bit
to be ti l ted to sidetrack a well. In 1944, Miller patented a similar curve-dti l l ing
assembly (Fig. 2.10a) in which thc bit t i l t direction could bc oricntccl to dcflcct
the borehole in a particular dircction. lt was assumed that, aftcf initial
orieniation, the assembly would continue to dri l l in a consistent direction. ln
1952, Sanders used a curve-dril l ing asscmbly (Fig. z.l0b) whose near-bit
reamer caused the bit to the inclined. This system also incorpolated a flexiblejoirrt to allow su{Iicicnt tilt to drill short-radius curvcs. The curvc direction
was detcrmincd by the orientation of a whipstock, again it was assunred that
thc asscnrbly would continuc to dri l l in a consistent dircction.
In 1964, (Fig. 2.10c), Frisby proposed an assembly that used an eccentricstabilizing sleeve to control the bit tilt to orient the tilt in a parlicular direction
and to function as a stabilizer to minimize bit wobbling and oscillation. The
eccentric sleeve could be positioncd eithcr above or below thc flexiblejoint. It
was attashed rotationally to the ddllstrimg with a pin that was released by fluid
pressure when drilling mud was cilculated through the tool. This sleeve rs
similar to one proposed by Gilcs in 1955 for long-radius dli l l ing, cxccpt that
Gilcs slceve was oricntcd thc dri l lstring counter-clockwisc to cngage a lock toposition the sleeve in the desired direction.
Development was renewed in the 1980's. Holber (Fig.2.10d) and Schuh
workcd on dril l ing an unpredictablc radius ofcurvatutc causcd by instabil ity at
the dril l bit, cspccially when the bit dri l led an oversize hole or became
Dr: lU.S. Farahat
\-' , \ - -:,r\,,rt.rnlIolt"
NonmagneticDrl l l Col lar
Dri II irt 1; 7'c<: h n i qt es
OrlenlatlonKcy
Flex ib leDri l l co l lars
a ! olary)- ittott niliiiri ctilvi u.s.yint
.fitrces are,shown.
Fig. 2.
1)r. l\'LS. Irara hat
CII. II Drillitg Tcchniqucs 25
unstable as it crossed bedding panes. Burton addressed tlre problem ofpoor
oricl l tat ior l control by introducing a tron-rotat ing eccentr ic sleevc (Fig. 2.10c)
with splingJoaded blades to glip the wellbore and to lnaintain orientation as
the drilling assembly is wellbore and to maintain orientation as the drilling
assembly is advanced. Burton advocated periodic repositioning of the sleeve
so that a Dlanet curvc could bc dri l lcd.
Fig. 2.10 Historical evolution of tlrc rotaryt-guided slrcrt-radius atrve-drillin.g
tool.
Fig. 2.11 shows that the flexible a short-radius curve. Thus, to tilt sulficiently
to drill a short-radius allows the bit it has been used a non-rotating flexible
tubular steel shell made ofshoft lengths ofpipe. The lengths connect together
with articulated connectiorrs for flexibility. This flexible shell carries the
vertical thrust to the bit and acts as a sprirrg to facilitated building angle. A
flexible liner inside the shell contains pressure for circulating drilling fluid. An
internal drive shaft supported by bearing packs, carries torque from the
drillstring to the bit. The horizontal section is drilled with a similar technique
but longer flexible shell without spting action and stabilizer to control
direction as shown in Fig. 2.11.The hole is prepared first by milling a section
of casing and under-reamed. The whipstock is run ot'iented to the con'ect
direction and set, the angle building assembly is run into the hole. Sidetracking
begins by rotating the angle-building asserr.rbly as it guides offthe face of the
1987e
1}. l\ '1.S, Falahnt
( ' l l . 1 l l \ l l l t tH I 'nhu\ t t rs Ltl
whiPs lock ' S idc t r i l ck i r rg anc l r l l i l l i ng cor r l i r r t ro i r r lhc curvc t l l ro lo scc t i . . i r t a r ri 'creasiug upward angle in the di 'cct ion of the whipstock racc untir i t is bcinghodzontal. Then the angle building asserrbly is pulled out of the hole. Thestabilized drilling assembry is run, and the str-aight horizontal section is dri ed.Also, there is another version of thc systcm l.otates the bit with an articulatcclnrotor, which improve lrole guida'ce.'fhe welr is compretetr as an open rroreor a special f lexible type slotted l incr is r.un.
Fig. 2'I | ,4 scltetnntic .f o 'shorr-t'aditr,s rrriling racrtttiqrrc rr,sittry finirtradrillin g ioirtt.
/)r'. M.S. Fa ra hat
CIL DTiIi'tgTcchniqnes
2. 3 Mc tl i r t nt - Tu r n i n g-Bg1!!4;
Although the long-radius approach to drilling horizontal wclls is highlydeveloped and very successfirl, thc radius rcquircd restricts the applicationspossible. Medium-radius dri l l ing extends thc tecbniques so that build sectionswith a radius down to about 300 ft (90nr) can bedril lecl. I lolcs dri l lcd try
m€dium-radius techniqucs lrave scveral advantagcs conrparcd to long-radiuswells and almost no disadvantages. l lrey can be dril lcd with conventionaldri l l ing rigs, although they require some special, but now wcll-developed,
equrpnrent.
Mcrliunr-radius tcchniqucs usc rroir-irrl icrrlalcd tt i l l slrings nnd hcntt lnrrrlnrotors.' l hcsc arc thrcc principal r-ccluircnrcnts:The bottom-hole assenrbly must be able to dri l l along a trajectory with thercquircd radius. )
Thc dril lstring must be sufficiently f lexible to follow the dril l withoutmechanical failurc.
Tools used in thc hole must be able to be moved around lhe curved parts ofthe hole.
It is important to note that the third requirement l isted above limits the toolsthat cau bc used ir the horizontal part ofthe hole evcn through thc curvaturethcrc is ncgligiblc.
' fhese requirctrrctrts placc l inritations on whal can bc
achicvcd by mediurn-radius dri l l ing. Thc rcquircment for dri l lstring flexibil i tymcans dril lstrings must be snraller in dianreter for highcr curvatures. Atthclirnit, i t is necessary, e.g., articulated strings, coiled tubing type stringsstrcsscd beyond thc clastic l inrit, and strings nr.dc o f cxot ic highcr-strengththc nralcrials such as titanium, carbon fiber or steel-reinforced lroscs. Chargcsof this sort move the tcchnique bcyond thc boundary ofnornral mcdiunr-radius
dr i l l i ng .
The trend to using smaller diameter drillpipe goes along with the drilling ofsmaller diameter lroles. Another driving force moving (he teclrnology towardsstrlall dianreters is the inccntivc 1o dli l l horizontal drnihs starting with cxistingveltical wells. To do this, mctliunt-radius equiptnent thdt carl bc inscftcd downthc cxisting vertical well casing is nccdcd.
Dr. M.S. Ferahat
CH.II DtilingTechniqnls 2a
Drii l ing motors fof both the angle-build and angle-hold sections ofa medium_radius horizontal wcli must bc shorl cnorrgh to fass i l.ound lhc cut.vilut.c.Doublo-ti l t t l tolors arc ooll l l lon, particular' ly Ibr unglc-hold. l.hc ti l t in angrc_build motors is relatively Iarge and thc motors are not rotatable (steerable).
Medium-radius hole can be drilled fronr the side ofan existing cased verticalwell or from a newly dri l led open bole. Ifan existing vertical well istobeused, a rvindow is milled in thc cxisting casing at ihc dcsirctl Icvcl and awhipstock locked to the casing in the designed orientation below the window.'lhis lvhipstock dirccts thc nrcdiunr-r'adius ltr(l nrolor rlr i l l in thc rlcsircdazimuth direction.
2.3.1 Drillnhrcfor Mediun-R litts Driltins
' I lrc f irst mcdiurn-radius dti l l ing systcnr rvas dcscribcd by Dcch,flnd lcnhart in 1986. It allorvcd holcs l6 in. in diarrrctq. lohorizontal distance of 1000 ft with a build ratc ofabout 20 30nr
l lcarn, Sclrulrbc r l r i l l c r l to( r00 i0 .
'l'hc systcrn used a narrow,diarnetcr, spccial comprcssive sorvicc drillpipc
(CSDP) carrying larger-diameter wear knots.
I. ' igurc 2.12a shows thc two conrmoncst sizc ol'compre ssivc sew icc dr.il lpipc.'lhc pipc is ficqucnlly nxrrlc firrrrr tr(xt-lltfl lcli0,llsl(lrri l ic slccl l irl rrsc rrrrumagnetic survey instruments and in holes rvhere the build ratc are greater thanl5 i tO m (100 f t . ) .
In holcs rvilh a lowcr build ratc than | 5230 nr, hcavy-wall tlri l lPipo (c.g. I lovi-watc) is uscd. 'fhis pipc has a rvall tlrickncss which rlakcs it itt)orrt two alld ilhalf times as lreavy as standard dril lpipc (c. g. 62.5 Kg/rn for.4.5in.pipccompared to 25.3 Kg/nr for standard pipc). ln adtlition, I lcvi-rvllc piqrc hus, ineach 30 ft length, a centml upset section uhich behavcs sirnilarly to the wcafknots ir CSDP. Thc wear knots (Fig.2.l2b) kccp thc dril lpipc away frour thcwall of the hole in thc curved sectiol. This rcduccs both rotating andlongitudinal friction, resulting in less strikirrg. It is also through the wear knotshclp kecp thc cuttings in suspcnsion in thc dril l ing fluid.
1fr I I .S. Faribat
CII. II Dtillittg T cch iqxes
Compressive StrengthDrillpipe
COMPBESSIVE SEBVICE DRILLPIPE(CSDP)
2-7tA 3.1 t8 23 . 1 1 2 2 1 3 1 1 6 10120t3a
Fig. 2.12a
5"Wear-Knots
2-7 IB" s-1t2"
Fig- 2.12b Contpressive strength drillpipe 5 in -wectr-lutots.
/lr. l l.S. I.arahat
CII. II Dti ing lethuiqn.s 30
2.3.2 lf nlinnrllntli us Ilrilli rt g ll I ot o,'s .t nrl,l_t'st,'r,,s
Medium-radirrs, angle-build motol's typically have two bcnds in their length.Motors of lhcse types are showr in Fig. 2.13. Arotlrer nrotor sritable forbuilding angle in rnediun-radius holes is shown in Irig. 2.14. In this asscnrbly,a motor with a bend is jointed to the dli l lstring via a bend sub. 't he total t i l tofthe motor is equal to the sum ofthc two individual t i l t angles. ' l 'ablc 2.I showsthc holc chanrctctistic that can bc oblailcrl Lrsing nrcdiunr-r'rrrl irrs dri l l ingsystcms. for f ivc different motor sizcs. l lrc two largcst motor.sizc l lc l inri lcrlkr dli l f ing holc wi(h au arrglc-builci fatcof lcss l l] l | i | , 14730 nr(I00 l l) rr|<l rncvrcquirc rciatively large vcrtical holes. With thc lower degrec ofcurwaturc,Ilevi-rvate dri l lpipe can be uscd anclthere is complete flexibil i ty in thc use ofMWD.
Iful rl i l l ing shallow, nrccliunr-r'adius lrolizonllrl wcll, lyl)ictl l lr lcc Il l lStlcsctiptions arc spccificd lorlhisrvcll rsshowr in fig.2.l5 (con<lrrctor.JrolcB l iA) , I ig .2 .16 (su t faccJro lc B l lA) and F ig .2 . l7 (ho l i zon ta l - l ro lc l l l lA ) .Also, l i ig. 2.18 shows that the invefted dril lslring dcsign for holizontal holcscctiou.
Table 2.1 Typical nrediunt-radius drillitg paranrctcrs
Motor Slze oD 0r.) 8Mi,titttwl Dianeler al
Vdlic^lWe (inches)
6314 4 3t4
121 t4 a 1 t2 0t3 3/B I 5/8 7
t00 300I t 0 0t000
3 3t4
4 3l,l5 1 t 2
120 X4()u90l 2 A /
20 35286
3 3/r]
43145 l t ?
t20 340B00121) /
OPen l lo leCasing
Molor rlnn-forqt|o It ll)N M
"/30 nrnadius, l t
Steerir9crfnb l i ly "/30 in
Uso [rWD
85-190 100-2604500 28006103 3798
8-14 8-14 19-30715 410 715 410 300-2B0
2 . 5
Yes Yos Y05
20286
2.4
i , / / l t t i t t l l t " t ' / l t lCSDF / l IWDP CSDP or SDi ia lFrwDt, csr)r,
liHWDP
4 li'HWOP
Drl l l l ' l t ! '
D/: M.S.l.rrrhxf
CII. II Drilling T cchtiquL's 3l
EA,STMAN CHRISTENSENHORIZONTAL MOTOHS
Fig. 2.1-t.
DYNA-DRILL DOUBLE BEND MEDIUM RADIUS MOTOR
.,.,ii'tm:i,1{;#tr3,y3;ry1;,;1;,i;721;tr,"
Itig. 2.14.
1)r. N{.S. fiarahat
C . Dti ittg'Icch iqkcs 32
I49'
I
6.75" MWD Dlrocllonal S€nsor
5" Non-Msgn€llc Drlll Plpe(He8vy Welght)
5" Non-Msgn6tlc Drlll Plpe(Heavy Welght)
11.75" Stsbllhor(Non-Mognollc)
8" Bcnl Houslno Motor(Slnolo Bend)
-
12.125" Stablllzor
12.25" Blt
Fig.2.l6 Stu{at'e hole BII4.
Itig. 2. | 5 ('rttlrr tot. ltolt,
n ll/l.
5" Non-Maono c Drl ptpe(Hsqvy W6lght)
0.76" MWUDhoctlonsl Sonsor
Gemma Ray/Reststtvlty S€nsors
fn"'xil-$3p;iy" on u o,o.
11.75" Stsblll:sr(No|FMagnotlc)
8" B.nt Hourhrc Motor(Slngle Bond)
-
12.'125" Stsbtttz.r
IB'
70'
III
Dr. I\,1.S. Fllrrhrf
12.2!" Btl
CII. Driuilg'Icchniqu.s
E+6'rI
I37'
5" Non-Magnellc Drlll Plpe(Heavy Welght)
6.75" MWD
Olrecllonal S€nsor
Gamma Ray Sensor
Fsslstlvlty Sonsor
7.75" Stablllzer(Non-Magnetlc)
6.75" Ooubl6B6nlHouslng Motor
8.375" Stnbi l izer
Fig. 2.18 Invertetl drillstring desi.gn for horizontal lole section.
lrig. 2.17 Hot izo tal hole BIll
D/r Nl.S. Frrahat
CII. II Dri hry'lttl'|iquts 34
2.3.3 Hieh Medium a d Lov Saeed Drillins
l'he medium-radius technique can be used with both high-speed, medium-and
low speed lnolors: ]'hc types of motor uscd dcpcnds upon tlrc contlitions. lloth
rolling cone and fixed cutter (usually polycrystalline diamond compact (PDC)
bits can be used. Roll ing-cone bits are nearly always used with low andmedium-speed motors, i.e. for rotary speeds less than about 200 rpm. PDC bits
can be used with either low-speed or high-speed motors. Both categories ofbit
hlvc advantagcs an<l thcrc is corrsidclablc ovcllap irr lhoil rrpplicrrtiorr.
Roll ing-cone bits, operating at low speed, have advantages in hard rocks andthcy rcsp(nl(l sorli)wl) t b(jttef to cllbds lo c(nrtlol {l lc dircctiorr ol {lro lrtrlc. ()
l l tc othct l l tttt l , bccrusc tltcy lrtvc tttovirtg plrl ls lrtrrl bcrrirrl ls, lhcy rrc lrr)r(
s l rscc l ) l i l ) l c lo rvcar and havc to bc rcp lacr ' r l r r ro r ' c f i cqUL- r r l l y I ID( ' I ) i t s c ln hc
tusod at highcr specds and wil l frequcltly dli l l longcr scctions ol holc without
rcplrccnrent. Diamond and thennally stable diarnond bits are usually run onmcdiutn-and high-speed motors. Fig. 2. l9 shorvs the addition of hartl lacing
and tungsten carbide inserts for protectivc thc lcgs of roll ing-cone bits. Also,
|l ig. 2.20 shows a PDC bit that involves thc pl'otcctiotr of thc top ol-thc bit
rlcvcl with nattral clianrorrds, t lra{ can trc rrscrl rvilh (op-ciivc rigs urrtl rvith
backreanring for rcmoving cutting rvhilc dti l l ing thc horizontal scclion of well.
Fig. 2.21 shorvs other design charges for lrorizontal dri l i ing bits at inlprovcdstecrabil ity.
2. 3. 4 Mediutr- Rldius-Horizo ntq! Il/ell Sections
Medium-radius horizontal hole is comntonly dri l led in open lrolc as shown inFig. 2.22, but sidetracking in cascd holes is modemtcly common with lorverturn radius pattcrn ofabout 300 11. Motor asscrrrblics arc nrust conrmonly uscdas mentioned before. Tangents are used sornetimes; it is common to use ameasurement while dri l l ing (MWD).
,r. IU.S. Frrrh:ri
CII. II Drilling Tcchtiqucs 35
NATURAL DIAMONDS ON TOP OF BEVELFOR PROTECTION DURING BACKHEAMING
Fig. 2.19 Fig. 2.20.
2.3.4. I Vertical Sectiorr
It is the {irst section drilled from surface until the kick-offpoint (KOP) for a
horizontal well or newer well (Fig. 2.15) or section from surface until milling
windon' for recomoleted mature or old well for drainhole.
SIIOHTEFI FLAT'I ER PDC BITS FOR IMPFIOVEDSTEEBABILITY IN I-IORIZONTAL I.IOLES
Iton lones 1990
Fig.2.2I.
T[€ POC b lo r t lE r igh t learu ,esa shotl\ucil.;lnnk, lhl(dki prol i l c ! i rd s lu l , r ro , l 0a( ( ro lo | ( l lh .Theso leahrcs atu d{rsn.blo ld
Dr'. M.S. Farah:rt
ctl.II lrtiuitru t.thniqn.s 36
D-lt
vdt la ! lhd . i l , l l l . . l ,nJ . " .d ro . r . t i co o , t , , r , , rd i r ro c . j t , )u Dot , , rV . r ' l c r l d . r thn r rno t ro ! ro ,nnr lon c .D, i t ^ j , ,o . i , , , t u . i to r r t , , , , i t lv . r r l c . l ho lo p lusood.bJc t lo k lck o t t p . i j r rCur ! .d ho lo .ucr lon d , l t tod r tvo !0h 90- l rn r r . l i . .l l o rhonr . l I ' o lo 66cr lon dr i l lodcurv . i l ddd ho . i lon t . t ho to E .c r ton , .asod ,nd cuUFv(uu
Ititrg.2.22 A4ttliuut Iunt hori;ottIrtI u'tlL
2.3.4.2 Curved Sectiatt
' l lrc crrlvcrl scclion ofhorizontal holcs lrrms t hlouglr a 90' cu rvc lrcrn vc rcnl
lo horizontal wilh an avclage turn laclius ol- 3(X)-tt(X) l i . Ihis cun bc ckrncthfough the following:
C t r)i dotv for |ertictl well: At kick offpoint, thc scclion nril l ( lr ig. 2.23) ist t t t t r t r r l l l t c cns i t rg , i s t t r i l l c r l r tg i r rg I i r r r r l t j l o . \2 11 ls in ! , l l i V is g r ' l r r r r r r l rv i t l r
lhrcc stcps.
' lhlce diffcrent lrolton-hole asscll lblics afc uscd to sidc thc wcfll alicr sct
whipslock as shown in Frg. 2.24 shows typical conllguration ol notor
dcviation scction l 'or kick-off, bri ldirrg lnrl horizontal nlo(or irsscniblics-uscd
for drainhole in Egyptian-westem deseit.
/ lr ' . l l .S. I :rurh:r l
CIl. II Dri i,tg Tcchniqrcs 31
HI
Hydru l i c Jar
61 /4
61 /2
5 3 /8
4 3 /B
T,oaI
rI
It_
Bit Sub
Boot Basket
Sect ion Mi l l
Taper l ,4 i l l
5 1 t2
a 1 /4
1 /8
1 /2
5 1 t2
a 1 t4
Fig. 2. 2 3 tuIil I irt g ass enfu ly.
Dr'. M,S. Farahat
CH. II Dtilti g Techniqnes 38
J
A
J
A
B
Limber
= Molor , B= Bear ingi l , D= Bent hous ing ,
Bent-Housing Pad andBent - H ous ing
BentSub
Benl Sud -and
Benl -Hous ing
assembly , C :E : Pad , and
Ou ipu t sha f t anc lF : Ben t sub
Fig. 2-24 Motor deviati) sectian.
/ f / . NI.S, F:rrahnt
CIt- II Dri hlg Tc.hrirlt.s 39
Anglc-buikling continuous wilh thc sidclrack motor asscmbly. Dti l l ing insidc
cascd holcs (usually 7 in. diattrctct or I i lrgcr casirtg) is donc with strtall
diameter, slim-hole tools. A section of casing is removed by nil l ing, a
sidctrllcking plug is sot and drcsscd off. Somc opcrators prcfcr to sidclrack o t
olcascd hole with lowcr build ratc, itrcrcasing thc build latc allcl dli l l ing.r
part of curved section. Drilling and angle building operations continue,
rneasuring drift angle and dircction pcriodically. Inclined or first build arc
(curvc), straight (tangcnt) is clri l lctl to lhc rcqLtit.ctl dcplh. l 'hctt, a dircctional
motor assembly is run, and anglc-building contittucs in a slnooth curvc unli l
the hole becomes horizontal. The curved scction of the hole may be cased
before drilling the horizontal section, or both holc may be cased togetller.
Running of the casing dcpends upon the turn radius, lengtlr of horizontal
section, formation conditions, torquc and drag.
2. 3. 4. 2 Horizonto I S ectiott
Hotizontal section of medium-radius has angle of about 90o. The horizontal
section is drilled using low angle build stecrable nrotor assctnbly as shown itt
Fig.2.25. A common steerable assembly has a bend lrousing with a low angle
bend of 0.25'- 0.5", possibly with a very tlrin deflcction pad to prevcnt motor
housing (as shown in Ftg. 2.26) wear reaming nonnally is unnccessary
because the assemblies are rcflectively limber. Reaming car be done with a
nonaggressivc rcaming assenlbly, ifrcquircd. Thcn, dri l l ing contirucs unti l thc
torizontal scction is conrpleted.
Lastly, the features of this drilling method used for medium-radius horizontal
well, are given as follows:
tn this method, the turning radius from a vertical to horizontal direction is
about 300 to 800 ft.
Two systems are available to drill these drainholes. 'l hese systems used tn
general are: downhole mud motors and flexible drillpipe. One system
utilize build-motors for angle building al a rate of about 2dl100 ft. thc
horizontal potlion is ddlled by using angle hole-motors which drill at a rate
of about 30'/100 ft. Such system has bccn used succcssful to dri l l 1000 to
1500 ft long wells in fracturcd formalions.
/)r. N{.S. F:rrxhnt
(:IL II l)tilling I-u.hniques 40
Flcqucntly t l rcsc wcl ls al 'c r lso conrplcto(l usirrg slot lct l l i rrcr.s. ' l l rr : wcl lsc i ln l )c loggc t l r rs i t rg cornr r ro ro ia l l y i rv i r i l i rb l r : co i lo t l l r r l r i r rg ruor r r r le t lf i r ' rnnl iorr cvnlunl ion tools.
S tabl l lzed bentl lo us lng |no lor
Survcy too l
Pos l l i v r - . r l i sp l r rcc r r r o t r tr lowt r l to lc r r to lo r
SlecraLrlorac l i l ts o f cr r rva luro
Top s lab l l l re r
n = l ln(lhts ot curvnll| lo
Degrco ol l)cn(l
R
Ben l -hous lngs lab l l l zor
T14t ica I s tee r alt I e s),s te n.
/)r. M.S. Iarahal
Fig. 2.25
CH. II Drilling I'echniqrrcs 4l
olrrlrri:ur r-ir;:trl.iEir
ffiffiHm"TF-l lH. llw i-lN iiffi'1
tffillffillilrlH-r
Fig. 2.26.
Long-turn radius horizontal well classif icat ions are dri l led nrainly by deviat ion
in open ho1es. Wells in this classification are charactcrized by larger hole sizes
zurd alc vcry susccptiblc to lr igh drag and torquc lrccausc ol long opcn holc
section. Flole size range up 12.25 in cl iameter although srrral lct diarrcter holes
are lltote conln'loll.
We lls with a radius of crirvature of about 300 m ( I 000 ft) in the deviated
sectiorrs are commonly dr- i l led using the tcclrniques (as shown in Fig.2.27) a
stcerable bcnt nrr.rd nrotor and MWD to locate the hole as dri l l ing proceeds.
Also, therc are signif icant advantages in using top-drivc ralhcr t l ran totary
table drilling rigs, and top-clrive rigs ate commonly used in offshore
applications. Fer.v land rigs have had top-drive because of tl-re cost installation,
howevcr, nerv top-drive designccl spccif ical ly for land opcrations ar-e avai lable.
Dr. M.S. Farahat
CII. II Drillitrg I'ecluriques
[?or long-radius horizontal wells dri l l ing, the Navigation Dli l l ing Systenr(NDS) empty a NorTrak streeable motor with doubletilted U-joint housing(DT[J) as shown in Fig.2,2B. The systenr can dri l l direct ional prof i les andnrakc coutsc corrections without costly asscnr[rly changes.
42
Inlo$r.r l blado
slabl i lzor
0ouble-bend U0t0r conli[urationDrilex
f ' o5 i l l vo r l i r , ) l noo r l r l
w i l l l bon l l l ous ing
Fig. 2.21.
$teeraDle ntBtqi' xc0nf
iUurati0n
Pos i l i ve ( l i s l ) l acon !on l l o l o rw i l l t p l ( l an ( l l ) r r | t l l l r ) l [ ] i n ( l
( ' ' I : ir:. 2.29.Y ... 1 \ ' l f cf '^'- '-" 'J I I L J J
Also, thc D l 'U lrousing has two sl iglrt bcnds-[r 'st i rr onc cl i lccl iorr, t l rorr in thc
opposite-to slightly tilt the bit's axis fronr thc hole axis. ltcsulting ol-['sct anglccan bc configulccl fi'om 25" Io 78'Lo plovitlc doglcg capability up to 6'1100 ft
rvhile drilling in the oriented mode. \Mren thc rotary tablc is engaged while the
NorTrack motor continues to run, bit offset is negated and the NDS assemblydrills straight a head. To keep the well on course, otiented and rotaly sectionscan bc t l t c r r r i r lod w i thout t r ipp i r rg ou{ o l ' l l t c l ro lo . ' l l r c t lo t rb lc - t i l t t l cs ig l rbrings the motor axis back into alignment rvith the borehole axis, providing
/ ) r ' . Nl .S. l l : t r ' : rh:r t
CE.II Dti i'tg lechniqnes
directional control and consistent well path curvature with low bit offset and
nrirrinral housing, bcaring, and dr-ivc asscmbly strcsses.
2,4.1 Venical Section
It is drilled ftom surface or sea bed until KOP (Kick-off point) using
convenlional tools.
The cuwed section of horizontal tum holes through a 90" angle from
horizontal to vertical with an average tum radius of 1000-3000 ft. The first
stcp is to deviated and bcgin dri l l irrg thc curved scction. 'fhe same gcneral
procedures are used for drilling the high-angle directional and mcdium-turn
pattcrns. l{cduced anglcs of brri ld and longcr opcn holc scctions must be
ollowed. tt is necessary to establislr curualute and thcn drillcd witlr one of
several assembly options, as shown irr Fig.2.29 pattems with longer turn ladii
arc dti l lccl using ditectional dri l l ing tcchniqucs in thc carlicr part ofthe cuwcd
section. 'I his is mote common where bit walk and angle is about 20o.
-l'hen arr
angle is about 6d. Drilling continues to higher angles with rotary assenrblics
in a few cases, such as a hole with vety long tums- Normally, rotary
assemblies are less efficient for building angle and controlling direction at
lo horizontal with motor assemblies, drilling with steerable motor assemblies
as often as possible. Tangent sections slrould be drilled as needed. Tangents
are often placed at an inclination of 60'. Tangents are omittcd in some holes
that havc longer turn radii because drilling longer sections plavidcs tin'le for
morc rvcll path adjustments.
2.4.3 Horizontal Section
Horizontal sections of long-turn holes have angles of about 90o depending
upon fonnation conditions and well pattems. The horizontal section is drilled
with either a hold or low-angle-build sfeeable motor assembly. Procedures
2.4.2 Curved (Turnin
Dr. trt.S. Farih,rt
CIl. II lttiUh,E Tt?huiqu.s
similar to dr:i l l ing the horizorltal seclion of t lrc lncdium-lunr pattcrn alc uscd.Ro(ary nsscnrtrl ics arc scldonr uscd. Drag anrl torquc incrcirsc rvil lr irrr:rcasingdepth. Torque nay approacb the ma;rimurr linliting torquc-strongth ofthedli l lstring in very deep holes. This has occuLred even in a complctcly casedhole. Moto[ assemblies should be used here, since tl]e do not require rotatingthe dril lstring. Drag and torque maybe nrinit l ized with tlre correct type highqua l i t y mud sys lem and o thcr ac t ions .
44
Fig. 2-29 Long hutt horizontal well.
I lowever, this dri l l ing method (long-lurning mdius) has a turning radius of
1000 to 3000 ft in most cases alrd uscs mostly convcntional tools. A
combination ofdri l l bits with bcnl subs ancl downhole nrucl rnotors alc usco ro
dril l 2000 to 5000 ft long horizontal wells, sometimes reduces to 4000 ft long.
The advantages and disadvantagcs or i inrjtations ofthis dri l l ing method usedlor lo r )g l id ius hor izon ta l we l l . cnr r bc s r r r r r r r r r i zcd r . fo l lnws:
1 These wells can be cored, logged and treated.
2. Problems in cetnenting the lrighly deviated wellbores are furtllel
aggravatcd in horizontal wellbotes, especially in regald to displacement
frour the hole and unifoml comcnt placemcnt around tlrc wcllbolcs.
TI; II
\
iJ
br
Drl l l lns l l 'o 0 i l l l i r i ! l l ' o
CJ-r !Fdq9e !l-srr,/ / ,'1n"rl^i'r
/ / | soct ion
\+4rf
D/. M.S. ! i ,r .rh.rf
(:8. lI DtillinE li.hriqrcs 45
Rccont advlrrccs, howovcr, indicatc thc possibil i ty ofccnlcntirrg hotizorrtt l l
wclls and pcrforating them sclcctivcly.
A selective completion option, a major advantage oflong radius horizontal
wells, would facilitate producing only from the oil bearing zones and
shutting-offhigh walcl or gas producirtg zones.
A typical tuming of 1000 to 1500 ft roquires that thc well perletrates a
rescrvoir 2000 to 5000 ft a way l iom thc spudding point. l 'his lrrgc Iatcrrl l
space requitcment l imits tho trse of this technique in many shorc ficlds
where the typical vertical well spacing is l0 to 80 acres. However, this
types oftechnique is very useful in offshore drilling
D,-. Nl.S. F'Ar:rhat
CIL III Har tt: ofllotiznalal tt'c|lr 46
Cunprulr III
PLANNING OF HORIZONTAL WELLS ANDDRAINIIOLES GnonlrTnv
I
l-Qeagg11y of Horizontal ll/eu or Drainholc
Wcll dianrctcr', wcll tnrjcclory antl shapc rvithirr lhc rcsclvoir havc a sigrrif icarrt
impact on costs and overall rvcll success. c. g. productivity and recovery.
Consequcntly gcometry is a crit ical aspcct of horizontal rvcll dcsign.
i.I lTell Diameter
The diameter of horizontal section is the easiest well geometry element to
identify. It should bc the snrallest dianrctcr', \\,hich u'i l l allow thc following:
l. Use of controllablc ancl dti l l ing asscnblics and hydraulic programs to
achicvc placcrrrcnt objcclivcs anrl holc stlbil i ty.
2. Sufficient clcatancc to run thc neccssalv cvaluation tools.
3, Sufficient clearance to install the requircd complction, production, and
wolKover equlpmenr.
4. Sufficicnt diarnctcr for ccononricil producfion.
l lowcvcr, t lrc init ial hotizontal wcll in a ficld dcvclopmcnt shoulcl bc dcsigncd
wilh largcr dialnctcr to allow running an cxtra string of casing in case of
unexpected hole problems, e. g. influx of rvater or gas. I lolc diamcter can
possibly bc rcduced once dril l ing/conrplction placticcs and concsponding ltolc
,D,: IU.S. l':rrrhat
CIL III I'ttrti'tg ttl Ilorizotttt tvctls 4',7
conditiors have been evaluated on the first well. Also, the well diameter
sclcclion is tcstrictcd by thc cliamclcl of cxis(ing vcrtical wcll 1() bc rc-ctltctcd.' l he lcsll icted diameter may litnit well lcngth, cvaluatiorr.
Completion or produotion opclation options. ' l ' lrcsc consctptcuccs utust bc
considered early during the wcll trajectoty design.
lL lV_ g!!,ProfiLe
' fhc nlost increasing woll goomctly aspect is t lre wcll plofi1e withirr l lrc
reservoir as shown in Fig. 3.1 that i l lustratcs horizontal rvell profi les used for'
d i ffcrcrrt app I ications.
Fig. 3.1 llasic well profilcs.
1.., l, t
3.2.1 Flat wells: are uscd inhornogeneous rcscrvoirs to solvc watcr or gas
coning problems. Thjs is the easiest and least expensive design shape to
accomplish, but it provide thc lcast options over thc well l i fe.
j,2.2 []nddotittg 'ells: ^re used in reservoirs containing impertneablc
barlicrs that scpalatc thc l€scrvoit 's iDto two oI n]olc isolatcd reservoirs.
Dr. ['1.S. F:lrnhat
CH. III Ptautittg ofnotizohtdt utetls 4a
i,2.3 Upword inclined welk: arc tsed in dirty rcservoirs where gas coning rs aproblcrn. As the gas intcrlacc nrovcs downwarl and clr(crs thc lal crrci of lhchorizontal wcll. ' Ihe
end ofthe wcll can be plugged and production contimred.' lhis wcll plofi lc has thc advanlagc thrt it loculcs nll of t lrc f luirl lcvels lrrr rrI l i vcs l l r ( i ( ) l l t i ( ) l o l l r l r rgg i r rg l r r rc l i t l r c c r r t i r r . l ro r izor r t r r l scc t io r r r r r r r l l r r rxhrc i r r l lthc well as a vcrtical rvell.
3.2.4 Dotptut'ard itclined *ells: are used in dirty resewoirs where waterconing is a problcnt. As thc watcr interlace moves upward, waiel comes lDtothe far end of the well f irst. The inclined well can therefore bc pluggcd backand corrtinues to bc produced after watel breaktlrrough.
3.2.5 ll[ultilct'el wells: are used with sand lcnscs and with rcscn,oirs sepnratedby inrpcnncable banicrs. ' lhesc v,clls have a higlrer challenge/risk in tcrms ofhajeclory control but provides for dual brcak thr.ough in the rvcll s l i fe byiso l r r l i r rg o r 'q r l r rg .g i r rg t l rc lo rvcr s tcp r r l ld un( :c ( ) r r r r i c $ , te r l l r x l l l ( - t i (n r o r j r rs_
3.2.6 Mt l i hrot,(:h: Sllort radii are widcly uscd. Multi branch rncdium antrlong radii wells are beginniug to be usccl and should find widcspr.cacl usc in thclcxt l-cw ycafs duc to thcir inrprovcrl ccotronrios and incr-cascd t|rlr irragc arca.
j.2-7 Gmrit.1, drainocc l,cl ls: ar.e bcirrg dri l lcri in dcplctc(l rcscrvoir.s wil l l lrodlivc nechanisnr other than gravity. It is l ikcly that gravity drainage wclls canbe t tser l in l rcavy o i l s t rcnrn l io , r , l i ng p ro jcc ts .
3.2.8 Conple.r tell sltopes: conbine molc than one oftire abovc well sfierpesand are useri in rcsovoirs with con4rlcx gcology thrt varics widcly ovcr lhclength of horizontal rvell.
1.3 D esigttllOt'i.zot, to l lt ellI!4ie.'tot!
In accordance with the horizontal wcll dril l ing, ther.c arc thrce scotion rrarlcly:L yertical sec(iol; it is dril led from sca bed (rnud lirc) unlil kick-offpoint
(KOP).
l)/'. M.S. Iarahrt
CIL III Planning of llorizontol llclls
Ttutting or curvetl or angle build section: it is drilled from kick-off point
(KOP) to the end-of-curve ([OC). ' l 'his section incluclcs thc f irst-bui ld arc,
t lrc straiglrt tangcnt, thc sccontl- l l r i l t l iu 'c.
llorizontal section: it is drill(xl lronr thc cnd of sccond-hrrild nrc (llOC) to
thc end ofproposed distartce to be dr:illed horizontally in thc pay zone, ill
accordancc with t lrc typc o[ 'hor izorrtal wcl l to bc dri l lcr l .
The design of horizontal well rnentioned here is a part of Farahat's researclr
publ ished by Cairo university. 6{r ' International conference, Feb. |999. l 'his
. design is basecl on the conccpt of tlre sirnple tangent build curvc. The three
major scctions that fomr a horizontal u,el l or drainholc aro showlt in Fig. 3.2.
Thus, from this Figure, the thtee section may be designed as l-ollows:
,1 -Ha - V
3.
V € G E O M E T N YA A S I C g U t L
olI
D C U N
H-|
Fig. 3.2 Design of ltorizontol v,ell trajectotlt using lhe sinrple
vEnncALsEcr ioM n
tangent build c:ut ve nrelhod.
Nl.S. |rarah:rt
CH.III Planni'ry of Hotizottol tlclk 50
l. Thc build-radius of the first-build arc:
R: 5730 / B, ( l )
2. lleight of the fir'st-build arc:
D' : R(Sin lr-Sin I1),
3. Height ofstraight tangent
D, : L, Cos Ir,
4. lleight ofthe second-build arc;
D,: R(Sin !-Sin lr),
5. The iength ofthe first section ofhorizontal well: KOP
KOP : TVtLD,-Dr-Dr,
6. The displacement ofthe first-build arc:
(2)
(4)
II, = R(Cos Iicos I), (6)
7. ' l:hc displaccrncnt of thc stmight langcnt:
H, : L2 Sin Ir,
8. The displacement of the second-build arc:
lIr : R(Cos Ir-Cos It,
9. The length ofthe first-build arc:
(3)
(5)
(7)
Dr M.S. I'arahat
. (8)
CH.III Platui g of lrorizon,tt Welts 51
Lr : 100 ( l i l r ) /8 ,
10. The lcngth ofthe second-build arc:
L3 : 100 (I,- lr)/B
(e)
( l0)
||. Ihc rrcusulcd dcpth atlhccrxl of lho firct-l)uiltl afc:
MDr : KOP l- Lr,
l 2 . ' l hc rnc l r s r r r c r l dcp l l ) a t t l r c cn ( l ( ' f s t | 1 r i gh t t | r ogc l :
MDr=MD,+Lr ,
13. The mcasured depth at the end ofthe second-build arc:
MD3 : MD' -F L3,
The lengtb ofsecond section = L, + L2 + L3 or MD3-KOP.
( l t )
( t2)
(13)
t4. The length ofhorizontal section or third section: H (14)
This length is selected according to the tuming radius of horizontal well to beploposcd.
EX. l: During dril l ing a horizontal wcll in Egyptian dril l ing concession, thefollorving data wcre requircd to design this well trajcctorl, namely:Minimum expected anglc build fate:8?100 ft.Minimum tangent lcngth = 120 ftr anScnr rngte = )u.
Tarrgcnl angle 90'al S000 ft TVD.Design well trajectory.
EalJlti!2!fl. 'Ihe build-radius ofthe first-build arc:
R: 5730t8 = 5730/8: '1 t6 f t
Dr: iU.S. Ihr:rhnt
cn.III Phn iry ofrrotizontat ttlerts 53
MD, = 16P 't t, = 8206 + 625 - 8831 ft.
12. The measured depth at the end ofstraight tangent:
MD, : MDJ J Lr : 8951 -F 500 = 9451 ft.
I-cngth ofsccond scction: Lt J [_, + Ll: 625 +120 + 500 : 1245 ft.
14. Length of horizontal section or third section = H proposcd length inaccordance wi th R: 716 f t , where R:800 f t I , I :3000 f t . thus, R: 716 f t ,H will be 2685 ft.
1'hus, the proposed lcngth ofholizontal section:26g5 11.
The measured or drilling depth ofhorizontal well
: KOP + Iength of tuming section I lenglh ofhorizontal section.= 8206 + 1245 + 2685 - i2136 ft.
The displacement oflrorizontal rvell path or trajectory: Ilr + II2 + FI3 + Il :265 -t 92 1, 460 +2685 : 3502 ft.
The tnre vertical dcpth ofhorizontal we path or trajectory: 9000 ft.
,r. ^t,S. Fr|.ahrt
CI{. It Dtilli'ry Probt.ns 54
Csaprer IV
Dn rr,r,rNc PRonr,nnrs AssocrarnD wlTlrHonrzoNur,Wrll
DRIT,T-INc Aun TIII i IR REMEDY
l 'here are four nrain problems during dril l ing horizontalnarncly:l . Dc l ivcr ing wcight to lhc b i t .2. I{cducing torque and drag forccs.3. llolc cleaning.4, I'rotcction of watcr-scnsitive shalcs-5, I)ir cctionill control.
wells and drainlrolcs,
4. I D eQ'r:e ry,Wihlt la t h e Bit-
Applying sufficient bit weight for optinral dri l l ing rate that is oftcn a proorcrn!
cspccially at highcr anglcs ancl whilc dli l l ing the hofizontit l; scction.
Corlverrtiorral bit rveight for efficient dli l l ing is about 2000 5000 lbfpcl inchofbit dianrctcr. ' l he available bit weiglrt f lom a givcn asscnrbly thcorelically is
teduccd by a lactor related to the cosine of thc dli l t angle.' l lr is cosinc
approachcs zcro as the holc angle rpp|orclrcs q{t '. Mot.rl asscrnblics dri l l
eff iciency with less bit weight than ro(aly assernblics. They cornpensate for bitweight with highor rotational speed of turbincs and motors.
Bit wcight may bc increased by rcducing drag and krrque. Bur often this is notsufficient Ibr an optinral dril l ing rate in holcs with highcr anglcs and inhorizontal sections. Bit weight is o{Ien increased by using the split assembly
,/. M,S. Frrrhat
:r:tCI IY Dt illit'8 I'knttuLs
which diving the botton hole assembly into two parts as shorvn in Figure 4.1aar rd 4 .1b .
l l C o l l a r s
e n l a l c o m p r e s s l v e
[.4WD Pulser rReslr icters u b 1 I s u b
tEtllloEl'.lffiD c:: _-l o
I I *.*"^"\ ./ \I c o l l a r s - j
- D o w n h o r e \.-.------____- Molor
\-------- \
r i l l C o l
e O r i l l t
[.4WI
l " N ol c
nl l 3-1,/2' Dg
fi.0'..,, oU
E r D e r i\se, v ic';:,h
Fig. 4.1a Generalizcd ,lt illstr ing conf gtrnliott
c5.
Fig. 4.1h Achievirtg uleight on bit tllrouglt contpresstve
forces using split a,tsentblies.
Dr. M.S. Frrihrt
(11. l l l r i l l i4 hr o ' t 5('
' l ' hc lowcr par t o f the assenrb ly , i t rc lL rd ing lhc b i t , n ro to r , d i rcc l iona l conho l(ools, and the nonmagnetic coilats are lcl l at lhc bottom ol thc dr.i l lslring. Ihcfcnlaindcr ofthc dri l l collars arc placcd in lhc vcll ical holc or irr an up1rcrourved hole that has a low drift. The two sections are connected withconlprcssion pipc or in sourc cases hcavy lvcight or rcgular t lr i l lpipc us strownin Fig. 4.2. 'fhe
dril lstring is completcd in the conventionnl rnanner rvil lr<hil lpipe from the top of uppor sectior to thc surf'ace. Split bottom holeassemblics reduce drag and torque so that nlore weighl can bc appliecl to theh i t fo r d r i l l i r rg f t rs te r .
I reav}1,leight Comp- Drj[p,po roorivo cotiar
pipe drill
I"ig. 4.2 Conponents oJ ltot<ttn lnle assenbll,.
' fhe heavicr dri l l collarc ate more cflcctivc placcd in thc vcrtical holc scction
as conrparcd to placing them in the horizontal or.highly deviatcd hole scchon.' lhcy
cxcrt ntorc down q,ard folcc to thc lorvcr dri l ls0 ing and lcss folcc on tltcsidc of lhc rvcllbore.' l 'he forcc is trarsnrittcd by lhe comprcssion or dri l lpipcto the lower half of the assembiy in the high argle or horizontal hole section.Part ofthe dowtq,ard lorce is sti l i lost due to sonre drag and torque.
' l 'he cornprcssion pipe or dri l lpipe connecting the two assonrbly sectiorr
logcthcr opcr tcs in contprcssion, so thal l l lc risk of hilurc inclcascs. l)r. i l l ingrvi{lr a sllccablc assenrbly and rotating thc dri l lstr. ing slowly, also is
I
/ ) / : l , l .S. Fxrnhnl
CII. lt' Irtilliug hlnn! l : r /
r r ' ( r .p l r l ) l ( . . ' l l r c j r r r l r t t t r t l x ' t t c r l r r i rc r r l l t t t r ' I t l i v t ' rh i l l ( . t ' l i r f t l i t r r r r r t r l i r r l t l v
r r l rovc i l l i r I c l l cc t i vc . j t l r i t tg t r r r r l l r t t t t rp i l tg . lh is i t t c tc r tscs lhc wc ig l r l i r r l l t c
lowcr asscmbly. One athactive is positioning the jar butnpcr sub olr top of thc
lower half the assembly and let tlre compression pipc pl'ovides woigh lol the
jarring action. Also, a jar bumper sub should always be placed near the top of
thc upper halfofthe assembly.
4.2 Reducins Torque and Dras Forces
Drag is a lorce restricting the movdment of the dril l tools indirections parallcl
to the wcll path. ' l orque is thc lorcc rcsisting rotational lrrovonrcnt. Dril l s{rir lg
rub and slide against thc wall oflhc |olc during rotation and nippittg as part of
rcgula[ dri l l ing activit ies. Drag and torquc are nleasurcrncnts of this frictional
Icsistance to thc movement ofthe dril l tools.
Drag is rncasured in thousruds of pounds over or undcr the free hanging
wcight ot thc dri l lstring. 1'orque is tncasurcd in loot poutrds ofapplied torqttc.
It is inlportant to have a good weight in<licatot attd torquc-ttrcasttt ittg
cquipnrcnt. l lxoess drag and torque causc dircctional dri l l ing pr'obtcrls
espccially in turning and horizontal soctions of horizontal well, oftctt vcry
scvcrc in thiswell. lhc dli l lsl l ing can lail [tom lctrsion tluc kroxccss drag ot'
twist olf cluc to exccss tolquc. I l i thcr casc lcavcs an obsttttction in thc holc
requiring fishing, Open holc drag causcs key seats that, in turn increasc drag
and torquc. Drag increascs the risk of sticking in kcy scals ancl dif lcr.cntial
prcssurc sticking. Dlag also lcducc availablc bit wcighl scvcrcly al hrghcf
anglcs.
Eliminating all drag and torquc is not practical, but prcvcrrtive actions lcdrrccs
thcnr to acceplablc lcvcls. l l is bcst to dcsign thc wcll pattcrn for a minitttLtttr
r r r r rbc l o l -c l rangcs o l i tng lc a r t r l a low i r r tg lc o l b t t i l t l o r r l rop . l i xccss t l t i tg i r r l r l
torque arc tcduced by placilg casing in tlre hole. Drag incrcascs as thc sinc ol'
holc anglc incrcases. As lhis anglc apptoachcs 90", thc stl ing wcight is
transfeued from hook load to drag weigh. Reatning reduccs dtag and torquc
causcd by key seats and rough rvcllbore. Thus, it is itnportant to drill smooth
cr.u.res and straight inclined or ttuning scction. Reducing dril lstring wcight
rcduccs dtag and torque at high quality of tnttd with goocl chcntical arrtl
,r),.. M.S. Frr.hxt
CE.II' Dtiuinql'toblens 5 6
physical propcrtics which are essential. Oil basc nrud should be considctcd fot
more demanding situations because of its good lubricating qualities.
4.3 Hole Cleanins or Cuttinss Removol
A particular problem that arises in dril l ing horizontal wells is thc difficulty o[
removing rock cuttings frorn thc horizontal seclion of thc rvcll. -l hc sourcc ofIhc ploblctu is t l l l{ cull irgs tond to scttlc in lhc bollont ol thc lrolc rrttt l i t l lorv
the mud to pass above without tmnsporting thenr. Seltled cutl ings are
rrndesirable sincc they increase the friction in the hole and, if i t is latcr
colncntcd, proclrrcc poor ccnrcnt bonds- A grclr{ irnprovcnlcrl irr rcrrrovirg
cull ings has bccn achicvcd by using top-drivc dri l l ing rigs. lr lhcsc ri l ls, lhc
dti l lstl ing is roti lted by a largc. gcatcd clcctric ol hyrfiaulic (lr ivc nrok)f
(typically 400 hp to 1000 hp) rvhich slidcs up and dosn thc dli l l nrirsl on rails
(scc l l ig.4.3) rathcr t lran by tlrc convenlional rot.ry table ao(l Kclly. With this
arr?llgcnrcnt, it is possiblc to rotdtc thc dr i l l s{rirrg and kr cilculirtc rrrr,ul its l lrc
s l f i l g i s l c r rovc( l f i r )n r lhc l x ) l c . lh is l c r r r l s to kco l ) l l r c r I i l l c r r l l i rgs i r r
susponsion and to proviclc a nruch clcancl hole. lhc rcnroval of crrl l irrgs
rcduces l 'r iction bctwecn thc dri l l pipc and thc holc and rcduccs thc lcndcrrcyl in s t i ck i r r !1 . l lo rvcvcr ' , thc l I nspor l o l ' cu l l i | l gs by lhc n ru( l i s r r ro rc t l i l l i c r r l { i r r
a hofizontrl holc than in a vcrl ical one bccause llre cultings tcnd to scl(lc at {hc
botlulr of t lrc holc and thc fluid tcnds to pass abovc. I I igh fluit l vclocil ics arrtl
tnlbulcnce prornotc the transpoi of lhe cultings, but lhis can bc l inri{cd by a
tenclcncy for washouts in thc wall ol thc hole arrcl also by thc physicrrl capacity
o f thc n rud pun lp to p rov idc f low. ' lo p romotc tu rbu lc rcc , i t i s dcs i lab lc to
havc a low fluid viscosity. On thc othcl lrand, to rcstrict thc scll l ing of thc
solids whcn thc flow is stoppcd, a high viscosity is ncccssuly. ' lhcsc
conflicting requirements can be accomniodated, at least particularly, by
rnaking thc nrud a non-Newtoniarr plastic f luid rvith a high latio of yield point
to plastic viscosity. Polymcr nruds are conr only used lor this. AIso,
rnininrizing formation damage should alrvays be a majol concern in sclcctirrg u
mud system and particularly the chemical components within it.
In practice, a wide Varity of drilling mud compositions has been used for
dril l ing horizontal holes, depending upon the situation. Also, thctc can begood rcason to use oil-based tnuds to control shale swclling. They perlonn
D,.. N{.S. Frr:rlrat
CIL Il/ I)rilli P I'rohlrnrs 5!)
better than inhibited water muds in this lespect. Howevet, oil-based nuds are
difficult to dispose of in an environmentally satisfactory rlanner and they ate
t r rorc cxpcnsivc l l r l r r wl r (cr - -bascr l or rcs. As i r corr rprot t t isc , wi t lc r r t t t< l s l t l l - rv l t lc r
drilling fluids containing water-soluble polymefs are ollen chosen for drilling
horizontal wells. They can have good inhibition and lubrication qualities at a
glve
lower cost and without tire problems of n-rud disposal found with oil muds.
Polymer
sol ids is
r.nuds also improved drilling rates if the content of suspended
kept low.
Fig. 4.3.
4.4 Protectiort of Water Sensitive Sltales
Shale layers frequer-rtly tend to collapse in contact with fresh water. This can
be prevented by using oi l-bascd dri l l ing f luids. Thcsc f l tr icls trsual ly consist ol '
an invert emulsion of water in diesel oil together with other additives. Fluids
of this type have been used in the North Sca. Watcr-based nTuds can be
inhibited to reduce the attack on water-sensitive shales by the additiou ofNaCl
or CaCl2. These additives reduce the chemical activity of the water and its
tendency to penetrate into the water-sensitive shale. lnhibited water-based
Portab le Top Dr ive Dr i l l ing SysternI'lrol o <:o u rl e s.y Titsco l)ri lliu g 7'ecl t n olo gy
Photogruplt slrorvirtg portable syslem installed beby,rig's existing block, hoolt autl srvit,cl. Ilylrtulic ser-vice loop goes lo pump skitl. Torque ruck is lastcuedlo hack of derrick.
Dr. M,S. Farahat
Cn. Iv Dritti',8 t'tohten's 60
[ludi are nol as cffcctive as oil-based nruds for the plotectior of shales, butthcy arc {eaper and less damaging environmentally.
l lcccnt rcguli l l ions intcndcd to protcct thc cnvifonlncnt rrc nrrking thc usc ofsalt-bascd muds more diff icult for land operations. Offshore sallbascd fluidsarc acccptabic, but thcrc arc rcstriction on thc usc ofoil-bascd nrutl.
4. 5 D irectio nal Contr o I
Ovcrcoming thc forcc of glavity is a fundamental ploblcrn ir dilcctional andho|izontal dri l l ing. The bottom hole assembly (BHA) is a heavy weighthanging on the bottom ofthe drillstring. Thc BllS must ovcrcome thc lcrrcc ofgravity with a strong side forcc for directional drilling. 't his for.ce is appliedrvith stabil ization, f ir lcrums and operating techniqucs. Morc cornnron bottonrholc asscnrblics havc onc point ol-lcvcr.agc ootltact witl l t lrc wall ol thc lrolc,such as a bent. BHA's with multiple points of wall contact abovc the bit can becontrollcd more accurately. Three points of contact definc a constant arc ofcuwature corresponding to the desired build rate of the motor assemblies.Motors asscmbly can be fixed or adjustable. Fixed assemblies have twoaligned lulcrum suppolts for building angle accuratcly and at higher ratcs thanadiustable assemblics. Adjustable assemblics are more flexible for use invarions situations, especially the steerable versions. The term steerable has aspecial meaning in the oil industry.
Most motor assenrblies are steerable in the sense that turning the drill srrrngchanges the course in order to dri l l ths hole in thc desired direction. Thesteerable BHA consists of bit, down-hole motor with build in dog-legtendency, measuremcnf while dri l l ing survey system may allow to continuctrackirrg ofwellborc path (as shown inFig.2.27).
Positive displacement motors developed power from a rotot-srarorconfiguration, as fluid is lolccd into thc opcn cavity ofthc nrotors hclical thcmotor output shaft drives the bit directiy, thcrcby'eliminating the need for dtj l lstri g rotation. The build tendency ofthe motor systcm, referrecl to as dog lcgestablish€d by use of bent housing motor (normally 0.5'to 1.5" angle bendscoupled with under gauge stability ). On the motor itself and iust above the
,r. NI.S. Fnrahrt
CII. It' DriIiIg P,oblcms 6l
nrotor by varying th€ bcnd in thc nrotor housing as wcll as stnbilizcrpllcclncnls glugcs. l\{o dif lcrcnl dli l l ing rnorlcs arc uscrl wil lr s{cclatrlc
systenr. lhe first oriented mode (slit l ing), the motor rvilJ producc angle
changcs rcsulting frotr motor dog-lcg tcndcncy, makirrg it possiblc kr charrgc
the build or direction of*'cl l course.
l)oglcg lcndcncy ol lhc systcrr is dcsigrrcd kr prorit lc irrrglc charrgcs grcatcl
l l l an w l l : r1 l l r c r l c l i l r l l l y r rcc< lc t l , so l l ru l l l r c r rn io t i { l o l t l r i l l i r rg c r r r r l r c t I rnc r r rrolary drilling nodes. lt is possible to obtain overall build or turr rate neededfot u'cl1 patlr rvithout tripping.
4.5.1 Ckssiftcstiotr of bottom hole ss1eJlblias (BHA's)
Thcsc arc subdivided into rotary and molor classificfl l iols, l l l lA can bc hrrlhcr
divit led into categor ics. ' l 'hc
kind of equiprnent and posil ion in BilA nolmallyclassifics the asscnrblics the assembly type. The various typcs of urotordcviation section are shown in Fig.2.29. BIIA's are nsntcd basctl on usagc aslistcd in tlrc followins table.
4.5.2 Medsuri g ittstntments
Measrtring instruments record drift, direction, and tool
nreasurcmcnts for directional and horizonlal operations,
lacc of thc basic
to providc accuratc
8il..1's
Natnc (usacc
Linrber , nrotof
Deviation or sidetrack
e build
Rotary. or motor
Anele hold Rotary, ol rnotor
Reamin
fishing
D/' iU.S. Farahat
CIL Il' DtiIi"E hoht.Dts 62
conlrol, somc tcclrniqucs arc applicd such as l lrc stccr.i lg tool or MW!) arcgivcn below. fhe advantage of MWD over steering tool is that MWD can beused in both rotary and oriented motor phases drilling.
4.5. 2. I St.\'t'ing turol
An instrument package contains a modified magnetic single shot and otherinstrunrents (as shown in Fig. 4.4). A coder conveds the nrcasured data toclcctl ical pulse, and a scndcr transnrits (hcsc clata to lhc sur'f ircc l l ough ashiclt icd clcctl ic conduit. Surface equipment includcs a rccordcr to covert theclootrio pulscs and digital or TV typc displays. ' l 'hesc
inslr.urrrents arcavailable immediatcly at the surface for usc to control hole direction. lnopcfalion, the instlunrcnt package is lowcrcd and raised rvilh a shieldedc lcc : l l i ca l co l (h r i t (cab lc ) on thc rcc l o fa rvcnch pos i l ioncd on a t ruck . ' l ' hcp i r t : k i rgc sca ts i r r l r rccc iv i rg o r ins l runrc l l s r rb i r l l r c dcv i l l i l g lDo lo l i t sscnr r ) ryiurd lcrnains in thc holc duling thil l ing. l{otary asscmblics can not bc usc(lwilh stccring tools. 1hc dril lstring rvith dircctional nrotor asscmbly on bottornir lor.vcrcrl l)af{rvly into thc holc. l hc i lslrruncnt l)ackagc is lorvclcd insicic l lrcrh i l lslring on a cablc tluough asitlc cntry sub out into lhc anntrlar sltacc. l hcrrlhc cablc rrrrl dri l lslt ing arc loqcrcd logclhc[ \\, i1h lhc cal)lc oUtsidc andparallcl to thc dri l lstring.
d!,2. 2 M ea $tr e m e n t-w h i I e d r i I I i u g ( M ll D)
Mcasurcnrcnlrvhilc (MWD) rccords nlcilsurctncnls at or ncar lhc bit whilcdti l l ing continues.
' lhe data are transporte(l immediately to tlre surlacc as
pressulc pulscs in mud column covcrcd by a codcr storetl in a storage clcr ice,and transmitted to thc surface.
' l 'hc instruntcnt packagc has [ratterics or a snrall
turbinc gcncrator driven by circulatirrg nrrrd for a pou'er supply as shown inIrig.4.5. A conrhlon systent has a rnud pulscr that rcccivcs storcd data andconvcrts it into high-fiequcncy pressurc pulscs in l lrc rnud lop a sctsit ivc
llessu[e detector at t lre surface. Sulface cquipnrent includcs a decoder toconvelt the pressure pulses to elect cal pulse, digital or Tv-type dispiays andlccordcb as shown il Fie.4.6.
/). lll.S. Farrhnt
CII. IV D,'illing Prcbleus 63
\
lllt(lltte k, Sltttcc RflJi t
. Nott.tuaE'ftric Dt ill Colhi
St,rJey Stc.\ i ETool
' lluleshoc Oricnrltrg Sub
'Dc,tt Sub
Rotnthry ltit Stl,
l loat lor-r t
ConT puter & Pr inter
Powor Non Maonet lcCablo Drl l l Col lar
Bont.--
Fi.g. 4.4 Survey steering tool.
Dr'. M.S. lralahat
CIL IV Dtilling lhblens 64
DIAGRAM OF TELECO's MWD TOOL
Allernolo,
Hon-Moqnclic(ollor -
0ircr l ionulSenror
Fig. 4.5.
'l'hclcforc, an M WD systenl cotl'lpriscs:
2 .
1. A dowr-rhole tool assembly, consisting of a special non-magnetic drillcollar housing the sensors and electronics for measurement andtransnrission functions (Fig. 4.5).
A surlacc systcur fol' thc detcction and clccoding of the IVIWD signal andconrputati<rn and display ol ' thc M WD clata as shown in l1ig. 4.7 .
Mud flow
I
Dr. l\{.S. Fnrahat
lD t r , r , ro" , r r . t - ,qrr , , r r , ,of i ) t o," , r ,o" r : . " "" ,n
A r l n a q l r i \ n ' a ^ l i ' r r , r l
i ---
1"",, .,j ,'r;;r.r;;11
t ; r n r r u - l ) i r r ( l i ' n r i ' l S , ! \ l ( r r l
sof ro , l , ln . r r , r t n . r r I "n r r tl l " . r I ' o r . r t I rn !x r i , ' r , r .
Ar l 14 . ' l rhs . ,6 r . r , / fo i i
)ii,';
t t r \ i i t i v i t l - ( ; r r f l r r r n . l ) i r t ( t i o r r r lS l 5 l t r l l
STEEYEAS9€I'ELY
rgo|.A-agf-MIltY
Fig. 4.6 Measurentetft wlile drilling (MWD)
I)r'. M.S. Fnraltat
CIL IY Dti i'19 Problens 66
Rlc Fr-oon fisTEra_ -
l = _ _ - _ _ _ - . - - _ - _ - ]
DRII-LERs
NoN-r^cdErrc "-- ""*l
x4.lV.D. D^r ^aulsmoF P^cxacE
Fig. 4.7 Nerv MWI) tool.
L.E.D,DISPLAY
/)r'. l\4.S. Irat.aha{
CIL lY Driuiltg I'toblents
l \4Wl ) sys lc r r c lu r l ) r r rv i ( l c . us in l l v : r r io r : j r l i l l i t c t r l cor r rb i t r : r l i o r rs lhc l i r l l rw i r r l l
irr l 'olrrrlt ion:
l . Sr rvey in lo rmat ion : d i lec l ion . inc l ina l ion and loo l lacc rcad ings .
2. Fd-nlation inlormation: gamma ray, r€sistivity, rreutron and densityreading.
3. Mechanical information: downhole weight, toaque, shocks, flow and
temperature readings.
Also, thcre are three distinct types of MWD transmission systen currcntlyavailable:l. l lrc positivc pulsc systcnr: in lhis systcnr a plungcr- typc vllvc
nlonrcntarily obstructs mud flow, giving risc to a trrnsicnt pcak i l lstandtripc pressure (Fig. 4.8).
2. '[hc rcgativc puJsc systcm: in thc syslcm, a valvc nr(nrcnliri ly vclls a
poftirn of thc mud flow to thc borcholc arrnulus, gcrrcrl l ing l lr lnsicnl
drop in standpipc pressurc (Fig.4.8).
3. The continuous wave system: in this system, a spiming, slottcd rotor and aslotlcd stator lepeatedly obstruct mud flow, rathq l ike a rotary valvc or asitcr. 'Ihis gcncratcs a continuous low frcqrrcncy l luc{ualion in sfandpipcpre isure in tlre region ol'30 psi cxactly l ike a low pitchcd hum. 'I he carrierwa e is modulated, rather like an FM radio transmission, to convcy
infi rmation to surface.
!!9.!! lllD truts mk s io n svste nt
The mcdulator generates a repeated se[ies of flucluation in staudpipe pressure
by pcri.rdicaily obstructing nrud flow as the rotor vanes occlude tl le statiotr
slots. ' lhus, the 12 l lZ MWD carrier wave is generated. ' l 'his construct
flcrlrrcrr;y wrvc is modulrrtcd, ot cnclosc(|, by pcriorl ic t lcrcclctaliorr of l lrc
modulaor rotor whiclr introduce phase shifts into the carrier wave. ' lhis
rnotlrrla ion tcclrrric;uc is vcry closcly corr:pirr ':rblc lo ficrlrrcrrl ly to ficqtrcrrcy
mo<lula jon (tiM) radio broadcasting, as shown in Fig.4.9.
,/: l\t.S. [1lralr,lt
CII. IY Drilliug l\lthlcu's 68
+t-,-_______,_
TimeMDASURIIMBNTS IVIIILIt DIII I-I-ING
Fig. 4.8
4. 5. 2. 3 G eo steeringuElLlpt11elllLgrul lrt st r unrcntatio tt
'I'he newest lrlarket developing in MWD is fol geological steerirg, sonletimesci\l lcd geosk'ctittg or ravigatiol ofthe well coutsc, accolding to MWD lithology measuremert. A geological specialist, engineer, or geoscientist is usually
at the rvellsite fof interpretafion of the dala bcing neasured. To be effective,these new systems lequire uteasulem€nts closer tlre bit.
PositivePulse
NegativePulse
Co ntin uo usCarrierWave
[-{
ilnlilml]ilm
Pressure
Tinre
/ l / . [ { .S. l r : rrrhi t
Fully Closed
Valve opens and closes5 times per rotation
Al 2.4 rotations per seconda 12 Hz carrier wave is crcate(l
Padially Open
Titne
lra stu is.t ion r)tsten1.
60Fully 0pen
P
Po-
Es!!p44!!!!
' l ho rv l ro lc MWt)- l i l l ro lugy nrc lsr r lc r rcr r ls or gcus lccr i r rg cr l r r ipr r rcr r t is s l rorv lif Fig. 4. 1 0, whicJr compr.ise:l. A downholc tool asscmbly, consisting of a specirl non-nragnctic cLillcollar'I to t rs i t t l l , l l t c sc t tso ts , i r r t r l r : l cc ln r l i cs l i ) r l t c i * i l t ,L l le l l s l rn t l l r l r rsnr iss io r rlLnot ions , as shown i l l r ig . 4 . I L
2. Surface system for the detection and decoding of the MWD signal and
conrpLrtalion aud display of thc M!VD dala, as slrowl i l lr ig. 4. 10.
l)/r M.S. Farahat
< II. Il lrtiqing I'hn)tu s 70
i;G
6
l,;
!.?
{
I A 5 !
I
t ,E
E;q;
t'z5a5
c8oi i i
?- .
I i:l r i
i l,{'
q t
t t
st:!
o
Ir)
Fig, 4.10 Geo.rtecring lc(h iqrrc.ah l(Jh
ilql-c)
,/. NLS. Ihrahat
CII Il/ Dti i E l"ohlzn's'71
I Slt uttt (trhtlio,t:
The advanced MWD or Cieostocring system can providc, using varrousdiflcrcnt combinations, the following infornration:l. Survey infornration: direction, inclination and tool face rcadings.2. IoDnation inl 'orftationt gamnta ray, reccptivity, ncuh-on and dcnsity
rcir(lt g.
J. Mcclranical infomtaiiorr: dorvnltole weight, torqrrc, shocks, f low arrd(cnrpcrature lcadings.
4. I., i tho logy irrformation: geological markers and/or thc top of |cscrvoir,forrration dip, stratigraphia control i ir thin and dipping lcservoir.s, highrcsolution seismic mapping ol'complcx gcological slnlclul.cs such as sil l ldomcs, local fault structurcs and con.rplex layeled procluclion zonc.
Apnlicatiotts:
Thc new MWD or geostcering systen is csscrrtial fbr pr.ccise r.vcll positioniugu,hich is crucial to tlte success of dril l ing advancetl horizon{al and extended_rcach wells.
IU.]Y.I). I)OWN IIOI,E SYS'INM
l;-T- - - aAI rLnY
< 3 6
^?," I-to
u| l l t I
Fig. 4.11 I4\I.D dov,n hole sys/en.
/ ) / M . S . I ' x r : r h x l
CIr- Y Drilst,i g Dcsign 72
CHaprBn V
DnrllsrRnc DnsrcN
Many different traiectories can be used to drill a horizontal well to a given
la rgc t . lwo cdr l ro r n l tc r ' r t l t i vcs l r l c s l ro rv r r i l l I ig .5 . l . l ro r r r l l r i s l ig r r le , t l r c
broken linc shows the traicctqry that would be followed if there were a
curs lu t t l l t c l ius o l ourv t lu rc . l l t c t l r j cc to ty , l cp ic tc r l I ry l l r c so l i r l I i t r c s l tocsl r i l l l r r r ' c r r rv : r l r r rc n l l l r c s l r r r l , r ' r r r r rc r ' l c r l l , y r r l rn l l ( | | l sc r ' l i on lo r r r ro l l r . r c r r rvc r l
section at the botton'I. This tangelt trajectory has been used fiequently, but it is
not as common now as it oncc was. The main reason for using it was to givc
.nore flexibility as the reservoir is penetrated. A difficulty with thc constantradius approach is that, if it is found not to be practicable to achievc thc radiusofcuwature assumed, the holc may end up too deep. In somc cascs, when thishas occutred, the long-radius BllA chosen init ialJy has bcen rcplaccd by arrredium raclius on to allow morc rapid deviation. With rnodem adjustablemotors, such a change can be achio,ed by motor adjushncnt. It is nowconrnron 1o d l i l l r v i l l r a cors lan l 8 to l l /30 nr ( l (X) l ' t ) l r r r i k l la to o r lo r rsc 15"to 20'130 m (100ft) rate up to 65"to 75'and thcn finish the angle-build sectionat 7'or 8'130 m.
IRAJECTOFY WI IH I I IGHFI | BUILD nA iLAND TANGENT SECTION
Paih lor co.rl6nt n \
Fig.5.L
D/. M.S. Fnl.'lh^t
CII. Y Dti sttitry Desigt'
In dril l ing vertical wells, fi-iction betwecn the dril lpipe and the wall ofllre hole
has little effect upon the weight on the bit (WOB) This weight is basically the
buoyant weighl oflhe dril lstring in the hole less the pull on the rig block Tt is
adjusted to the desired level by the driller' When drilling inclined, and
particularly hot'izontal holes, friction has a much greater effect ln the
horizontal section, the drillpipe lies on the bottom of the hole and its weight
does nothing to drive the bit folward; mther, its weight multiplied by the
coefficient of ftiction of friction results in a force that decreases the weight on
the bit. As the hole is clrilled farlher horizontally, the weight on the bit
decrcases. This effect is commonly reduced by using lighlweight pipe ir the
horizontal section of the hole and heavier pipe or ddllcollars in the verlical
section. Suclr a string is refetred to as inveded. The makeup of an inverted
string used to dril l an early, very long hole in the Norman wells field is shown
in F ic .5 .2 and Salam f ie ld as shown in F ig 41.
INVERTFD DRILL STRING
- i2l mn' HEV|',ATE to SUFFACE
Fi9.5.2.
I'lowevcr, suggestions have been made for using lightweight exotic materinls,
e. g., aluminum, titanium, or carbon-reinforced plastics, in the horizontal
scction ol'holcs. Irr gcncral, howevcr, thcsc havo bcen considotcd too costly
and it has not been found necessary to develop drillpipes of this lype'
/ r . M . S . F n l x h : r l
a l l . I l r i l lnr iq : I r , \ ign l1
Heavy- Weight Dri l lp ipe
Spiral Dri l l Collar
Compressive S treng th Dri l lpipe
MWDAngle Build Molor,207100 ft.
Btl
Fletr ievable WhipstockI"ig- 5-3 Drillslring ltsign /br lrilling tlnti gsc(tiou ol ttulitrn" nulitu
horizontal utell or draithole usittg MlltD tool.
The analysis of the forces on the drillstring as they affoct dmg and torque ateof great interest to dri l lels and several contpanies lrave devised contputer
;rtogtatrrs loL this analysis. ' lhcsc clcpcncl upon a knowlcdgc (ol ollcn an
assunrption) ofthe coefficjent of friction between the pipe and the hoJe andnlost stem.
Accotdingly, a torque and drag progtam developed by Maurer Engineeringwas uscd in the dril lstring design. The following assumptions/design criteria
were used:
l. A maximum of 15000 lb weight on bit (WOB) would be required.
/)/ . M.S. trarrhat
( t t . t lh i lh t r i r t : I r 's i ( i
2. ' lhc nraxinrttnr WOR worrld hc rcqtt ircd clrr l ing <lr i l l inl; in lhc oricrrtct i
rrodc (sliding) al' l D (total dopth).
3. It would be acceptable to rotate tlre dril lpipe u'hile in compression as long
as the critical buckling load and thc nlaximum bclldillg stress wele not
cxceeded.
75
' Ihus, an jnve ed dril lstring wottld be
spcc i f i ca t ions . An invc t tcc l d t i l l s t t ing c lcs ign
above thc legular dli l lpipe, as shown in Fig.
5 .6 .
Heavy- Weight Dri l lp ipe
Spiral Dri l l Col lar
design
dr i l lp ipc
ancl Fig.
r Angle hold. . \^r / DTU, 1"
. Sta bl l lzed
motor- 4" I 10rotary
0 fr.tools Retrlevable
Whipstock
MWDBil
Compressive Strength Dri l lpipeFig. 5.4 Drillstring de;ign for drillin g ltorizontal section of rcdiutr raditt.t
lnrizutlul tvt ' l l ot rlnitholc u,ting l, l l l /1) trxtl.
' l lrrrs, l lrc rcgular dli l lpipc as shorvn in l l i1. 2..12 and Fig. 5.7. lvottld bc rtttt in
co tnp tcss ion . F ig . 5 .8 shows t l r r r t thc c t i l i ca l b r rck l i r rg lo l t l wot tk l t r t r l l r c
cxcc<: r l t : r l < i r | in1 ; r ' ( ) l ' r l i ( ) r . n l so . l r i1 l .2 . IB |c I r 'uscr r l s l l r c r l r i l l s t I i r t1 l l l t t l l w( ) t l l ( l
bcuscr l k r t ! i l l l l r c8 l /2 i r r . l ro l c .
D/: M.S. Irxr:thrl
CIl. Y Dti striry Desigli 76
AnctleFlole
Build BottonrAssembly
Hcavy - Weiglr t Dri l lp ip c
Dril l Collar
Compressive Strength Dril lpipe
Angle Build Motor,1.7 '/ f oot
Survey Tool
Bir
Retrievable Whipstock
1 i11. 5.5 l) illstr ing lesigrt JU'drilling tut i g se(tion oJ ucliuttr,tudiushotizoutul tvell or dmlnhole usitlg steet'ing st!rve\, lool.
Dr. i\{.S. Irarnhat
I l l . , I t t i l l t r l ' t ' t i I t t l l l t t'/7
Anqle l"lold BottonrHole Assemblv
Heavy- Weight Dril lpipe
Spiral Dri l l Collar
Angle hold motoroo
c S t a bil ized rotary to ors
Bir
Fig. 5.6 Drillstring tlesigrtfor tlrillirtg hr.u'izorltdl sec on ol redirutt-r'rtdius
horizonta.l t'ell or drai hole using sleeing sut ret' tool
1he specified BHA s ale shown in Fig. 5.9 thtough 5. i2. Otrly lwo stabil izcls
rvoulti bc trscd; onc on tlrc rlotor-[]clt ing ltoLtsing attd otrc ittrttrcclialcly alxrvc
the rno{of. Fig. 5.9 and 5.10 shorvs that BILrys dcsign ftrl dli l l ing holizontal
scclior rlrcdiurr-radius ol'hotizonlal wcll Lrsing sliding tnodc and r-olaty nrode.
A lso , r ig . 5 - l l and 5 .12 s l rows t l ra t I J l l . (s dcs ig i l c r | d r i l l i ng lu rn ing scc l ion
and horizontal section oflorg-tadius ofholizonlal ucll.
F[om case history op an opposed-bore dual horizontal u'cil iu tbc ALrslion
Clhalt formatior ol SotLth fex:rs (t-lSA), it is lbund thst: in thc 121/2 and li l/2
Compressive Strength Dril lpipe
Ir: h'LS. Ihl:lhnl
(:11.Y Dri nri g Dcsisn 78
i r vc r t i ca l l x )1cs ,4 .5 i r cL i l l p i pc l r rd 6 .25 i n r l r i l l co l l l l s wou ld bc uscd i n
conventionl l t [ i l l iug configlrral ions. tfor the 6.25 in. hole, lhe lol lowing strategy was
phnllc{1:
I. lolque arxl r l l i rg woLrld be nrininrizcd by running 3.5 iD, 15.5 lb/ft dl i l lpipe in the
l ro r i zon l i r l l r o l0 i r r l c f v r l s .
2 . ( i r r ( i e S l l 5 r l r i l l p i l r c wor rk l bu r r s rx l i r r l l r e ho f i zon t i r l ho le . ' l l r e h ig l r l ens r lu
slrenglh ol this pipe is lot^ted in compression thfoLrgh the high cloglegs in the
cuwij ( lulning sl jcl ioD).
3. ALlequale 3.5 in heavy weighl dri l lpipc woulcl ruD in the verl ical hole to proride
wcighl od L)it (WOll) and to ovcroonrc holc d.ag whilc orieDled.
4. l lcrrding slrcsscs i nrersurelrent whilc dri l l i l tg col lar corDeclions and in t l te
downholc nrotor would be mininrizccl with nonntagnetic, coft lpressive seNlce
d f i l l p i pc (NMI (S i ) l ' ) asshowr l i n l r i g . 2 l 2 i np laceo l r oumagoe t i c d r i l l co l l a r s .
ArticulatedPlpe
Co mp re ss lveStreng thPip e
Fig. 5.7 lllidtlttel drillpipe dDtlcatnptessi|e sr'et\th (ltillpipe 5in-\rutt-ktlats
D . N l .S . F : r | r h i t
CII. I' Dtt st'i'ry Desig 79
i
!-ig. 5.8 Buckling lootl ts. hole anglefot'4.5 i , 20 ft tlrillpve.
AnEIe Hold MotorString Stabilizer
Section
Bearing Housing with
Ceniralizer / Stabilizer
BirFig. 5-9 BLl,'l rlesign Jor sliding mode dw'ing drilling horizonlal seclion oJ
netlhn>rulius tlf horizontal u'ell or drairthole.
Dr. vl.S.Ihrnlrt
CII. I' Dti rhitls D.,!itn llll
Angle Flotd ToolRotary
SpeclalDr l l l Str lng
Stabi l lzerSccl lon
Bir
Itig. 5.10 Special drill.slring de.signJttr t'otdt.t'nnde dL!ritg drilling horizontol
scclion oftitediukt iddius ofhori.o ttl t<:ll or dtuittltolc.
s
Dr. A'1.S. I i ' :rrnhrt
C -V Dti s it'g Desis 8I
lu4otor Section
Kick - olf Sub
Upper Bearing HousingCentralizer / Stabilizer
with
StringSt abilizer
Bent Sub
Angle Build Motor20"i 100'
Tilted Drive Shafl
Bir
lrig. 5.1 I l) I t.4 desigu Jbr drilling ttutting sectie,n o1f long+atlius cj horizot Ltu I
nell.
I). l \ t .S. lrnrrhat
CIL I/ IrillstrirB D.sigu 82
Strinq Stabilizer AnEle Hold Motor1-4" / 100'
Motor Section
Double TiltedU - Joint
Bearing Housing withCentralizer / Stabilizer
Bit
Fig. 5.12 lllJA design.[or drilling ltorizolttal section oflong rodius ofhu izrtttttl m,ll.
A jo in t o t NMCISDP tesenrb les a lo in t o f 3 .5 i r r . hcavy-wc igh t d r i l l p ipc . I t i snra ul'actured by mill ing the OD o1'a 4.' i5 in. tool joints. ' fwo
I ft lougsections, evcnly spacecl ol tLre pipe bodv, are lefty unnril lccl to for.rn wearknots as slro\,vlt in Flg. 2.12. A fulJ joint oi NMCSIIP is rrrn above the MWDcollal and a |0-ft joinIwith no wear rlragrctically isoiate thc M\\rD scnsors.
D/: i\t.S. nrr.rhat
CH,Y Dti ltti,tg Dtsigtl rJ3
Srrgsr irr&Aryt: pLtstLt( ll!!r!!L cun, el h ole ltllJllJtirSgttlilJ!
' l ' he < l i i l l s l r ing pas : ; i rg a long r r c r i rvcd l ro lc i s bent l i kc a bca tn anc l i s s t rcssc( l
accorclingly. ' l he rrraxirnunr lerlsi le slfess in the wall of t lre pipe cau be
estimalod as showrr in Fig. 2.13 and is givcn by the following equation:
o,= Maxirnrrrn strc:;s: E (Ii,"/R),
where E is Youug's nrociulus ofclasticity, R* is the radius ofthe dril lstr: ing arrtl
I { i s thc r a r l ius o l e r r r va turc o l ' tho l ro i " .
lf, in adclit ion to bcing around lhe cttn ature of the hole, the dril lstring is also,
rotating, tlre stiesscs at any point on the circumference of the string vary l'iorD
tensile to corrplcssive as i l rotates. This tcnds to cause metal l i t iguc. lrr
addil ion, bccuusc l lrc pipc is not continuous, but in sectious jointcd l)y
couplings, the stfcsses are greoter thaD calculated fiom the simple eqttatit 'n
above. It follows then, that if equation (1) is to be used thcre should bc a
srrbstanlial l irctof ol sirfoty. Nazzcl (1990) suggests fol stecl collars, n stfcss ol'
20000 psi combiDeri with a factor of safcty of2, should bc used.' lhis rcsul{s in
a value of 10000 psi {o be used in the above equation. Ihis value is used in thc
follorvirtg cxamplc.
Ex. I:
Cirlcrrlatc l lre radirrs ol 'cuwature to u,hich a cylindlical ddllcallaI carr bc bcrtl
wil luruL cxccctl irrg ir lunsilo stloss ol 70 Mpa (100{-}0 psi), assrttrt irg Yo ug's
nrodLrlus ol'clastici ly is 200000 Mpa (29'k10'' psi) and ttre collar diamctel is
127 r r rn r (5 i r r . ) .
Sohttion:
R = [f)lo,]R,- = 12.01)0001701*|27121*.001 n- l8l m(s95 1i).
01= tcns i lo s l rcss , ps i (Mpa) .
1lr M.S. [ 'arrhrrt
CII. l, Drillstuing DesiC" 84
Or,R = [E/ol R," : [29 * 106 / 1000]* 512*Ll I l2l = 604 ft
l hcrcfore, thc values in thc following table werc calculated ir the same
rrraincr' (using Eq. l):
' l ' ab lc 5 .1 : C 'a lc r r l r t l cd t l i l l oo l l r r l r I r la fo r L r1 . 1
Collor dianreler Re drudi s Angle-buikl
Ifiches ft "/to -
50 2.0 71 234 24
15 3.0 107 152 l6
100 3.9 l . l3 469 12
125 4.9 17,) 586 9.6
150 5.9 2t4 703 8.0
I / i 6.9 250 820 6.9
200 '7.9 286 93'7 6.0
Flom this tablc it b€ seen that even large-dianretcr dri l lcollals are sttff icicntly
l lcxiblc lo bc uscd lor long radirrs dri l l irg, c.g. (r ' l30 nr (l(X) lt). Willt tttcclittttt
radius d|i l l ing, these is an increasing restriction on the dianrctct oflhc tt lbulars
that can bc uscd as clogleg sevelity "/30rrr is irtclcasul. A cliatttclcr of 75 nrnr is
needed for a devia{ion of 16"/30m (R = 107 nr or'352 ft).
For no axial load, an allowable bending slress of 18000 psi ensures Grade E
pipe rernains below the fatiguc cmlurancc l imit of 107 cyclcs. CratJe S pipe a
maxinrum allowable bending stress of 21 000 psi.
Dr. l I .S. l tarahnt
CIL V Dti shi'19 )).sign 85
Le pth of s rigid c)'litrder wlticlt cttn ass along e g!!t!9!L!!,ell willry-q-tdistortion1'lre limiting lcngth, L, of a rigid cylinder that can pass along a hole section of
curvature radius, R, can be calculated from the geometry of the diagram tn
F is .5 . l3 .
GLOMF tRy or nrcro cvrrr,roen rr,r cunvEo Hoir
Fig. 5.13.
Using Pythagoras theorem for the triangle marked with the heaqr broken line:
R'?:(L/2F+(R-AD),,Or,(r./2F : R'?: (R'z 2RAD + (AD)1,
Which if we neglect thc AD'term becomes,
| 2 sq. root (2RAD).Note that R and AD nust be in tlre same units as L.
Dx 2:
It is planned to build an articulated motor consisting of straighl cylindrical
scctions jointed togcthcf with flcxiblc particulated joints. Assumitrg tho motoris 95 nrm in diamcter, what woultl bc the maximum lcngth of nrolor section il-
.)r. M.S. lr.lrahrt
Solutiort:
l. Calcrrlate radius ofcunr'atureI IR/ l80 10 /20 lhus . I l - 36 rn .
2 .LD= t l z l 95) / 1000 : 0 .02( r n rL = 2 sr1 root (2*86*0.026 = 4.2 m or 13.9 ft.
'I he allorvable lengths for the same hole and tool diamelers and for other buildrales are calculated below.
Table 5.2: Calculable 5.2: C culated accountab enslh date.
"/30 rn (100 ft) R Calculntcd L
M ft m Irt
25 69 225 3.8 12.4
20 88 282 4.2 13.9
t5 I l 8 316 4.9 16.0l0 172 564 6.0 19.6
5 344 1128 8.5 27.8
Thc fol| 'wing lable shows thc calculatecl clcflmnce, AL), nleas!rc(l in nrrrr andinches, rcquircd to accommodate 10. 5 and 2.5 m long lools in holes havingcr lvc t r r r , n rd i io [50 , 100 ar rd 200 rn .
( l l . I l r i l ln t i t { l t . \ i ry t BG
i t is desired to dri l l holcs with a deviation of20 /30 nr (100 ft) and ifbcndingofthe nrotor section is to be avoided . Tlre hole diameter is to be l2l mm.
,,.. M.S. rrrahaf
( IL I I t r i lh t , i rg t t , \ ign lt7
Table 5.3: Cl rcc rcqurrco t)erween DolL- ano toot olamc
___fglefr"jm
Itl rrdius
r:T::Bole dianretcr'-tool C)l)
L: 10 nt or 32.8 ft
50 t64 250 !,.8
100 32ii 125 4.9
200 6e6 63 2.5
L:5mor16.4 f t
50 164 63
100 323 3l 1.2
200 656 _L 16 ll n oL: ) -S n or 3-2 f t
50 t64 16 t,.6
i00 328 8 0.1
200 656 4 t).2
tween d i lct-s.
Although calculations of this types i l lustrate the dii ' f iculty of conductrrrg ast!aighl k\)l along a curvcd hole. thcy assunte thc.c is no berr,-l i irg slrcssexerted by the string abovc arrd bclorv thc tool, i. Fi., i1 is i issrrrnerl the
conncctiorl is madc b1,a l leriblc.joinl. or lhlt (hc lool is conncctcrl to flcriblc
sub. Lr the bcnding rnoment applied to it, at cithor cnd, by thc connectingtubulars.
l). ilt.lt Ixr ri[nt
(IL l I lt'.ll (i,rpltaiu! 88
Crr,lp ren VI
II on rzoxt'al Wur-r, Compr,nrtonTncHnrqrms
' l he conrpletion of a horizontal well or drainltole must be choseo iu thc l ight of
thc f r r t r r r r ' cvo lu t ion o l ' thc na turc : o f thc l lu ic ls p tx i r rccd a long {hc l ro r izor r ta l
, ' oll or dr airrlrole and thc sclcctivc production nceds tl lat ivi l l ensLrre.
I)?.finilitrc cottrylelio,r: the choice of the partitioning of {he drainhole and of
tlrc cornp,,sit ion of thc l iner nrust bc nradc vcry qrrickly. I 'hc dccision nray bc
l ' ; rscd , ' r r r la ta l i t ' u r thc geo log ica l sLr rvcy and { ion l MWI) o t gcos tc t r i t tg
{cohnique or rvireliue logging. ,A.nothcl option rnigl]t consist in parti l ionlng
ilre drainhole independently of the characteristics of the reseruoir. IIorr,o,er,
this choice rvhich technioally is nol idcal, may lead to very high conrpletion
,rrsts in nraly field cases.
I anltorarl' <trrrtpleliotr: fot' consolidatcd fotnrations wlrere o|en-hoieproductior is possiblc, thc dcfinit ive choice ofihc cornpletion rnay be dcfr.rrcd
irnd a dccision ti iketr laler on according to tlrc production data. In pla(i icc,
r:clcctivc l)rocfuction rvil l be decided on only rvlrcn unwanlccl f luirls bcgin l,r bc
prroduccd. 1hc cltoicc ntay also bc dcfcllcd if i t is possiblc to rrrr irr an'rrrcemcnk:d pcrloratcd l it lcr and lo rcl)l:rcc i l latcr by a sclcctivc conrplcliorr.
' ,\/hcrcls tltc lcrnpotary conrPlctiorr solution is prcfcrablc, it is not alrvays
{i asiblc. ' l 'hc
diffcrcncc betwcen thc lwo possibil i t ics i ics in the (lata flvailablc
lirr choosil lg thc lype ofconrpletion and in the ti l lre betwecn the acquisil icn of
t l resc da l ; r i r r rJ t l r c r r r r rn i r rg in the I ine l
Dr., \1.S. l 'xrr ihi i l
CH. YI tt cll Conu't.tior 89
Thus, in any case, the solution to be adopted will consist in choosing a typc of
cornpletion that is suited both to the geological characteristics encountered and
to the optirrrum conditions for selective production via the dtailhole lt is
thcrefore, necessary to have tecbniqucs for:
1) Describing a resenoir from a horizontal well or drainhole
2) Estirnating the production incrcases that may be obtaiued as tlre rcsult of
selective production.
6. 1 C o tnplelipn4lepbtplpsles fu -Ultq:! t9!:!4 a4t4tlQ!!r,at!!s!4s!li !!Borelrcle
Fig. 2,2 shows the radial borehole condition after drillstring placoment. At that
point the system consisting of a horizontal radial borchole continuing a
drillstring with its drillhead in place. To provide sand control or florv
regulation, the radials may be completed by altemative ptocesses.
The firct process involves only an FSD (flexible sand barier) and includes:
l. Elcctrochemical cutoffofthe dril lhead from the dril lsl l ing.
2. Pumping down of the FSD through the open-ended dfillstrjng to permit a
barbed spear anchor to cxpand agrinst the fonrration.
3. Withdmwal ofthc dLil lstLing to lcavc thc IISD arrchtncd in placc.
ll he second altemative process involves use of thc drillstring as perforation,
ard the FSD with:
l. Electrochemical cutoffthe drillhead fro the drillstring.
2. A two-step (two-life) gmvel packing process to provide 10096 fi l l of the
radial borehole annulus around the drillstring.
3. Electrocbemical perforation of the drillstring along its entire leogth
dowrrholc aftcr thc first l i ft ofgravel packing.
4. Placement of the FSD within
ontering the drillst.ing through its perforations.
Electroche,trical c..rojtt the first electrochcmical process is io cul offthe drill
hcad at the rose of thc drillstring after placement. Ihe cutoff tool is simple an
insulatcd rnctal t l isc connccted by an clccttic cablc to an clccttic wcll or powcr
I),-. M.S. rauhflt
CII..VI llall Cornpletion 90
srlrlroe. A cablc stop is placed on the cablc that rvill stop at the top of therlrillstring and accurately locate the cutting tool at the desired position.
'llre elecl r-ocherrrical cutoff tool has been usecl succcssfully in thc field to cut
o ff mole than 500 drillstring. The advantage of electrochemical cutting overcxplosivcs is that no slrattered pipe or shar-p edges are l'ornred. The tool is vcrycost effcclive and reliable downhole.
lllectroch c nical perforatiort: perforation by electrochcmical proccsscs isirocornplislred downhole after the 1.25 in dlillstring in place. A flexible lube(l; ig. 6.1) rs pumped down t lre veft ical workstr ing and through the 1.25 in,hi l lstr ing. The perforat ion tube continuous an insulated f lexible conductorr l i thin thc tube wall . Small porls l ined with elcch' ical ly conductivc rnatcrial;rrc installed irr the tube and connect to the corrductor within the nerforation-lrrbe wall. When bl'ine is punrped down the well and enters the perlorationlrbes, a. jct of electrolyte f low thtough each pod. An eleclr ic welder is used to( r cate il litc 1,1"'"r, cnrrcnt) in the perforation tubc conduclor.. Ilach gror-tlrr :colnes rrn clcctrocheur ical dri l l ing jet. ' f l ic
result is a scries of ol igrted
lx'r ' forat ioirs in the 1 .25 in. dri l lstr ing. ' rhese pcrforat ion tools provicle aboutI r0 sirrrultancorrs pcrforat ions that can bc or. icrr lcd in any dircct ion.
Radia lTube
.l
P o r l o r n l o r .Csnt ra l i zor F ins
Coox ia l E loc l r i ca lBra id Conduc lo r
Fig 6. I Llectrochenical perforator.
1)r. IVI.S. l'arahat
CII.l/I lYc Contletio,l 9 l
I,',lB (Jtcxibte saul bttt't icr): A tlcxiblc slotlcd lincr was clcvclqrcrl b bc rrsccl
alone or to back up the perforations.
I t i s a l rc l i ca l l y l i ) l l l r c ( l n rc l . l lL rbc , s r rpcr f i c ia l l y s in r i la r ' lo cor rvcn l ion l l
f lcxiblc-metal conduct for electrical wirirrg.' l 'he FSI3 nray bc ptrrrlpcd out ol '
thc cutoff nose of thc | .25 in dli l lslring and ancllored into thc fomration by IIn
expandi|g set of barbs on a spcer. The dril lstring can then be pullcd back 1()
leave the bare FSB anchored in place
Alternatively, the FSB nray be punrped down the dril lstring 10 serve as an
inncr slotted l iner fot thc petforations. Fig. 6 2 shorvs a schcnlatic and two
cr.oss sections of the FSB. Figs 6.3 and 6.4 show schenratic placerrents ion a
formation. lnitial tests shows a combined effect of good sand exclusion and
effective transpqrt of high viscosity oil througb the helical joints at low
pressurc drop.
WITI] PENFONATED RAOIAL 'UE:
I
wn rr n^ur l l ruaF :MrvEDCross-sect ion
,.-".,,ffi.n***L"*-"9tr"3Opened Joint Cross*sect ion
Schemat ic Representat ion
Fig.6.2.
D/. M.S. F^rnlt,rt
Itig. 6.3.
AL W lI/cI CoDtl'ltlio' 92
Casing
Vert ica lS lot ted L iner
Sucl<er Rod
H A V Z O N E
L l t LL I l r i t r i r r l r i l l l l l l l L l l i I l l l l l l l l l i l I r r L r l t l
Pump
Fig. 6.4 Completed radial systent with gravtty clrainage.
llorizontal gravel packing: gravei packing can be accomplished by a twoJiftl i l l ing proccss wjth a watet/gfavel slurry. In the first l ift, gravel is puntped
tlown the ddllstring and out of its cutoff nose. Conventional sutface gravel
paoking equipnent is used. Aftcr leaving thc open nose of the dlillstring. the
g,r'avel sluny flows back toward the wellbore through the horizontal boreltole
rnnrlus around the dril lstring. Fig. 6.5 shows thc proglessive stagcs ol'grtvcl
packing.
lo glavcl pacl< successfully dulirg thc ll lst l i l l, tlrc matcfial nlust bc puttrpcd
lt a sufficient rate to ensure trunsport of the gtavel within tlrc 1.25 in
rlri l lstring. It is found that a suitable pumping mtc is in excess of 7 ft3/sec.
oncc thc slurty rcenters the attnulus of thc horizontal tadial borcholc, which is
typically about 4 in. in diameter. This larger diameter of the radial borehole
r:luses the sluna mixtures to slow and tlre gravel to scttlc, fonning a dune
ilirai'|F'|rerii11 r , n r r , , r r i n rL r r l r r i i r r n r ! r I
[i '."]0"
i l ( sand Barrier
l+li+u+
Dr-. Nl.S. I^r:rhrl
CIL I'l tl'tU Con'tndiou 93
within the annulus that trroves fiotn tlre nose ofthe dli l lstring bacli toward thc
vcrtical wellbotc. As tlre dune parlicularly l i l ls thc radial botcholc atttttt l tts, an
ullage ( a flow space with a flat bottom and curvod top) is created between the
lolr of lhc radial borcholc anri lhc tlcposilcd grnvcl t lttnc lhc rrl lagc rs l lrc
foundalion of the self regulating characteristics of this horizorrlal gfavcl
packing lrtoccss. tf gravcl gradrrally closcs off lhc trl lagc in a slandoll it
causes the fluid velocity to increase and thus ctode out, caflyi l lg rl lole ol thc
gravel back toward the wellbore. lf the ullagc enlarges, thc vckrcity of the
sluny slows and more gmvel settles, fonning a higher duue.
Gravol Mov6m6ntin First Li l l
Grevel Mov€mentin Socond Lirt
:1,6) secrion or Hon?onrJr 3D'ehoto
h) 1000/0 Fill Cotrrplelion
Fig. 6.5 Progres"sive .s/agcs of grat,el pa<:kittg.
At tcasl, Fig. 6.3 ancl Fig, (r.4 show total cotrrplction sys(cttrs itrcotpotrtt ittg
FSB alone or gravel packing and perforation and FSB placenrent in the
cfi illstring for the ullta-short radius ladial systcnl.
e)Gr.vel Floa lhrouglr !li.qe
c) conlinled Mov€menl
d) Conclusion ol First Lllt
D,: lV.S. Farihrt
CII.l/I I|. Co',' tthn 94
Radius of Horizotttsl Welk Dreinholes
(t,2 Comnletiorr r S h ort-Rad iu s, Mctli u n -Ratli
lr ig. 6.6 and Fig. 6-7 slrows a schematic diagrams of vafious com!llctionr)ptions for shorfradius, medium-radius and long-radius of horizontal wcllslnd drainholes. These completion aspects are described below.
hh ro n rD1 . r ' i h h , , , r n rn sd r ( r i r oo " l
An oxoninlo "l.lldpo coorpl6lior ronrosDnli'rlr somo oll||. oDlloirs.v.ilnl,ln
Fig.6.6 Tailpipe contplelion in open hole ofhorizontal tt'ell.
Basic Types o l CoDrt le t ion Jor l lor i rohtat We s
-\ \r--\-\-l i r s l n r t c l l l i ' r r i n o t r r t r h r l .
-[-]-lr-. ) C r1 . ( l , . r n rn i l i t r ( l t r I o r r l ( ( l
'r) s!dr(l lhs h n,,m htri.n i r I nh r l , s . i { n { r i n i t l ( l ' s
Fig.6.7 Basic f,pes of coutplel ion for horizontol well,s.
.D,r IU.S,l iar.hit
a lL I l l t t l l 1 . ' , t t ld ld t 95
6.2.1 Oaen hole compluiott
Open hole completion is incxpcnsive but is l imitcd to complction reservorr
rocks. Accotdingly, it is diff icult lo stimulato this opcn holc (| i ig. 6.7 up Icft)
arrd to control either injcction or production along the well length. A few earlyhorizon{ll wclls hnvc bccn oorrrplctcrl ()l)cn holc but lho l)rcsL:rrl lrcrrtl is u wayfiom using openhole completions, except in formations such as Austin Chalk.
6,2.2 Tail comolelion and sl.otted lhrcr conryletiotr
Fig. 6.6 shows the tailpipe completion in open hole of horizontal well. Thistailpipc cornpletion is intcndcrl to rclrcscnt only sornc of thc options availablcfor well completions. In some reservoit, or parts of the [cscrvoirs, the
horizontal well may be managed by non-cemented lines.
l herefore, tl'te main purpose of inscrting a slottcd liner in a horizontal well isto guide hole collapse. ln addition, a liner provides a convcnicnt path to insertvarious tools such as coiled tubing (CT) in a horizontal well. Slotted lincr rsinstalled in open hole when the reservoir is unconsolidated or looselyconsolidated sands (Fig. 6.7- up rigbt). Also, cased, ccmcntc<l anil perforated
liner which is expensive and is used in long horizontal section (Fig. 6.7 dorvn
lcft). Slottcd l iner in opcn hole with blank sections and external casing packcrs
(liCP's). This is intermediate fomr ofcompletion technique.
However, there are five tlpes ofliner have been used, namely:l. Perforuted liner: where holes are drilled in the liner befrore landing the
liner into the open hole ofhorizontal well.
2. Slotted li er: where slots of various with and depth are rnillcd along lhcliner length before landing the l incr into lhe open hole oI lrorizortal wcll.
3. Prepacked liners.' slotted lirrers provide limited sand control bv selected
hole size and slot width sizes. However, these liners aro susceptible to
plugging in unconsolidatcd forrnations, rvire wrapped slotted lin€rs havo
been used effectively to control sand production. Recently, the use of
gravel packing for effective sand control in horizontal wcll has bccn
succcssfully provcd. ' lhc rrairr disadvarrtagc of a shrltctl l ino is l lr i!t
Il,r. M.S. Falihilt
CE. Yl we Co tl.ti'n 96
.t.
effective wcll stimulation could be dimcult, due to thc open annular spacc
between the liner and the wcll. Similarlv selective Droduction and
injection procedures are diffi cult.
Llnu'wilh I,o lal lsolnlion: roocntly, oxlcrrol cnsing l)rokus (l i( ' l"s)
have been installed outside the slotted liner to provide a long horizontals€ctiul into several small seclions. This method provides l imited zone
isolation, which can be used for stimulation or production control along
thc rvcll path or length.
Cenreried and perforated lirtet: liner is possible to cement and perforate
mcdium and long radii horizontal wells. Cement usod in horizontal weil
completion should havc significantly less free water content than used for
verticirl well cementing. This is due to gmvity in a horizontal well, where
ftec v,ater segregates near the top poftion of the well and heavier ccment
settlcs at the bottom. ' l
his results in a poor cement job. To avoid this, it is
imporl.ant to conduct a frec water test for cement at least 45'. In additior.
the conventional API free water test is conductcd in the vertical position.
Also, Fig. 6.8 and 6.9 show schematic ofproduction liners in both well Ilrryar
3HZ and well Salarn-7l{Z irt Egyptian westem desert. Fig.6.10 shows anothcr
case history for rveil completion status.
,D / . M .S . Ia raha t
CIL YI lr'. (ot'rlctit,' 97
oW .oz0 l l t v o I
.oo ' ! ! 01 ! Lv : t o t . t s t : l s -A .2 , / ! I
{ , z l 0 l l - 8 Z ! 6 0 l l 9 5 C ) $ t V l S . Z / l I
, s z t 60 t I v II A I Y U : t d d Y - l J . z / t
( , 1 1 6 0 t - . 8 z 9 o t )c s 3 c : l l l o - l s . z / t 9
{ , e z s o t - , 0 2 ? 0 t )9 5 t ) l N v _ t € - z l l 9
( , 8 Z l O l - . 1 c 9 6 )0s3 o? I lo l s .z4 t
, 00 1c9e l v31 l i vs u f l dYoY . z / t s
lrt i;= d
: <
* ' , ! ;d ; . t
f . F
; l <
. 0 9 ' 9 8 9 6 l VB X d 9 S 3 ' I Y N A : t I X !
. 0 0 ' 8 c 4 8 I Yu 3 l N 3 W 3 C S O H . Z / ! I
B=ooz N z t srr -IooF d i
Fig. 6.8 Schenntic ofproduction liner ir well llayar 3HZ.
D,. M.S. l 'arahrt
CH.I'I lrle Con c,iou 98
6 0 4 '
t 6 5 4 '
l 7 t 4 '
7 4 3 0 '
f5f4.t2'
Fit. 6.9 Scllematic ofproductiotl li er in well Salam-7Hz.
7 6 S 6 '
Dr M.S. Farahaf
CE VI WeIl Cottltletiotl 99
i i . : i i i i i , , , . ; , . , . ; , ; . ; . : : : : . : : : : , , i , , r r rLr:.: r-r:t':.:r:59o|l6nple|c<lF6eoi&dbn
Fig. 6.10 Final conrpletion stalus
Barenburg 39 a
ip"
E ! ! Fg l 9 !
Dr-- M.S. Farahat
CII. |'II Cl & L\!!! lli:turi.\ llJll
CuAIrEn VII
APPLICATION oF COII,ED TunTNc TxHonlzol{raL DRTLLTNG
AND MULTI-LATERAL CnsB Srunrss nNnHtsroRrns
7. Uegiled Tu hi n g-D ri!!!r!g
l(ccently, thcrc has been activity in dri l l ing ho zontal wclls usirrg coilcdtrrbing for the drill string together with a bent mud motor. Coiled tubingcquipmenl, rather than a conventional dri lJ rig, is used. Seveml successfulholes havc been dril led in the Austin Chalk using this techniqLre. Although thisl,..ohniquc is rrot yct viable commercially, {hc prospccts lb| thc {irturc ap|cal
11ood.
' lhe equipment used to dri l l the first hole with coiled tubing is shown in lrig./ .1,7.2,1 .3,7.4. The sidetrack hole from an existing vertical well was dril ledrvith 2 in. OD coiled tubing for a horizontal lcngth of 504 m (1652 ft).
.Ihe
Iubing had a tensile strength of 60000 lb and the tubing injector could exert apush-pull force of60,000 lb.
One ofthe problem inherent in this technique is that the coiled tubing, because
i{ is coming from a reel, canrrot be rotatcd to orientcd the dril l nrotor. l hrs tras
hoen overcome by using an orienting devicc bchind the dril l nrotor A srrb is
lrcing <lcvelopcd that can be arljustcd l ionr lhc sutl icc via a wilclinc t<r
oriented thc drill face. The diameter of the hole drilled by this techniquc has
hcen too snrall to allow the nse of MWD cqrripnrent, but wirclinc stccring
lools arc used successfully. MWD tools arc now availablc c. g., advrnccd
MED (geosteering tools) that can probably be adapted to this sewice. Since
coiled tubing normally has a wireline within it, this does not prcsent thc sitnrc
problen as that found with jointed drill strings. The method may develop to
,r-. tr|.S. F:|rrhrt
CH.l/II CT & Case |lisbties I01
, cd6d iubhs */sLih.
cdr rbqlerr! h. coioldd
adtuiqbh ro!. uP subch!cr vdrl8rc|
Fig. 7.1 Wellbore and directional BHA.
D' l l
H
IL]
uUilflIqia
Coi led Tublng Conneclor
Navl-Drlll
Slarthg Mlll
Whlpstock Assemblyl -Dr l
E tr i th C7Irig.7.2 Wit1.loi.t, cuttiqg assenl ies Fig.7.3
,r-. M.S. Farahnt
l)1t,4 for
CH. l/ C7 & Cas. llistotics lD2
: i l { . p 1 S[ep 2 S L e p 3 S L e p 4 Sl.cl) a)
Fig. 7.4 Sicletr.ack pl'ocedures.
\\/here it is usellul for the rcworking and re,completion of existiug wellslithout lcquir-ing a dri l l r ig. I-Iowever, several inprovements are necessary
Lcfore tlrc method can be cornpetitive econornically.
r 'oiled trbing dti l l ing may be particularly useful fol under balancc dril l ingl)ccausc it is not neccssary to conlinually added new sections of dr.i l l ; lrPc.l lcvcral colrparrics atc acting dcvelopirrg tools l ir l coilcd tubing dr i l l irrg.
!
.2 Mttltilmunl Cose Stndies
t\lultilatcral wells are considered by many to be arnong the nrost in'rportantlcchnoJogical bteakthroughs to be introduced to the oil and gas industry.'l-heyplovide lhe capability to drain the resen,oir more efficiently resulting in anincrease(l rate of rocovery in most reservoirs. Industry leaders have estinrated
Dr-. M.S. Farahai
Cn. UI CI & Cls( Ilhtotias 103
ll)irt lhc use of nrultilateral systems will allow rccovery r tos to inorcase t{)l]( lwccl 30 1() 6() Itorccnl o I l ly(lr()cit I hols i lr lr lacc.
Some tlri l l irg scrvices coltinue to be thc leader in the new gcreration ofn r | r l l i l i l l c r f l l c l i l l i ng and conrp lc l io t r sys lcn ls . O r n r | l l i l l r l c ra l : rys lc l l t s i l r cdcsigncd for case of use and can be customized to sewice nearly allmulti latcral dri l l ing needsi The following case studies offer.just a fewc\ilurplcs ofwhal wc car accornplish rvilh locrrs on cttslonrcr scrvico.
22.!:eqe_1 (Fir1,5)
In 1996 and 1997, Sperry-sun successfully installed several 95/8 in RMLS1MRetrievable Multilateral System for Occidental petroleum of eatat Ltd. fronrol' lshorc rig SANTA FE 127 locatcd irr the ldd El Shargi f icld, Ofti lror.c ealar.in tlrc Arbian Culf. ' Ihe RMIS provides full-bore access to the lat,:ral whilcnrairtainirg unrcstrictcd acccss to lhc rrain wellbole bclorv l lrc latcr;t l. Onc o['thesc wclls was dril led as a dual lateral with a single 5 in. complction whiclrpcrmils seiective reentry of eithcr lateral uti l izing a special krol string installedor coilcd tubil1g.
Occidental had determined that the ISND Shuaiba Formation recovery wouldbc enhanced by drillirrg multilatcral wellbores in both the Shuaiha A and BMembers. Historically, production from vertical wells in this ficid has bcenlow, yiclding only 300 bopd, u?ith rates up to 3500 bopd being achievcrl in rarcinstances where wells intersected faults. Occidental also deci<lcd tha,. it wasimperative for the futurc managontent of the Shuaiba reservoit to desi.rn intothese wells the ability to leenter each wellbore selectiv€ly. The mosr cost_effective method to aclrieve this is thc use of multi lalcrutl dri l l ing an<lcomplction technology. With thc use of multi latcml. actual proclur:tronpcrfon'nance has matched or exceeded expectations with increases 600y0 rrverptevious production rates. lnitial production rates have averagcd 4056 bopclpcr fateral, with individual wells producing up to 7724 bopd frorn both theShuaiba A and B. lollowing sevcral weeks of production, the wclls travestabil ized, with one well, averaging 6000 bopd combined production fr.onrboth laterals.
D,. N{.S. F'nmhrf
a lL l / I ( 1 , \ ( - t1 ! ' I l ^ t l r i ' s l l l t l
Fig .7 .5
1)r. N{.S. Far ahat
CH. VII CT & Case fiisto es 105
This well was planned and drilled dual lateral well with medium reach
horizorltal wellbores in both the Shuaiba A and B. the 9 5/8 in ploductiou
casing was run to 6138 ft. MD. The RM LS windows was set at 5476 ft. MD
with thc KOP at a 78 inclination at 5488 ft. Ihcjunction ofthe upper Shuaiba
A lateml with the prinrary wellbore was cemcnted at 4817 ft MD at a 90.4
irrclination. The lowcr was thcn dril led to 12686 MD. This welJ is currently
being flowed as a Shuaiba dual lateral producer br.rt wil l evenhrally bc placcd
into scrvice as a powered water injection well.
7.2.2 Case 2 (Fip. 7.6)
Sperry-sun comploted thc first 9 5/8 in LTBSTM cemented lateral for Mobil of
Canada in November 1996. thc installation of the 9 5/8 in LTBS in well
AD 10-35/1D16-35-18- 17-W3 in Battrum, Saskatchewan, Canada was only thc
third such commercial application ofthis technology worldwidc.' l lr is was also
tllc first lateral reentry nade to on flate an annular casing packer for stagc
ccnrenting.
This well was drilled to drain two Roseray sand zoncs separated by an
impermeablc laycr multi latcrals arc cxtremely effective irr draining rcservoirs
separated by impenrcablc rock layers and in decreasing ovemll capital costs
rcquired to devclop rcscr-vcs.
ln this heavy oil application, a 9 5/8 LTBS window joint was installed in the
nrain casing strings arr 8.5 in main bore lateral was dli l led fronr thc cusing
shoe and tlren lined with 5.5 in wire wrapped scrcens. A secondary 6.5 in
lateral was drilled and lined with 4.5 in rvire wrapped screcns through thc
LTBS windows. The lateral was reentered using a completions dcflection tool
to inflate the ACP and stage cement thejuncture ofthe main casing and lateral
l inet. After removing {lrc complctions dcfiection tools, full-borc acccss to both
lrtcrals is availablc.
./)r. M.S. Farrhat
( t l . I l l ( -1 . \ (nr I l i \ !u i^ l l l ( t
Fi14.7.6.
/ ) / ' . N{.S. Fr[r l ! : r f
C . I tl ( 7 tr Ca\. tttsL,i.s
7.2-l!sss ltf!c,7.])
During Septcrnbcr 1996, Spcrry-sun antl Dresser Oil -l
ools succcsstirl ly dri l lcdand completed a biplanar multi lateral rvcll using Sperry-srrn s L'l BS l,ateralTie-Back Systcm with selective through-tubing reentry and isolationcapabilities provided by the Dresser Oil Tools LRS Lateml Reentry System.Thc muftilateral 2l1I)-l7AlB off the Bravo platfotm- was conrpletcd forPhil l ips Petroleum Norway in thc Eldfisk Field in the Crcatcl Dkofisk arca ofthc Norwcgian Sector in the North Sea.
Phillips Petroleum chose to use the LTBS and LRS prirrarily f{)r selectiveisolation and shut-in capabilities rvhile maximizing the productive flowconhol. The combined system also allows access to the primary casing whilemaintaining full-bore access to the laterals, which may be re-enlcred at anytinre dLu-ing the life of the u,ell. Without the usc of these spccialized systenrs,Phillips could not economically producs the remaining reserves in thisrcscrvoirc.
Zone the higher pemreability Cbalk formation knorvn as the Tor- as well as asecoud hodzontal latcml in thc shallower Ekofisk forrnation. l)rclimirrrryproduction results suggcst that thc upper lateral wil l producc approxirnrtcly 26% of the total ilcrenental recovery expected from this wc]|.'lhe reser.ycsrecqvered from the tighter Ekofisk lormation would havc bcen left in placc b_va sllntlald Udfisk horizontirl rvcll-
Tlris well was the first cornmercial multiJateral systern appliczrtion in theNorwegian North Sea featuring a non-restricting 3.81 in through-tuning rncithrough bore ID, reentry and isolation nrcthod-Drcssc| Oil ' fool s I lts. A 7lirrcl t ic-back, 5.5 production l incr, and , 4.75 in opcn Irolc aud rrrult i latcralsystcnr provided the lough-tubing lccntfy. The LRS was successfully uscd toisolate the upper lateral while perfomring 10000 psi (BHP) fr.ac job in lower.latcral. This was also thc fir 'st Norwegian Nolth Sea well to uti l izc a pre-millcd
lateral drilling rvindo*-Sperry-Sun s I-TBS.
t0't
/)r. lU.S. Farahat
CIL t'II CI t Crse l/isrorn,s 108
Fig. 7.7.
D/: M.S. F:rrrlr:rt
CE t/II CI & Cav llistt,i.s 109
12.4 Case 4 (Fig, 7.8)
In Febnrary 1q96. Spen)/-Sun. along u irh Nederlandse Aardolic MaatschappijB. B. (a joint venfure between Shell and Exxon) and pressule ConlfolEngineering Limited (PCE), successfully combined their expertisc to achievethc rvorlds first selective through-tubing.feentry into a multilateral well RTDl . l . loca ted in thc Ro l le ldanr F ie ld in t l re \c rhcr iands .
Spcrry-Sun Downhole Tool Developmenf Group and pCE worked closclytogether to modify and develop PCE s MLR MLrlti lateral Reentry Systcm.making it compatible with Specry-Sun s LTBS lateral Tie-llack System. Thcintegrated system uses components developed by both Speny sun and pCF inoldcr to deploy equipment such as a through-tubing deflection tool on coiletlhrbing, thus allowing selective reentry into lateral wellbores.
l'l lrrough-tubing coiled tubing reentry to the lateral was a fundamentalrcquirement of this project as was the need to improve productiorr. 'l'his
wellwas designed to reach different reserves in the sane rcsenoit rvhich wcrcscparated by layers of diflcring permeability. NAM wantcd to reaoh nrorc ofthc field and increase the dr.ainagc area. ln thc init ial prodnction phrse, rccrrtrywas not required. Ilowevel, the reentry operation was cauicd out ilnyway, lc\confirm that it will be achievable when NAM determines the need lbr reentrv.
After successfully drilling and lining the rnain wellbore, a lateral was <lrillcdorrt of the primary casing using the I-TBS. This lateral was thcn comDlclcdwith a l inel which was tied back to the pr imary casing. Then, Lrsing SperrySun s upper muleshoe assembly, the MLR nipple was latched across the LTIISptemilled windorv and held in place using the SSDS latch systen. fhis acrior)allowed NAM {o dcploy PCE s throdgh tubing deflcction tool coilcd tubingard set it in the MLR lippJe asscnrbly. Sclcctive through tubing access to theIateral wellborc rvas confinned as a dumnry plug was run in smoothly and thcnretrieved fiom the PCE nipple located in the lateral liner. Finally, thedcflection tool was rctrieved on coiled tubins.
,,: M.S. Farahat
Lil. l'll (:1 li (.:tt? Ilistutit | | l{'l
' fhis aclrievcrnenl rvas a null i latcrai anrl conrplction
l r |cakthrorrgh. l1 provcs thc lcasibi l i ty of sclcct ivc to thc i i r tcfr l
thc pel lor nranoc of well servicing opelations.
Fig.7.8.
t cchno log i ca l
rvcl l l torc i irr
Dl lV.S. Falahrf
CH. VII CT & fnsc llisktii.s 111
Z. 1 UUWblelsLeqrcHi s t"olLc t; e_ ! _0'i c. 7. Y
' I his f irst nrulti latcrl l wcll in thc Middlc l irrst wrs tl i l lctl irr l\, larclr l996. lhc
conrpietion consistcd of two horizoltal la{crals cnconrpassing about 3500 fl of
crposed hole in each leg (Fig. 7.9)
' l he operator dri l lcd the lower lateral scclion as an extcnsion oflhc parent rvcll
borc. The uppcr' latcral well section exited out a 9 5/8 in., 40lb/ft p,rrcut c'rsrrrg
string into an 8.5 in. hole. A 7 in l incr was set through thc build unti lhorizontal.
'| his liner was set with a composite joint across the hollorv whipslock face as
<liscrrsscd cnrlicr. ' l 'he l incr rvas ccnrcnlc(1. rrnd lhc l l lclal rvirs t:orrrplctcd thcn
llow tcstcd for 2 weeks.
' l hc lowcr parcnt wcll borc was llrcn rcoponcd, lnrl lhc.jrrnc{ion \vls l lrcssrrrct( sted. Bccause of the vcrticfl l ly penrreablc naturc of lhc l irrnralion in whiclr
l lrc cxit wirs placc(1, ccnlcnt sqtrcczcs wcrc ttcc<k:rl at l lrc.jurcti()r l() plss l lrc
I 'r)sit ive and negative pressurc tcsts.
l ' lugs wcle thcn pullcd fionr thc prrcnt nrrtl latcral wcll bolos usirrg full grugc
rnd tlrrough-tubing divelters and a window bushing asscnrbly. ' l hc rvinclowsbush i t rg assc tnb ly was u l t in ra tc ly Ic f t in thc . junc l ion , and a 4 .5 in . lL rb ing s l r ing
r r s r r r r r i r thc l r l )pc r conr I l c t i rn ) .
' lhis installation took longer to run lhan anticipatcd, ncvertheless, both wcll
l 'ores became productive. The oricntation nipple and mating lock dcvicc
r',,orkcd well. Bascd on tlr is cxpcficncc, Drodifications rvcrc rradc to thc
rlcflectols, enhancing efficiencies and besl practicc ptoccdulcs.
, / . i \ ' I .S. txrihrt
CH. VII C7 & Cose Ilinoli.s 112
Fig.7.9.
, / . [ ' I .S. Farahnf