q

Effect of additives on drilling in hard rockH. El.SHAlL R. HAECKER. P. SOMASUNOARAN AND S. GUPTA

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.-.AtP. SI.ln.I.~.a"'"~ IINIsIt .. Y8l1Y. --- .. ~ ..3!. 81i1ina18Stript sMed,. - _I.. 1m... K~led Iwl8ica/ion .1.. DisCISsiII"':1 peer.r "..is ~11

SME.II~~

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IntroductionImproving drilling efficiency is

of prime importance to the mineraland oil industries. Drilling is techni-cally a material-disintegration pro-cess and is carried out by subjectingmaterials to different types ofstresses, depending on the drillingbit and applied forces. As with anyrock comminution process, drillingis inefficient as far as energy con-sumption is concerned. Therefore, a cost-effective im-provement in the drilling rate is needed. Reported datain the literature indicate that the addition of chemicaladditives may produce beneficial drilling and grindingeffects (Somasundaran and Lin,1972; EI-Shall, 1980; EI-Shall and -

Somasundaran, 1984; Somasun-daran and Shrotri, 1995). In addi-tion, there could be unavoidableeffects (both beneficial and detri-mental) that arise from difficultiesin controlling the chemical composi-tion of the environment during drill-ing. --

additives on drilling rates using ~ous drilling machines. For instanc:tSchreiner and Denim (1941) fou~that the penetration rate of ~quartzite was higher in the pr~of Ala) than it was in water at-But this was only when the bit Wjslightly dull. Also, the effect w~found to increase with Jecrea$i!ljjmachine pressure. Thus. the ob-\

I served effects could also be d~)dent on the type of stresses applied. In addition ~inorganic reagents, organic additives were also found ~;enhance drilling rates, as reported by Strebig et at(1969). The authors concluded that, with a low SUdaal~tension additive, the solution w~ .- wet the surface better and wau "

Abstract cause an increased penetr,1t.ion rat ~Rock disintegration processes Westwood and c !"

are usually inefficient and costly (Westwood, 1972,1975;operations in mineral beneficia- and Latanisiontion, mine development and oil well al., 1975)preparations. Thus, there is a strong rates with the surfaceneed for improving the energy effl- erties. The researchersciency of unit operations such as quartz was drilled 13 timesdrilling and comminution. The ef- water under chemical conditi~fects of selected cations and anions with a zeta potential of zero. Tbetlon drilling efficiency in a hard rock also reported that theri! was n~formation (Dakota Sandstone) change in the drilling rate 111 a ~e~.were studied. The zeta potentials granite using a tricone bit W1th fand the tensile strengths of the zeta-potential-controlling surfac~drilled samples were measured un- tant solution. On the other hand. ~der similar chemical conditions. same investigators obtained a thr~ r.-The chemicals tested included Mg- fold increase in drilling rate USlnf,~

CIl' NazCOp AIClp NaCI and thesamechemicalconditionsandJ.JDodecylammonium chloride. The diamond bit. They thus attributed, .

results indicated that drilling rates the absence of effect to the type ofj

can be enhanced or retarded de- drilling bit.pending on chemical conditions In addition to the eO'such as the solution pH and the tal effects on drilling, severotype and concentration of reagents. (Rehbinder, 1931; SchreinerDrilling. data are. correlated with Denim, 1941; ~hepherd, 1955, ~ 96'mechanical (tensile strength) and herd, 1959; LIchtman et al.. 1 '

interfacial (zeta potential) proper- Boozer et al., 1963;. ~ties of the rock formation. The me- al., 1967; Westbrook and Jorgenscchanisms involved are discussed in 1965, 1968; Strebig et al.. 1~light of Rehbinder's and West- Westwood, 1972, 1975: We~tW()(.. -.~_:-:_- 11).,').\1/ )0010

In the last 50 years, researchershave investigated different ways ofincreasing drilling efficiency, includ-ing the use of chemical agents to in-fluence the surface properties of thedrilled solids. Much of this interestresulted from work done by Reh-binder et al. (1944). In their study, itwas found that the addition of elec-trolytes increased the drilling rate inrocks such as granite and quartziteby 20% to 60%. These effects wereattributed to the adsorption of ionson the microcrack surfaces, thus pre-venting the reheating process. Otherresearchers (Schreiner and Denim,1941; Shepherd, 1955; Johnston andParker, 1957; Shepherd, 1959;Lichtman et aI., 1962; Strebig et al.,1969; Westwood, 1972, 1975; West-wood and Latanision, 1972; West-wood et al., 1974; Tweeton et al.,

Environment pH 3.0Drilling Strength0.0 0.0+25.7 -50.0+25.1*+20.1 -44.0

Percent changepH 6.0

Drilling Strength0.0 0.0+20.7 -32.0

pH 10.5Drilling Strength0.0 0.0+29.4 -53.0

AirWater

10-2 M NaCI.Cash balance

+33.6 -42.0 +18..0 -42.0

for the tensile strength and drilling experiments (azeta meter was used for these measurem~nts).

MaterialsCore samples representing a hard rock formation

(Dakota Sandstone) were used in this study. The coresamples were about 3OO-mm- (12-in.-) long and 57-mm-(2.25-in.-) diam. For the drilling tests, the core sampleswere cut into 25.4-mm- (l-in.-) long disks. Inorganicchemicals (MgC12, Na2CO3 and AIC13) were purchasedfrom Baker Chemical, and dodecylammonium chloride(DDACl) was obtained from Eastman Kodak. Deion-ized distilled water was used in all tests. The ionicstrength was maintained constant by adding 10-2 NaCIacquired form Fisher Scientific.

Equipment and procedureDrilling experiments. Drilling tests were performed

using a custom-made setup. which included a O.75-kW(l-hp) electric motor rotating a drive shaft at 86 rpm. Theend of the shaft was fitted with a 9.4-mm-(O.4-in.-) diampolycrystalline diamond bit supplied by InternationalPetroleum Engineering Co. (IPEC). A lathe grip wasused as a sample holder. It was connected to the hydrau-lic cylinder of a manual hydraulic pump containing anactuator and pressure gauge. An electric timer. to controlthe drilling time, was placed between the electrical out-Jet and the motor. A schematic of the test setup is shownin Fig. 1.

al..1974;Tweeton et al., 1976) suggested a strong influ-ence of chemical conditions on the mechanical proper-ties of materials.

For example, Rehbinder (1931) indicated that liq-uids. water in particular, played an important role in thefailure process of materials and that these effects couldbe amplified by adding surface active reagents. Boozer etal. (1963) reported a decrease in the ultimate strength ofsandstone when tb.:: pores were saturated with oleic acidor amine solution.

In a different investigation, Hammond and Ravitz1963 observed that water vapor caused a 40% to 50%decrease in the fracture strength of silica compared to itsvalue in vacuum. Their data showed that environmentswith polar molecules caused the maximum effect.

An example from their study indicated that sodiumcitrate decreased the yield strength of Indiana limestoneby about 25%, as compared to the value obtained in wa-ter alone. Westt.,.ook and Jorgensen (1965) observedthat, in almost all the cases, water caused a decrease inrock hardness.

In another study, Westbrook and Jorgensen (1968)r~ported that organic and inorganic reagents produceddIfferent effects on different minerals, such as MgO,CaF 2 and quartz.

They correlated the observed effects with surface-charge properties of the materials in different environ-ments. E!1g~lmam et al. (1967) reported granite to besofter ~t Its Isoeleclric point.

It IS the objective of this research to investigate in-n.uence of additives containing anions and/or cations of~Ifferent valency on the drilling rateIn hard rocks. Correlation of drilling FIGURE 1rates with mechanical and interfacialp,roperties of drilled rocks, under Schematic of the equipment used in the experiment.sImIlar chemical conditions is an-other objective of this study. '

Hylluic pimp Reid '~'e--- J- I / '20

~~dchose

~~

envirO11m~n-:veral reports:hreiner andI, 1955; Shep-et at.. 1962:

ngelmaon ~I

Id Jorgensen.~t al.. 1969:>; \,. .:(wood

Swildl boxExperimentallne experimental study included:

- .

Hy~dc~l..YI'" ~ Rcxt ~/' ~ r--:J;;:I- -=-,-.,

0\

~« ---'I'=:=:"'!=J=~'= ~

r~::~~:ftl ~G

drilling experiments using a ro-tary drill,tensile strength testing utilizingthe "Brazilian test" procedureand

electroki'c 't~~~llrpmpnt.. of

TABLE 2

Zeta potential values, and percent change in drilling rate and tensile strength of DakotaSandstone in presence of different environments as compared to NaCI solutions (1.5. = 10-2 M

NaCI).f)f loading.

Ilken out of so.e loading pIal.jack. The load

IX) lb/min). TIlt

ige results are.

pH 3.0% Change

pH 6.0% Change

pH 10.5% Change

Zetapotential.

mV-7.0

Zetapotential,

mV-17.0

Zetapotential,

mV-30.0

Drillingrate

4.33.8*

0-15.7

-15.4*-2.9

-4.1*

-5.4-7.2*-11.6

-8*

Drillingrate-12.4-6.8*

0-1.4

-4.5-

-24.5

Drillingrate-17.0

Tensile-10.4

Tensile+17.3

EnvironmentWater

Tensile9.7t:eta pJ;ential ~

ld in an agate f5 mesh). Then.t

lesh) material ~e required pH *ation using a ~.~n transferred ~

10-2 M NaCI

0.01% AICI3

0+15.6

+18.8*+5.3

-7.0+8.0

0+1.9

-13.0+18.0

0-3.7

-1.5*+13.5+7.3*

+7.4

0+5.1

+6.5.-19.4

-27.0-26.0

4.0 +24.1 -5.0 +5.00.05%MgCI20.2% Na2CO3 +13.0 -7.0 -8.0

-11.7.-20.0

+21.8 .14.0 -12. -33.0

10-5 M Amine +6.2+12.4*

.;e.o +22.9 15.0 -20.0+8.7 -6.4

ease ttlC drill. ~Ilues obtained :i show that anchieved at anOn the otheri1as decreased :"

ded to all the :

ct of NaG on f

;andstone are:,bt increase in ~d by t!,e data. i

d lkalin t an a e~

,a decrease of i., The tensile f% with NaG

;son to water. ~IlS is found 10 ;~onditions, as f, . ~InterestIng 10 k

Isile suenglh ;

*Duplicate tests

The effect of divalent anion (CO3-2) is studied byusing sodium carbonate solutions at different pH condi-tions. The results are given in Fig. 4 and in Table 2. Thedata indicate that the addition of Na2CO3 causes a de-crease in the drilling rate and an increase in the tensilestrength in acidic and neutral pH solutions. In alkalinesolut.ions, however, an improvement in the drilling rate isobserved. Zeta potential data, given in Table 2, suggest aslight change in zeta potential, indicating no adsorptionis taking plac.::. I t is also well known that CO3-2 does notadsorb on negatively charged sandstone. The reasons forthe observed changes in drilling rate and strength valuesas the pH increases are not clear at this time, and furtherinvestigation is needed in this regard.

of such highly surface-active species (in alkaline aminesolutions) is confirmed by several researchers, as re-viewed by EI-Shall (1980).

ConclusionsThe effects of different additives on drilling rate, ten-

sile strength and zeta potential of sandstone (represent-ing hard rock formations) were investigated. Under thetested conditions, the results suggest the following:

Effect of trivalent cations. To study the effects oftrivalent cation, (Al+3), AICl3 solutions were used, andthe results are plotted in Fig. 5. The results show that thisadditive influ':rtces the tensile strength and drilling rateonly in acidil.. conditions. These effects could be due toadsorption of positively charged cations (Al+3 andAl(OHh+) on the negatively charged sandstone surface.These species are predominant at low pH values. Thisadsorption could also be responsible for the changes inzeta potential values given in Table 2.

Drilling rates in wet conditions are much higher thanin air.The drilling rate can be enhanced, compared to drill-ing in water alone, under selected conditions of re-agent type and pH solutions.The drilling rate is found to increase under chemicalconditions that reduce the tensile strength.

FIGURE 4

- 3 shows thelsile strength. (

~ (>20%) de-

e neutral pHpH results in~ting to men-~ solutions isher than the

~ stat;:,-. thatrlgth, all im- \ld vice versa. ~

drilling rate ~line solution!vely charged t.

negatively (~ta potential ~. t2 IS added at f)f MIi/OH) ,

Effect of 0.02% sodium carbonateon the drilling rate and tensilestrength of Dakota Sandstone (I.S. =10-2 M NaCI).

- Water- ~q Ra8-.- Tensie Stl9ngth

,Effect of dodecylammonium chloride (DDACI). The

effect of organic additives such as DDACI. was investi-gated, and i;.c' results are shown in Fig. 6. Also, in thiscase, the in',erse relationship between tensile strength~nd drilling rate can be noted. A decrease of nearly 20%In the drilling rate is evident in the neutral pH range.

H?wever, a small measurable beneficial effect is ob-tamed in the alkaline medium (pH 10.5). This effect

c.ould possibly be attributed to the adsorption of posi-:Ively charged, highly surface-active species (ion-molecu-ar Complexes) in this pH range on a negatively charged

~hndstone Sil,"face. The decrease in zeta potential v~lue atIS pH (T:; 7\ ~~., ~1~~ h~ ~..~ .~ .J.~ ~A~~ ~- -4'

2520

& 15c~ 10u... 5c

3 0...GJa. -5

-10-15

-~

\'\.: V I' I~Water

A

~

FIGURE 5

Effect of 0.01% aluminum chlorideon the drilling rate and tensilestrength of Dakota Sandstone (I.S. =10-2 M NaCI).

~20

15

& 10c2 5u.. 0-c

3 -5...a. -10-15-20

Water '.10.5 Iy3

'~'" ~~ ;...

pore fluids on the deformation behavior of rock subjected to triaxj4J

compression," in Rock Mechanics, C. Fairhurst, ed., Pergamon Press,

New York, pp. 579-625.El-Sball, H., 1980, "Effect of Chemical Additives on Grinding;

Dr. Eng. Sci. Thesis, Columbia University, New York, NY.El-Shall, H., and Somasundaran, P.,1984,"Physico-chemic;" as-

pects of grinding: A review of use of chemical additives," Powder 1'ech.

nology Journal, 38, pp. 275-293.Engelmann, W.H., Terichow, O.H., and Selim,A.A.,l967,"Zeu

potential and a pendulum scherometer studies of granite in a solution

environment," US Bureau of Mines, RI7048.Farmer ,I. W., 1968, Engineering Properties of Rocks, E. and F.M.

Span Ltd., London.Hammond, M.L., and Ravitz, S.F., 1%3, "Influence of envir<'n-

ment on brittle fracture of silica," J. Am. Ceramic Society, Vol. 46 :0.

7, pp. 329-332.Johnston, T.L., and Parker, E.R.,1957 ,"Preliminary investigation

of surface effects in flow and fracture," Sixteenth ONR Tech Rept. Ser.127 ,Issue No. 16, University of California, Mineral Research lab, Janu.

ary.pH

FIGURE 6

Effect of DDACI on the drilling rateand tensile strength of DakotaSandstone (I.S. = 10-2 M NaCI).

30

-A.,

Water' ~

1..5 r,i.

6 I'~ ,

-8"

. 200»

; 10.cC,)... 0c.~ -10.a.

-20

.30

Lichtman, V.I., Schuken, E.D., and Rehbinder, P.A., 1962,Physico-Chemical Mechanics of Metals, Academy of Science, Moscow,

USSR.Rehbinder, P.A., 1931, "Hardness reduction through adsorblion

of surface active agents," Physik, Vol. 72, pp.191-205.Rehbinder, P.A., Schreiner, L.A., and Zhiyach, K.F., 1944."Hci d-

ness reducers in drilling - A physico-chemical method of facilitating

the mechanical destruction of rocks during drilling," Akad Navk. Mc»-cow, USSR; 1948, Trans. By Council for Scientific and Industrial Re-

search (CSIR), Melbourne. Australia.Schreiner. L.A., and Denim. A.A.. 1941, Gorny :Zh., Moscow.

Vol. 18.Shepherd, R.. 1955, "Rotary drilling developments." Mine and

Quarry Engineering, Vol. 21. No.8, pp. 329-335.Shepherd, R.. 1959, "Improving and efficiency of rotary dri! Ig

shotholes," Transactions, Institution of Mining Engineers, England.'. "I.

113, Part 2, pp.1029-1048,August.Somasundaran, P.. and Shrotri, S., 1995, Grinding Aids - A Re-

view of their Use. Effects and Mechanisms, Selected Topics in MineralProcessing, Wiley Eastern Ltd., New Delhi. India, pp. 47-65.

Somasundaran, P., and Lin, LJ., 1972, "Effect of the nature of tbeenvironment on comminution processes," I and EC Processes Des.

Dev.

pH- Water--- Drl81g Rate-.- Tenste Strength

There is no obvious relationship between either thedrillability or tensile strength and zeta potential ofthe samples studied.Reported data may be used as an indication of thepossible effects of studied reagents on mechanicalproperties of these rock formations. However, amore comprehensive study is needed to simulate theindustrial conditions.Further research is recommended to investigate themechanism-controlling effects of different environ-ments on the disintegration processes..

Strebig, K.C., Schultz, C. W., and Selim, A.A., 1969, Mining £1;';;'

neering, Vol. 21, No. 10, pp. 73-73.lWeeton, D.R., et al., 1976, "Influence of Surface Active Chc i-

cals on Drilling and Fracturing Rock," US Bureau of Mines, Report of

Investigations. RI. 8186.Westbrook, J.H. and Jorgensen, P.J.,1968,Am Mineralogist. Yolo

53, pp. 1899.Westbrook,J.H.,and Jorgensen, PJ., 1965, Trans-AIME. Vol. 2"..3.

pp.425.Westwood, A.R., 1972. "Adsorbtion sensitive mechanical beh:lv-

ior of glasses." Symposium on Mechanical Aspects of Interfaciall'llt'.nomenu, Extended Abstracts, 163rd Meeting, ACS, Boston, MA, Af I.

pp.101.Westwood,A.R.,1975,"Environment enhanced disintegratio/l "thard rocks," Con! On Research in Excavation Technology, Vail. CO.October 21-24,1975, Colorado School of Mines. Golden, CO, pp. 86-

91.

AcknowledgmentPartial financial support from the Engineering Re-

search Center (ERC) for Particle Science and Technol-ogy at the University of Florida, the National ScienceFoundation (NSF) under grant EEC-94-02989 and theIndustrial Partners of the ERC is acknowledged.

Westwood. A.R.. and Latanision. 1972. "Environment SensitiveMachining and Surface Frothing," NOS Monograph. 1972.

Westwood, A.R.. Macmillan, N.H., and Kalyconcu, R.s., lQ7.J.'.Chemomechanical phenomena in hard rock drilling." Trans AIM f. Y.D..f..r..n"A~