Control of shale swelling pressures using inhibitive wáter-base muds

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Copyright 1998, Society of Petroleum Engineers, Inc.

This paper was prepared for presentation at the 1998 SPE Annual Technical Conference andExhibition held in New Orleans, Louisiana, 2730 September 1998.

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Abst ractOver the years wellbore stability in shales has been achievedusing oil base muds, however water base muds still plague theindustry. Up until now it was not obvious what mechanismswere in operation during such shale/water base mudinteractions. The research reported herein discusses thedevelopment of swelling pressures when water base muds arein contact with a troublesome North Sea shale. A mechanistictheory is presented that focuses on increases in total porepressures that are reflected in swelling pressures. The results

obtained showed that different mud filtrates produce swellingor shrinking pressures that are related to the type of saltpresent and its ionic concentration. Fluids tested included de-ionized water and solutions of CaCl2, Potassium Formate,Glycerol, Methyl Glucoside and NaCl/Methyl Glucoside. Therange of swelling pressures measured were from +2800 psi(swelling) to 1400 psi (shrinkage). In addition to swellingpressures, the compressive strength of the shales was alsomeasured under downhole insitu stress and conditions after thechemical interactions were complete. Strength reductions ashigh as 35% were measured for certain fluid systems.

IntroductionBorehole stability is one of the largest problems

encountered during the drilling of wells. It is estimated to costover $500 million each year.

One major type of wellbore instability is associated withshale formations, which, in a typical well, represent 75% of allthe formations drilled. In the past, one solution to theshale/wellbore stability problem has been the use of oil basemuds, which can eliminate the flow of water and ions intoshales. Although oil base muds provide a definite solution to

the shale/mud problem, environmental concerns restrict tuse, and in many cases water base muds are now beconsidered as a required drilling fluid. The identificationimproved water base muds for shale stability is the primobjective of this paper.

Shales are sedimentary rocks that have distinct laminlayered characteristics and a high clay content. Shales therefore subjected to phenomena such as hydration, swell

shrinking, and strength reduction when exposed to water ions. The mechanisms controlling these reactions are vcomplex and are not fully understood. These reactions refrom the hydrophilic nature of the clay particles, whichsomewhat altered by both the chemical and mechanenvironment. The chemical effects are due to intermolecular forces between the clay particle, the ionic pfluid inside the shale, and the composition of the drilling flThese chemical effects result in a continuous change in spore pressure and composition. This study focuses on movement of water and ions in contact with shale thareflected in the development of swelling pressures. Ibelieved that by controlling the swelling pressures, sfailure at the wellbore wall can be prevented.

ObjectivesIn addition to the identification of improved water b

muds, a second objective of this paper is to understandphenomena that control shale swelling. Many studies hbeen conducted concerning the behavior of shale in the mglobal wellbore stability problem, but no acceptable thethat predicts or describes the complex mechanismsavailable.

This study attempts to quantify the swelling pressure efof various fluids in contact with a cretaceous age shale namSpeeton. It also attempts to identify the driving fac

behind this swelling phenomena as well as the prefedrilling fluids when drilling shale formations. An experimestudy that was performed using samples of Speeton shaldescribed in this report.

Literature ReviewTroublesome shales have been studied for a long time,

they not only plague the petroleum industry but also mining and civil engineering industries. Many diffe

SPE 49263

Control of Shale Swelling Pressures Using Inhibitive Water-Base MudsMartin E. Chenevert and Vincent Pernot, The University of Texas at Austin



2 MARTIN E. CHENEVERT, VINCENT PERNOT SPE 49

theories have been presented to explain the swellingphenomenon of shales, such as capillary suction, osmosispressure, and hydraulic pore pressure imbalance. Until nowthe experimental results are not totally and effectivelyexplained and understood.

Low et al.1 presented the osmotic pressure equations fordetermining the swelling properties of soil water. This theory

suggests osmosis as a mechanism for swelling pressuresgenerated by shales. The theory is based on the principle thatthe shale itself acts as a semi-permeable membrane, whichallows for the generation of osmotic pressures between thefluid in the shale and the drilling fluid. Chenevert2 used thisosmotic pressure theory to explain shale control, using theconcept of balanced activity.

Chenevert et al.3went further to develop the total aqueouspotential concept for shale-fluids systems. In this model thehydraulic pore pressure was coupled with the osmotic pressureto produce a total aqueous pressure.

Barbour et al.4 presented a theoretical description of twopotential mechanisms for osmotic volume changes. The first

one, osmotic consolidation, occurs as a result of changes in theelectrostatic forces between the clay particles, whereas thesecond, osmotically induced consolidation, occurs because offluid flow in or out the clay in response to osmotic gradients.Fritz et al.5supported the osmotic theory as a basis to explainwater and ion transport in shales. They reported that claymembranes were not ideal and that the degree of idealitywas a function of the membranes cation exchange capacity,porosity, and concentration of pore fluid. They suggested thatthe ideality for a given shale-liquid system could bedetermined by the measurement of swelling pressures, whichwould then be used to calculate a reflection coefficient. Thereflection coefficient is the ratio of the measured swellingpressure divided by the theoretical swelling pressure for aperfect membrane. Mody et al.6 took a similar approach,postulating that membrane efficiency is a function of theconfining pressure acting on the shale.

Ballard et al.7 investigated water transport through shaleand concluded that shales do not act as semi-permeablemembranes and that ions can freely diffuse through them. Bolet al.8 came to the same conclusion after running a series ofexperiments, stating osmosis was not observed. In both ofthese studies the shales used did not represent typical shalefound in highly stressed environments.

Pashley et al.9describe the hydration forces and chemicalmechanisms behind the ion movements between micasurfaces. This analysis takes into account the molecular

interactions between the clay particles and the ions in thepores and drilling fluids. Heidung et al.10 presented a modelfor hydration swelling based on an extended version of theporoelastic model and Darcys transport equation.

Recently Santarelli et al.11 discussed the swellingphenomenon and came to the conclusion that swellingpressures are caused by gas present in the pore structure of therock, which induces capillary effects. They concluded that it isunlikely that swelling actually occurs under downholeconditions. Santos et al.12 concluded that rather than the gas

contained in the pores driving the swelling process, the wis controlling the reaction that is occurring in the rock. Botthese hypotheses are questionable and neither can explainshale stability success achieved when balanced activitybase muds are used.

Concerning the influence of the drilling fluid on strength of the shale, and the tri-axial loading procedure u

to measure it, Cook et al.13

discussed the influence of strain rate on the strength value. They recommended an upstrain rate wherein the strength value obtained is indepenof the strain rate.

The references listed above were used as a basis forstudy reported herein.

Osmotic TheoryThe key to determining the true effective stress acting

rock is to determine its total effective pore pressure. highly argillaceous compacted rocks (such as shales) thivery difficult to do because they have low permeability can also exhibit high levels of osmotic suction that can

treated as a negative chemical pore pressure. It may sremarkable that argillaceous rock can have a liquid in its pthat exhibits an osmotic negative pressure and also havpositive hydraulic pore pressure at the same time. Aquechemical potential theory (Low 14) shows that the water inshale is in a state of chemical tensile stress (relativeatmospheric pressure), which can be treated as a negative ppressure. Classic osmotic cell experiments show that ipossible to have positive hydraulic pressures and negaosmotic pressures acting at the same time (Shomaker et al.

Energy considerationssuggest that the total free energargillaceous rocks is the sum of many components includthe potential of the clay to adsorb water. Bolt et al.16discuss such potentials and present equations for calculathe forces in the neighborhood of the clay platelets and soliquid interfaces. Further discussions of these clay adsorpforces are presented in the works of Aylmore et al.17.

In order to quantify the osmotic pressure component ofpore fluid it is necessary to perform certain measurements calculations.

One expression for the molar free energy of a liqui

called the fugacity (fi). It is a measure of the escap

tendency of the water and is related to the chemical potenof a system (ui) by the equation

B(T)i

fRTlni

u +

=

WhereR = gas constant, liter atm/oK moleT = absolute temperature, oKB(T)= a constant for a given substance at a gi

temperature, TThe excess chemical potential of water in a rock (at a fi

temperature, T) may be written as the chemical potential ofwater in the rock (u) minus the chemical potential of wate



SPE 49263 CONTROL OF SHALE SWELLING PRESSURES USING INHIBITIVE WATER-BASE MUDS

its standard state (uo) or

=

++

=

0f

fRTlnB(T)

0fRTlnB(T)fRTln

0uu

... (2)

For practical purposes, the fugacity ratiof/f0 can bereplaced by the vapor pressure ratio P/Po, where P is the vaporpressure of the water in the rock and Pois the vapor pressureof water in its standard state. This can be done because thecorrection factors used in going from fugacity to vaporpressure for the pure solvent is nearly equal to the correctionfactor of the solution, therefore, their ratio is unity.

Equation (2) thus becomes

0P

PRTln

0uu =

...................................................... (3)

Assuming the liquid to be incompressible, the osmotic

pressure potential (P) of the water is related to the chemicalpotential u-uoby theequation

PV

0uu

=

.................................................................(4)

WhereV= the partial molar volume of the water,liters/mole.

Equating each expression for the chemical potential of thewater, we have

0P

PlnRT

PV =

or

0P

Pln

V

RT

P

=

...............................................................(5)

Thus we have an equation that allows us to calculate the

theoretical osmotic pressure potential (P) of the liquid withinthe shale by the measurement of the relative vapor pressureP/Po of the water within the shale. It should be pointed outthat for an osmotic pressure to develop that is equal to thetheoretical osmotic potential, a perfect membrane (which

prevents ion passage) must exist.When determining the aqueous energy potential it is not

necessary to determine the effect of each energy potentialacting on the water within the rock. Rather it is sufficient todetermine only the net equilibrium chemical potential of thewater in the entire rock-water mass, considered as a unit. Thisis done by determining the aqueous relative vapor pressure(relative humidity) in equilibrium with fluid within the rockand then relating this measured quantity to the osmotic

pressure potential of the water in the rock. In this fashionaverage osmotic pressure potential of the water is determin

Equation (5) shows that if the aqueous relative vapressure of the liquid in the rock is less than 1.0, a negaosmotic pressure potential exists; the magnitude of negative osmotic pressure potential is related to the logariof the relative vapor pressure. This pressure is believed t

equal to the suction pressure which is equal (but oppositsign) to the swelling pressure that may develop under imembrane conditions.

Swelling Pressure DevelopmentLet us suppose that we have a two-phase closed sys

containing pure water in one phase and moist shale (whwater activity is




dfa

wa

ln

V

RT

P

=

.............................................................(9)

where adf is the activity of the drilling fluid and aw is theactivity of the water in the shale. This final expression can be

applied to calculate the osmotic pressure generated when ashale contacts a drilling fluid with a different activity.

Effective Stress TheoryThe "effective stress" principal as presented by Terzaghi18

is:(1) Increasing the external hydrostatic pressure produces

the same volume change of the material as reducing the porepressure with the same amount.

(2) The shear strength depends only on the differencebetween the normal stress and the pore pressure. This impliesthat the effective stress, rather than the total stress, determines

whether or not the rock fails due to the external load.In equation form, the effective normal stress () is equalto the total normal stress () minus the hydraulic pore pressure(Ph).

= - Ph..... (10)

Terzaghi developed his effective stress theory for clasticrocks, which do not contain elements capable of developingosmotic pressure potentials. For argillaceous rocks, whichcontain clays and ionic pore water, it is necessary to add the

osmotic pressure potential (P) to the hydraulic pore pressure(Ph) so that the total effective pore pressure can be obtained,thus:

PT=Ph+P...(11)

Thus for calculating the effective stress of argillaceoussaturated rocks, equation (10) becomes

0P

Pln

V

RTh

P-

=

.. (12)

It should be pointed out that if the argillaceous rock is leftin contact with pure water the liquid in the shale will equalizewith the pure water, then P/P0 would eventually equal 1.0,

therefore the P component would be zero, and the effectivestress equation reduces to equation (10).

Biot introduced the term

(Biot constant), which takesinto account grain contact areas over which the pore pressuresdo not act. Applying this concept, equation (11) becomes:

=

oP

Pln

v

RTh

P ...(13)

Terzaghi's arguments lead to an effective stress law with = 1. For soils, this is a reasonable assumption. For rocks,

however, the deviation of from 1 should be taken into

account. For shales it is seldom less than 0.95.

Reflection CoefficientAs mentioned above, for a rock to develop the theoret

value of swelling pressure as determined by equation (10)

necessary that a perfect membrane exist, thereby restricmovement of ions into or out of the shale. For water bmuds, this is not the case. Both water and ions flow intoshale because a perfect membrane seldom (if ever) exists. Aresult, a swelling pressure less than the theoretical vdevelops.

The ratio of observed swelling pressure to theoretswelling pressure provides a membrane efficiency quanFritz 19discusses such a ratio and refers to it as a refleccoefficient. This coefficient is useful in relating the relaeffectiveness of various shale/salt water systems to resflow into shales.

North Sea Speeton ShaleIn this study the cretaceous shale Speeton was used. T

shale is an offshore marine shale, cored from a depth of ab5,000ft (1,524m) and preserved as closely as possible fexposure to air.

Properties of Speeton Shale. The composition of interstitial pore fluid and mineralogical composition of Speeton shale are presented in Tables 1 to 4. (OBrien 20).

The cation exchange capacity as reported by OBrie17.6 meq/100g, and the water activity is between 0.84 0.86 at 75F and atmospheric pressure. Independent wactivity tests were performed at the University of Texas unthe same conditions, and values between 0.84 and 0.86 w

confirmed. All shale samples used in this study were storea dessicator that maintained a relative humidity of 84%.

Description of Swelling TestFig. 1 shows a shale sampleinstrumented for the swel

test.During testing, fluid enters through the inlet line, fl

through the porous disks and circulates around the samFinally it flows out through the top fixture and exits throthe outlet line.

The entire assembly shown in Fig 1, is placed inside a chamber. Other equipment items used in the test includedexternal LVDT for measuring movement of the piston du

shale breakage, pressure transducers for the confining pore pressures, a load cell, a constant volume pump, and a View data acquisition system.

Test Procedures and Test Conditions. A typical test performed over a seven-day period and included 6 phasesa compressibility measurement, (2) an application of in-effective stresses (2680 psi), (3) an introduction of simulpore fluid (100 psi), (4) an adjustment of pore fluid confining stress to downhole conditions of 2720 and 5400




respectively, (5) the swelling pressure test using the test fluidat a pressure of 2720 psi, and, finally (6) a compressivestrength breakage test while holding the pore fluid andconfining pressure constant at 2720 and 5400 psi respectively.

Swelling Pressure ResultsSwelling pressure tests for seven drilling fluids in contact

with Speeton shale were performed. The fluids included de-ionized water, 0.78 and 0.40 water activity solutions of CaCl2,0.78 water activity solutions of Potassium Formate (KCOOH),Glycerol, Methyl Glucoside, and Sodium Chloride/MethylGlucoside.

Swelling Pressure of De-Ionized Water (aw = 1.0). Theconfining pressure time curve of Fig. 2 shows results for de-ionized water in contact with Speeton shale.

As water is sucked into the shale by osmotic forces thetotal pore pressure increases, therefore it is necessary toincrease the original confining pressure (5400 psi) so as tokeep the bulk volume of the shale constant. The sample stops

swelling when a confining pressure of 8120 psi was reached,which translates into a swelling pressure of 2720 psi (8120-5400 psi).

After 2-1/2 hours the sample begins to shrink andcontinues to do so. This shrinkage is thought to be caused byionic flow out of the shale into the de-ionized water beingflowed past the shale. Analyses of the de-ionized water beingremoved from the cell showed an initial high concentration ofNaCl (See Fig.3) which decreased with time.

Shrinkage data taken in this test after 2-1/2 hours does notrepresent what would happen in a real wellbore. In the lab test,the shale is of limited volume (3/4 x3/4 x 2) therefore itsionic content can be depleted with time, whereas a shaleformation has an unlimited amount of ions which can replacethose removed at the wellbore wall. For this reason resultsobtained after 2-1/2 hours are not used in the calculation theswelling pressure.

Three repeat tests were performed using de-ionizedwater and near identical results were obtained.Swelling Pressure of 0.78 aw CaCl2 Solution. Aftercompleting the base study using de-ionized water, studieswere performed using various mud filtrates (ionic solutions)that had water activities less than 1.0. The first system was aCaCl2solution that had a concentration of 230,000 ppm and awater activity of 0.78. This activity was chosen because it wasbelieved to match that of the shale sample.

Fig. 4 shows that no positive swelling was observed. The

confining pressure had to be reduced from 5400 to 5100 psi inorder to maintain a constant volume, which translates into aswelling pressure of -300 psi. This result is a definiteindication that the presence of the CaCl2 in the contacting fluidwas able to control water flow into the shale through theprocess of osmosis.Swelling Pressure of 0.40 aw CaCl2 Solution. In order tofurther evaluate the osmotic concept, the next fluid run was aCaCl2solution that had a water activity of 0.40. After 10 hoursinto the test, as shown in Fig. 5, the confining pressure had to

be reduced from 5400 to 4000 psi in order to prevent samshrinkage, which translates into a swelling pressure of -1psi (4000-5400 psi).Swelling Pressure of 0.40 aw KCOOH Solution. A thebased on molecular size and solubility suggested thaconcentrated solution of potassium formate (KCOOH) wonot only be able to produce the low water activity neede

control water flow into the shale, but would also provide laions that would not penetrate the shale and thus assisproducing a more efficient membrane. With these conceptmind, a KCOOH solution that had a 0.40 water activity tested. As shown in Fig. 6, this fluid produces shrinkagedid the 0.40 water activity CaCl2 solution. In this teswelling pressure of -1200 psi (4200-5400 psi) was measurSwelling Pressure of 0.78 aw Glycerol Solution. Vardrilling muds that contain glycerol have had some succesminimizing wellbore stability problems. Using thobservations as a guide, a glycerol solution that had a 0water activity was tested. Very unusual results, as displayeFig. 7, were achieved.

As shown, swelling pressure peaked at 3000 psi (855400 psi) after only hour, dropped back to near zero, tpeaked again to a value of 4100 psi (9500-5400 psi) at hour, then decreased and held constant at -1300 psi fromhours on. Using the final value of 4000 psi, a swelpressure of -1400 psi (4000-5400 psi) was calculated.Swelling Pressure of 0.78 awMEG Solution. A test wasto investigate the effect of Methyl Glucoside (MEG) soluon the Speeton shale. As shown in Fig. 8, no swelling presdeveloped over the first four hours followed by a gradincrease, reaching a final value of 4300 psi (9700-5400 after 5-1/4 hours. These data suggest that Methyl Glucoproduces an impermeable coating on the shale's surface forfirst four hours, then tends to act like a fresh water systhereby producing excessive swelling pressure. Because ofirregular behavior, the osmotic pressure theory was applied to this system.Swelling Pressure of 0.78 aw NaCl/MEG Solution.

response achieved whith a 0.78 water activity solution of Nand MEG was irregular, similar to that of the glycerol testshown in Fig. 9, peak swelling pressure values of about 4psi (10,000-4500 psi) were obtained. Because of the irregbehavior, the osmotic pressure theory was not applied to system.

Membrane Partitioning Coefficients.

As shown in Fig. 2, for the de-ionized water experimthe shale reaches a swelling pressure of -2720 psi. Accordto equation 1.9, it should have reached a theoretical value o

( )( )3487p237atm

0.1

84.0ln

018.0

2980.082

1.0

0.84ln

V

RTP ====

(

Applying the concept of reflection coefficient (CR)discussed by Fritz19the coefficient becomes:




0.783487

2720

pressureswellingofvalueltheoretica

pressureswellingofvaluemeasured

RC === .

..... (15)

This means that only 78% of the theoretical swellingpressure is "reflected" in the actual swelling pressureachieved.

An analysis of all swelling pressure data is presented inTable 5. It is interesting to see the wide range of membranepartitioning coefficients achieved, from 0.94 for the glycerolsolution to 0.08 for the 0.4 awKCOOH solution.

Shale Strength TestAfter completing each swelling pressure test, the confining

pressure was returned to 5400 psi, and the sample was brokenat a strain rate of 2.8 x 10-3 min-1 while maintaining theconfining pressure and pore pressure constant at 5400 psi and2720 psi respectively. The loading rate of 2.8 x 10 -3min-1 isbelieved to be sufficiently slow for the pore fluid to bleed out

of the shale when being compressed and thereby maintain aconstant pore pressure of 2770 psi. This conclusion wasreached by performing other shale strength tests at rates as lowas 1.0 x 10-3min-1, and nearly identical strength values wereobtained.

Table 6 presents results for the various strength tests,as well as one breakage test run on a native shale sample.Deviatoric strength is calculated using the equation :

..... (16)

The typical breakage curve shown in Fig. 10. Displays aplastic type of failure. A 2% offset method was selected fordata analysis. Using a shale strength of 7111 psi for the nativeshale, the relative strength of Speeton shale after beingcontacted with the various shale/fluid systems is shown in theright hand column of Table 6. Two of the solutions, namelythe 0.40 aw KCOOH and the 0.78 aw MEG were able tomaintain shale strength. All other solutions produced a 25 to35% decrease in the relative shale strength.

Because of the limited number of shale strength testsperformed, it is difficult to do a detailed analysis of thevarious shale/fluid systems beyond that given in Table 6.

Conclusions1. De-ionized water in contact with the Speeton shale

produces swelling pressures in the range of 2400-2800 psi.2. The reduction of water activity by the addition of

various salts can greatly reduce the swelling pressure, andeven cause it to become negative.

3. Shales have a natural leaky membrane that can bequantitatively categorized through the use of membranereflection coefficient. In our tests these coefficients variedbetween 0.94 and 0.08, depending on the type of chemical

dissolve in the water.4. In general, salt solutions that have a very h

concentration of ions have the lowest membrane refleccoefficient, and conversely solutions with the lowconcentration of chemicals have the highest membrreflection coefficients.

5. The strength tests show that shale strength can

maintained when 0.40 aw KCOOH, and 0.78 aw MEG flare used. In addition, the strengths are reduced by 25 to 3when 1.0 awde-ionized water, 0.40 awCaCl2, 0.78 awCa0.78 awGlycerol, and 0.78 awNaCl/MEG fluids are used.

6. The equipment and experimental technique presenherein are able to satisfactorily determine the swelpressure and compressive strength of shales exposedvarious fluids.

Nomenclature

fi=fugacityR=gas constant, liter atm/K moleT= absolute temperature, K

u= chemical potentialP= pressure, psi

V= partial molar volume of the water, liters/moleP= osmotic pressure potential, psiaw= activity of the water in the shaleadf= activity of the drilling fluid

= normal stress, psi= normal effective stress, psi

Ph= hydraulic pore pressure, psi

= Biot constantCR= reflection coefficient

Acknowledgments

We gratefully acknowledge the financial help providedthe Gas Research Institute and members of the UT DrilResearch Consortium for this study. Shell ReseaNetherlands supplied the well preserved Speeton shale for study and we cordially acknowledge their contribution. research work of Mr. Jiang Zhang and Ms. Kangping Wduring the early stages of the project is appreciated.

The help from the staff of the Petroleum EngineeDepartment of The University of Texas at Austin is higappreciated.

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for Determining Thermodynamic Properties of Soil Water Science, V. 86, 251-258.

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Netherlands, March 11-14.4. Barbour S.L., and Fredlond D.G., (1989): Mechanism

Osmotic Flow and Volume Change in Clay Soils, Geotech. Journal, Vol 26.

)2(inareasectionSample

(lb)loadaxialAdditional(psi)strengthDeviatoric =




5. Fritz S.J., and Marine I.W., (1983) : Experimental Support for aPredictive Osmotic Model of Clay Membranes, Geochim.Cosmochim. Acta 47, 1515-1522.

6. Mody F.K., and Hale A.H., (1993) : A Borehole Stability Modelto Couple the Mechanics and Chemistry of Drilling Fluid ShaleInteraction, SPE/IADC Paper 25728, Presented at SPE/IADCDrilling Conference in Amsterdam, The Netherlands, Feb. 23-25.

7. Ballard T.J., Beare S.P., and Lawless T.A., (1992) : Fundamentalsof Shale Stabilization : Water Transport Through Shales, SPEPaper 24974, Presented at the European Petroleum Conferencein Cannes, France, Nov. 16-18.

8. Bol G.M., Wong S.W., Davidson C.J. and Woodland D.C. (1992) :Borehole Stability in Shale, SPE paper 24975, Presented atthe European Petroleum Conference in Cannes, France, Nov.16-18.

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10. Heidug W.K., Wong S.W., (1996) : Hydration Swelling ofWater-Absorbing Rocks: a Constitutive Model, InternationalJournal for Numerical and Analytical Methods in

Geomechanics, Vol. 20, 403-430.11. Santarelli F.J., and Carminati S., (1995) : Do Shales Swell? A

Critical Review of Available Evidence, SPE/IADC Paper29421, Presented at SPE/IADC Drilling Conference inAmsterdam, The Netherlands, Feb. 28-March 2.

12. Santos H., Diek A., Roegiers J.C., and Fontoura S., (1996) : CanShale Swelling be (Easily) Controlled?, Presented atEurock96, Rotterdam, The Netherlands

13. Cook J.M., Sheppard M.C., and Houwen O.H., (1990) : Effectsof Strain Rate and Confining Pressure on the Deformation andFailure of Shale, SPE/IADC Paper 19944, Presented at theSPE/IADC Drilling Conference in Houston, Texas, Feb 27-March 2.

14. Low P.F., (1960) : Physical Chemistry of Clay-WaterInteraction, Advances in Agronomy, Vol. 13, 269-327.

15. Shoemaker, David P., Garland C.W. and Miller J.W., (1989) :Experiments in Physical Chemistry , Mc Graw-HillPublishing Company, Fifth edition

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18. Terzaghi K., (1932) : Die Berechnung der Durchlassigkeitszifferdes Tones aus dem Verlauf der HydrodynamischenSpannungserscheinugen, Wien Math-nturw. Kl. Abt., Sitz.Alad. Wissen, Vol. 11A, No. 132, 125-138.

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Processes : a Review, Clay and Clay Minerals, V. 34, No. 2,214-223.

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SI Metric Conversion Factorsin. x 2.54* E+00=cmlb x 4.54 E-01 =kgpsi x 6.894 757 E+00=kPa

* Conversion factor is exact

TABLE 1 - COMPOSITION OF INTERSTITIAL PORE FLUID

FOR SPEETON SHALE (CATIONS)

CATION CONCENTRATION (mg/l)

Sodium 31,300

Calcium 586

Magnesium 61

Potassium 423

Strontium 20

Iron 15

Barium 1

Lithium 0

TABLE 2 - COMPOSITION OF INTERSTITIAL PORE FLUID

FOR SPEETON SHALE (ANIONS)

ANION CONCENTRATION (g/l)

Chloride 43,100

Calcium 4,790

Bicarbonate 1,390

Carbonate 0




TABLE 3 - MINERALOGICAL COMPOSITION OF

SPEETON SHALE, WHOLE SAMPLE

CONSTITUENT % by weight

QUARTZ 9

FELDSPAR 3

CALCITE 12

DOLOMITE 1

PYRITE 2

SIDERITE 2

TOTAL CLAY 71

TABLE 4 - MINERALOGICAL COMPOSITION OF

SPEETON SHALE, 2m FRACTIONCLAY % by weight

KAOLINITE 31

CHLORITE 3

ILLITE 25

SMECTITE 8

MIXED LAYER 33

TABLE 5 - MEMBRANE PARTITIONING COEFFICIENT FOR

VARIOUS SPEETON SHALE TEST SOLUTIONS

TestNumber

Test Fluid

TheoreticalSwellingPressure,

psi

SwellingPressure

Measured

psi

Membrane PartitioninCoefficient

1 De-IonizedWater

3487 2720 0.78

2 De-IonizedWater

3487 2300 0.69

3 De-ionizedwater

3487 2800 0.80

4 0.78 awCaCl2

-1482 -300 0.20

5 0.4 awCaCl2

-14,839 -1400 0.09

6 0.40 awKCOOH

-14,839 -1200 0.08

7 0.78 awGlycerol

-1482 -1400 0.94

8 0.78 awMEG

-1482 NA NA

9 0.78 awNaCl/MEG

-1482 NA NA

10 De-IonizedWater

3487 2600 0.75

TABLE 6 SHALE DEVIATORIC STRENGTH RESULTS

Test Conditions Deviatoric Strength

Relative Strengt

Fluid a 2% offset Deviatoric(psi) Strength/7111

Water 1 5179 0.73

Water 1 5333 0.75

Water* 1 5200 0.73

CaCl2 0.78 5333 0.75

CaCl2 0.4 5155 0.72

KCOOH 0.4 7467 1.05

Glycerol 0.78 4622 0.65

MEG 0.78 7111 1.00

NaCl/MEG 0.78 5333 0.75

Native shale 1 7111 1.00

* A strain rate of 1.00x10-3min-1was used in this test.




Fig. 1 - Instrum ented Shale Sample

Fig. 2 Swelling Behavior of 1.0 awDe-Ionized Water Solution

Fig. 3 Equivalent Ionic Strength vs. Time Plot

Fig. 4 Swelling Behavior of 0.78 awCaCl2Solution

LVDT

Porous Disk

RadialDisplacement

Sensor

Inlet Line

Porous Disk

Sample3/4x3/4x2

Porous Disk

Outlet Line

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 2 4 6 8 10

Time (hr)

Confining

Pressure

(psi)

0

10000

20000

30000

40000

50000

60000

70000

0 2 4 6 8 10

Time (hr)

Equival

entNaClConcentration

(ppm

)

3500

4000

4500

5000

5500

6000

6500

7000

7500

0 2 4 6 8 10

Time (hr)

Co

nfining

Pressure(psi)




Fig. 5 Swelling Behavior of 0.40 awCaCl2Solution

Fig. 6 Swelling Behavior of 0.40 awKCOOH Solution

Fig. 7 Swelling Behavior of 0.78 awGlycerol Solution

Fig. 8 Swelling Behavior of 0.78 awMEG Solution

3500

4000

4500

5000

5500

6000

6500

7000

7500

0 2 4 6 8 10

Time (hr)

Confining

Pressure(psi)

3500

4000

4500

5000

5500

6000

6500

7000

7500

0 2 4 6 8 10

Time (hr)

Confining

Pressure

(psi)

0

2000

4000

6000

8000

10000

12000

0 1 2 3 4

Time (hr)

C

onfining

Pressure(psi)

0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10

Time (hr)

Confining

Pressure

(psi)




Fig. 9 Swelling Behavior of 0.78 awNaCl/MEG Solution

Fig. 10 Typical Shale Strength Curve

0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10

Time (hr)

Confining

Pressure

(psi)

0

500

1000

1500

2000

2500

3000

3500

0 10000 20000 30000 40000Axial Str ain (m icr o in /in)

AdditionalLoad

(lb)

2% offset

Control of shale swelling pressures using inhibitive wáter-base muds

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