terapaper enhancement of ift reduction i-1323

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Abstract

IPTC 15140

Enhancement of IFT Reduction in Surfactant Flooding by BranchedAlcoholsMariyamni Awang, SPE, Iskandar Dzulkarnain, Mohamed Wahyudeen Zakaria, Universiti Teknologi PETRONAS

Copyright 2011, International Petroleum Technology Conference

This paper was prepared for presentation at the International Petroleum Technology Conference held in Bangkok, Thailand, 79 February 2012.

This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarilyreflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor SocietyCommittees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum TechnologyConference is prohibited. Permission to reproduce in print is res tricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, IPTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax +1-972-952-9435

Published research showed that alcohols are able to reduce the interfacial tension (IFT) between surfactant and oil when added

even in small amounts. Much of the work had focused on primary alcohols. This paper presents our preliminary investigationon the effects of branched alcohols on interfacial tension changes in crude oil- sodium dodecyl sulphate mixtures. Branchedalcohols are chosen because many forms of bio-waste contain a significant number of branched components and a cheaperproduct is expected if the natural structure of the feedstock can be exploited. Our results show that 0.5 wt% of branchedalcohols result in similar amount of reduction caused by 1 wt% of sodium hydroxide. Sodium carbonate gives betterperformance than sodium hydroxide or the branched alcohols used, however its use is limited to low salinity conditions. More

studies will be conducted with an emphasis on the effects of branching, solvation ratio and salinity.

Introduction

Chemical flooding is limited largely by the cost of chemicals such surfactants. However, literature has shown that severaladditives such as alcohols are able to further reduce the interfacial tension (IFT) between surfactant and oil when added evenin small amounts. Consequently, the chemical cost is reduced by using a lower concentration of surfactant. Branched alcoholsare chosen because many forms of bio-waste contain a significant number of branched components. A cheaper product is

expected if the natural structure of the feedstock can be exploited in the production reactions. The oil palm industry inMalaysia generates a large amount of waste and a newly introduced crop, Jatropha oil is a potential feedstock. Alcohols suchas ethanol and propanol have been used as additives in surfactant flooding. However, not much work has been conducted onbranched alcohols. Interfacial tension directly affects the microscopic displacement efficiency in surfactant flooding andtherefore, a low IFT system indicates good microscopic efficiency can be achieved. This ongoing research investigatesinterfacial tension change in a surfactant/crude oil system using branched alcohols as additives.

Branching effects

Surfactants derived from branched alcohols showed improvements in IFT reduction with an increase in branching. Varadaraj,Bock et al. (1991) produced branched Guerbet surfactant (C16BGS) to compare its properties with linear Guerbet surfactantssuch as C16LE5S and C16LGE5S. Branching was found to increase the critical micelle concentration (CMC) for air/watersystems and decane/water systems. The effectiveness of the surfactant, defined as the difference between surface tension atCMC and surface tension of pure solvent, was found to increase for all air/water and decane/water systems tested when theGuerbet surfactants were used. The branched Guerbet surfactant showed a bigger increase in effectiveness. In a later study,Varadaraj, Bock et al. (1992) related the surface-acting properties of branched sodium dodecyl sulfate to the branching of thehydrocarbon chain. Anionic surfactants with double branched hydrocarbon chain and cationic surfactants with unbalanced

hydrocarbon chain were tested by Upadhyaya, Acosta et al. (2006) to prove the effect of tail-branching. Experiments wereconducted by mixing the two types of branching i.e. double-branched and double branched, double-branched and unbalanced,unbalanced and unbalanced. While anionic and cationic surfactants tend to react unfavourably, a mixture of double-tailed and

unbalanced tail surfactants was found to form minimum precipitation and other undesirable phases. At the same time increase


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in oil solvation was observed. Literature showed that branching effects of surfactants have been studied in many industries.Branching of alcohol is not of much interest in the oil industry for the reason that branched surfactants are derived frombranched alcohols and their behaviours are expected to be similar. Nevertheless, combinations of alcohols and surfactants arenot always compatible and further investigations are needed.

Experiment

Sodium dodecyl sulphate and calcium chloride at different concentrations are prepared. Alkalis (sodium hydroxide and sodiumcarbonate) and branched alcohols (2-methyl 1-butanol and 2-methyl 2-butanol) are mixed in the solutions to evaluate effect ofbrine water chemistry and compatibility of these additives in the surfactant solution. The mixtures are shaken and left toachieve equilibrium at room temperature for at least 24 hours. The mixtures are then observed for precipitation and IFT

measurements are made. Materials and experimental conditions are listed in Table 1.

Results and Discussion

Experimental results show an improvement in IFT reduction when branched alcohol is used as a co-solvent in surfactantflooding. Comparison with caustic agent such as sodium carbonate and sodium hydroxide indicate aqueous stability for theproposed co-solvents at room temperature under high salinity conditions. The performance of the alcohols was favourable

when compared with alkalis which are cheaper. For example, a mixture of 0.5 wt% 2-methyl 1-butanol in 0.1 wt% sodiumdodecyl sulphate (SDS) gives an IFT which is only slightly higher when compared with alkali (1.0wt% NaOH at 0.1 wt%

SDS). It can be seen that only half of the concentration of alcohol is needed to achieve a similar effect. Apart from theconcentrations of the additives, the effects of water salinity are also investigated since it is known that alkali-surfactantmixtures tend to precipitate in the presence of salts. The remainder of this section will discuss the following:

i. Effects of branched alcohol on aqueous stability.ii. Effects of branched alcohol on surfactant interfacial activity.

Effects of branched alcohol on aqueous stability

Visual assessment is made to evaluate the aqueous stability of the mixtures. This provides a quick screening method inphase behavior testing. Prior to mixing crude oil, the aqueous mixtures containing the surfactant and additives (either branchedalcohol or alkali) are agitated and allowed to settle down in ambient temperature for at least one hour. The fluids are then

visually inspected for cloudiness or phase separation. A clear and stable solution is desired as this indicates compatibility ofsurfactants with electrolytes in the resulting microemulsion when oil is added later. Solutions with precipitate or phase

separation will be screened out as this may lead to plugging or delayed propagation of the surfactant slug as it is injected intocore or reservoir rock. Consequently, injected slug should be single phase micellar solution to ensure transport of surfactantslug through the reservoir.

Figure 1-4 shows aqueous mixture behavior of two sets of alkalis and branched alcohols in SDS. Both are mixed in 3.5

wt% brine. Quick inspection reveals both 2-methyl 1-butanol and 2-methyl 2-butanol result in transparent solution whenmixed with the anionic surfactant. Addition of sodium hydroxide and sodium carbonate to the aqueous solution results inwhite precipitate forming at the bottom. This implies limited tolerance to high salinity environment for both caustic agents.The results also suggest viability of using branched alcohols as co-solvent in the surfactant slug mixture under the sameenvironment.

Effects of branched alcohol on surfactant interfacial activity

Studies are conducted to evaluate the effect of adding branched alcohol into a surfactant solution. Comparison is made withsodium hydroxide and sodium carbonate under varying salinities and pressures. Figures 5 6 show effects of percentage IFTreduction for both alkalis and branched alcohols in 0.2 wt% SDS. The same effect in 0.1 wt% SDS is observed as shown in Fig7 and 8. From these results sodium carbonate seems to reduce IFT better compared with both branched alcohols. However IFTreduction for alkali depends on the concentration used. In both SDS concentrations, increasing the alkali concentration seems

to effect further reduction in IFT. This can be observed in Figure 5 and Figure 7 for both sodium hydroxide and sodiumcarbonate at 0.25 wt% and 1 wt% respectively. At 1000 psia and 0.2 wt% SDS, 1 wt% sodium carbonate can reduce IFT up to72% compared with 0.25 wt% at only 5%. In summary, the alkalis show a nonlinear reduction in IFT.

Increasing the pressure seems to affect IFT reduction in both alcohols only slightly. However, this is opposite for solutionsof both alkalis particulary at low concentrations. In Figure 5, increasing the pressure to 1800 psia seems to increase IFT to24% and 12% respectively for both 0.25 wt% sodium carbonate and sodium hydroxide.


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Alcohol branching seems to affect IFT reduction as well. Both 1 wt% and 0.5 wt% 2-methyl 2-butanol show less reductionin IFT on average than 2-methyl 1-butanol of the same amount. This trend is consistent in both figure 6 and 8. It appears thatmore branching actually increase the IFT. However these findings need to be substantiated with other alcohols with morebranching.

Although sodium carbonate seems to be effective in reducing IFT, its usage is limited in high salinity environment.Precipitate formed as both alkalis are mixed in SDS at 3.5 wt% brine. Figure 9 and 10 show effect of salinity in IFT reduction.

Branched alcohols seem to offer more tolerance to high salinity. In Figure 9, 1 wt% 2-methyl 1-butanol could reduce 71% oforiginal IFT. Almost the same reduction can be achieved by using 0.5 wt% of the same alcohol. Sodium carbonate at 1 wt%also brings similar reduction albeit at a lower salinity. This implies savings in the chemicals used since 0.5 wt% of 2-methyl 1-butanol reduces IFT equally well as 1 wt% sodium carbonate does but at half the concentration and several times the salinity.

Conclusions

From the studies conducted, branched alcohols seem to affect IFT reduction in high salinity surfactant solution. Comparisonwith alkalis suggests sodium carbonate is better although it lacks compatibility in highly saline aqueous mixture. Morebranching seems to result in lesser reduction although more samples need to be tested to validate this finding. This observationis contrary to the effect observed by earlier researchers who studied branched Guerbet surfactants. All the results presented are

preliminary studies aimed at understanding behavior of branched alcohols in chemical flooding. Further studies will beconducted to investigate the microemulsion phase behavior particularly on the effects of branching, solubilization ratio and

optimal salinity.

Acknowledgement

The authors are grateful to Geoscience and Petroleum Engineering Department, Universiti Teknologi PETRONAS for support

given in preparation of this work.

References

Upadhyaya, A., E. Acosta, et al. (2006). "Microemulsion phase behavior of anionic-cationic surfactant mixtures: Effect of tailbranching." Journal of Surfactants and Detergents9(2): 169-179.

Varadaraj, R., J. Bock, et al. (1991). "Fundamental interfacial properties of alkyl-branched sulfate and ethoxy sulfatesurfactants derived from Guerbet alcohols. 2. Dynamic surface tension." The Journal of Physical Chemistry 95(4):

1677-1679.Varadaraj, R., J. Bock, et al. (1992). "Influence of hydrocarbon chain branching on interfacial properties of sodium dodecyl

sulfate." Langmuir 8(1): 14-17.


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Table 1: Chemicals used and experimental condition

Chemicals Sodium dodecyl sulfate (0.1 and 0.2 wt %).

Sodium carbonate and sodium chloride (both at 0.25 and1.0 wt %).

Branched alcohols 2-methyl 1-butanol and 2-methyl 2-butanol (both at 0.5 and 1.0 wt %).

Brine solution at 0.05 and 3.5 wt %.

Experimental condition Experiment performed at room temperature.

IFT is measured at 1000, 1400 and 1800 psia.

Figure 1: Aqueous mixture of sodium dodecyl sulphateand sodium carbonate in 3.5 wt% brine

Figure 2: Aqueous mixture of sodium dodecyl sulphateand sodium hydroxide in 3.5 wt% brine

Figure 3: Aqueous mixture of sodium dodecyl sulphateand 2-methyl 1-butanol in 3.5 wt% brine

Figure 4: Aqueous mixture of sodium dodecyl sulphateand 2-methyl 2-butanol in 3.5 wt% brine


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Figure 5: IFT reduction in 0.2 wt% SDS at 0.05 wt% brine



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Figure 8: IFT reduction at 0.1 wt% SDS at 3.5 wt% brine


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Figure 9: Effect of salinity on IFT reduction at 0.1 wt% SDS

Figure 10: Effect of salinity on IFT reduction at 0.2 wt% SDS

terapaper enhancement of ift reduction i-1323

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