)PE 0002 ~or~~of"IME

WETTABlllTY OF RESERVOIR MINERALS BY flOTATION ANDCORRELATION WITH SURFACTANT ADSORPTION

by Hehmet S. Celik and P. SomasundaranColumbia University

~ 1900. Amerk:an k1Stitute of Mini1g. MetaIkKgM:aI, and ~ ~. Inc.This ~ was IX'ese"Ied at ~ SPE Fifth ~ Symposam on QIfieId and Geo4hennaJ Owni$try, held in Stanfcwd. Caifomia, May 28-30, 1900. The material is ~ ~~ by the auU1Or. ~ to copy IS restricted to an abs1rad 01 ootno-e than 300 words. Write: 6200 N. Central Expwy.. DWIas. Texas 75206.

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in imparting oi1-wettability to rock surtaces5 duringpo1ishing can aJ.so lead to misleading res1l1ts that arenot representative ot the originaJ. samples. EquallY'important aJ.terations in surface regosity can producechanges in both the equilibrium contact angle andthe nature ot hysteresis that is important in deter-mining the residuaJ. oi1 saturation. Even thoughultralov interfacial tension is often conSidered asthe criterion tor the disp1acement of oil, it is tobe noted that one cannot rea1lyo isolate the ultralovinterfacial tension criterion from that of a low con-tact angle criterion since those two are related to /

each other by the Young' s equation:

ABSTRACT

Minerals can undergo significant alterations inwettabi1ity upon adsorption of surfactants on them. Amethod that appears promising for measuring vettabi1ityis flotation using air or oil extraction. Unlike con-tact angle. it does not require such drastic treatmentsas polishing. Good correYation was obtained in thepresent study between wettabi1i ty as determined by flo-tation and adsorption density. Both air flotation andadsorption exhibit maxima in the same concentrationrange. Zeta potential of particles measured under thesame conditions. however. sh9VS a continuous increasein its negative value with sulfonate concentration.Correlation of these data suggests that sulfonate mono-mers adsorb in increasing amounts below as vell asabove the critical micelle concentration but with a re-jverse orientation. There is however a decrease in mea-~sured surface excess. possibly due to such factors as I

precipitate redisso1ution and micellar exclusion. :

{}." 1,Yos = Yws + row Cos..

{~}

A cClllbined approach using adsorption, vettabilityzeta potential and surface tension shows promise as a .valuable method for the study of mechanisms of interac-:tion of surface active agents with minerals. i

IRTRODUCTIOB

Information on wetting characteristics of reser-voir rocks and changes in them is of much use for stu-d7ing the performance of oil recovery systems. Inmicellar flooding systems adsorption or precipitationof surfactants on rock surface can change the wetta-bill ty of the rock and in turn the oil recovery fromit. Wettability is usually determined by means ofcontact angle techniques. This technique however re-quires preparation of the coarse mineral sample bymeans of polishing after the samples are also mountedon plastics and polished and then cleaned using vari-ous solvents and leachants. All the above pretreat-ments of the mineral samples can be e~cted to affectthe surface roughness as well as surface compositionof the samplel-3. Smearing of the mineral surface by

contaminants during polishing can also be of signifi-:ant effect4. On the other hand, removal of bitumin-

OUS or organic coatings that have a governing role

Where the Yost YWS. and YOW are respectively interfa-cial tensions ot oil/solid. water/solid. and oil/waterinterfaces and e is the contact angle measured throughthe aqueous phase. Furthermore. an oil-displacementmechanism dependent on a "deterge~-type" behaviorcannot yet be ruled out. Wettability together withinterfacial tension plays a maJor role in achievingthe displacement ot oil from the pores ot the reser-voir rocks. Both of the above properties can be ex-pected to be aftected by the addition ot surtactants.For ex~le. recovery of oil from silica systems isreported -8 to increase through a wettability reversalpossibly due to adsorDtion ot amine as well as reduc-tion of oil/w~ter int~rfacial tension. The governingmechanisms by which surfactants enhance the displac~~ment are not however fully understood.

It is known that information on variation -of wet-tabili ty of minerals as a function of surfactant con-centration when combined with data for such interfa-cial properties as adsorption and zeta potential canprovide an insight into interfacial mechanisms thatgovern processes such as imbibition and drainage ordisplacement. In order to develop an accurate under-standing however it is noted that it is necessary to

determine the above properties using similar mineralsystems. Both adsorption and zeta potential are de-termined using dilute suspensions ef mineral fines.Suction ~otential technique f~~~termining imbibi-References and illustrations at end of paper.

263

.". ..

WE'rrABILITY OF RESERVOIR RI.REPIA~ BX ~ATIOB AND CORRELATION WITH SURFACTANT ADSORPnON

tion/drainage characteristics also uses mine~ tineseven though at a much higher solids concentration.It was the aim ot this study to develop a techniquetor determining a relative measure ot wettabili tyot mineral tines. The methods appear promising:a) Flotation using air bubbles or oil droplets;b) Oil extraction usually known as liquid-liquid ex-traction; and c) droplet pick up.

weight was used for flotation tests as- vell as oilextraction experiments. 99+% gold label decane pur-chased from Aldrich Chemicals was used in the liquid-liquid extraction experiments. HaCl and KNO3 used foradjusting the ionic strength and HaOH and HNO3 used~or adjusting the pH were of reagent grade. All thesolutions were made using trip1~ distilled water.

Variables

Variables selected for this series are sulfonateconcentration, pH, ionic strength and type of addedinorganic electrolytes.

In this study, resu1ts of tests using a simpleflotation are presented and correlated with data ob-tained for adsorption and zeta potential for thesame systea. In addition to the advantage thatpolishing is not required for the use of the flota-tion technique, it can be considered as a more pre-cise measure o~ hydrophobicity. Since it is knownthat contact ang1e requirement for flotation canvary anywhere from a fraction of a degree to severaldegrees depending on the mineral type. Thus forgalena vhi1e less than a degree is sufficient forflotation, for oxides such as quartz a contact angleof degrees is required. Based on the Young's equa-tion

Experimenta1 Procedure

The minerals used here have been found to exhibitlong-term effects. In order to minimize the effectsof such long-term alterations o~_the correlation be-tween adsorption and flotation, the times of reagen-tizing of the mineral with the solutions were chosenhere to be the same as those used in adsorption,i.e., four hours for limestones and saodstones. Re-agentizing was done by tumbling the solutions in theabsence of air for the desired time.

YSA = Yaw + YWA Cos e

where YSA, Ysw and YWA are intertacial tensions otsolid-air, solid-water and water-oil respectivelYand 6 is the contact angle. One requirement at airflotation is that YSA should be higher than Ysw.The required difference between the two interfacialtensions will depend in addition to surtactant ad-sorption on the bubble surface, essentiallY uponthe tendency for hydration ot the original mineral.In oil extraction, it is possible to have the solidsin oil phase, vater phase or at the intertace de-pending on the following criteria9-11:

It YSO > YWO + YSW' the solid will be dispersedin the water. .

If Ysw > YWO + YSO. the solid will be dispersedin tche air.

If Ywo > YSO + Ysw or if none of the three in-terfacial tensions is greater than the sum of theother two, the solid will collect at the water-oilinterface with a larger portion of the solid remain-ing on the water side of the interface if Ysw > YSO

and e is less than 90° and on the oil side of theinterface if Yso < Ysw and e is greater than 90°.

Flotation was conducted using the 8Odiried Ha11i-mond tube set-up shown in Figure 11 ~ . The lower partof the apparatus consists of a glass well with a fri t-ted glass disk with a maximum pore size of 40 micronssealed to the bottom. The glass well is connected atthe bottom to a suPPly gas or oil to produce air bub-bles or oil droplets. The upper part consists of a~ glass tube with a stem just above the bend. Aflowmeter is connected to the top of the tube to mea-sure the fluid flow. The Ha11imond tube containing apolyethYlene coated magnetic bar is placed on a mag-netic stirrer and this enables controlled stirringof the mineral in solution. '!'tie flow rate is con-trolled by adjusting the pressure head. Hydrophobi- I,

city or non-wettability can be quantitatively deter-mined by means of the modified Hallimond cell sinceimportant variables such as the flow rate ~ stirring ~

pulp density ~ pH of the solution and t~ of flotationcan easily be controlled. In the present case nitro-gen is introduced at the rate of 20 cm3/min. for tenseconds. Stirring time is 20 seconds. The pH ismeasured after reagentizing and before flotation and~in some cases where a large change in pH was expectedduring f1otation~ also after flotation.

~e fraction of the mineral levitated during theteat is calculated from dry weights of the floated anaun:floated material.

EXPERIMEn'rAL

Materials

The following minerals were used tor this study:

a) Bedford limestone -. there were no impuritiesdetectable by X-ray diffraction.

b) Agricultural limestone - this limestone con-tains 5% quartz and 5% dolomite as impurities

c) Berea sandstone - 50 x 100 mesh and -400

mesh tractions were used for the wettability studies.

d) We11-cry.~11zed untreated kaolinite

Wettability tests in the presence of oil were per-formed under the conditions similar to Lai et aliO.The liquid-liquid extraction tests were made in a 150ml pyrex separatory funnel containing 100 cc of sur-factant solution and 25 cc of decane. One gram of-400 mesh mineral was first conditioned with the 100cc of surfactant solution by stirring for 20 minutesat 2500 rpm. 25 cc of oil was then added and stirredfor another 20 minutes at 2500 rpm. The particleswhich have acquired hydrophobicity were collected inthe oil phase while those that were not wettable byoil were retained in the aqueous phase. After comple-tion of the stirring the solution was allowed for 5m1nutes to achieve a clear Phase separation and thenthe~ two phases were collected separatelY, dried,weighed, and the recovery of mineral fines in the oiphase was estimated.

Details of limestone, sandstone and kaolinitesamples have been given in earlier papers12,13.

The methods used for determination of the adsorp-1tion density has been described earlierlS. BrieflY it!

Reagents

Mah~ sulfonate-M~i.c~nt_ains 37% oi~ by

264

N.S. Celik and P. Somasundaran

consisted of agitation of a given volume of the sur-factant solution at a known concentration ~ th thedesired amount of solids for tour hours and deter-mining the loss of surfactant from a sample of thesupernatant solution after centrifugation. Tbe sul-fonate concentrations were determined using the two-phase titration technique with a IDixture of dim.idiumbromide and disulpbine blue as indicator.

Electrophoretic mobility of samp1es is measuredusing a Zeta meter after reagentizing, before f1ota-tion. Zeta potential is evaluated from the mobi1itydata in the standard manner.

RESULTS AND DISCUSSIOB.

facial region than into the bulk, above the maximumthe additional surfactant is partitioned more favor-ably into the bulk region. Recalling that the sur-factant concentration at the adsorption maxima haveusually corresponded to the critical micelle concen-tration, a possible reason for such an effect can beconsidered to be solUbilization of surfactant c~plexes by micelles or possibly even exclusion of mi-celles or similar surfactant aggregates from the inter~acial region. Either process will permit sur~aceexcess to decrease even if there is an increase in ad-sorbe4 monomer, which increase will in turn permit thezeta potential to become more negative. It is to benoted at this point that flotation is the result o~both surfactant adsorption and th~ manner in which itis adsorbed; i~ the monomer can be assumed to adsorbin increasing quantities, the decrease observed forflotation above the 1 g/l or sulronate wil1 suggest areverse orientation of the adsorbent in this rangewith the bydrophi1ic head of the sulfonate turnedtowards the bulk so1ution. Decrease in ~lotation inthis range cannot be attributed to any change in ad-sorption at liquid/gas interface since surface tensionstudies using these sulfonates have not indicated anypossibility for such change in adsorption. In summarythen, below the critical micelle concentration thesurfactant species adsorb on the mineral in increasingquantities with increasing surfactant concentrationwi th the non-polar tai1 turned towards the bulk makingthe mineral non-wettable and increasingly negativelycharged. Above the critical micelle concentration,monomeric species possibly continue to adsorb in in-creasing quantities but with a reverse orientation,making the mineral less non-wettable and more nega-tively charged; some surfactant complexes that nor-mally adsorb are solUbilized by micelles or possiblymicelles or such aggregates are excluded from the /

interfacial region in this surfactant concentrationrange causing the adsorption (surface excess) to de-crease with increase in surfactant concentration. :

Results obtained ror the bydrophobicity of lime-stones, as measured by f10tation, are given in Fig-ures 2 and 3, a100g with those obtained for adsorp-tion density and e1ectrophoretic mobility. It ap-pears fr<:a the data presented here that f10tationcan be a good measure or wettability. Reproduci-bility as indicated by the dup1icate points in theplot is fairly good. It is interesting to note thatthe flotation goes through a aaximua as does the ad-sorption density. Zeta potentia1, however, continuesto become .ore negative in the complete range stu-died. An analysis of the data, f10tation, adsorp-tion, and zeta potentia1, with an understanding ofwhat these three interfacia1 properties mean, canassist us in providing information on the m01ecularmechaniSDIS by which these surfactants adsorb at th~interfaces.

Similar results obtained for the wettabili ty ofBerea sandstone as a function of sulfonate concentra-tion are given in Figure 4. Maxima in hydrophobicityare seen in these cases to correlate with those ob-served earlier for adsorption of sulfonates on these

minerals12.

Errect of concentration of WaCl on the vettahili- i

ty of limestones was investigated ~ a su1fonate con-centration of 10 g!l. Results from these tests aregiven in Figure 5. There vas considerable precipita-tion of sulfonate vhen the HaCl concentration exceededabout 5 x 10-2 M. KRO3 addition vas also found to.have an effect on the wettahility of Agriculturarlimestone (see Figure 6). Effects produced by thesereagents are of such a magnitude that it would appearuseful to study them in detail in the future. I

For flotation to occur. the mineral must be hy-drophobic. The hydrophobicity is imparted in casessuch as the present one by the adsorption of sur-factants on th~. However. the degree of inducedhydrophobicity is determined. in addition to sur-factant adsorption density. also by the configura-tion of the adsorbed species and even by the extentof adsorption at the other interface. namelY. liquid/gas in this case. Zeta potential. on the other hand.rerlects. under constant ionic strength conditions(in this case up to 5 g/l of sulfonate) the changethat has occ~ed at the solid/liquid interface aloneowing to the adsorption or sulfonate by mechanismsother than ion exchange and can be considered to befairlY independent of the orientation of the adsorbedmolecule. Adsorption density; dete~ined here. isthe Gibbs surface excess; i.e.. excess of surfactantthat is present in the interfaci~ion over andabove what is present in the bulk. It is not thetotal amount of surfactant that is present on themineral. The adsorption data could also be influ-enced to some extent by any precipitation of the ad-sorbent complexes in the system. On the basis or .these considerations. one can analyze flotation. ad-sorption and zeta potential data given' in Figures 2and 3. Results obtained for mineral extraction using oil

are given in Figure 7 as a function of tbe surfact~tconcentration. A maximum is obtained in tbis casealso and, interestingly, is located at a concentrationlower than that corresponding to the maximum in theabsence of oil. It is also interesting to note incontrast to air flotation, oil flotation is signifi-cant even without the addition of the sulfonate. Theoil flotation is possibly due to organic contaminantsthat are present with most natural minerals whichassisted by an oil coating is able to impart suffi-cient hydroPhobicity to the mineral particles. Suchcoadsorption or oil can also take place with the sul-fonate and this in turn can lead to the required rirst I

For the case of Agricultural 1imestone. the ad-sorption (surface excess) and f10tation decreaseabove about 1 g/l of su1fonate. however. suggeststhat there is no decrease in the tota1 su1fonate ad-sorbed on the minera1. Any decrease1n ~ su1-fonate. that is anionic. on the mineral shou1d havecaused in zeta potentia1 to become 1ess negative vi thincrease in su1fonate concentration. The inferenceis then that there is a decrease in surface excess. .

but not in the total amount on the mineral. Thuswhereas below the adsorption maximum the added sur-factant is partitioned more favorably into the inter-

265

..."~~nITY OF RESERVOIR MImw.s BY FLOTATION AND CORRELATION WITH SURFA~ABT ADSORPTION

~layer coverage and a maxi!!!l-!l!! at a lower sul1'onateconcentration than in the absence of oil. Formationof a second laver with a reverse orientation as wellas micellar solubilization at the higher sulfonateconcentration range can be expected in the presenceof oil at a 1ower sul1'onate concentration than inthe absence o~ it. The results demonstrate that re-latively lower levels of surfactant additions raresufficient to produce wettabili ty reversals.

K~karni, R.D., Somasundaran, P., "Effect otPretreatment on the Electrokinetic Properties otQuartz," Int. J. Miner. Process., Vol. 4, 1977,p.89-98.

Kulkarni. R.D.. Somasundaran. P.. ~e Effect ofAging on the Electrokinetic Properties or Quartz I

in Aqueous Solution." in Oxide-Electrolyte Inter-faces. pp. 31-44. American Electrochemical Soci-~Prlnceton. B.J. (1973).

CONCLUSIONS .. Bangs. L.B.. '~steresis of Contact Angles in the ISystem Benzene-Water-Quartz." M.S. thesis. M.l.T.Cambridge, Mass. (1962).

Flotation and oil extraction techniques arefound to be satisfactory for investigating vettabi-li ty of reservoir mi~eral fines and effect of sur-factants on it. Good correlation W8$ obtained inthis stuq between mineral flotation and surfactantadsorption with both ~operties exhibiting a maxi-mum near critical micel1e concentration. Above cri-tical micel1e concentration, vbile adsorption (sur-face excess), which is a measure of partitioning ofthe surfactant between the interfacial region andthe bulk, had shown a decrease with increase in sur-factant concentration, flotation, which is dependentupon both the amount of surfactant adsorbed and theconfiguration of it in the adsorbed state, also ex-hibited a decrease. However, zeta potential, whichis directly related under constant ionic strengthconditions to sulfonate adsorption (other than byion exchange), showed a continued increase in itsnegative value. Oil extraction also exhibited amSlxi!!!1~ but at a lower sulfonate concentration thanthat of air flotation owing to interactions betweenoil and surfactant possibly both at the solid/solu-tion interface and in the bulk.

5. Wagner, O.R., Leach, R.O., "Improving Oil Dis-plac~nt Ef'ficiency by Wettabil1 ty Adjustment, II

Trans. ~, Vol. 216, pp. --65-72 (1959).

6. Miche~s, A.S. aDd Timmins, R.S., "Chromatogra-phic Transport ot Reverse Wetting Agents and ItsEffect on Oi1 Disp1acement in Porous Media,"Trans. AIME, Vo1. 219, p. 150 (1960).

If Leach, R.O., Wagner, O.R., Wood, H.W., and Harpk~C.F., "A Laboratory and Field Study of Wettabili-

1ty Adjustment in Water Flooding," Trans. AIME,Vol. 225,1968, p. 206.

8 Mongan. N.. "Ro1e o~ Wettabi1i ty and Intertaci~Tension in Water fiooding." Soc. Petro Eng. J..June 1964. p. 115.

~

9.

These observations suggest a possibility thatsulf'onate might be adsorbing in increasing amountsbe10v as veIl as above the critical micelle concen-tration but with a reverse orientation with theionic head turned towards the bulk solution in thehigh concentration range; precipitate redissolutionby ~celles and micellar exclusion. it any. howevergive rise to a decrease in measured surtace excessand thus to a maximum in the adsorption isotherms.While these possibilities are to be tested. it isclear that a combined approach using several tech-niques such as adsorption. zeta potential. vetta-bili ty. surface tension and oil displacement usingthe ~ mineral/surfactant systems is valuable torthe study of mechanisms governing the intertacialprocesses of these systems.

Raghavan, S. and Fuerstenau, D., "On the Wettabi-Ii ty and Flotation Concentration of SubmicronHematite Particles with OCtylbydroxamate as Col-lector," in Advances in Interfacial Phenomena ofParticulate/Solution/Gas Systems, Somasundaran,P. and Grieves, R.G., eds., AIChE Symp. SeriesV. 71, No. 130,1975 p. 60-67.

Lai, R.W.N. and Fuerstenau, D.W., "Liquid-LiquidExtraction of Ultratine Particles," Trans AIMEVol. 241,1968, pp. 549-555.

10

u Fuerstenau, D.W., Chander, S., and Abouzeid, A.M."The Recovery of Fine Particles by Physical Se-paration Methods," in Beneficiation of MineralFines, Somasundaran, P. and Arbiter, R., eds.,'"i:fiiF:; 1919, p. 18.

ACKBOWLEOOMENTS

12. Banna, B.S., Goyal, A., and Somasundaran, P.,"Surface Active Properties of Certain MicellarSystems for Tertiary Oi1 Recovery," WorldCongress on Surface Acti ve Agent~, P~ 239presented at the Seventh International SurfaceActivity Congress, Moscow, Sept. 12-18, 1916.

Support ot the Department ot Energy- (DE-AC-l.9-79BC-l.OO82) , the National. Science Foundation (ERG-78-ll. 776), Amoco Production Co., Chevron Oil Field Re-search Co., Exxon Research and Engineering Co., GuJ.tResearch and Devel.opDent Co., Marathon Oil Co., MobilResearch & Development Co., Shell Development Co.,Texaco Inc., and Union Oil. Company ot CaJ.itornia isgratetuJ.ly acknovl.edged.

Soum.sund«ran, P. and Hanna, H. S., "Adsorption ofSulfonates on Reservoir Rocks, II SPE Symposiwn on

Improved Oil Recovery, 241, Apri1 16-19, 1978,Tulsa, Ok1ahoma. .

]0'.

Somasundaran, P.. and Moudgil, B., "The Effect ofDissolved aydroc~bon Gases in Surfactant Solu-tions on Froth Flotation of Minerals," J. Coli.am Int. Sci., Vol. 47, No.2, 1974, pp. 290-299

14.

~CES

1. Somasundaran, P., "Preatreatment of Mineral Sur-faces and Its Effect on Their Properties, n in

Clean Surfaces: 'lbeir Preperation and Character-ization for Interfacial Studies, pp. 285-306,Marcel Dekker, New York, N.Y. (1970).

Cel ik. M.. Goyal. A.. Manev. E.. and SomasundaranP.. "The Role of Surfactant Precipitation andRedissolution in the Adsorption of Sulfonate onMinerals." SPE Paper 8263 Presented at 54th An-nual SPE Meeting. Las Vegas (1979).

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266

MS-AA/AGAICULTUAAL LIMESTONEI = 10-2~ NoC' pH' 8.1 :to.lSOLIDS = 1 *I. CONTACT TIME. 4 HAST . 22:t 1.C FLOT. TIME. 10 SEC

-100..~e

~

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Z0

0.2 .::Q.a:0

0.1 ~..

-80

-60

~

i-tO

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CONCENTRATION (g/.()

Fig. 2 - CClTelati00 of flotati00, ad~tioo aIM! zeta potential of ~ysulfooate-AA/ agricult\ral li.stOOl syst. in the presence of NaCI.

I-'A7'Y0

MS-AA/8EDFORD LIMESTONEI -10-2 ~ NaCISOLIDS = 1%

T-22i:l°C

pH . 9.3% 0.1CONTACT TIME. 4 HRS

FLOT. TIME. 10 SEC

-100

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Fig. 3 - CCMTelation of flotation, adslX'Ption am zeta potential of MahoganysulfCllate-AA1 Bedfcrd I i.stone syste8 in the presence of MaCI.

0.01 0.1 1 10

CONCENTRATION (9ft)

Fig. 4 - Hyd~lcity of Barea sandst~, as Easured by its flotatioo,as a functioo of coantratioo of IIh(XlallY sulfonate-AA.

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. AGRICULTURAL LIMESTONE

T [0 8EDFORD LIMESTONEA RP 1(»4OSO ~ AGRICULTURAL LIMESTONE

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11.0

0.5

40

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-»

80

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Fig. 6 - Effect of Kf'3 addition 00 the hyd~icity of agriculturalli.stone, as EiS\I'ed by Its fJotati00, as a function of concentrationof ~y sulfCXlate-AA.

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