P. SomasundaranH. Shafick Hanna

Columbia U.

Reprinted from the June 1985 issue of

SOCIETY OF PETROLEUMENGINEERS JOURNAL

Adsorption/Desorption of Sulfonatesby Reservoir Rock Minerals inSolutions of Varying SulfonateConcentrationsP. Somasundaran, SPE, Columbia U.H. Shafick Hanna, Columbia U.*

reported.l-6 to exhibit shapes that have not been en-countered elsewhere. Our past work 7-11 on abstraction

of dodecylbenzenesulfonate on Na-kaolinite clearlyshowed the complex nature of the process, which dependson a number of system variables such as the nature andconcentration of inorganic electrolytes, surfactant concen-tration, pH, and temperature. Under certain conditions,the systems exhibited a maximum in the region of CMCand, in some cases, a minimum at higher concentrations.Most interestingly, the presence of the maximum in theabstraction isotherm depended strongly on the type of in-organic electrolyte in the system.

From a practical point of view, it would indeed be usefulto be able to control the abstraction of sulfonates by rockminerals by controlling the inorganic electrolytes in thesystem. However, laboratory batch-type adsorption testscannot be used directly for micellar flooding systems fora number of reasons. One important consideration in thisregard is that the reservoir rocks are exposed to surfac-tant solutions of varying concentration as the surfactantslug advances through the reservoir. To examine the roleof this effect, the abstraction behavior of sulfonates bykaolinite during incremental increase and decrease in sur-factant concentration has been determined in this study.Comparison of the abstraction isotherms obtained by con-ventional batch-type tests (B-isotherms) with those ob-tained by stepwise changes in surfactant concentration(S-isotherms) and the deabstraction of isotherms ofsulfonate upon dilution of the system should help indeveloping an understanding of the surfactant abstractionbehavior as well as the phenomenon of abstractionmaximum.

Abstract

In micellar flooding, reservoir rocks are exposed to sur-factant solutions of varying concentrations as the surfac-tant slug advances through the reservoir. Therefore, theattachment and detachment of sulfonates with rocks thatare already exposed to surfactant solutions of higher orlower concentrations is of major interest. In this study,the abstraction behavior of purified Na-dodecylbenzene-sulfonate on Na-kaolinite by stepwise increase in surfac-tant concentration is detennined. Deabstraction* occurringafter reductions in surfactant concentrations at variousstages also is determined. Most importantly, the resultsof incremental abstraction, individual abstraction, anddeabstraction showed the system to exhibit hysteresis ormemory effects. Also, abstractions obtained at various pHvalues and during stepwise changes in pH exhibitedmarked differences.

The deabstraction isotherms showed the presence ofmaximum in certain cases, indicating the occurrence ofmaximum on the abstraction isotherms to be a realphenomenon. Possible reasons for the hysteresis are con-sidered, and the practical implications of these memoryeffects on micellar flooding and depletion experimentsusing cores are discussed.

IntroductionLoss of surfactants owing to their interactions with reser-voir rocks and fluid is possibly the most important factorthat can detennine the efficiency of a micellar floodingprocess. While there has been considerable work withdilute surfactant solutions, mechanisms by which surfac-tants interact with rocks in their critical micelle concen-tration (CMC) range have not been studied in detail.Nevertheless, some limited data that have been reportedin the literature do suggest that the adsorptioncharacteristics of systems made up of concentrated sur-factant solutions (above the CMC) are markedly differentfrom those of systems involving dilute solutions.

Adsorption isotherms above CMC have been

Materials and Methods

Kaolinite. Kaolinite used was a well<rystallized Georgiasample with a B.E.T. surface area of9.8 m2/g [105 sqft/g]. Homoionic Na-kaolinite prepared according to aprocedure described earlier 10 was used for all die adsorp-

tion tests discussed here.. Haw willi !he U. of AIab8na.

'TheIemlS abe4radion and de8b8Ir8Ction - ~ MICe in !he 8uIfonaI8 ~;x;,-.aldti.-ec:, Ih8f8 II InY8IabIy - ~ of !he ~ and 1hef8kwe,!he - ren-.d by fie rock can kICIude 1hIt wtICII ~ as well as 8rIYIh8I gels 8II8dI8d M !he rock « ~ in Paf8a.

Surfactants and Chemicals. Sodium dodecylbenzene-sulfonate (DDBS) purchased from Lachat Chemical Inc.(specified to be 95 % active but anal~zed to be 85 %) waspurified in the following manner. 0 The material was

~ 1~ Society of ~ Engi~

JUNE 1985 343

'!'0E..

...

..ftzw0

~~!i

'E

~E..

,:..

~w0Z0-=

~;

FIg. 1-Kinetics of abstractlon/deabstraction upon dilution ofDDBS from Na-kaolinite. (Abstraction density is express-ed as p.mole of surfactant per m2 of the solid.)

Fig. 2-Kinetics of stepwise abstractioo of COBS by Na-kadinite.

dried first and then extracted by using dry distilleddiedtylether in a Soxhlet apparatus. The last 30 to 40%fraction was collected and the residue after evaporationwas recrystallized four times from acetone. The productassaying 98.1 % sulfonate showed no minimum in surfacetension Ys. concentration. Infrared spectra indicated it tobe predominantly p-DDBS with trace amounts of theo-DDBS isomer.

The inorganic salts used to adjust the ionic strengtl1 andpH were of A.R. grade. Triple-distilled water was usedfor all tests.

Abstraction. Batch abstraction tests were conducted intightly capped 5-dram Pyrex vials. Desired amounts ofthe Na-kaolinite were wetted by water or salt solution for2 hours before the addition of surfactant solutions. Thevials then were subjected to wrist-action shaking for giventimes in an incubator maintained at the desiredtemperature. At the end of the test, a sample of the super-natant solution was centrifuged at 1,500 g for 20 minutes.The liquid above the mineral layer was mixed thoroughlyand the resultant supernatant was analyzed for residualconcentration of the sulfonate by using die two-phase titra-tion technique with a mixture of dimidium bromide anddisulfine blue as indicator. Abstraction of the surfactantis calculated from the difference between the initial andthe final sulfonate concentration (see Appendix). Note thatadsorption in the absence of precipitation, obtained byusing the concentration difference technique, is the Gibbsadsorption or surface excess and must be distinguishedfrom total adsorption. However, any precipitation in thesystem can contribute to the observed difference in con-centration. We attempted to minimize this effect byresuspending the precipitate (by gentle stirring) that ap-peared to collect on the top of the mineral bed during cen-trifugation and by analyzing it as a part of the supernatantsolution. Nevertheless, any trapping of precipitate insidethe mineral bed or deposit of precipitate on the mineralparticles would lead to values that are higher than thosefor adsorption alone; therefore, the phenomenonmonitored by the present data is referred to as abstrac-tion and the value calculated from the concentration dif-

ferences is called "abstraction" rather than adsorption." Abstraction" by the mineral includes adsorption and

precipitation on the mineral but is not expected to includethe loose precipitate in bulk solution.

Stepwise Abstraction. Incremental abstraction (stepwiseabstraction) experiments were conducted by agitating aknown weight of the surfactant solution with the desiredamount of the pre wetted Na-kaolinite for given times ina weighed glass centrifuge tube of 5O-mL [5O-cm3Jcapacity. The change in surfactant concentration after thefirst step was determined after 72 hours' equilibration.In the second step, a predetermined volume of the super-natant was removed from the system and an equal volumeof the surfactant stock solution of desired concentration,identical in pH and ionic strength to the supernatant, wasadded and agitated for 24 hours and centrifuged as before.To account for possible evaporation and other losses, theweight of the centrifuge tube after each addition orremoval of samples for analysis was recorded. Theamount abstracted was determined from the changes inweights and surfactant concentration. The procedure usedfor calculating the abstraction density is given in the ap-pendix.

Adsorption isotherms obtained in this manner will becalled "S-isotherm" (continuous stepwise abstractionisotherm) while the traditional abstraction isotherm willbe referred to as "B-isotherm" (batch adsorptionisotherm).

Deabstraction (Dilution). These experiments were con-ducted by stagewise dilution of the mineral/surfactantsystem that has been pre-equilibrated with surfactant s0lu-tion at the desired pH, ionic strength, and temperature.Solid/liquid ratio was kept constant by removing thedesired amount of the supernatant before introducing thediluent adjusted to the required pH and ionic strength.After dilution, the system was equilibrated for 24 hoursand the supernatant was analyzed for surfactant concen-tration. This equilibration time was chosen since no fur-ther change was observed in bulk concentration.Abstraction density was calculated using the proceduregiven in the appendix.

SOCIETY OF PETROLEUM ENGINEERS JOURNAL344

sulfonate concentration die stepwise abstraction exhibiteda definite decrease. To ensure equilibrium, a contact timeof 24 hours also was selected for die stepwise abstractiontests. Note that, as in batch tests, die starting point ondie stepwise abstraction is after 72 hours of equilibration.

Abstraction/Deabstraction Isothenns. Results of batch-wise abstraction (B-isotherm) followed by stepwisedeabstraction obtained upon dilution for the DDBSIkaolinite system in various electrolytes at pH's of 4.6 and6.6 are given in Figs. 3 through 6. It is clear from thesefigures that the systems exhibit a certain amount ofhysteresis. In certain cases, dilution isotherms exhibit amaximum around the same concentration where abstrac-tion maximum was obtained. This clearly suggests thatthe abstraction maximum obtained is a true maximum andnot an experimental artifact. However, it is interestingto note that the abstraction maximum on the deabstrac-tion isotherm depends to a large extent on the value ofthe maximum concentration of the surfactant solution thatthe mineral had come in contact with before any dilution.When the maximum predilution surfactant concentrationis not too different from the concentration where theabstraction isotherm exhibits maximum, the dilutionisotherm is found not to differ significantly from theabstraction isotherm. At higher maximum predilution con-centrations, hysteresis is significant.

The effects of pH on the hysteresis phenomenon at10-2 aIKi 10-1 kmoUm3 [2.83 X 10-4 and2.83XIO-3kmoUcu ft] NaCl are shown in Figs. 3 and 4, respective-ly. Abstractionldeabstraction isotherms are characterizedby high abstraction and marked hysteresis at pH 4,6(natural pH) when compared to the corresponding effectsat pH 6.6. It should be noted that the maximum amountof DDBS in an acidic pH range corresponds to 100 and

ResultsAbstraction/Deabstraction Kinetics. Initial tests con-ducted on the equilibration of dry kaolinite with water atvarious pH values and ionic strengths showed this proc-ess to involve at least two steps. 8 Similarly, abstraction

of sulfonate by kaolinite involved a fast and a slow step.The kinetics of abstraction of sulfonate during batch testsare discussed elsewhere. 8

Results obtained for the kinetics of abstrac-tion/deabstraction of sulfonate on dilution from two dif-ferent initial concentrations of sulfonate are given in Fig.1. These initial concentrations were chosen with the helpof results obtained for the batch abstraction tests in sucha manner that the equilibrium concentrations after 72hours of conditioning corresponded to (1) a value closeto the maximum (initial sulfonate 15.9 mol/m3 [0.45moUcu ft]) and (2) a value well above maximum (initialsulfonate 30.4 moUm3 [0.86 mol/cu ft]). It is evidentfrom Fig. 1 that the abstraction decreased initially andthen increased marginally above approximately 50 hourswhen the initial sulfonate concentration was 15.9 mol/m3[0.45 mol/co ft). On the other hand, when the initial con-centration was 30.4 mol/m3 [0.86 moUcu ft), abstractionattained the equilibrium value in almost ten minutes. Thesmall increase observed in both cases at longer times(greater than 50 hours) is suggested to be caused by theactivation of sulfonate adsorption and possibly evenprecipitation of it by the aluminum species released slowlyby the kaolinite. 8 To minimize these long-term effects,an equilibration time of 24 hours was chosen for the subse-quent tests.

Kinetics of stepwise abstraction for an initial concen-tration of 33 moUm3 [0.93 moUcu ft), indicated in Fig.2, shows that the system attains equilibrium within 4hours. It is most noteworthy that upon increasing the

150

1.0

OOOECYL8ENZENESULFONATEI No'"KAI)L"ITE

-2 3I - 10 kmol/m NaC1

TEMP.- :SOt. I.C

SOLIDS. 200 k9/m'

A8S. TIME. 72 HRS.-6- ABSTRACTION AT pH 4.6 t. 0.1--';7-- OEA8STRACTION ATpH 46tOJ.-0- ABSTRACTION AT pH 6.6tO 1

OEABSTRACTION AT pH 66t.Oi

-e""0E..

,..'tonz...0z2l-V4~l-onm4

~

IIItOO~

cw

~u~III

~..I

~50°

2

~,- 0",'.:--.~9..~ -

~';-~'-o..-v -.- '- .

-~.,

1.0

.-;

I~~O. . ~..;:;:a~b_~_.~~. . I~~ -- ---~ -~ 0

0.00 20 40 60

R£SIOUAL CONCENTRATION, mol 1m3

Fig. 4-Abstraction/deabstraction of OOBS/Na-kaolinite systemin 10 -1 kmol/m3 NaC!.

Fig. 3-Abstraction/deabstraction of DDBS/Na-kaolinite systemin 10 -2 kmoI/m3 NaCl.

345JUNE 1985

6.0

5.u

4.0

3.0

2.0

Fig. 6-Abstraction/deabstraction of DDBS/Na-kaolinite systemin 10-2 kmoUm3 NH.CI.

112% of monolayer (with a molecular parking area of33.7 A 2/mo1ecu1e) at ionic strengths of 10 -2 and 10-1

kmol/m3 [2.83x10-4 and 2.83x10-3 kmol/cu ft]NaC1, respectively. The corresponding deabstractionvalue from the highest surfactant concentration does notexceed ro to 70% of monolayer coverage. On the otherhand, the results obtained near neutral pH values indicatemuch less hysteresis and the deabstraction isotherms tendto approach the abstraction isotherms, particularly at lowerNaCl concentrations. At this pH, the maximum abstrac-tion at 10-2 and 10-1 krnol/m3 [2.83 X 10-4 and2.83 x 10 -3 krnol/cu ftJ NaCI was found in the range of

25 and 35 % of monolayer coverage, respectively, whilethe corresponding value for deabstraction was about 20%monolayer.

ft)). Further increases in the sUrfactant concentrationresulted in a shallow decrease in the adsorption density.The reproducibility of the results was confirmed by con-ducting triplicate tests. Some scatter was observed in theregion of adsorption maximum.

S-lsothema-2. This test was perfonned at an initialSDDBS concentration of 15.9 mol/m3 [0.45 mol/cu ft],which is above that corresponding to the maximumabstraction. An increase in surfactant concentration in thisregion produces a decrease in the abstraction density.

S-lsothema-3. This test corresponds to an initial SDDBSconcentration of 30.4 mol/m3 [0.86 mol/cu ft] and theisotherm is characterized by a region where the abstrac-tion decreases slightly and then by a region of constantabstraction at residual concentrations higher than 40mol/m3 [1.13 mol/cu ft],

If the initial points of S-isotherms are connected to thepoint of abstraction maximum, an isotherm (similar to theB-isotherm) obtained previously from batch tests shouldresult. It is noted that the decrease in abstraction in S-isotherm-l is not as marked as in B-isothenn. However,S-isotherm-2 appears to be similar to the B-isothenn.

An attempt was made to measure abstraction/deabstrac-tion by incremental increase and decrease in DDBS con-centration using the same kaolinite sample. The resultsobtained by such tests (given in Fig. 8) indicate that thephenomenon of hysteresis exists even at high surfactantconcentration.

The effect of pH on stepwise abstraction at a surfac-tant concentration below the CMC is shown in Fig. 9.The S-isothenns obtained at both pH's studied exhibit ashallow maximum around the CMC of the surfactant. Asexpected, the abstraction capacity of Na-kaolinitedecreases with the increase in pH. The effect of stepwiseincrease of pH from 4.5 to 8.2 on the abstraction capaci-

SOCIETY OF PETROLEUM ENGINEERS JOURNAL

Stepwise Abstraction Isothenns. Stepwise abstractiontests were designed to simulate more or less a continuousadsorption test conducted on one and the same kaolinitesample by incremental increases in DDBS concentrationof the system, as described earlier. Three initial concen-trations were chosen in a way to cover the followingregions in the B-isotherm. These are (1) the region belowthe CMC of DDDS where the rising part of the B-isothermis expected to pass through the maximum, (2) the regionjust above the abstraction maximum, and (3) the regionof highest equilibrium concentration. Results obtained inthese regions are illustrated in Fig. 7 and denoted byseparate solid curves. All abstraction tests were conductedat constant pH, ionic strength, solid/liquid ratio, andtemperature conditions.

S-lsothenn-l. At very low residual concentrations (lessthan CMC), abstraction of DDDS increases (as expected)with surfactant concentration to reach a maximum in theregionofCMC (6xlO-4 kmol/m3 [1.7XIO-5 kmol/cu

346

t IDODEC YLBENZENESULFONATEI No -KAOLI N ITE

6 L s

NE

"0E~

>-'"t-U)ZW0

z

Q..-u<S-It:t-II)aI<S-

[ -*- 4.5 j: OJ

pH:

~ 5.3 j: 0.1

~--, sI = 10-1 kmol/m3 ~CL

SOLIDS = 200kg/m3T = 30 j: 10 C

CONTACTHRS = 72+24/STEP

O' I I I I I

0 10 20 30 40 50

RESIDUAL CONC.,moVm3

Fig. 9-Effect of pH on stepwise abstraction of DDBS/Na-kaolinite system in 10 -1 kmol/m3 NaCI.

Fig. 7-Stepwise abstraction of DDBS by Na-l<aolinite in 10-1kmol/m3 NaCI.

Ag. 8-Stepwise abstraction/~raction of DOBSINa-kaoIinitesystem in 10-1 kmoI/m3 NaC!.

Fig. 1 O-Comparison of pH dependence of stepwise abstractionand batch abstraction.

ty of kaolinite, conducted on one and the same sample,is illustrated in Fig. 10, along with the effect obtainedpreviously for individual samples at each pH. It is evi-dent that the abstraction obtained during stepwise increasein pH is higher than that obtained by individual samplesconditioned at different pH values. This further suggeststhe unusual adsorption behavior of the sulfonate/kaolinitesystem showing hysteresis.

JUNE 1985

DiscussionSeveral physicochemical processes can be expected to takeplace when clays are contacted with electrolyte or sur-factant solutions and to contribute to determining theoverall behavior of the resulting suspensions. The majorprocesses include hydrolysis of the mineral surfacesspecies, ion-exchange, electrostatic adsorption, anddissolution of the clay.

347

5

;j

4

3

iIi

. DODECYLBENZENES~FONATE INo-KAOLIN'

~

-- INDIVIDUAL ABSTRACTION

- STEPWISE ABSTRACTION."

~

7"-'-

~.E"0e'-

~I-0Z...QZQFucc

i

..e

-0eoK

z2:

~a:I-zWuz0Ut-

C

~ "

~ \s ,

-2 -"~~~ ~L::I - 10 ~1/mJ N°zS°. .SOUDS - 200 k9/mJ

T-30t1-CpH - 4.4 % 0.1CONTACT HRS - 72... 24/STEP

o~ 1~ ~ ~ ~. 5::> ~ioRESIO~ CONC.. IftOVJftS

Fig. 11-Comparison of stepwise abstraction and batch abstrac-tion of DDBS by Na-kaolinite in 10 -2 kmol/m3

Na2SO.o

pH

Fig. 12-Solubility Ys. pH of kaolinite. 12

tion. The marked decrease in abstraction when increasingthe pH from 4.5 to 5.5 in batch tests correlates well withthe similar ~rease in die concentration of released AI3 +

species in this pH range (see Fig. 12). The dissolved AIcan affect the adsorption process in several ways. AIspecies can readsorb on the clay surface, making it morepositive and, in rom, enhancing the adsorption of negative-ly charged sulfonate. Dissolved AI also can react with thesulfonate both in the bulk and in the surface region,leading to bulk/surface precipitation. Our recent studieswith the supernatant of clay prepared around pH 3.9 didshow such sulfonate precipitation.

In tests where pH is increased in a stepwise manner,part of the AI released from the solid under low-pH con-ditions can adsorb or precipitate on clay and, in eithercase, can increase the sulfonate uptake by clay. Precipita-tion of AI as colloidal AI-hydroxide and adsorption ofsulfonate on such colloidal particles also cannot be ruledout. It is also possible that the sulfonate adsorbedchemically on clay under low-pH conditions does notdesorb totally as the pH is increased. Indeed, these fac-tors can lead to higher sulfonate abstraction in tests inwhich pH is increased in a stepwise manner.

Presence of a maximum in an abstraction isotherm hasbeen considered to result from a number of reasons, suchas micellar exclusion,6.10 presence of a maximum inmonomer concentration above CMC,2 impure ormulticomponent nature of the surfactant, 13 and the

precipitation of surfactant/multivalent ion salts belowCMC and their redissolution by micelles above CMC. 14

SOCIETY OF PETROLEUM ENGINEERS JOURNAL

It was found that both the equilibration of the kaolinitewith water and abstraction of sUlfonate by the kaoliniteinvolve a fast and a slow step.8 The slow step was at-tributed to the slow release of aluminum species bykaolinite and the resultant activation of sulfonate adsorp-tion or the precipitation of sUlfonate.

Past studies using kaolinite do not appear to have con-sidered the possibility of an intermediate metastable con-dition. Implications of this finding when interpreting data(for abstraction, equilibration, etc.) obtained in the pastunder metastable conditions should be noted.

As mentioned earlier, the abstraction of sulfonate byNa-kaolinite may involve electrostatic adsorption, ion ex-change, metal-ion-activated adsorption, or even surfaceprecipitation. Therefore, the term abstraction, which in-cludes adsorption and any other precipitation reaction onthe mineral surface, is used in the discussion to describethe "composite adsorption process."

The results given in Figs.. I through II clearly show.that the abstraction of DDBS on Na-kaolinite exhibits amaximum and, most importantly, significant hysteresiseffects. The appearance of a maximum in the dilutionisotherm further suggests that the abstraction maximumis a real phenomenon and not an experimental artifact.

Comparison of the batch tests with the stepwise increasetests (see Fig. 11) shows that the decrease in abstractionabove the maximum is sharper in former cases than inthe latter. In other words, the excess sulfonate requiredto decrease the abstraction by a certain amount from itsmaximum value is lower in batchwise tests than in step-wise tests.

The significant difference observed in the pHdependence of abstraction of stepwise and batch-typeabstraction tests indeed shows the important role of re-leased aluminum species in governing sulfonate abstrac-

348

~

5

o.

01i

21

require careful analysis that will take into account anysulfonate that is desorbed during flusing before extrac-tions of the adsorbed sulfonate.

AcknowledgmentsWe gratefully acknowledge the support of the DOE (DE-AC 19-79BC-l0082), Natl. Science Foundation(82-01216), Amoco Production Co., Chevron Oil FieldResearch Co., Exxon Research and Engineering Co., GulfR&D Co., Marathon Oil Co., Mobil R&D Co., ShellDevelopment Co., Standard Oil of Ohio, Texaco Inc., andUnion Oil Co. of California. We also thank K.P.Ananthapadmanabhan for helpful discussions.

In this system, precipitation and redissolution can be con-sidered to be a major phenomenon, since tests conductedwith clay supernatants (containing multivalent ions suchas AI) did show precipitation in certain sulfonate concen-tration ranges.

The differences between the S- and B-isothem1S alsocan be accounted for on the basis of precipitation-redissolution phenomenon. A major difference betweenthe two types of tests above CMC is that in the case ofthe stepwise test, precipitate formed at lower sulfonateconcentrations during previous steps has to be redissolvedwhen the concentration is raised above CMC, while inthe case of the batch test, the precipitation process itselfis prevented (retarded) by the micelles that are presentin the system from the very beginning. Redissolution ofthe precipitate nucleated on the solid may not be rapidand, therefore, equilibrium might not be always attainedin S-type tests. Under these conditions, the S-isothermscan be expected to exhibit a shallower abstraction maxi-mum than the B-isotherms.

A careful analysis of the role of the various factors incausing an abstraction maximum and hysteresis in thissystem indicates that the abstraction maximum is causedby the surface precipitation of surfactant/multivalent ioncomplexes at sulfonate concentrations below CMC, andtheir redissolution is caused by micelles above CMC. 15

The absence of reversibility (or presence of hysteresis),on the other hand, is considered to be caused by the for-mation of bulk precipitates, as opposed to surfaceprecipitates, upon dilution. 15 It is to be noted that the

bulk precipitate is reported as bulk sulfonate and not asabstracted sulfonate. Details of this mechanistic interpreta-tion are discussed elsewhere. 15

References

1. Trushenski, S.P., DaubeD, D.L., and Parrish, D.R.: "MicellarRooding-FIuid Propagation, Interaction, aIK1 Mobility," Soc. Pet.Eng. J. (Dec. 1974) 633-45; Trans., AIME, 257.

2. Sexsmith, F.H. aIK1 White,H.J. Jr.: "The Absorption of CatiooicSurfacIants by Cellulosic Materials," J. Colloid fnter:{oce Sri. (1959)14, 630-39.

3. Fava, A. and Eyring, H.: "Equilibrium and Kinetics of DetergentAdsorption," J. Phys. DIem. (1956) 60, 890-98.

4. Day, R.E., Greenwood, F.G., and Parfitt, G.D.: "Effect of HeatTreatment on the Adsorption of Sodium Dodecyl Sulphate fromA~ Solution on Spheron 6," Proc., Foordl IntI. Congress Sur-face Act, Brussels (1964) 1005-13.

5. Saleeb, F.Z. and Kitchener, J.A.: "The Effect of Graphitizationon the A~ ofSurfactants by Carbon Black," J. Chern. Soc.(1965) 167, 911-17.

6. Mukerjee, P. and Anavil, A.: ., Adsorption of Ionic Surfactants to

Poroos Glass," Adsorption at Interfaces, Symposium Series, ACS,Washington, D.C. (1975) 8, 107-28.

7. Hanna, H.S., Goyal, A., and Somasundaran, P.: "Surface ActiveProperties of Certain Micellar Systems for Tertiary Oil Recovery,"Proc., Seventh Intl. Surface Activity Congress, Moscow (1976) 3,892.

8. Hanna, H.S. and Somasundaran, P.: "Equilibration of Kaolinitein Aqueous Inorganic and Surfactant Solutions," J. Colloid Inter-face sa. (1979) 70, No.1, 181-91.

9. Hanna, H.S. aIK1 SomaswKJaran, P.: Improved Oil Reco~ryby Sur-jadonI and Poi}mer ~g, D.O. Shah aIK1 R.S. ~ (eds.),Academic Press Inc., New York. City (1977) 221-32.

10. SomasUlMiaran, P. and Hanna, H.S.: "Adsorption of Sulfonates onReservoir Rocks," Soc. Pet. Eng. J. (Aug. 1979) 221-32.

11. Celik., M. et aI.: "The Role of Surfactant Precipitation andRedissolution in the Adsorption of Sulfonate on Minerals," Soc.Pet. Eng. J. (April 1984) 233-39.

12. Siracusa, P.: "Desorption of Sulfonates from Clay," MS thesis,Columbia U., New York City (1982).

13. Trogus, F.J., Schec:hter, R.S., and Wade, W.H.: "A New inter-pretation of Adsorption Maxima and Minima," J. Colloid Inter-face Sci. (1979) 70, 293-305.

14. SomasuOOaran, P.: "Adsorption From Flooding Solutions in ProusMedia," annual report submitted to the Nad. Science Foundation,Washington, D.C.

15. AlWldlapadInanabhan, K.P. aIK1 Somasundaran, P.: ,. A Mechanism

for Abstraction Maximum and Hysteresis in Na-Kaolinite-Na-Dodecylbenzeoesulfonate System," Colloids and Surfaces (1983)7, 105-14.

ImpUcations of Abstraction Maximumand Hysteresis

The results presented in Figs. 3 through 11 clearly in-dicate the presence of an abstraction maximum and con-siderable hysteresis for the adsorption behavior of theNa-kaolinite/SDDBS system. Comparison of the stepwiseabstraction with the batch abstraction suggests that retard-ing abstraction by maintaining a high surfactant concen-tration is probably easier than deabstracting thealready-abstracted sulfonate by raising the bulk sulfonateconcentration. Dilution isotherm shows that a significantamount of sulfonate can be deabstracted from the surface.In other words, flushing the core with water subsequentto the advance of a surfactant slug can remove theabstracted sulfonate from the surface. The beneficial ef-fect of this washing can be realized only after developinga better understanding of the form in which the~ sulfonate is released into the system. The sug-gested mechanism for the abstraction maximum andhysteresis 14 indicates that the sulfonate deabstracted after

dilution can form bulk precipitates, which, in turn, canplug the pores. This aspect of the problem is being in-vestigated currently.

The results presented here clearly suggest that specialprecautions are required to interpret the results obtainedusing the "core tests." In these tests, before the adsorbedsurfactant is extracted, the entrapped solution is flushedwith several fluids. Such steps can cause desorption ofdie abstracted surfactant and thereby lead to low estimatesfor surfactant abstraction. Adsorption tests using cores

APPENDIXCalculation of Abstraction Valoes for Batch andStep IsothermsAbstraction density in batch tests is reported in mol/m2and is calculated as follows:

r=(Cj -Cr)(~). (A-I)

JUNE 1985 349

at the end of this period. If C r2 is the residual concen-tration at the end of Step 2, adsorption density r2is given by

. .(A-4)

wherec; = initial surfactant concentration, krnol/m3

[kmol/cu ft],C r = residual surfactant concentration, krnol/m 3

[kmol/cu ft],S = solids concentration, kg/m3 (lbm/cu ft],

andA = surface area, m2/g [sq ft/g]. Eq. A-4 can be repeated for any number of steps, such

thatFor stepwise abstraction-dilution tests, calculations are

performed as follows: Cin=r n-IAS

Cr(II-t) Vr(II-l) +CS<II-1) V 8(11-1)first-step adsorption=r1 =(Cn-C'l)-

M.(A-2) (A-S)+; v

forIn stepwise tests, a certain volume of supernatant V sis replaced by the same volume of the electrolyte (con-centration of the surfactant in the added solution, C s = 0)or by the same volume of a surfactant solution of desiredconcentration (Cs =finite value). Therefore, the totalamount of surfactant in the system at dIe beginning of dIesecond step is given by

n~2,

r =( c. -c )-/I III naSA

SI Metric Conversion Factorscu ft x 2.831 685

of (OF - 32)/1.8Ibm x 4.535 924

sq ft x 9.290 304*

E-02 = m3= DC

E-OI = kgE-02 = m2

Ca=(rlAS+ (A-3)

.~ facIor Is exact. SPEJ

OrIgInal ~ r-'ved in die ~ of ~ Engineers office Jan. 28.1-' p~ 8O:c8I*d b ~ Nov. 23, 1~ R8YI8ed ~ received JIdy3, 1*. P8II8f (SPE 1~ fiIst ~... 1- SPE kII. ~kIm on 0IfieIdand GeoItIenM a.emi8tIy held In DaIas Jsn. 25-27.

where V is die total volume of solution in die system andVrt equals V-Vst-

Widi die new initial concentration. C 12. die adsorptiontest is continued for a predetennined length of time anddie supernatant is analyzed for surfactant concentration

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