Stefan Iglauera, Yongfu Wua, Patrick Shulera, Yongchun Tanga,∗, William A. Goddard III b
a Division of Chemistry & Chemical Engineering, Power, Energy Environmental Research (PEER) Center, California Institute of Technology, Covina, CA 91722, United Statesb Division of Chemistry & Chemical Engineering, Materials and Process Simulation Center (MSC), MC 139-74, California Institute of Technology, Pasadena, CA 91106, United States
a r t i c l e i n f o
Article history:Received 6 December 2008Received in revised form 19 January 2009Accepted 20 January 2009Available online 29 January 2009
Keywords:
a b s t r a c t
We examine here the suitability of alkyl polyglycosides (APG) for improved oil recovery (IOR) applications.In recent years, these nonionic carbohydrate-based surfactants have become a significant commercialproduct (80,000 tons/year) with widespread use in household and agricultural products. Our laboratorystudy determined several characteristics of common APG surfactant formulations, in particular theircapability to create low interfacial tensions (IFT) with n-alkane hydrocarbons. Our formulations includeda wide range of alcohol cosurfactants with APG surfactants. We found APG–cosurfactant combinationsthat exhibit low IFT values of 0.01 mN/m or less versus n-octane. Our laboratory tests confirmed these
APG formulations can provide useful IFT properties that are largely independent of both salinity andtemperature. We report a coreflood test conducted on a Berea sandstone core using a selected formulation
as hi
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nhanced oil recovery that exhibits oil recovery
. Introduction
.1. Background
Surfactant enhanced oil recovery (EOR) has been performed forany years, particularly in the 1970’s and 1980’s when the technol-
gy was put on a sound scientific basis. Recently, because of highil prices, this technology has experienced a large boost.
The present study considers alkyl polyglycosides (APG), a class ofurfactants largely ignored as candidates for EOR applications. Thiseglect is due at least in part because APG surfactants were notvailable as a large volume commercial product during this earliereriod of intense interest in chemical EOR in the United States.
APG were described initially over 100 years ago, first recognizeds a potentially useful surfactant type in 1934 (Bertsch, [28]), andhen largely ignored until the 1980’s. APG has gained favor as eco-omical processes were developed to manufacture them on a largecale, and also because there has been an increased drive to useurfactants with favorable, low toxicity characteristics like APG forrange of applications. APG surfactants now see widespread use
n household detergents, cosmetics, and agricultural products [8].
recent estimate for worldwide capacity for APG surfactants is
0,000 tons/year [1]. APG has been considered only briefly for EORpplications, with one U.S. patent issued on this topic [2].
APG formulations have some interesting and potentially usefulproperties as EOR agents; the most important characteristics aresummarized as follows.
1. When mixed with a hydrophobic cosurfactant (e.g. an alcohol), amiddle phase microemulsion may appear, and in some cases thiscan generate a low interfacial tension (IFT) (0.01 mN/m or less).This behavior is caused by alcohol molecules entering the surfac-tant monolayer and thereby changing its curvature [3,4] or rigid-ity [32]. Low IFT values are highly relevant for oil production asIFT is inversely proportional to the capillary number Ncap, whichdetermines residual oil saturations, oil recovery respectively[5,6]. Some encouraging phase behavior/IFT data were reportedwith simple n-alkanes as the oil phase [2,7–11,13–15,17,34].
2. A remarkable property for these APG formulations is that theyare reported to have a phase behavior and IFT that is largelyindependent of temperature and salinity [8,16,17]. Surfactantformulations that create a low IFT irrespective of temperatureand salinity would be very useful for oilfield EOR applications.Commonly used surfactants in the petroleum industry (i.e. alkyl
sulfonates, “crude oil sulfonates”, [5,31,33]) generate ultra-lowIFTs, but these IFTs are temperature and salinity dependent.Because of the geological circumstances of oil reservoirs,temperature and salinity variations are expected to reducecontrol and predictability of surfactant EOR processes directlyincreasing economic uncertainty.
S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59 49
Nomenclature
APG alkyl polyglycosideCaCl2 calcium chlorideEOR enhanced oil recoveryHLB hydrophilic–lipophilic balanceIOIP initial oil in placeIOR improved oil recoveryIFT interfacial tension (mN/m)k carbon number in APG alkyl chainn average number of sugar groupsNaCl sodium chloridePG2062 Agrimul PG2062PG2067 Agrimul PG2067PG2069 Agrimul PG2069
3
pmas
•
•
•
•
2
2
ciC
o
TC
P
AAAHA
Sor residual oil saturationwt% weight%
. The presented work focused mainly on alcohols as cosolventssince their water–oil distribution coefficients depend onlyweakly on temperature, though significantly on their carbonnumber [18]. Moreover, alcohols are comparatively cheapsubstances.
Theory and molecular modeling indicated that having a largeolar head group combined with the nonionic character of the APGolecule is consistent with the observation that the phase behavior
nd IFT are largely independent of changes in the temperature andalinity [10,11,19].
Other motivations for focusing on APG surfactants were:
They are available already as commercial products and usedalready in significant quantities for other industrial applications.They are manufactured from renewable resources so that theircost is largely uncoupled from the price of crude oil.APG surfactants serve as a practical example of a sugar-basedsurfactant; for which there are thousands of other possiblesugar-based surfactant structures that might further improveproperties. A related point is that the behavior of the APGproducts may offer insights into improving the application ofbio-surfactants [20]. Our work may suggest improvements inmicrobial enhanced oil recovery technology.The APG surfactants are non-toxic.
. Experimental methods
.1. Materials
The study focused on the behavior of three different commer-
ial alkyl polyglycoside surfactant products, whose basic structures shown in Fig. 1. These products were supplied by the Cognisorporation (PG2067, PG2069, and PG2062).
The difference among these three products lies in the numberf sugar head groups n and alkyl chain lengths k (Table 1).
able 1hemical structure information for commercial APG products investigated [37,38].
roduct Agrimul PG2067
lkyl chain (wt%:wt%) 8/10 (45:55)verage alkyl chain length, k (C-atoms) 9.1verage, n (number of sugar groups) 1.7LB 13.6ctivity (wt%) 70
Fig. 1. Molecular structure of an example alkyl polyglycoside [16].
The HLB (hydrophilic–lipophilic balance) value is a measure ofthe oil/water solubility of the surfactant, where lower HLB numbersindicate higher oil solubility, while higher HLB indicates greaterwater solubility. Activity is the mass percentage of surfactant in themixture, the rest is water. The HLB for these surfactants were givenby the suppliers.
We obtained from Aldrich the various alcohols used as cosurfac-tants (ACS grade).
For the hydrocarbon phase n-octane was used (Aldrich). Wealso investigated the effect of o-xylene, n-hexane, and n-dodecane(Aldrich) on the IFT. All oils were of ACS grade. Other studies haveshown that IFT and phase behavior of crude oils can often be rep-resented well by n-alkanes ranging from n-hexane to n-decane [5].
The brine used was de-ionized water with 2 wt% sodium chlo-ride.
Molecules with an even number of carbon atoms in a straighthydrocarbon chain are easily biodegradable, while those with anuneven carbon number, a ring or a branched structure have a lowerbiodegradability. This is true for the APG molecules and the alcoholcosurfactants. Therefore branched and ring containing alcohols andalcohols or APGs with an uneven carbon number in the formulationdeteriorate the biodegrability of the mixture.
2.2. Interfacial tension and phase behavior
Test tube samples were prepared with 5 ml of aqueous sur-factant/cosolvent/salt formulations and 5 ml of hydrocarbon. Aftermixing well for several hours, they were allowed to stand for atleast three weeks to allow the fluids to come to phase equilibriumat ambient conditions. The phase characteristics of each systemwere recorded (i.e. the relative volumes of the aqueous and oleicphases, and, if present, the middle phase) and the interfacial ten-sions aqueous phase–oleic phase were determined with a spinningdrop tensiometer (Temco Inc.) as described in detail by Cayaiset al. [30]. Several experiments were reproduced, showing thatthe spinning drop method had a maximum standard deviation ofapproximately 20%.
2.3. Surfactant solid adsorption
APG surfactant adsorption from 2 wt% NaCl brines was mea-sured onto kaolinite clay. All of these tests were conducted at 25 ◦C
Agrimul PG2069 Agrimul PG2062
9/10/11 (20:40:40) 12/14/16 (68:26:6)10.1 12.5
1.6 1.613.1 11.650 50
5 Physicochem. Eng. Aspects 339 (2009) 48–59
wpw
(((
t1ca
sgmtw
2
o
cwso
1mtAca
3
3
bhatbFta
tes[
Fig. 2. IFT measured for equilibrated samples containing PG2062 and small n-alcohols.
TP
P
PPP
0 S. Iglauer et al. / Colloids and Surfaces A:
ith a weight ratio of liquid/solid of 20, and for a mixing exposureeriod of 8 h. Kaolinite (obtained from the University of Missouri)as selected as the adsorbent of choice because
1) it is among the most common clays found in oil reservoirs,2) it may be obtained in a fairly reproducible form, and3) it is a stable material (e.g. will not swell when immersed in
water).
The composition provided by the supplier for the kaolinite hashe following major components (wt%): SiO2 44.2, Al2O3 39.7, TiO2.39, Fe2O3 0.13, with trace amounts of sodium, manganese, cal-ium, potassium, phosphorous, and fluorine. The specific surfacerea is about 10 m2/g.
After the 8-h exposure period, the sample is centrifuged and theupernatant analyzed for residual surfactant concentration via aravimetric method. Knowing the activity of the starting surfactantaterial and brine salinity, one can calculate the mass of surfac-
ant that is left in the supernatant solution after evaporating off theater solvent.
.4. Coreflood test
A coreflood experiment was conducted for a selected APG/1-ctanol system for which ultra-low IFT was observed.
In the 1-octanol/PG2062 coreflood experiment, a cylindri-al Berea sandstone core (length = 304.8 mm, diameter = 25.4 mm)ith approximately 200 md water permeability was utilized. All
teps occurred at room temperature and ambient pressure with n-ctane as oil phase, and a waterflood residual oil saturation of 30%.
A 0.4 wt% PG2062 surfactant (0.2 wt% on an active basis) –.2 wt% 1-octanol cosurfactant formulation in 2 wt% NaCl wasixed and a 0.25 pore volume (PV) slug was injected. After injec-
ion of the surfactant slug, 1.5 PV drive polymer solution (250 ppmlcoflood 1235 (Ciba Corp.) in 1 wt% NaCl) was injected. Chemi-al injection happened at 0.06 ml/min, or about a 3 ft/day frontaldvance rate.
Incremental oil recoveries were measured against time.
. Results and discussion
.1. Interfacial tension versus cosurfactant type
The cosolvents evaluated included linear aliphatic alcohols,ranched aliphatic alcohols, aliphatic cyclic alcohols, aromatic alco-ols and an ester (methyloctanoate) and a carbonic acid (octanoiccid). The chain length of the cosolvents ranged from propyl-o docosyl chains (C3–C22). The aqueous phase had 2 wt% com-ined APG/cosolvent concentration and a salinity of 2 wt% NaCl.igs. 2 and 3 show IFT results for the PG2062 APG surfactant andhe smaller linear aliphatic n-alcohols (Fig. 2) and the larger linearliphatic n-alcohols (Fig. 3) investigated.
The surfactants alone (2 wt%) did not form middle phases, andhe IFT reached low, but not ultra-low, numbers (Table 2). The low-st IFT was observed for PG2062, the most lipophilic molecule of theet. The recorded IFT values were consistent with literature values16].
able 2roperties of pure surfactant (2 wt%) mixtures.
roduct Relative volume ofoleic phase (%)
Relative volume ofmiddle phase (%)
G2062 0 60G2067 60 0G2069 50 0
Fig. 3. IFT measured for equilibrated samples containing PG2062 and large n-alcohols.
All pure alcohol systems (2 wt% alcohol) had 50 vol% oleic phaseand 50% aqueous phase characteristics except 1-octadecanol, whichhad 30 vol% oleic phase, 15 vol% middle phase and 50 vol% aqueousphase. Note that for an alcohol alone (2 wt%) the IFT ranged betweenseveral mN/m up to 30 mN/m.
The observed IFT values for small (Fig. 2) and large (Fig. 3) n-alcohols reached a minimum for 1-octanol as a cosolvent. IFTs werealso low for 1-hexanol as a cosolvent. For smaller and larger alkylchains the recorded IFT values were higher. Apparently cosolventswith an optimal HLB exist, in the presented case this was 1-octanol.
The IFT behavior versus APG-n-alcohol ratio was fairly constant.This suggests that low IFT conditions may be attained with lowconcentrations of APG surfactant. One example is described by Tang
et al. [21].
One explanation for the synergistic action of the added cosol-vent n-alcohols is that they pack at the interface so as to decreasethe curvature of the interfacial layer and thereby reduce the IFT[3,4,17,32]. Sabatini et al. [35] suggested the concept of a “hydropho-
Relative volume ofaqueous phase (%)
Average alkyl chainlength
IFT (mN/m)
40 12.5 0.73540 9.1 2.450 10.1 1.08
S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59 51
bTmuas
oasThat
iaoIutf[nmd
Fig. 6. Phase diagram of 1-hexanol/PG2062 mixtures.
Fig. 4. Phase diagram of 1-propanol/PG2062 mixtures.
ic linker” as a physical model for the action of these cosurfactants.hat is, an additive may work by linking the oil and surfactantolecules better at the interface. This theory is supported by molec-
lar modeling work [19]. Our general observation was that virtuallyll alcohol cosolvents act to decrease the IFT of the main APGurfactant.
Figs. 4–11 display the recorded phase behavior of the brine-n-ctane–APG-n-alcohol systems. As a general trend, low IFT valuesppeared when middle phase emulsions [22,29] appeared, con-istent with observations described by Shinoda and Friberg [23].he existence of a middle phase emulsion is an indicator ofydrophilic–lipophilic balance [22,36]. Balzer [7] mentioned thatlkylpoly glycoside micelles have a pronounced rod-shaped struc-ure.
A large middle phase emulsion indicated a low IFT, especiallyf both, oil and water, were solubilized; however we did not findny easy direct relation between the volume of the middle phaser the quantity of solubilized oil and/or water and the measuredFT. We tried to relate IFTs with solubility parameters (Hansen sol-bility parameters and Hildebrand solubility parameters [24,25]) ofhe involved molecules, also trying to incorporate weighing factorsor their relative mole fraction, but this led to no conclusive result
10,11]. Clearly, IFT for these quinternary systems (NaCl, water, APG,-octane, cosolvent – in fact pseudoquinternary as the used com-erical APGs were mixtures) is a highly complex phenomenon
etermined on the molecular level. We were able to calculate IFT
Fig. 5. Phase diagram of 1-butanol/PG2062 mixtures.
Fig. 7. Phase diagram of 1-octanol/PG2062 mixtures.
trends for these APG systems, but could not compute exact numbers
[19].
Fig. 12 summarizes data that compares the IFT measured forthe three different commercial APG surfactants. The trend is thatincreasing the alkyl chain length of the APG surfactant decreases
Fig. 8. Phase diagram of 1-dodecanol/PG2062 mixtures.
52 S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59
Fig. 9. Phase diagram of 1-octadecanol/PG2062 mixtures.
tw
Prlt
lowest IFT among this group of cosolvents.The associated volume fractions observed are displayed in
Figs. 15–17.In Fig. 18, the influence of aromatic cosurfactants on lowering
Fig. 10. Phase diagram of 1-eicosanol/PG2062 mixtures.
he IFT, all other parameters being constant. This is in agreementith literature data [16] measured against n-decane.
Closer inspection of the data in Fig. 12 indicates that the IFT forG2067 and PG2069 (average alkyl chain lengths of 9.1 and 10.1,
espectively) also had lower IFTs as the cosurfactant alcohol chainength increased from n-propanol to n-octanol. (This is the samerend as shown for the PG2062 surfactant in Fig. 2.)
Fig. 11. Phase diagram of 1-docosanol/PG2062 mixtures.
Fig. 12. Increase of APG average alkyl chain length decreased the observed IFT.
The results in Fig. 13 present the same IFT data as described,but with a different perspective by plotting IFT against the alcoholcarbon number. Fig. 13 plots the IFT data of the 0.8 wt% APG sur-factant/1.2 wt% alcohol formulation. These IFT data in Fig. 13 stillindicate that the longer alkyl chain APG product (PG2062) pro-vides the lower IFT, and that 1-octanol is the best tested choicefor a 1-n-alcohol cosurfactant at these process conditions.
Experiments were conducted in order to examine the effect ofother alcohol cosolvents, we focused on the PG2062 APG productbecause its formulations with small n-alcohols gave the lowest IFTvalues (Fig. 2). Another series of tests (Fig. 14) examined a seriesof C6 alcohols as cosolvents, with the variation being the alcoholstructure. A straight aliphatic chain alcohol (n-hexanol), a branchedchain alcohol (4-methyl-2-pentanol), a saturated ring (cyclohex-anol), and an aromatic ring structure (phenol) were tested. Resultsshowed that the straight chain (1-hexanol) structure provides the
the IFT of APG formulations is presented. 1-naphthol decreased the
Fig. 13. Experimental data showing the influence of the number of carbon atoms inthe n-alcohol cosurfactant on IFT for selected APG/alcohol formulations.
S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59 53
Fig. 14. Comparison of IFT behavior for different C6 alcohol cosurfactants.
Iienaw
Fig. 17. Phase diagram of phenol/PG2062 mixtures.
Fig. 15. Phase diagram of 4-methyl-2-pentanol/PG2062 mixtures.
FT values to ultra-low levels (approximately 0.001 mN/m). Anotherntriguing effect of aromatic alcohols is that they were effective
ven at very low concentrations. 1-napthol and benzylalcohol (phe-ol was not tested at this concentration range) showed IFT minimat low concentrations (<0.1 wt%). It is hypothesized that alcoholsith a similar water solubility could also lead to ultra-low IFT
Fig. 16. Phase diagram of cyclohexanol/PG2062 mixtures.
Fig. 18. Comparison of IFT behavior for different aromatic alcohol cosurfactants.
values. The volume fraction plots for these systems are shown inFigs. 17, 19 and 20.
In Fig. 21 we present the results of our IFT analysis ofbranched alcohols. These did not reach ultra-low IFTs, probablybecause the HLB was not optimal (4-methyl-2-pentanol was too
hydrophilic while 2-butyl-1-decanol, 2-hexyl-1-decanol and 2-decyl-1-tetradecanol were too lipophilic.). The phase behavior ofthese mixtures is shown in Figs. 22–24.
Fig. 25 presents measured IFT values for surfactant formula-tions containing PG2062 and C8 cosurfactants analog to 1-octanol,
Fig. 19. Phase diagram of benzylalcohol/PG2062 mixtures.
54 S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59
Fig. 20. Phase diagram of 1-naphthol/PG2062 mixtures. Undissolved 1-naphtholparticles were observed for 1-naphthol concentrations larger than 1 wt%.
Ff
baTs0t
Fig. 23. Phase diagram of 2-hexyl-1-decanol/PG2062 mixtures.
perature (Fig. 28) and salinity (Fig. 29). Our observations are
ig. 21. Comparison of IFT behavior for different branched aliphatic alcohol cosur-actants.
ut with different functional groups (carboxylic group: octanoiccid; ester group: methyloctanoate; and alcohol group: 1-octanol).
he alcohol was the best performing cosurfactant, while the esterhowed the highest IFT values, though still low, being around.5 mN/m. Figs. 26 and 27 shows the phase behavior recorded forhe octanoic acid and the methyloctanoate system.
Fig. 22. Phase diagram of 2-butyl-1-decanol/PG2062 mixtures.
Fig. 24. Phase diagram of 2-decyl-1-tetradecanol mixtures.
3.2. Interfacial tension versus temperature and salinity
Measured IFT results in this study confirm that APG/alcoholformulations may be largely indifferent to both changes in tem-
in accordance with data observed by Kutschmann et al. [13](temperature-independence) and Nickel et al. [26] and Shinodaet al. [27] (salinity independence). According to Nickel et al. the
Fig. 25. Comparison of IFT behavior for C8 cosolvents, including ester, alcohol, andacid groups.
S. Iglauer et al. / Colloids and Surfaces A: Physi
Fig. 26. Phase diagram of octanoic acid/PG2062 mixtures.
I2
iAm(
Fm
Fig. 27. Phase diagram of methyloctanoate/PG2062 mixtures.
FT remains constant even at very high NaCl concentrations (up to0 wt%).
However, we observed a slight increase in IFT with increas-
ng temperature for all investigated systems except for the 0.8 wt%PG2062/1.2 wt% 1-hexanol system for which we recorded a maxi-um in IFT at 50 ◦C. This exception might be a measurement outlier
standard deviation is around 20%) or it is in fact a maximum.
ig. 28. IFT is nearly independent of temperature for these APG2069/n-alcohol for-ulations versus n-octane.
cochem. Eng. Aspects 339 (2009) 48–59 55
The general APG IFT behavior (i.e. temperature and salinityindependence) is desirable because in oil reservoirs, salinity andtemperature will vary from zone to zone. This behavior means thatone may formulate just a single aqueous based surfactant solutionthat is able to mobilize the crude oil as efficiently in spite of thesetemperature and salinity differences.
The salinity in the reservoir brine may vary in both in areal andvertical extents. Mature fields that have been subjected to yearsof waterflood (the primary targets for surfactant EOR) often havesubstantial differences in salinity, for example, due to contrastsbetween the injected and original formation brine.
A common approach in surfactant EOR is the so-called “salinity-gradient” design whereby the salinity is reduced step-wise fromthe formation water, surfactant slug, and polymer/water drive. Themotivation for this design is to generate a low IFT, middle phasemicroemulsion condition in-situ, with the following drive solutionsdesigned to put the surfactant back into the aqueous phase in orderto avoid excessive chemical loss by phase trapping. One problemwith this approach is that it may be difficult to locate sufficientfresh water sources to cause this gradual reduction in salinity. Also,maintaining target salinities both in-situ and in the chemical solu-tions becomes more difficult as the chemical project continues. Thisis important because the performance of most (anionic) surfactantsystems is sensitive to salinity.
Having a single surfactant formulation that is quasi-indifferentto salinity would be an advantage in the EOR design. WithAPG/cosurfactant formulations, one might accomplish the sameobjectives of having low IFT in-situ and avoiding surfactant phasetrapping by changing the ratio of the APG/cosurfactant duringchemical injection. In addition, per Fig. 29, there is the possibilityof formulating for low IFTs for reservoirs containing high salinityand high hardness brines.
The phase behavior as a function of temperature recorded forthe 0.8 wt% PG2062/1.2 wt% 1-octanol formulation is displayed inFig. 30. Please note that the x-axis is not to scale. Figs. 31 and 32show the influence of salinity on phase behavior for the 0.8 wt%PG2062/1.2 wt% 1-octanol formulation at 30 ◦C and 50 ◦C. Fig. 33presents the influence of salinity on phase behavior for the 0.8 wt%PG2062/1.2 wt% 1-octanol formulation at 30 ◦C. The abscissae ofFigs. 31–33 are not to scale. It appears that more aqueous phaseis solubilized at higher temperatures or higher salinities.
3.3. Influence of hydrocarbon type
While the APG2062/1-butanol formulations with aliphatichydrocarbons as oleic phases (hexane, octane, dodecane) reached
Fig. 29. IFT is nearly independent of salinity for this PG2062/1-hexanol formulationversus n-octane.
56 S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59
Fig. 30. Effect of temperature on PG2062/1-octanol phase behavior.
Iwlp
stv(b
Fig. 33. Effect of salinity on 1-hexanol/PG2062 mixtures at 30 ◦C. Note: the 11 wt%point is 10 wt% NaCl + 1 wt% CaCl2.
0.8 wt% PG2062 for octane. The o-xylene again reached the lowest
Fig. 31. Effect of salinity on 1-octanol/PG2062 mixtures at 30 ◦C.
FT values of approximately 0.5 mN/m (Fig. 34), lower IFT valuesere attained with an aromatic oleic phase (o-xylene). The formu-
ation 0.4 wt% PG2062/1.6 wt% 1-butanol with o-xylene as an oleichase reached ultra-low level, approximately 0.015 mN/m.
The phase behavior of these PG2062/1-butanol mixtures ishown in Figs. 35–37. Generally an increase of 1-butanol concentra-ion led to a decrease in the middle phase (microemulsion phase)
olume fraction and an increase in the oleic phase volume fractionshown for octane in Fig. 5). The 1-butanol behavior is of relevanceecause it is a relatively cheap chemical.
Fig. 32. Effect of salinity on PG2062/1-octanol phase behavior at 50 ◦C.
Fig. 34. Effect of oil type on the IFT for PG2062/1-butanol formulations.
Several APG2062/1-octanol formulations with aliphatic oleicphases reached very low IFT values (cf. Fig. 38). A minimum valuewas attained at a concentration of 1.2 wt% PG2062 for hexane and
IFT values compared with the aliphatic oils (o-xylene formulationswith a PG2062 concentration of 0.8 wt% and 1.2 wt% were not mea-sured).
Fig. 35. Phase diagram of 1-butanol/PG2062 mixtures; oil type is n-hexane.
S. Iglauer et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 48–59 57
Fig. 36. Phase diagram of 1-butanol/PG2062 mixtures; oil type is n-dodecane.
Fs
a
Ft
Fig. 39. Phase diagram of 1-octanol/PG2062 mixtures; oil type is n-hexane.
Fig. 37. Phase diagram of 1-butanol/PG2062 mixtures; oil type is o-xylene.
The phase diagrams for the different oils are presented in
igs. 39–41. The volume of the middle phase microemulsionshrinks with a decrease in APG concentration.
Generally the IFT values were lower when the oil phase waslighter alkane (from dodecane, to octane, to hexane), or was
ig. 38. Effect of oil phase composition on the IFT with PG2062/1-octanol formula-ions at room temperature.
Fig. 40. Phase diagram of 1-octanol/PG2062 mixtures; oil type is n-dodecane.
o-xylene, an aromatic compound. These trends in terms of oil chem-istry influence on IFT observed are consistent with what is reportedin the literature when the surfactant is an alkyl benzene sulfonate[5], the conventional choice for EOR applications. The beneficialeffect of having an aromatic oil is particularly pronounced for the
APG2062/1-butanol blend.
Fig. 41. Phase diagram of 1-octanol/PG2062 mixtures; oil type is o-xylene.
58 S. Iglauer et al. / Colloids and Surfaces A: Physi
F2
3
f1cuiid
3
si
3
Buistoe
23
4
5
6
ig. 42. Measured plateau adsorption of APG surfactants; 20:1 ratio of solution:sand,5 ◦C.
.4. Aromaticity
Observations regarding different alcohol cosurfactants and dif-erent hydrocarbons revealed that aromatic cosurfactants (e.g.-napthol) and aromatic hydrocarbons (o-xylene) have a signifi-antly beneficial effect on lowering IFT and in terms of achievingltra-low IFT systems. Also, in case of the aromatic cosurfactants,
t was observed that low concentrations were efficient in reduc-ng IFT. We speculate that aromaticity plays a significant role inetermining IFTs.
.5. Surfactant adsorption
Maximum adsorption measured for the three commercial APGurfactants (PG2067, PG2069, and PG2062) are shown, left to rightn Fig. 42.
.6. Coreflood experiment
Fig. 43 displays the measured tertiary oil production for theerea sandstone core. The core was conditioned to waterflood resid-al oil conditions (waterflood Sor = 30%) prior to surfactant slug
njection. A significant amount of additional oil was produced,
lightly more than 50% tertiary oil recovery (which correspondso an 85% oil recovery of IOIP). This proofed the effectivenessf the surfactant formulation in terms of enhancing oil recov-ry.
Fig. 43. Tertiary oil recovery observed after APG2062/1-octanol injection.
[
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cochem. Eng. Aspects 339 (2009) 48–59
4. Conclusions
Key findings from this study include:
1. Alkyl polyglycoside surfactants may be formulated with alcoholcosolvents in brine solutions that can create ultra-low IFT (inter-facial tension) approaching 0.001 mN/m, or less, versus simplealkane or Xylene hydrocarbons.
. APG with larger alkyl chains had lower IFT values.
. There was an optimum alcohol chain length (1-octanol was thebest alcohol tested in these studies) for generating low IFTs.
. There was an optimum cosurfactant/APG molar ratio which gen-erated the lowest IFT.
. In one test series an alcohol function led to lower IFT values thanan ester or carboxylic function on analog molecules.
. Some of these APG formulations may generate a low IFT that islargely independent of both salinity and temperature effects.
7. A low IFT APG formulation showed good oil recovery results in acoreflood experiment, circa 85% of initial oil in place was recov-ered in a tertiary surfactant (Agrimul 2062/1-octanol) flood.
Acknowledgments
We thank the Department of Energy (DE-FC26-01BC15362) forproviding financial support for this project and we thank Chevron-Texaco and Akzo Nobel for technical assistance. We also thank theCognis Corporation for supplying APG surfactant samples.
References
[1] K. Hill, O. Rhode, Sugar-based surfactants for consumer products and technicalapplications, Fett/Lipid 10 (1999) 25–33.
[2] D. Balzer, Process for the Extraction of Crude Oil From an Underground DepositUsing Surfactants, U.S. Patent 4,985 (1991), p. 154.
[3] D.J. Mitchell, B.W. Ninham, Micelles, vesicles and microemulsions, J. Chem. Soc.,Faraday Trans. 2: Mol. Chem. Phys. 77 (1981) 601–629.
[4] R. Strey, M. Jonströmer, Role of medium-chain alcohols in interfacial films ofnonionic microemulsions, J. Phys. Chem. 96 (1992) 4537–4542.
[6] A. Abrams, The influence of fluid viscosity, interfacial tension, and flow velocityon residual oil saturation left by waterflood, SPEJ (October) (1975) 437–447.
[7] D. Balzer, Alkylpolyglcosides, their physico-chemical properties and their uses,Tenside Surf. Det. 28 (6) (1991) 419–427.
[8] D. Balzer, H. Lüders (Eds.), Nonionic Surfactants, Alkyl Polyglycosides, SurfactantScience Series, 91, Marcel Dekker, New York, 2000.
[9] T. Förster, et al., Physico-chemical basics of microemulsions with alkyl polygly-cosides, Progr. Colloid Polym. Sci. 101 (1996) 105–112.
10] S. Iglauer, Y. Wu, P.J. Shuler, M. Blanco, Y. Tang, W.A. Goddard, III, Alkylpolygly-coside Surfactants for Improved Oil Recovery, Paper SPE/DOE 89472, SPE/DOEImproved Oil Recovery Symposium, Tulsa, OK, April 17–21, 2004.
[11] S. Iglauer, Y. Wu, P.J. Shuler, Y. Tang, M. Blanco, W.A. Goddard, The influence ofAlcohol Co-surfactants on the Interfacial Tensions of Alkylglycoside SurfactantFormulations vs. n-Octane, ACS 227th National Meeting, Division of PetroleumChemistry, Anaheim, CA, USA, 2004.
13] E.M. Kutschmann, G.H. Findenegg, D. Nickel, W. von Rybinski, Interfacial tensionof alkylglucosides in different APG/oil/water systems, Colloid Polym. Sci. 273(1995) 565–571.
14] W. von Rybinski, B. Guckenbiehl, H. Tesmann, Influence of co-surfactants onmicroemulsions with alkyl polyglycosides, Colloids Surf. A: Physicochem. Eng.Aspects 142 (1998) 333–342.
15] Y. Wu, S. Iglauer, P.J. Shuler, Y. Tang, M. Blanco, W.A. Goddard, Synergistic effectof alkyl polyglycoside and sorbitan mixtures on lowering interfacial tension andenhancing oil recovery, in: ACS 227th National Meeting, Division of PetroleumChemistry, Anaheim, CA, USA, 2004.
16] K. Hill, W. von Rybinski, G. Stoll (Eds.) Alkyl Polyglucosides, Weinheim, VCH,1997, ISBN: 9783527294510.
17] M. Kahlweit, G. Busse, B. Faulhaber, Preparing microemulsions with alkylmonoglucosides and the role of n-alcohols, Langmuir 11 (1995) 3382–3387.
18] M. Kahlweit, R. Strey, G. Busse, Effect of alcohols on the phase behavior ofmicroemulsions, J. Phys. Chem. 95 (13) (1991) 5344–5352.
19] W.A. Goddard, Y. Tang, P.J. Shuler, M. Blanco, S.S. Jang, S.T. Lin, P. Maiti, Y. Wu,S. Iglauer, X. Zhang, Lower Cost Methods for Improved Oil Recovery (IOR) viaSurfactant Flooding, DOE Project DE-FC 26-01BC15362, Final Report, September(2004).
20] F. Peypoux, J.M. Bonmatin, J. Wallach, Recent trends in the biochemistry ofsurfactin, Appl. Microbiol. Biotechnol. 51 (1999) 553–563.
21] Y. Tang, P.J. Shuler, Y. Wu, S. Iglauer, Chemical System for Improved Oil Recovery,US-Patent Application 20060046948 (2006).
22] R.N. Healy, R.L. Reed, Improved Oil Recovery by Surfactant and Polymer Flood-ing, Academic Press, New York, 1977.
23] K. Shinoda, S. Friberg, Emulsions & Solubilization, John Wiley & Sons, New York,1986.
24] J.H. Hildebrand, The Solubility of Non-Electrolytes, Reinhold, New York, 1936.25] C.M. Hansen, Hansen Solubility Parameters, A User’s Handbook, CRC Press, New
York, 2000.26] D. Nickel, T. Förster, W. von Rybinski, Physicochemical properties of alkyl polyg-
lycosides, in: K. Hill, W. von Rybinski, G. Stoll (Eds.), Alkyl Polyglycosides, VCH,Weinheim, 1997.
27] K. Shinoda, T. Yamaguchi, R. Hori, Bull. Chem. Soc. Jpn. 34 (1961) 237.28] H. Bertsch, G. Rauchalles, U.S. Patent 2,049,758 (1934).29] M. Bourrel, R.S. Schechter, Microemulsions and Related Systems: Formulation,
Solvency, and Physical Properties, Marcel Dekker, New York, 1988.30] J.L. Cayais, R.S. Schechter, W.H. Wade, The Measurement of Low Interfacial Ten-
sion via The Spinning Drop Technique, Section 17, Surfactant Applications, 1977.
[[[
cochem. Eng. Aspects 339 (2009) 48–59 59
31] J.L. Cayais, R.S. Schechter, W.H. Wade, The Utilization of petroleum sulfonates forproducing low interfacial tensions between hydrocarbons and water, J. ColloidInterface Sci. 59 (1) (1977) 31–38.
32] P. DeGennes, C. Taupin, Microemulsions and the flexibility of oil-water inter-faces, J. Phys. Chem. 86 (1982) 2294–2304.
33] P.H. Doe, W.H. Wade, R.S. Schechter, Alkyl benzene sulfonates for producing lowinterfacial tensions between hydrocarbons and water, J. Colloid Interface Sci. 59(3) (1977) 525–531.
34] H. Kahl, K. Kirmse, K. Quitzsch, Grenzflächenspannungen in mehrphasigen Mis-chsystemen mit Alkylpolyglucosiden, Tenside Surf. Det. 33 (1) (1996) 26–32.
35] D.A. Sabatini, E. Acosta, J.H. Harwell, Linker molecules in surfactant mixtures,
36] K. Shinoda, J. Colloid Interface Sci. 24 (1976) 4.37] Cognis Corporation, Technical Data Sheet, 2004.38] R. Garst, Alkyl polyglycosides – new solutions for agricultural applications, in:
K. Hill, W. von Rybinski, G. Stoll (Eds.), Alkyl Polyglycosides, Weinheim: VCH,Hill, von Rybinski, Stoll, 1997.
