OTC 5808

Deepwater Drillingby L.C. Chita and A.L. Cordeiro, Petrobras SA

This paper was presented at the 20th Annual OTe in Houston, Texas, May 2-5, 1988. The material Is subject to correction by the author. Permissionto copy is restricted to an abstract of not more than 300 words.

References and illustrations at end of paper

This paper presents the drilling programevolution, from the first well up to now,showing the improvement of efficiency andcosts control as well as the alternativesselected to overcome the problems facedduring the operations. Among theachievements, a special attention is givento a new permanent guide base, designed anddeveloped by PETROBRAs, which allows toimprove the spud in of exploratory wellsand the subsea completion.

INTRODUCTION

At the end of 1984 PETROBRAs started,with the drill ship Pelerin, operationsutilising dynamic positioning (DP) rigs.The first well, 1-RJS-219A, in 853 meterswater discovered a giant oil field namedMarlim. In 1985, six wells were drilled inwater depths between 621 and 942 meterswith two DP ships - Pelerin and Ben OceanLancer. Due to the excellent resultsachieved, PETROBRAs managed to operate in1986 four drill ships, having contractedthe PAC NORSE I and the SEDCO 472. Duringthis period, thirteen wells were drilled inwater depths varying from 550 to 1250meters. In 1987, eight wells were spuddedin by using the OS SEDCO 472 and thesemi-submersible SEDCO 709. In this period,the national record of 1565 meters waterwas achieved with 1-RJS-367 well, at theAlbacora field.

GENERAL CONDITIONS OF OPERATION SITE

the operation siterestricted to Camposof the wells were

The description ofconditions will beBasin area where 90%carr ied out.

Water Depth - In a first stage, the area infocus was situated between 400 and 1000mwater, where the impossibility of diversintervention and resulting necessity ofspecial equipment had to be considered. Theconcentration of wells in these watersreSUlted in the discovery of fields whichshowed good prospects of being extended toeven more deeper waters. As a consequence,in OCT/86 a second stage initiated withrigs capable to work in waters up to 1800m.

This large quantity of wells providedPETROBRAs the informations necessary todevelop new techniques and new equipmentwhich increasingly proved to beindispensable for the effective reductionof the drilling costs and for having thesewells onstream in the future.

The exploration efforts wereconcentrated on the southeastern drillingdistrict in an area located at CamposBaBin, bet~een the latitudes of22 and 23 §outh and longitudes of39,5 0 and 40,5 East, distant 190km fromMacae where the support baseis located. In this strip, largestructures were discovered as Marlim,Albacora and South of Marlim (yet to bedelimited). In addition to this area, onedry well (1-BAS-80/978m water) was carriedout in Jequitinhonha Basin and other two(1-SES-92/1110m water and 1-SES-93/1112mwater) in Sergipe/Alagoas Basin, withpromising results (FIG. 01). Despite thegreat depth, the exceptional proximity ofthe coast (35km) makes this area to becomeof great interest for future development.

end of 87,wells in deep

using dynamic

ABSTRACT

From Dec/84 until thePETROBRAs have drilled 28waters (deeper than 500m)positioning units.

17

2 DEEPWATER DRtLLING OTC 58 08

- Inadequacy of the equipment availableon the market.

- High currents in the sea bottom.

- High inclinations of the sea bottom.

- Possible disconnections of the risersystem caused by a vessel "drive off".

The combination of long riser columnsexposed to the action of the current, hightraction levels and the "excursion" itselfof the drilling unit, are responsible forthe high stresses on the wellhead, makingnecessary a complete knowledge of the soil,the cementing conditions and the behaviorof casings as structural elements.

In all locations drilled in watersbeyond 600m along the Brazilian coast, theformations showed low fracture gradient(FIG. 05), mainly on the surface layers. Asa reSUlt, the cementing operations of thestructural casings (30" and 20") on theirupper sections, which would assure a goodfoundation to the wellhead, became achallenge. The low temperatures at seabottom (_4oC) and the long length of thelanding string that creates additionalpressures by the free-fall effect, alsocontributed with difficulties to thecementation of those casings.

Although less critical, the low fracturegradient of the deeper formations causesmodifications on the casings' program,reducing their lengths in order to attendthe "riser margin" and "kick tolerance"criteria.

werethethethe

- High stresses on the wellheads.

- Diving impossibility.

- Formation of hydrates.

In addition to these ones, thereother existing problems such asparticularities of each area,limitations of the equipment oravailable resources:

Waves and Winds - The oceanometeorologicalconditions of the area with occurrenceabove 60% are: winds of 13 to 24 knots inthe NE direction and waves of 1,2 to 1,8meters height, with periods from 7 to 8seconds. The bad weather conditions,generally occuring in winter time, are theresult of cold masses coming from theSoutheast, whereas its intensity can beforeseen 24 hours in advance.

Currents - The current profile is fairlycomplex and is closely related to themovement of water masses in South Atlanticand to the relief of the sea bottom.Through current meters installed on thedrilling units, records of the intensitiesof the currents were obtained. Althoughsignificant variations from location tolocation took place mainly due to thebottom relief, the typical profile would bethe one showed in figure (02), where asurface current ranging from 0,5 to 2,5knots can be observed, which decreaseswith depth with an inversion of directionoccuring between 200 and 500 meters andnormally reaching 0,5 knots at the bottom.

Bottom Profile The drilling area i~

located in the continental slope, asubmarine region extending from 200 to morethan 2000 meters of depth and locatedbetween the shelf and the abyssal zone. Theshelf has a gentle declivity, around 0,2%,whereas the slope shows a much moreaccentuated dip, varying from 3 to 7%.These values are totally altered by thepresence of canyons and faults which cutthe slope and values up to 84% may occur.

Sea Floor - The typical profiles for theMarlim and Albacora areas, according tofigures (03) and (04) present a layer ofvery soft clay in the first meters and withincreasing resistence with depth. It can benoted in Marlim the presence of anabnormally rigid portion between 10 and 40meters of silty clay. The water contentof up to 70% on the surface layers gives anindication of the soil fragility.

PROBLEMS FACED DURING WELL DRILLING

The exploration of Campos Basinrequired, in the course of time, a drillingactivity in waters increasingly deeper. Asthe water depth increased, the greater werethe operating difficulties encountered and,when it was decided to spud in deep waterswith DP units, it was previously known thatsome typical problems would have to befaced, such as:

- Low fracture gradient of formations,of the surface layers as well as ofthe deeper ones.

- Low temperatures of the sea bottom.

The high declivity of the slope and theweak soil have been making difficult theuse of anchored rigs and instalation ofsubsea structures, like templates, due tothe complexity of the foundations. Althoughnot confirmed, there are indications ofslidings on the sea bottom, particulary inthe BTeas near the canyons.

The conventional wellhead equipment, ingeneral, proved to be inadequate to thecharacteristics of the operation site. ThegUide systems as the temporary andpermanent guide bases (TGB and PGB) wereresponsible for long time losses during thefirst wells. Mechanical running tools likecam-type ones, proved to be simple,

18

OTC 5808 CHITA & CORDEIRO 3

reliable and of easypack-offs were in partclear-sighted methodologyfor their landing.

handling. Themodified and a

was established

and different depths.

- Simplify the handling consideringnormally restricted areas ofships.

thethe

PLANNING

WELL SPUD-IN

- Have an installation method which beeffective for the various areas of use

To identify and solve the operationalproblems and equipment deficiencies,PETROBRAs selected an engineering team fromthe Drilling Department with the followingincumbencies:

The constant fracturing problemsoccuring during cementing of the 30" and20" casings had to be overcome so as not tocompromise the well structure. Computeranalysis were carried out for simulatingthe free-fall effects in order to obtainthe best combination between the slurry

- 1,80 meters in height.

This TGB together with the double Jrunning tool were responsible for a greatreduction in rig time spent in the start ofthe wells.

- Caisson housing for easier handling.

- Running tool closed and with sealing.

- Side outlets for cuttings return,preventing it from going out throughthe upper portion of the base.

To speed up the installation process,eliminating the necessity of trips andreentries, a double J system was developedfor the running tool. The TGB was alsoequipped with level indicators formonitoring its inclination during and afterits installation.

With the results of the soil analysiscarried out in laboratories and the dataobtained by the current meters, it wasverified the necessity of changing thestructural casing program so as to ensurethe wellhead stability. In this change,the option was the use of the caissonnot only as a foundation of the TGB butalso as structural casing, by altering its6 to 7 meters length into 14 meters and its42" diameter into 46" or 48". Other changeswere required, such as in the 30" x 1"B type and 20" x 5/8" X52 type columns,which became 30" x 1 1/2" B type and 20"x 1" K55 type in the first 25 meters.

The installation of the TGB caisson iscarried out through jetting with the bitpositioned near the caisson shoe. The "BHA"is equipped with a bottom motor with thepurpose of facilitating the functionning ofthe double J R. Tool and eliminating theexcessive tilt problems which were occuringin the drilling of the 36" well and which,inclusively, caused the loss of some wellstarts.

As a foundation for the TGB, a caissonwas chosen which would be run in togetherwith the TGB and would work as a pile.After experiments with prototypes,PETROBRAs' new TGB shows the followingfeatures:

theto

operating- Observe contractors'procedures.

- Verify their suitabilityBrazilian coast conditions.

The first step of the group was todevelop a procedure which could ensure thelaying of the TGB at the sea bottom. Aftermaking some attempts with lateralextensions, greater heights and indicators,it was verified that the available designsdid not meet. the needs and were notadequate for the type of soil, making itnecessary to develop a new TGB design inorder to meet the following purposes:

- Minimize the burying effect duringdrilling the 36" well.

Have effective foundation ensuring itsstability even in low resistancesoils.

- Point out the shortcomings of eachprocedure and to standardize thepositive points.

- Coordinate the adoption of solutionsand of new procedures and equipment,by avoiding as much as possible theintroduction of more than one noveltyfor each operation.

- Normalize the solutions adopted withsuccess.

After determining the environmentalconditions of the operation site andknowing the limitations of the drillingunits and equipment, it was able toestablish plans of action to overcome thedi fficul ties.

This group have been coordinating thestudies and designs by working inconjunction with the Research Center,Regional Drilling Districts, ProductionDepartment and equipment supplyingcompanies.

19

4 DEEPWATER DRILLING OTe 5808

characteristics (density x viscosity) andgeometry of the landing string. In order tobetter determine the surface fracturegradient and knowledge of the soil, a conepenetrometer specially designed foroperating in waters up to 1.500 meterswas developed in conjunction with anational soil engineering enterprise forobtaining better data by means of in-situtests.

The density of the slurry is the mostimportant factor for the success of theoperation and this density has beenmaintained at 11 to 12 Iblgal through theuse of special additives such as the hollowglass microspheres and with combinations ofextenders with viscosifiers andaccelerators. The inspection of the successof the operation is being carried outthrough the observation of the return atthe sea bottom with the aid of tracers suchas mica.

USE OF THE ROV'S

Although all the rigs were equipped withlast generation ROV's and the servicesrendered by these vehicles are excellent,it is advisable to reduce as much aspossible their use, at the risk of greattime losses.

One of the main difficulties encounteredby the vehicle at the operation site wasthe excessive current at the bottom, whichsometimes prevented its use for variousdays. Moreover, the failures of the vehicleas well as of its cable are relativelyfrequent.

Experiments made with kevlar cablesshowed that this is not the appropriatematerial for working with the umbilical ofvehicles without cage. The vehicles withcage proved to be more advantageous whenoperating under strong currents while thevehicles without cage proved to be moreflexible and effective in areas of lowerbottom currents.

In order to minimize the use of theROV's, the operating procedures andequipment were adapted or modified toallow, with greater safety and reliability,the use of the rig conventional TV's. Amongthe modifications and adaptations, thereare:

- Use of rechargeable mini-beaconspositioned on the TV's guide.

- Break-away arms to allow the runningin of the TV to the extremity of thesurface casings and stabilizeddrilling strings (Fig. 06).

- Telescope system on the TV's guide.

20

- Compensated guide cables.

- Observation locations positioned atseveral angles facilitating the accessof the TV.

- Use of beacons on the TGB.

These resources eliminated the need forusing the ROV's, although they are stillused when the conditions are favorable.Certainly they make the operations moresimple and increase the yield of theoperation.

WELL DESIGNS

The drilling programs of the wellsmentioned in this paper have a remarkablesimilarity, even because their greatmajority was drilled in two fields, Marlimand Albacora, whose hydrocarbon producinghorizons are located at similar depths.Even the wells spudded in Jequitinhonha andSergipelAlagoas Basins keep thisuniformity, as they have similar waterdepths and stratigraphy with the deepwaters areas of the Campos Basin.

In this way, an abstract of the designof these wells would be: (Fig. 07)

- 46" or 48" jetted caisson - 12 to14m.

- Phase I of 36" - 70m - 30" csg.

- Phase II of 26" - 350 to 450m20"csg.

- Phase III of 17 1/2" -- 700 to 800m - (Albacora/Sergipe)- 1000 to 1300m - (Marlim).

13 3/8" csg.

- Phase IV of 12 1/4" - 600 to 800m ­9 5/8" csg.

- Phase V of 8 1/2" - 500 to 700m7" liner.

Another benefit from the similarity ofthe programs was the acquisition ofexperience in the area, enabling theoptimization of the various items andoperations which influence the drillingitself. Among the main modifications, theadoption of the simultaneous drilling andreaming can be cited - 14 3/4" bit plus 171/2" underreamer - which contributed for aconsiderable gain in time. Another majorimprovement, was the optimization of thebit program, mainly during the 8 1/2"phase, with the introduction of thePDC-type bits.

OTC 5808 C~tTA S CORDEIRO 5

DRILLING FLUID

WELL COMPLETION

These fluids, although of higher cost,have had success in the drilling ofswelling shales, ensuring wells with goodcaliper and good penetration rates.

studies have been carried out at CENPESPETROBRAS' RESEARCH CENTER - with a view

to inspect the operation conditions and tominimize the risks of possible formation ofhydrates.

Main features:

Tool for removing the guide funnel.

c) A cap was designed for protection tothe wellhead in addition to work asa guide system (reversed funnel) forequipment to be installed afterremoval of the funnel.

a) The funnel release takes placepreferably by means of thrust andshearing of the four attaching boltsapplied through a mechanical tool runin with the drill string, whichlodges in a profile located at theupper part of the funnel. Optionally,the system is provided with a remotedevice actuated by ROV, whichcollects the shearing bolts,releasing the funnel (Fig. 09 and10). With the removal of the funnel,a free area is promoted for therunning-in of a production base withor without guide posts or any othertype of guide.

b) The high pressure housings keepinternally the features of eachmanufacturer. Externally, however,the systems will be standardized andthe housings will have the same typeof external profile, that is: thesame support on the 30" housing,profile for H-4 connector and aspecial profile in order that, afterremoval of the funnel, it may receivethe production base. This profilemakes unnecessary the use of anextend adapter, now being used, whichensures the elevations between theconnections of the flow lines andthose controlling the "WCT"(positioned at the production base)and the connection of the "WCT" onthe high pressure housing, bothelements having to be fittedaccurately and simultaneously.

- Standardization of the whole externalprofile of the high pressure housing.

- 30" housing.

- Protective cap for the high pressurehousing.

- Tool for installing and removing theprotective cap.

RESULTS

The immediate effect of the applicationof the new tecniques and equipmentdescribed in this paper was a considerablereduction in drilling times andconsequently in the costs involved.

following

removable

avoided dueof polution,of greater

cases of gassolubi tili ty

more risks to

presents the

Guide Base with

The systemcomponents:

- Permanentfunnel.

Up to the present, no case of hydratesformation has been recorded, mainly becauseno kick case has taken place. In productiontests it has been occurred formation ofhydrates in the manifold, but that has beensolved with the injection of glycolupstream the choke.

The confirmation of the discoveries oflarge reserves in deep waters imposed achallenge for the development· of newtechniques for their exploitation. The useof anchored floating units and subseacompletions is the prioritary system chosenby PETROBRAS in face of the largeexperience acquired by the company. Aimingat the future exploitation of the producingwells by means of subsea completions, theengineers of the Drilling Departmentdevised and developed a wellhead systemshowing a high versatility adopted as astandard for equipping new wells (Fig. 08).

The oil-base fluid has beento the increase of the risksin addition to being a fluiddifficulty of operation ininflux where there is a highof the gas in oil, bringingthe operations.

In the initial phases of the wells, afairly viscous fluid with a density between9,5 and 10 Ib/gal is being used.

For the following phases, the most usedfluid is the salted type treated withpolymers with salinity ranging from 60000to 70000 PPM. In the last wells, successfulexperiments were made, as substituting thepolymers for polyacrilamide, therebyeliminating problems as the bit ballingduring the 17 1/2" phase, mainlyconsidering the simultaneous reamingoperation. This fluid with salinity between35000 to 50000 PPM will probably have itsuse extended to the other phases of thewell. - -------

21

6 DEEPWATER DRtLLtNG OTe 5808

Figure (11) shows the evolution sufferedin the time spent for the well startconsidering from the "spud-in" to thelanding of the 16 3/4" housing. It can beobserved that presently 4 to 5 days arerequired, compared with an average of 20days for the first wells (until the end of85), therefore a reduction of approximately80%.

ACKNOWLEDGEMENTS

The authors wish to express theirrecognition to their colleagues ofPETROBRAS' Drilling Department who, withtheir comments, enriched this work.

REFERENCES

As an effect not yet measured, the useof PETROBRAS wellhead system as a standard,will undoubtly result in a significantoperational economy, taking into accountthe large number of wells foreseen for theMarlimlAlbacora fields.

Simultaneous 17 1/2" underreaming whiledrilling 14 3/4" phase resulted in adrilling rate 30% faster than before.Moreover, the optimization of the wellprograms associated with the use of PDCbits, after JAN/87, resulted in aremarkable improvement of the drillingperformance in the 8 1/2" phase, as shownin figure (12).

The average drilling rate has beenannually increasing, even with the averagewaterdepth also increasing (Fig. 13).

By its turn,meter has beenshown in figureless than in 85the cost/meterwith equivalent

the average annual cost perincreasingly reducing as

(14) and, in 87, it was 45%and only 24% higher thanachieved in shallow watersrigs.

EPIFANIO, Demarco Jorge; RODRIGUES,Renato Sanches and PILOTO, Paulo Roberto"The new gUide bases design improve spudin and sub-sea completion in deep water"In: DEEP OFFSHORE TECHNOLOGY CONFERENCE,4, Monaco, 1987.

PETROLEO BRASILEIRO S.A. - DEPARTAMENTODE PERFURACAo.: "Manual de Opera95es emAguas Profundas". Rio de Janeiro, 1987.1v .

CHITA, Luiz Carlos and RODRIGUES,Renato Sanches"Perfura95es em Aguas Profundas noBrasil Inicio dos p090S" In:Congresso-Latino Americano dePer fura9~0, 5, Buenos Aires, 1986.

COELHO, Osmond and DE LEPELEIRE, Rubens"Cimenta9go de Condutores em P090S deLamina D'agua Profunda Estado daarte." In: PETROLEO BRASILEIRO S.A.- Encontro Tecnico Interdepartamentalsobre Explota98o em Aguas Profundas,Rio de Janeiro, 1987.

CONCLUSION

The maintenance of PETROBRASinvestiments for exploration in deep watershas resulted in significant successes asthe discoveries in Campos and inSergipe/Alagoas Basins. These discoveriesgive the necessary support to thedevelopment of the exploratory program.

The difficulties faced have beensystematically bypassed with theapplication of new procedures anddevelopment of new equipment, rendering theoperations increasingly simple andreliable. The standardization of thesesolutions results in the reduction ofoperation times with the consequentreduction in costs.

While PETROBRAS goes to a drillingoptimization phase, on the other hand itmakes massive investments in Research andDevelopment for the exploitation of thereserves discovered and, in a near future,it can be foreseen the entering intoproduction of the Brazilian fields locatedin deep waters.

22

CORDEIRO, Andre Lima"Ensaio de Penetra9~o do Cone - CPT".In: PETROLEO BRASILEIRO S.A. - EncontroTecnico Interdepartamental sobreExplota98o em Aguas Profundas, Rio deJaneiro, 1987.

32

CURRENT (KNOTS)

o2

- SUMMER._.- WINTERE::JTRANSITION

ZONE

200

800

3000 -l-....-...l--r---I..._.....L.._--L_---J._......j

\\ (\ I

\ I

:::i:~:\i~;~._.~~ii~~~I .

: )I .

: /I .

: II .

: II .

: II .

! I1000..J.... ---l.__J......i. ...I

::I:l­Q..UJo 600a::UJ!;(~

Ciia::~ 400UJ

~

~o

\ fJ~I-BAS-'SF 0

UITI~ONHABASIN'

SERGIPE/ALAGOAS / :'

BASIN /~.:oS"00 0

~-:.r'CV 1;.,:(,.> <JpOOoS'

(. r...·· I-SES-93.,' :.......

... :S;'-SES -92

-=-_ -- \C, ~ l i- - .. ~ ALBACORA \':'-U :

:3\TLANTIC FIELD -M{;:"Y'IOCEAN CAMPOS ,',' 0° Ei :

BASIN <.;~~~'~)f d~,;~.' 0 h.1J

Do-° 0+'rvo/ ,;.... t I

d.'MARIMBA ,/; ARUM• FIELD / t FIELD

Fig. 1-Brazlllan deepwater exploration basins.

SW .....__---...~~ NE

Fig. 2-Campos Basin current profile.

SOFT TOHARDSILTYCLAY,WITHLOCALLYFINEQUARTZYSAND

o 100 200 0 40 SO

{WP

ATTERBERG LIMITS WLWATER CONTENT - w

~

E

::I:l­Q..UJo

100

I i

II i Io 100 200 0 40 eo

ATTERBERG LIMITS -[ ~~WATER CONTENT - w

Fig. 3-Albacora field typical soli profile. Fig. 4-Marllm field typical soli profile.

23

TV CABLE

COM'ENSATEDWIRE ROPE

TVGUIDE FRAME

/

Flg. 6-R.entry assembly.

DRILLSTRING~

BREAK AWAY_ARM SUB

13 14 15{ Lb/gall

II 12GRADIENT

9 10

FRACTURE

o S.F.

500~-1--Y~-+-+-+--_---+--1

1000 +--..::>>k---I....

1500

3000+-~+---I

2500 - .0- j- -- -

3500

E

~ 2000a..wCl

fig. 5-Fracture gradient x water depth.

FUNNEL

FUNIL

Fig. 8-Petrobme deepwater wellhead atackup.

13\'elg

18 95t8'elg

51'2' In

7 PHASES

attLsI [ i j , I I

WATER

":-~:-:::::

~OUGOCENE

~

7"In

9felg

6 PHASES

MUOUNEh--.-,...,..-1" 1000 +-c-'----l'='-""''''''-+-~~y-..,,..,,,.."''!''t

~IL~J r== l~l.bl"" E l::=- 3;~elg - i= - cag

20" :t: == 20"elg Ii: ~~ MIOCENE elg

~ =~2OOOi=~

'---

~

Fig. 7-Deepwater casing program and lithology.

Fig. 9-Funnel releasing system details.

46" HSG ,>-l-..-LL IALOJ. 46"

Fig. 10-Removing the funnel.

RIGS

50o PELERIN DS+BEN O.LaPACNORSEIo SEDC0472 DS@SEDC0709SS

40

en~ 30o

20

10 ~~!\: \: \

+-----+ \. ~

>- 100c't:I.....E

w!;ra:

50

z0

~a:I-WzWa.

YEARSFig. 12-0rllllng performance at BY2-ln. phase.

6765 66

YEARS

Fig. 11-Alg time from spud In to 16~·ln. housing setting (by well).

25

>..g 75"­E

w!;:( 500::

Zo~ 250::I-

~wa..

500E....

::J:I-a.. 1000wCl

0::w 1500~3f

100

;e!!-

0::\.!JI-w~

"- 50-ן

m0()

YEARS

D MAX. a. ~ AVG WATER DEPTH

Fig. 13-0rllllng performance and water depth.

85 86

YEARS

87

Fig. "14-Average costs.

26