minerals by Sac el al.,2,3 Gale and Sandvik,. Hill elal.,s Hurd,6 and Somasundaran el al.',8 have beendiscussed earlier. 9 Bae el al. observed the presence ofa maximum for abstraction in the systems they in-vestigated. Other recent studies on abstraction onreservoir minerals include those of Malmberg andSmith, 10 Trogus el al.,11 and Lawson and Dilgren.12The phenomenon of abstraction- maximum andminimum is of much theoretical and practical in-terest. Howevcr, mechanisms of surfactant ab-straction in such reservoir/surfactant systems are notyet established fully and as such their abstractionbehavior generally cannot be predicted. Also, nofully substantiated reasons exist to account for thepresence of the maximum or minimum. Our ob-jective is to study the abstraction behavior of relevantsurfactants on reservoir rock minerals under variousexperimental conditions to understand themechanisms involved in this interfacial process andto identify conditions under which surfactantretention can be minimized. Results obtained herefor the abstraction of recrystallized dodecYlben-zenesulfonate by treated kaolinite in variousinorganic electrolytes are given with a summary ofresults obtained previously for the abstraction ofcertain sulfonates by Berea sandstone, agriculturallimestone, and Bedford limestone.

AbstnctAbstraction of Mahogany sulfonate AATM andrecrystallized dodecylbenzenesulfonate by Na-kaolinite, sandstone, and limestone was studied as afunction of relevant variables such as pH, ionicstrength, and type of inorganic electrolyte added. Inmost cases, such factors tiffect not only the ab-straction capacity of the solid particles, but also theshape of the abstraction isotherm. Particularly, theinorganic species in the system were found to in-fluence the abstraction and the desorption ofdodecylbenzenesulfonate by kaolinite, based upontheir size and solvation properties. Thus, appearanceof a maximum in this system was related to thepredominance of smaller exchangeable "structure-making" ions. Introductions of larger "structure-breaking" ions tends to eliminate such maxima. Therole of ions (such as silicate, phosphate, chloride,calcium, sodium, ammonium) are examined andpossible mechanisms are discussed. Implications ofthese observations in developing the capability tocontrol abstraction should be noted.

IntroductionA major problem that affects the efficiency of ter-tiary oil production by micellar flooding is the loss ofsurfactants from interaction with minerals and theirdissolved components. Troshenski et al.1 have ob-served the existence of a retention maximum near thecritical micellar concentration range followed by aminimum for the system Berea sandstone/Mahoganypetroleum sulfonate-isopropyl alcohol micellar fluidat IIO.F (43 .C). Similar studies on reservoir rack

OfIglnal manuacrlpt received In Soei8ty 01 ~lroIeum Engl- otf~ Feb.15. 1878. ~ accep~fOt publlc.,1on Sepl. 27,1878. A8¥t8ed menu8Cr1ptreceived April 2, 1879. ~ {SP£ 7O5eI nrat ~~ ., lhe SPE.AIME FifthS~lum on Im~ Method. lor 011 ~, held In Tul... April 18-17,1878.

Th'. peper will be Included In the 1878 7r8"..ctlon8 YoIume.

"Now wlttl the Miner.' "-_r_ln... 01 the U 01 AI.b8m.

BackgroundOur previous work9.13 clearly has shown that thenature of the abstraction isotherm obtained dependsto a large extent on the type of sulfonate used. themorphological and mineralogical characteristics ofthe rock, and the type of electrolytes present insolution,'For a dellnltlon ot the term e.tracllon. - the ucllon on "AbetrectlonProcedure."

0031~705\1SOO.2&.., t979 8oclety ot Pelloleum EnOin-.t8 of AIME

AUGUST.m UI

P. Somasundaran, Columbia U. .H. S. Hanna,- Columbia U.

Abstraction maxima were obtained for Mahoganysulfonate AA by previously unwetted Berea sand-stone9 (Fig. IA). Isotherms of dodecylsulfonate(reproduced in Fig. I B) exhibited only positiveslopes, but concentrations studied were restricted topremicellar range because of solubility problems.Increase in ionic strength from adding NaCI in-creased the abstraction in all cases. Abstractionmaximum was sensitive to the amount of NaQ added(Fig. 2). At lower NaCI concentrations, themaximum occurred for Mahogany sulfonateAA/Berea sandstone system; at an intermediateconcentration of 2.5 x 10-2 mol/dm3 NaCI, theisotherm exhibited a maximum, followed by ashallow minimum; at still higher concentrations, theabstraction maximum was not present. Na2SO.addition also caused an increase in abstraction, butthe effect of this uni-bivalent salt was less than that

1ft

MAHOGANY SlA.FONATE M /BEREA SANDSTONE

1 . 10-1 M NoCI

,... 8.I~O.1S/L . 1:1

TEMP. . 30 ~O.2.CABS. TIME . ~ HOURS

0..-w?;...~

-E....EZ2...

~c...(/Im~

caused by the addition of the urn-univalent salt,NaCI. Addition of Na2HPO. depressed the ab-straction of the sulfonate under all conditions.

Abstraction isotherms of sodiumdodecylsulfonate, sodium dodecylbenzenesulfonate,and Mahogany sulfonate AA by two types oflimestones (Bedford limestone and agriculturallimestone) and those of sodium dodecylsulfonate,sodium dodecylbenzenesulfonate, and Aerosol OTTMby synthetic calcium and magnesium carbonates alsoexhibited a maximum under all conditions.IJ Theaddition of NaCI, Na2S04, and Na2HPO4 also hadnoticeable effects on the abstraction of sulfonate bylimestones. In this case, mineralogical and mor-phological characteristics of the absorbent werefound to influence the abstraction markedly. Theporous type of limestone (Bedford) had a lowerabstraction density under natural pH conditions,possibly because of the concentration of the silicateson the surface of the particles after the dissolution ofexposed calcite and magnesite and the nonwetting ofpores. Interestingly, agricultural limestone wasfound to abstract more sulfonate than Bedfordlimestone in the alkaline pH range, possibly becauseof the activation of the exposed silica on the formerby dissolved calcium and magnesium species in thispH range (Fig. 3).

Clearly these results show that the type ofinorganic species present in the system plays a majorrole in controlling the abstraction behavior ofsulfonates by mineral solids. To establish the role ofeach ion clearly and to elucidate the mechanismsinvolved, however, we must conduct studies on asystem comprising purified and well-characterizedminerals and surfactants. This study therefore wasconducted with sodium dodecylbenzenesulfonatepurified by soxhlet-extraction and recrystallizationand kaolinite treated with NaCI solutions to produce0

0 10 20 30EQUILIBRIUM CONCENTRATION, ,II (ACTIVE)

Fig. 1A - Abstraction of Mahogany sulfonate AA TM byground Berea sandstone sample (after Hanna andSomasundaran,' courtesy of Academic Press Inc., New

Yor1< City).

pH . 8.1 to.1S/L . 1:1

TEMP. . ~~ 0.2.C

A8S.TIME' 4 ~

SULF~ATE AA/KREA SANDSTONE

IIJ?;...

~~....E

z2;...uCc""iiimc

1iw,

z2...uCc.....c

-0- '"16'" "_C'-Z'"~~ i "-CI_.'"1O_ ij "-CI

--- 1"10 "_CI

--mi. E~

0 - -.1 --'---

0 10 20 30EQUII..18R1UM COMCENTRATION,9/1 (ACTIVE)

Fig. 2 - Effect of NaCI eddltlons on abstraction ofMahogany sulfonate AA fractions (after Hanna and8omasundaran,' courtesy of Academic Press Inc., New

York City).

0 0 2.0 4.0 ..0 ..0 10.0E~IL"RIW ~NTMT1ON, . £.../1

Fig. 18 - Abstraction Isotherm of sodiumdodecylsulfonate by kaolinite (after Hanna andSomasundaran,' courtesy of Academic Press Inc., New

York CIty).

SOCIETY 01' PET8OUUM ENGINE£8S J(R/aNALm

o.e

O.~

0.2

precipitation values obtained using the concentrationdifference technique is the Gibbs adsorption orsurface excess and must be distinguished from totaladsorption. Any precipitation in the system,however, also can contribute toward the observeddifference in concentration. We attempted tominimize this artifact by resuspending the precipitate(by gentle stirring) that appeared to collect on top ofthe mineral bed during centrifugation. Nevertheless,any trapping of precipitate inside the mineral bed orits deposit on the mineral particles would lead tovalues that are higher than those for adsorptionalone; the present phenomenon therefore is referredto as abstraction. The value calculated from the

Na-kaolinite. Effects of important parameters suchas salinity, type of electrolytes present, pH, aging,and dilution resulting in desorption were determined,and the data were analyzed to understand themechanisms involved.

Materials and MethodsMineralA well-crystallized ~ample of Georgia kaoliniteobtained from the clay repository at the U. ofMissouri was used. The surface area of this sample(as determined by nitrogen adsorption) was 9.8 m2/g.Homo-ionic Na-kaolinite was prepared from thissample as follows: (I) the kaolinite sample waswashed repeatedly with water under intense agitationuntil there was no change in the conductivity of thesupernatant water; (2) the solids were repulped with2M NaCI solution and mixed ata high solid-to-liquidratio for IS minutes; the pulp was diluted andremixed for 2 hours, allowed to settle and decanted,and this washing procedure was repeated until a pHof 7 and a constant conductivity of the suspensionwere reached; (3) the NaCI-treated solids wererepulped using 1M NaCl at pH 3, mixed at a highsolid-to-liquid ratio, diluted, and washed severaltimes with water until a pH of 7 again was obtained;(4) during the last washing in Step 3, the fine clayparticles were separated from the coarse impuritiesby decantation; and (5) the Na-kaolinite thus ob-tained was filtered, dried, and stored dry.

Sulfonate

Sodium dodecylbenzenesulfonate (SO ODS) specifiedby Lachat Chemicals Inc. as 9SO/o active was purifiedrlfSt by drying under reduced pressure overphosphorous pentoxide at SO' to 6(}.C and then byextraction by dry distilled diethylether in a soxhletapparatus. The first part of the extract (20 to 30wtO/o) was discarded and the latter fraction (30 to 40wtO/o) was collected and, after evaporating thediethylether, the residue was recrystallized four timesfrom acetone. A product assaying 98.1 ~o SOODSand showing no minimum in surface ten-sion/concentration curve was obtained (Fig. 4).Infrared analysis of the purified material indicatedthe presence of the p-OODS isomer associated withtrace amounts of the o-benzene isomer.

Abstracdon ProcedureAbstraction tests were conducted by agitating aknown volume of surfactant solution with the desiredamount of solids for given times in an incubatormaintained at the desired temperature. At the end ofthe test, a sample of the supernatant solution wascentrifuged at 1,500 G (14 715 m/s2) for 20 minutes,and the supernatant was analyzed for the residualconcentration of the sulfonate, using the two-phasetitration technique with a mixture of dimidiumbromide and disulphine blue as indicator.14 Ab-straction of the surfactant is calculated from thedifference between initial and final sulfonate con-centrations. Note that adsorption in the absence of

Fig. 4 - Surface tension of recrystallized sodiumdodecylbenzenesulfonate as a function of concentration In

10-2 and 10-1 M NaCI solutions.

wAUGlISTl979

concentration differences is called "abstraction,"rather than adsorption. Abstraction by the mineralwill include adsorption and precipitation on themineral, but not the loose precipitate in the bulksolution.

Results and DiscussionAging of Kaolinite in Aqueous SolutionsInitial tests conducted on the equilibration of drykaolinite with water at various pH values and ionicstrengths showed this process to involve at least twosteps. Similarly, abstraction of sulfonate by kaoliniteinvolved a fast and a slow step, the latter possiblycaused by slow dissolution of aluminum species fromkaolinite during prolonged contact with water andthe resulting activation of sulfonate adsorption. ISPast studies using kaolinite do not appear to haveconsidered the possibility of an intermediatemetastable condition. Implication of this on theinterpretation of data obtained under metastableconditions should be noted. Furthermore, kaolinitesamples, even when stored dry, have been found toundergo changes in abstraction capacity during aperiod of months.

silicate minerals, H + and OH- ions are consideredto be potential-de.termining ions for kaolinite.16Thus, with a decrease in pH, the number of positivesites on the kaolinite particles is ex~ed to increaseand, thereby, can lead to an increase in adsorption ofthe anionic sulfonate. While this mechanism canexplain the results obtained at low pH values, itcannot account for abstraction equivalent to the 12to 250/0 surface coverage obtained above neutral pH,and therefore suggests the possibility for the presenceof other mechanisms.

Ion-Exchange Process. Information on the nature ofion-exchange possibilities can be obtained byanalyzing the data obtained for pH changes in akaolinite/dodecylbenzenesulfonate system at variouspH values. In the present case, while the final pH ofthe system in the acidic range was always higher thanthe initial value (pH of 3.1 shifted to - 4.6), theopposite was true in the neutral and alkaline pHrange (pH values of 7 and II shifted to - 6.5 and -9.6, res~ively). These observations can be ex-plained in terms of the amphoteric character of theterminal aluminum ions on the kaolinite surface. Inthe acidic pH range, the sulfonate ions can exchangewith the surface OH- ions, leading to an increase inthe pH of the solution. Such a mechanism has beensuggested earlier by Muljadi et al.17 for the ad-sorption of phosphates on clays. The increase in pHobtained here, however, accounts for only an SO/osurface coverage by dodecylbenzenesulfonate, incontrast to the abstraction equivalent to the 45 to1000/0 surface coverage actually obtained. Thedecrease in pH in neutral and alkaline solutions isdiscussed next.

Interaction with Multivalent Ions. These differencescan be accounted for by taking into consideration thepossible dissolution of the octahedral aluminumfrom the edges of kaolinite particles:

v,.AI~i2°s<°H)4(S) + 'hH20 = AI3+ H4SiO4 + 30H- pK = 38.7.

Effect of pHThe effect of pH on abstraction of sulfonate wasmarked (Fig. 5). Note that abstraction is given hereas a function of pH at constant equilibrium con-centration of the surfactant. The sulfonate ab-straction by kaolinite is seen to decrease markedlywith increase in pH, particularly in the acidic pHrange. Anionic dodecylsulfonate ions and micellescan adsorb on kaolinite surface because of eitherelectrostatic attraction of the ions to the positive siteson the kaolinite surface or ion exchange involvingeither CI- or OH- ions on the mineral surface, oreven chemical interaction in the bulk and solidsurface between the sulfonate ions and multivalentcations.

FJectrostadc Adsorption. As for most oxide and

The dissolved AI3 + and its hydroxy complexes can beexpected to react with the bulk surfactant spe<:ies toform aluminum sulfonate complexes that can easilyadsorb on kaolinite surface. Precipitation ofaluminum sulfonates in bulk solution is anotherpossibility that must be investigated.

The drop in the pH of the clay suspension from IIto 9.5 can be attributed to the formation ofaluminate ions, which is accompanied by OH-consumption as shown by the following reaction,IS

VzAI2Si2°.s(0H)4(S) + 'hH20

+ OH- =: AI(OH)4 + H4Si04 pK = 5.7.

Sulfonate can adsorb in this case by exchangingwith the aluminate ions. Surface coverage expectedfrom this ion-exchange reaction is 7 to 80/0 of themonolayer coverage, which is close to the observed120/0 under alkaline pH conditions. Ion exchangetherefore can be considered a major possible

U4 SOCIETY Of' Pr:ra0UtlM ENGINEDS JOUMAL

there is only limited specific adsorption of Na + andCI- ions on kaolinite,22 (2) Na salts often are used inpreflushing experiments, and (3) Na + is one of themajor dissolved ionic species in underground waters.We found during these experiments that the additionof salt also will produce a decrease in the pH of thesuspension because of the ion exchange between thesurface H + ions on kaolinite and added Na + ions.The units respectively for 10-2 and 10-1 M NaCIsolutions initially at about pH 6 to 8 certainly willhave their own effect on the adsorption of sulfonateon the mineral. Therefore, to evaluate the real effectof ionic strength alone, tests were conducted bymaintaining the pH at the desired value throughoutthe experiment. A summary of the results obtained ispresented in Fig. 7 as a function of pH at two con-stant equilibrium surfactant concentration levels.These results show that abstraction of sulfonate bykaolinite is enhanced, but only slightly, by an in-crease in ionic strength. Further increase in ionicstrength produced salting out of the surfactant.Much larger effects of ionic strengths reported in thepast must be attributed partly to simultaneouschanges in pH and the resulting increase of surfaceacidity of the clay mineral because it is clear from acomparison of data given in Figs. Sand 7 that pHeffect is of a larger magnitude under these conditionsand because pH seldom is reported as being con-stantly monitored during tests. Note at this point thatthe surface state of kaolinite is much more complexthan that expected on the basis of its ideal crystallattice structure. Buchanan and Oppenheim20

mechanism under alkaline pH conditions. The role ofaluminum species and the change in their relativeconcentrations on pretreatment of the kaolinite incontrolling the adsorption and precipitation ofsulfonate in fact can be significant. For example,even though the area occupied by the positivelycharged terminal-edge groups on kaolinite does notexceed 2 to SO/. of the total available surface area,19the actual coverage obtained for sulfonatecorresponds to a closely packed monolayer underacidic pH conditions. Such coverage can be madepossible by the generation of secondary positive sitesowing to specific adsorption of Al3 + ion and itscomplexes to the basal negative kaolinite crystal. Thedata given in Fig. 6 show clearly that the dissolvedaluminum species in the acidic pH range are mainlyAI3 +. Such AI3 + species can be expected to causeincreased adsorption as well as precipitation ofdodecylbenzenesulfonate on mineral particulatesbelow pH 6. Above about pH 8, AI(OH)4- willpredominate, and these ions will minimize ad-sorption of similarly charged sulfonate. Similarsuggestions also were made by Wayman21 andSwartzen-AIlen and Matijevic.22 who have con-sidered the possibility of reactions of such aluminumcomplexes as AI~OH)ls3+. AI(QH)2+, AliOH)24 + ,and Al3(OH)63 + with sulfonates.

Effect of SalinityFor the study of the effect of salinity on the sulfonateabstraction by kaolinite, we chose NaCI as thesupporting electrolyte for the following reasons: (I)

pH

Fig. 8 - Solubility-pH diagram for kaolinite (afterBuchanan and Oppenhelm,aG courtesy of CommonwealthScience and Industrial Research Organization, Melbourne).

AVGlST 1m 225

negatively charged mineral surface and the anionicsulfonate and thus, in effect, enhances the possibilityfor its adsorption on this mineral.

So far, we have examined the effect of a generalincrease in ionic strength on adsorption. In the nextsections, we will discuss the role of the type ofelectrolyte used.

considered it as a porous metal hydroxy regioncomposed of either silicon or aluminum species.d~nding on the pH. They noted that any ex-planation of the small. but measurable. cation-exchange capacity of kaolinite in terms of the brokenbonds at the crystal edges must be reassessed in thelight of such a possibility.

On the basis of these discussions. we propose acombined mechanism to explain the observed effectsof salt addition on the sulfonate by kaolinite. Thiscombined mechanism accounts for both (1) theincrease of surface acidity of the kaolinite and theresultant ion-exchange capacity and (2) the decreasein the compression of the double layer with 1ncreasein the ionic strength as well as salting out at higherionic strengths. The compression of the double layeressentially reduces the repulsion between the

Effect of Uni-Univalent Electrolytes

Abstraction isotherms of dodecylbenzenesulfonateby Na-kaolinite in various urn-univalent electr'olytesat three pH values (natural pH of - 6.5, 9.4, and4.5) are given in Figs. 8 through 10. The type ofelectrolyte used affects both the extent of abstractionand, most interestingly, the shape of the isotherm.Distinct maxima appeared on the abstractionisotherms obtained in 10-1 M NaCl, KCI, andNH4COOCH3 solutions. On the other hand, no suchmaximum was obtained in 10-1 M NaN03 andN".4CI solutions. This novel observation on thedependence of the appearance of the abstractionmaximum on the type of inorganic ions is discussedlater.

We also observed similar reactions at electrolyteconcentrations of 10-2 M.23 In 10-2 M NH4N03'NH4Cl. KCl. and NaCI solutions, a limiting ab-straction of about 1.7 II- mol/cm2, corresponding to30 to 40"0 of a compact, vertically orientedmonolayer coverage, was obtained under natural pHconditions. Increase of electrolyte concentration

0 20 40 60EQUILIBRIUM CONCENTRATION, mM/1

Fig. 8 - Effect of addition of 1.1 electrolytes on theabstraction of recrystallized sodium dodecylben.zenesulfonate by Na-kaollnlte at pH 6.5 :i: 0.2 and M 10"'

Ionic strength.

1-1 ELECTROLYTES I

Na-DOOECYLBENZENESULFONATE/No-KAOLINITEp+i : 9.4 ~0.4 l' 10-'~ ~

-E...."0E4"-

z~,~

eJI!

~

...0C~...>0U

~~III~.oJ0

~2

~. ...' t .--- K CI

-- AH4CI-0-- ~H400CCH,

J. t---0-- NH.NO,. .-- NaCI

t StructIKe Breaking Ian. Structure Makin, Ian

SOCm'Y OF P£TaOLaJM ENGIN£DS JOURNAL-

V' . .. . - -0 20 40 60

EQUILIBRIUM CONCENTRATION, mMI t

Fig. 9 - Effect of addition of 1-1 electrolytes on theabstraction of recrystallized sodium dodecylben-zenesulfonate by Na-kaollnlte at pH 9.4 ~ 0.4 and 10-1 M

Ionic strength.

on clay than other ions, which they indeed do asobserved here. An increase in ionic strength generallyalso can be expected to contribute toward increasedadsorption because activation energy for ion mobilityand self-diffusion of water generally decrease withany increase in electrolyte concentration.27,29

The effect of the inorganic ions also is partly theresult of the differences in their capacity to exchangewith the ions of the clay and their effect on othersystem properties, such as critical micelle con-centration and micelle charge and size.

yields nearly a monolayer limiting coverage. Increaseof pH to - 9.4 does not alter the shape of theisotherms, but does decrease the limiting abstractionto 12070 of the monolayer in 10-2 M electrolytes andto 26 and 80070 of a monolayer in 10-1 M NaCI and10-1 M KCI, respectively. In acidic solutions, on theother hand, both the shapes and the limiting ab-stractions are different from those obtained underother pH conditions.

In 10-2 M electrolytes, the maximum abstractionobtained corresponds to nearly that of a bimolecularlayer. The dependence of abstraction on the pH andthe ionic strength was discussed earlier. As far as theeffect of the type of inorganic ion is concerned, theuni-univalent electrolytes increase the abstraction ofsulfonate by kaolinite under various pH and ionic-strength conditions in the order: NaOH < NaCI <N~COOCH3 < N~CI < N~O3 < HCI <KCI. Thus, monovalent cations increase the ab-straction in the order Na + < NH4 + < K +, whileanions increase it in the order CH3COO- < CI- <NO3-' These results generally agree with those ofWayman21 for the adsorption of aIkylben-zenesulfonate on kaolinite, illite, and mont-morillonite, and those of Mortensen24 for the ad-sorption of anionic polyacrylonitrile on kaolinite.

Most clays are known to show affinity for cationsin the order Li + < Na + < K + < NH4 + < Rb +< Cs + < Ag + . This also is the order of increasinghydrated-ion radius. Selectivity of the clays for theions is considered to depend on physicochemicalproperties of the system, such as hydrationcharacteristics of the solid surface species and theions. 16.2S Both the surface and bulk species affect thestructure of water. Enhanced adsorption is expectedof those ions that induce the same type of structuralchanges in water as the surface because they canaccommodate themselves more easily in the aqueousenvironment of the interfacial region in such a case.Inorganic ions have been reported widely to producealterations in water structure, with the effect foundto increase in the order Li + < Na + < K + < Cs +for cations and a- < Br- < 1- for certain anions.Thus, while K + is considered to cause a breakdownof the water structure and thus facilitate self-diffusion of water molecules, Na + is believed toinduce a more coherent structure for the water. Thisinterpretation is supported further by Konta andBorovec26 for the adsorption of water by homo-ionickaolinites. Relative capacities of adsorption werefound to increase in the order NH4 + > Mg + + >K + > Na + natural kaolinite> Li-kaolinite. Clayitself is - considered to induce a more coherent

structure in water. Higher activitation energy ob-served for movement of ions in water containingclay, compared with that in water without clay, isattributed to formation of such a coherent waterstructure around clay platelets. Inorganic ions thatcan affect the water structure around the clay par-ticles also can be expected to affect the mobility andconcentration of an adsorbing ion such as Na-dodecylbenzenesulfonate. Structure-breaking ionssuch as K + and NH4 + therefore can be expected to

cause a larger increase in the adsorption of sulfonate

":ffect of Vni-Bivalent ElectrolytesResults obtained for the effect of uni-bivalentelectrolytes (Na2S04. Na2C03. Na2HP04, andNa2Si03) on the abstraction of dodecylben-zenesulfonate by Na-kaolinite at various pH valuesare given in Figs. (,1 through (,3. For comparison,results obtained for the effect of NaCI also arepresented.

In contrast to Cl-, addition of SO;- produces lessabstraction under low-surfactant concentrationconditions, possibly because of specific adsorption ofsulfate ions leading to an increase in the negativecharge of the clay particles.30 Above the criticalmicelle concentration. SO;-, however, produceshigher abstraction than Cl-, owing possibly to thestructure-breaking effect of the former on adsorptionof micelles. No abstraction maximum is obtained insulfate solutions.

Effect of addition of phosphates and silicates ismost interesting in that the abstraction can be nearlyeliminated, even with small additions. Note also thatthe effect of phosphate is different in acidic and

AUGVST 1m U1

FIg. 11 - Effect of addition of 1-2 electrolytes on theabstraction of recrystallized sodium dodecylben-zenesulfonate by Na-kaollnlte at pH 6.5 ~ 0.2 and 10-1 M

Ionic strength.

straction isotherms without any maximum wereobtained under all conditions. Also. the abstractionwas limited under all conditions to about 8 to 1207, ofmonolayer coverage.

In summary. certain uni-bivalent electrolytes suchas Na2SiO). Na2HPO4. and Na2CO) can cause littleabstraction of sulfonate by kaolinite. Evidently. adetailed investigation of the effect of these salts whencontrolling the abstraction of sulfonates by reservoirrock systems would be useful.

Effed of Hi-Univalent FJectroiytesIntroduction of Ca(NOJ)2 or Mg(NOJ)2 to thekaolinite/ dodecylbenzenesulfonate system resultedin higher sulfonate abstraction than those observedin NaCI solutions. Tests were conducted in this caseat 10-2 M and 3 x 10-2 M ionic strengths sinceconsiderable precipitation of dodecylben-zenesulfonate salts often occurred under higherionic-strength conditions. Observed enhancing ef-fects of Ca and Mg species on sulfonate abstractionagrees with the reported effects of such ions on theelectrochemical properties of mineral particles. Thesebivalent ions can adsorb specifically on negativelycharged particles and can reduce their negative in-terfacial potential and even reverse it.J2 Suchalterations in potential making the mineral lessnegatively charged can indeed lead to increasedadsorption of the anionic sulfonate. In addition tothis, adsorption of sulfonate in the form of com-plexes such as CaDDBS + also must be accounted for

alkaline solutions in that in the fonner case no ab-straction maximum was obtained. This differencelargely results from differences in the nature ofphosphate species present under various pH con-ditions. While a significant amount of phosphate willbe present in the form of structure-breaking H2PO4under acidic pH conditions, structure-making HPOiwiU predominate under alkaline pH conditions. Aninteresting possibility in the clay/phosphate system isthe fonnation of new crystalline phases composed ofAlPO4 salts on the mineral surface.]1 Appearance ofsuch phases should be of significance when deter-mining the sulfonate abstraction by the solid.

In contrast to NaCI, introduction of Na2SiO]produces decreased sulfonate abstraction under allconditions of pH and ionic strength. Reduced ab-straction is related partly to the decrease of freealuminum species, expected when silicates are in-troduced into solution. Silicates wiU react withaluminum to fonn aluminum silicate complexes inthe solution and possibly on the mineral surface. Thisalso should result in a decrease in the available sitesfor sulfonate abstraction. Note that in the alkalineregion, negligible abstraction and, in some cases,even negative abstraction is indicated. This reagentthus appears to hold some promise as a sacrificialagent for actual applications, particularly because itperhaps can aid in mobility control.

The effect of addition of Na2CO] was investigatedonly in the alkaline range, owing to the instability ofthis salt under other pH conditions. Simple ab-

-

1-2 ELECTROLYTESI

Na-OOOECYLENZENES\A.FONATEI Na-~ITE-,,.. . .,e t 0_1 t . ~ .!.

1-2 ELECTROLYTES'

Na-OODECYL8ENZENESULFONATE/Na-KAOL~ITE-IpH . 9.~ t 0.3 I . 10 ~ ~ -z . . I~~!...A

;&-,

40 -----I teo

-------.-

If

I ~CIII

§CIII)-4..I

~

~

-E....\

Ne.\

~~.~ t Strucf... e...i"9 Ion. Structure M~ Jon

III0

100 C~III>

8~III~..J0

150 ;

z0~uoCc...~moC

-z0~ucC0-~

.- _9;.8

'.'NoCI

-.- -~~~

t Structure ereokint Ion. Struclu'e Making Ion

TE~ . 3Ot0.58 CSOLIDS . 20~

." .

0 ~ -' . , . 'U

0 20 40 60EOUILIBRIUM CONCENTRATION, mM/1

Fig. 13 - Effect of addition of 1-2 electrolytes on theabstraction of recrystallized sodium dodecylben-zenesulfonate by Na-k,aollnlte at pH ~.6 :t: 0.1 and 10-1 M

Ionic strength.

~I

0 20 40 60EQUILIBRIUM CONCENTRATION, mM / I

Fig. 12 - Effect of addition of 1-2 etectrolytea on theabstraction of recrystallized sodium dodecylben-zenesulfonate by Ha-kaollnite at pH 9.5 .. 0.3 and 10-' M

Ionic strength.

.x.rY .. ~ IM;~ ~ALZ8

. INoZSO.. INo HZPO.. .NoZSiO,

. .'«IZ"-°4. ,NoZS04

No2c'OJ. .NozSiOJ

as a possible mechanism by which the bivalent ionsact. Figs. 14 and IS indicate that maximum ab-straction is about two to three times higher in thepresence of small calcium nitrate than that in thepresence of magnesium nitrate. This is relateddirectly to calcium sulfonate's solubility being lowerthan that of magnesium sulfonate.

2-1 ELECTROLYTES I

Na- OOOECYLBENZENESlN..FONATE I No-KAOLINITE

~ pH . 6.6 ~ 0.291

\ ~-aM 3~~-aM . If -0= --8-- CalNOS>a\ . I'. -- --6--- M91HO)12

~

150NE

~ 7'0E~

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, S'r~'ure BreokinQ Ion!

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SOLIDS. 20%

Desorption of Sulfonate From Kaolinite Surface

We began desorption studies because the nature ofdesorption definitely can help us understand ttiemechanisms involved when controlling adsorption ofsurfactants. Desorption experiments were conductedby stagewise dilution of the mineral/surfactantsystem that was pre-equilibrated at desired pH, ionicstrength, etc. The variables, such as solid-to-liquidratios, pH, and ionic strength, were maintained atconstant values throughout the test. Abstraction-desorption results obtained at pH values of - 4.6and - 6.6 in 10-2 M NaCI solutions are given in Fig.16. The data given in Fig. 16 indicate that the systemsdo exhibit hysteresis, and equally important, that theisotherms do exhibit a maximum in the same con-centration range where abstraction maximum wasobtained. The latter observation clearly supports thepossibility that the abstraction maximum obtained isa true maximum, not an experimental artifact. Notethat the maximum abstraction density obtainedduring desorption depends on the maximum sur-factant concentration that the mineral had come incontact with before any dilutions. When suchmaximum precontacted surfactant concentration isnear the concentration corresponding to maximumabstraction density, the desorption isotherm does notdiffer significantly from the abstraction isotherms.

\.-z0~'JcI-C/Iec

"'.

..

.'. \\

".- ~-""' ,.=::::::::~:.:~ ~~ - ---

: ~

:1)0

&0,2

-~10-'! NoCI'--161!. NoCI

O' . . . . . . "u0 20 40 60

EOUILIBRItJM CONCENTRATION mM/1

Fig. 14 - Effect of addition of 2.1 electrolytes on the ab-straction of recrystallized sodium dodecylben-zenesulfonate by Na.kaollnlte at pH 6.6 . 0.2 and 10-2 M 3

X 10-2 M Ionic strength.

2 -1 ELECTROLYTES I

NO- OOOECYL8ENZENE~FONATE I No-KAOLWITE

pH' 9.2 t 0.48DI

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SOLIDS. 20%

A8S. TIME' 12 HRS.

-6-AesrRAI:rOf AT ptt 4.6 tOol--v--OESORPTION AT pH4.6t:OJ

-O-MSTRACT~ ATpH6.6tO.I,-.-DESORPTION AT pH6.6t:o.ll

Ne....-0e~

z0i=u"0:...'"m"

at...

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CIII

~

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SOLIDS. 20%

\

"e"-.'0e..

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,"'e,

"

"'-

~

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~..J0Z0

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2.0 z.o--6 -6-- ,---~~

1.0 1.0

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-- _.~ 10~ NoCI

o.u. . I . . . . '0

0 20 40 80EQUILI8RIUM CONCENTRATION. 111M/I

Fig. 15 - Effect of addition of 2-1 electrolytes on theabstraction of recrystallized sodium dodecylben-zenesulfonate by Na-kaollnlte at pH 9.2 z 0.4 and 10-2 M

and 2 )( 10-2 M Ionic atrength.

OU' I . . . .0 20 40 60

EQUILIBRIUM CONCENTRATION, mM/1

Fig. 16 - Abstractlon-desorptlon Isotherms ofrecrystallized sodium dodecylbenzenesulfonate by Na-kaolinite at pH 4.6 *- 0.1 and 8.8 *- 0.1 in 10-2 M NaCI

solutions.

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At higher maximum precontacted concentrations,hysteresis is significant.

favorable energetically than those in bulk water,micelles usually are excluded under such conditions.Even though monomers could continue to adsorbeven above critical micelle concentration, thenegative adsorption of micellar aggregates can leadto a reduction in the surface excess of the totalsurfactant above the critical micelle concentration.On the basis of these considerations, both Na + andCI- ions usually are responsible for the observedmaximum in abstraction from NaCI solutions. Incontrast to NaCI, N~N03 with both the cation andanion as structure breaking, facilitates adsorption ofthe micelle (in addition to the monomer), and theadsorption isotherm in this case has no maximum. Inthis regard, note that only in larger concentrations ofthese electrolytes (than those of ions released fromclay) can we observe their effects. Also, the effects ofalkali or acid added to adjust the pH and of thechange of ionic size caused by hydrolysis reactionsunder different pH conditions must be taken intoaccount. Thus, magnesium ions possibly can act asstructure-breaking ions in the alkaline pH rangebecause of their presence as hydroxy complexes (Fig.IS).

On the basis of the above considerations, thepresence of the abstraction maximum and itsdependence on the type of inorganic ions present insolution can at least be attributed partly to the in-compatibility of micellar-type aggregates with thestructured water around the particles and theresulting exclusion from the interfacial region. Onthe other hand, the differences in ion-exchangeproperties of various inorganic ions would result invarying amounts of ions, which on release from claycan cause surfactant precipitation. Thus, the largerions such as ammonium can be expected to undergoless exchange than the smaller ones and, hence, tocause less precipitation. Abstraction of precipitatedcomplexes by the particles at lower concentrationsand their possible solubilization in the surfactantmicelle at higher concentrations also can produce anabstraction maximum, which would depend on thenature of the electrolyte present.

Mechanism of Dependenceof Abstraction and Adsorption Maximaon Inorganic Electrolytes

Suggested explanations in the literature for theobserved maximum include decrease or changes insurfactant monomers concentrations,33 desorptionof surface micelles,34-surface contamination,3S andmicellar exclusion from the interfacial region owingto stronger electrostatic repulsion between theparticles and highly charged micelles than the formerand singly charged monomers.36 Alteration in thesolid properties such as effective surface area, owingto changes in particle morphology on excessivesurfactant adsorption of plugging of the surfacepores by surfactant aggregates, also has beensuggested as a possible reason for the above ad-sorption phenomenon. 13

From our study of the effect of electrolytes on theabstraction by kaolinite, we found that the ap-pearance of the abstraction maximum depends notonly on the ionic strength, but also on the type ofcations and anions present in the system. None ofthese mechanisms, except possibly the morphologicalalterations of the mineral particles, however, canaccount for the dependence of the presence of theabstraction maximum on the type of inorganic ionspresent in the solutions.

An important factor is the possible role of theproperties of water associated with a solid surfaceand the influence of inorganic ions on theseproperties when determining the adsorption ofsurfactant ions and micelles on that surface. Thus, inthe case of a surface that does not have much in-fluence on the structure of water around it, theadsorption process can be expected to proceednormally, reaching a limiting value at high con-centrations of the surfactant. On the basis of Hustedand Low's results,37 who observed that the diffusionconstants for ions through clay gels is 30OJo lowerthan in water, clay particles can be considered toinduce a structured region around them as well asinside them between platelets, through which themovement of ions, and, more severely, that ofaggregates, will be restricted. Certain ions, however,can cause the breakdown of such structures. Wang38reported the structure-breaking properties of simpleions to increase in the order CI- < Br- < I-. Thus,CI- ions have the least tendency to disturb thestructure of the water around the clay particles andcan accommodate themselves better in the structuredwater region than ions of larger diameter, such as I-.In the case of cations, the tendency to break thestructure increases in the order Na + < K + oS NHJand in the case of anions, a more complete series isgiven by the order COo- < HPOi- < CI- < NO) <SOl-. We see from examining the above series thatthe presence of both Na + and a- ions is compatiblewith a structured water region. Because transportand accommodation of surfactant aggregates such asmicelles in such a structured water region can be less

Conclusions

I. The nature of the abstraction isotherm obtainedfor sulfonates depends on the type of sulfonate usedas well as on the morphological and mineralogicalcharacteristics of the mineral.

2. Equilibration of kaolinite with water andabstraction of sulfonate by kaolinite involves bothfast and slow steps. The implications of the preserlceof an intermediate metastable condition duringequilibration on the past mechanistic interpretationsshould be noted.

3. The effect of pH on abstraction was markedbecause of possible adsorption of aluminum com-plexes on kaolinite in acidic solutions.

4. The effect of a tenfold increase in ionic strengthon abstraction of dodecylbenzenesulfonate by Na~kaolinite is limited. Effect of pH changes that in-variably' accompany changes in ionic strength mustbe recognized. However, salinity did have a marked

SOCIETY OF n:TaOLEUM ENGINEEas JOUMNALa

II. Tragus, F., Sophany, T., Schechter, R. S., and Wade, W.H.: "Static and Dynamic Adsorption of Anionic andNonionic Surfactant'," Soc. Pet.. Eng. J. (Oct. 1977) 337-344.

12. Lawson, J. B. and Dilgren, R. E.: "Adsorption of SodiumAlkyl Aryl Sulfonates on Sandstone," Soc. Pet. Eng. J.(feb. 1978) 75-82; Trans., AIME, 165.

13. Hanna, H. S., Goyal, A., and Somasundaran, P.: "SurfaceActive Properties of Certain Micellar Systems for TertiaryOil Recovery," paper 239 presented at the Seventh In-ternational Surface Activity Congress, Moscow, Sept. 12-18,1976.

14. Powers, G. W.: "The Volumetric Determination of Or~anicSulfonates or Sulfates by Double Indicator Method,"Communication C-225 , Amoco Production C()., Tulsa(1970).

15. Hanna, H. S. and Somasundaran, P.: "Equilibration ofKaolinite in Aqueous (norganic and Surfactant Solutions,"paper presented at the 52nd National Colloidal Symposium,Knoxville, June 12-14, (978.

16. Parks, G. A.: "Adsorption in the Marine Environment,"Chemical Ck"eanognrph)', 2nd ed., Academic Press Inc., NewYork City (1975) 241-308.

17. Muljadi, D., Posner, A. M., and Quirk" J. P.: "TheMechanism of Phosphate Adsorption by Kaolinite, Gibbsiteand Pseudoboehmite, Parts ( & 1(," J. Soil Sci. (1966) 17,212-247.

18. Stumm, W. and Morgan, J. J.: Aquatic Chemistry, WileyInterscience, New York City (1970).

19. Conley, f. and Althoff, A. C.: "Surface Acidity inKaolinites," J..CoIl. inter/. Sci. (1971) 37, 186-195.

20. Buchanan, A. S. and Oppenheim, R. C.: "The SurfaceChemistry of Kaolinite - I Surface Leaching," Aust. J.Chem. (1968) 21, 2367-2371.

21. Wayman, C. H.: "Surfactant Adsorption on HeterionicClayMinerals," international Clay Conference, Pergamon PressInc., Elmsford, NY (1963) 329-342.

22. Swart zen-Allen , S. l. and Matijevic, E.: "Surface andColloid Chemi~try of Clays," Chem. Revs. (1974) 74, 385-400.

23. Somasundaran, P.: "Adsorption from Flooding Solutions inPorous Media - A Study of Interactions of Surfactams andPolymers with Reservoir Minerals," annual report toNational Science foundation and a Consortium of Sup-porting Industrial Organizations, Columbia U., New YorkCity (Aug. 1977).

24. Mortensen, J. l.: "Adsorption of HydrolyzedPolyacrylonitrile on Kaolinite," Days and Day Mi"erals,Pergamon Pres~ Inc., New York City (1962) 530-545.

25. Berube, Y. G. and deBruyn, P. L.: "Adsorption at theRutile-Solution Interface - II. Model of the ElectrochemicalDouble Layer," J. Colloid inter/. Sci. (1968) 18, 92-105.

26. Konta, J. and Borovec, Z.: "Imbibometric Investigations ofHomoionic Clays Using Polar Liquids: I. Material withPredominating Kaolinite and Montmorillonite," in-ternational Clay Conference, Pergamon Press Inc., Elm-sf()rd, NY (1963) I, 261-275.

27. Martin, R. T.: .'Adsorbed Water on Oay: A Review," C/~v.'iolld Clay Minerals, Pergamon Press, Inc., Elm~ford, NY

(1962) 9,29-70.28. Low, P. f.: "The Apparent Mobilities of Exchangable

Alkali Metal Cations in Bentonite-Water Systems," Proc.Soil Sci. Soc. A mer. (1958) 22,395-398.

29. low, P. f.: "Viscosity of Water in Clay Systems," C'Iaysand Oay Minerals, Pergamon Press Inc., ElmsfQrd, NY(1960) " 170-1112.

30. Modi, H. J. alld Guerstenau, D. W.: "Streaming PotentialStudies of Corandum in Aqueous Solutions of (norganicElectrolytes," J. Phys. Cheln. (1957) 61,640-643.

31. Kittrick, J. A. and Jack~on, M. l.: "Electron Mi.:roscopeObservations of the Formation of Aluminum Ph('l~rhate~'rystals with Kaolinite as thc &>url.'e of Aluminum," .\'cit'nce(1954) 120, 508-509.

32. Somasundaran, P.: "Interfacial Chemistry of ParticulateFlotation," Advances in interfacial Phenomena of Par-ticulate/ Solution/Gas Systems, P. Somasundaran and R. B.Grieves, eds., A(ChE Symposium Series (1975) 71,1-15.

33. Corrin, M. L: "Adsorption of Long-Chain Electrolytes

effect on the abstraction of Mahogany sulfonate AAby Berea sandstone.

5. The effect of inorganic electrolytes dependsmarkedly on the type of cation and anion used. Anabstraction maximum is obtained only in inorganicelectrolyte solutions composed of (water) "structure-making" ions. No such maximum is obtained whenthere is a predominance of "structure-breaking"ions.

6. Exclusion of micellar aggregates from thestructured interfacial region around the particles(owing essentially to their incompatability with thisregion, and other phenomena that depend onsulfonate solubility, micellar composition, etc.) cancontribute toward the presence of abstractionmaximum. Structure-breaking ions facilitate tran-sport and accommodation of surfactant aggregates,eliminating the possibility for such exclusion.

7. Selection of reagents such as Na2SiO3 on thebasis of the above considerations and their role indecreasing the abstraction of sulfonate are noted.

AcknowledgmentsSupport of the National Science Foundation (ENG-76-08756) and Amoco Production Co., Chevron OilField Research Co., Exxon Research and EngineeringCo., Gulf Research and Development Co., MarathonOil Co., Mobil Research and Development Co., ShellDevelopment Co., Texaco Inc., and Union Oil Co.of California is gratefully acknowledged.

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~ Of' Pl:nOUUM INGINEDS JOtIaNALm