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Potential of a novel surfactant slug in recovering additional oil from highly saline calcite cores during EOR process – Synergistic blend of surface active ionic liquid and nonionic surfactant SHILPA NANDWANI, Naved Anjum I Malek, Mousumi Chakraborty, and Smita Gupta Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03419 • Publication Date (Web): 20 Dec 2018 Downloaded from http://pubs.acs.org on December 20, 2018

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Energy & Fuels

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Potential of a novel surfactant slug in recovering additional oil from highly saline calcite

2

cores during EOR process – Synergistic blend of surface active ionic liquid and nonionic

3

surfactant

4

Shilpa K Nandwani†, Naved I Malek††, Mousumi Chakraborty*†, Smita Gupta*†

5

†

6

Surat – 395007, Gujarat, India.

7

††Department

8

Surat – 395007, Gujarat, India.

9

*Email

Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology,

of Applied Chemistry, Sardar Vallabhbhai National Institute of Technology,

for

correspondence:

[email protected]

(Smita

Gupta),

10

[email protected] (Mousumi Chakraborty).

11

ABSTRACT

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In the present study chemical formulation containing surface active ionic liquid (SAIL),

13

(Tributylhexadecylphosphonium bromide) and a nonionic surfactant (TERGITOL 15-S-9)

14

has been prepared. The composition of the mixed micelle and the interaction parameter

15

between the SAIL and non-ionic surfactant at varying concentration was evaluated by

16

Rubingh theory. The most optimal formulation was then screened through phase behaviour

17

tests in order to determine optimal salinity for the crude-brine-chemical formulation system.

18

The optimal salinity for the oil/water/ surfactant system was found to be as high as 9.28 wt.

19

%. Dynamic light scattering (DLS) studies and small angle neutron scattering (SANS)

20

experiments have been performed to provide further insight into the size and structure of the

21

micelles formed by the SAIL and non-ionic respectively. Traditional lab-scale oil

22

displacement experiments were performed to study the effectiveness of the optimised

23

chemical formulation in recovering oil during surfactant assisted EOR process. Prolate

24

ellipsoidal shaped mixed micelles, formation of WINSOR III phase at high salinities, low

25

equilibration time and prolonged stability of the ternary phase system facilitate high oil

ACS Paragon Plus Environment

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solubilisation. It was observed that after secondary waterflooding process, during the tertiary

27

oil recovery process individuial nonionic surfactant at the same salinity recovered only 7.28%

28

additional oil whereas the optimised chemical formulation containing both SAIL and

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nonioinc surfactant in equimolar ratio recovered 16.68% additional oil.”

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Keywords: ionic liquid, nonionic surfactant, synergism, carbonate reservoir, high salinity,

31

surfactant assisted EOR process.

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INTRODUCTION

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The global energy demand is expected to follow an increasing trend in future. Conventional

34

(primary and secondary) oil recovery techniques leave behind two-third of the original oil in

35

place (OOIP). Moreover, exploration of new oil fields has also declined in recent times. Thus

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there is a dire demand to implement enhanced oil recovery (EOR) techniques in existing

37

mature oil fields so as to recover the residual oil trapped in the pores of the reservoir

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rock1.EOR may be defined as an oil recovery technique that comprises of either injection of

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foreign fluids or uses methods for energy dissipation, in order to recover the residual oil left

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behind after the conventional recovery processes2.Chemical enhanced oil recovery (CEOR)

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processes include alkaline, surfactant, polymer injection and any combination of these

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processes. In surfactant assisted EOR a surfactant slug is injected into the reservoir. When

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selecting a surfactant for a surfactant assisted EOR process it is critical to study the phase

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behaviour of the ternary system containing oil /water and surfactant. A surfactant forming a

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bicontinuous microemulsion or WINSOR III phase in the oil/brine surfactant system

46

considered to be in optimum formulation, meaning that its physicochemical properties are

47

such that it can generate an ultralow interfacial tension (IFT) between phases3-5.In addition to

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ultralow IFT, other criteria while screening surfactants for surfactant assisted EOR process

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depends on the type of reservoir(sandstone or carbonate), its ability to maintain ultralow IFT

50

under extreme reservoir conditions (high temperature and high salinity), low adsorption on


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reservoir rock, negligible phase separation in presence of polymer and easy availability at low

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cost6. Reportedly large number of surfactant assisted EOR processes have been conducted in

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low-temperature, low-salinity sandstone reservoirs and petroleum sulfonate surfactants are

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the most commonly used surfactants in surfactant assisted EOR process3. However, a vast

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number of world’s oil reserves are contained in carbonate reservoirs with a high reservoir

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temperature and high salinity formation brine7. Given that, surfactant assisted EOR process

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represents an active research area and has motivated many researchers to develop and

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evaluate potential of novel surfactants in recovering more residual oil from carbonate

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formations7-10.

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Ionic liquids have been often attributed as greener substitutes for traditional organic solvents.

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Ionic liquids (ILs) are thermally stable salts which are in a liquid state below 100⁰C. Certain

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unique properties such as a wide liquid range, negligible vapour pressure, variable viscosity,

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miscibility with water and organic solvents make many ILs perspectives for applications in a

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variety of electrochemical, catalytic, chromatographic separation processes11-15. It has been

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reported that certain ILs possessing long alkyl chain within the charged cationic group are

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capable of forming micellar aggregates in water. Among these, many ILs have much more

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pronounced amphiphillic character as compared to conventional cationic surfactants having

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the same hydrophobic tail length16. As a result such surface active ionic liquids (SAIL) pose

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to be an attractive alternative to the surfactants commonly used in EOR processes.

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Researchers have investigated potential of different ILs (pyridinium, immidazolium,

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phosphonium) in reducing IFT between crude oil and water system at varying salinities and

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temperature17-29.

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trihexyl(tetradecyl)phosphonium chloride to act as surfactant to reduce the IFT between

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water and oil, with the aim of using this IL in EOR. They found that the phosphonium based

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IL reduces IFT between the water–oil interface. A clear formation of Winsor III phase was

Lago

et

al.

evaluated

the

ability


of

the

ionic

liquid

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observed at 4% salinity with oleic phase as dodecane17. Recently Fernández‐Stefanuto et al.

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in their study tested ionic liquids derived from proline esters for surfactant assisted EOR

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process and found that they were able to form WINSOR III phase with n-octane as oleic

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phase and optimal salinity of 8.5 wt% at 348.15 K29. However to our best knowledge

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individual immidazolium, pyridinium, pyrrolidinium, phosphonium based SAILs may not be

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able to significantly reduce the IFT between crude oil and water to ultralow values i.e. < 10-

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3mN/m,

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addition it is a prerequisite that co-surfactantexhibits synergism with the SAIL used. There

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seems to be a few systematic investigations wherein the micellar formulations of surfactant

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blends containing ionic liquid and conventional surfactants have been made for the purpose

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of surfactant assisted EOR process. Rodriguez-Escontrela et al. investigated the potential of

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mixture of different surface active ionic liquids with internal olefin sulfonate(IOS) for

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application as surfactants in an EOR process. It was observed that anionic IOS with cationic

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surface active ionic liquids [P4

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octane and water having salinity as high as 15%30.Jia et al. found that a surfactant blend

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containing pyrrolidinium based SAIL and SDS (anionic surfactant)reduced IFT between

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water and oil31. In our previous work, surfactant

93

immidazolium ionic liquid and nonionic surfactants were prepared and examined for their

94

potential in reducing IFT between crude and brine. It was observed that at a high optimal

95

salinity (>30 wt.%), the formulation formed a Winsor III phase with crude oil thus reducing

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the IFT to ultralow values. Approximately 10% of additional oil was recovered from an

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artificially prepared sand reservoir, during surfactant assisted EOR process32.

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In the present study, a new formulation of phosphonium based ionic liquid and nonionic

99

surfactant has been investigated for its effectiveness in use as a surfactant slug for surfactant

100

assisted EOR process. Since interaction between ionic and nonionic surfactants in an

and use of other chemicals such as co-surfactant or alkalis may be necessary17–28. In

4 4 14]Cl

and [C12mim]Br formed Winsor III phase with n-

formulations containing long chain


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adsorbed film as well as a micelle is larger than that between a mixture of two ionic

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surfactants and also for a mixture of two nonionic surfactants33, a biodegradable nonionic

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surfactant, TERGITOL 15-S-9, has been used as co-surfactant. In the present study,

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interaction between SAIL and nonionic surfactant has been studied using Rubingh

105

theory34.Dynamic light scattering (DLS) studies and small angle neutron scattering (SANS)

106

experiments have been performed to provide further insight into the size and shape

107

morphology of the micelles formed in the surfactant formulation, respectively.

108

behaviour of the crude oil/ water/ surfactant system has been studied at varying salinities.

109

Effectiveness of the optimised chemical formulation in recovering additional oil during

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CEOR has been determined by performing core flooding tests.

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2. EXPERIMENTAL SECTION

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Phase

2.1 Materials. In the present work long chain phosphonium-based ionic liquid,

113

Tributylhexadecylphosphonium bromide [P4

4 4 16]

Br, was purchased from TCI Chemicals

114

(purity >98%).TERGITOL 15-S-9 (molecular weight 596 g/mole, 99% purity),was purchased

115

from Sigma-Aldrich. Paraffin liquid light oil, sodium chloride, benzene and toluene were

116

purchased from Finar Chemicals. Double-distilled water was used for all physiochemical

117

studies. Crude oil (API 39.87) used for phase behaviour studies was procured from ONGC,

118

Gandhar field, Ankleshwar, India. All the properties of the crude oil used for phase behaviour

119

studies are mentioned on our previous work32. A simulated carbonate reservoir was prepared

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by tightly packing calcite powder (acts as a proxy of carbonate reservoirs) in a core holder

121

(length-23 cm, diameter -3 cm). Calcite powder (200-250 mesh) was procured from RMR

122

micro minerals, Jaipur, Rajasthan. A schematic representation of the setup used for carrying

123

out core flooding experiment has been mentioned in our previous work32. The oil used during

124

the core flooding experiments was synthetic containing oil 75% paraffin liquid light oil,

125

12.5% Benzene and 12.5% Toluene by volume. Owing to certain restrictions on the usage of


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positive displacement pump only mixture of lighter fractions was used as oil in the artificially

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prepared calcite core.

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2.2 Methods.2.2.1 Surface tension measurements. The surface tension of individual

129

and mixed surfactant solution were measured using a KRUSS-T9 Tensiometer (Germany)

130

using the Du Nouy ring method. Five concentrated chemical formulations in which

131

TERGITOL 15-S-9 and [P4 4 4 16] Br are mixed in different molar ratios (mole fraction α [P4 4 4

132

16] Br

133

determined from surface tension vs. LOG of Concentration graph after following the general

134

experimental procedure. The measurements were conducted at atmospheric pressure and

135

room temperature. The platinum ring was cleaned and flame dried before each use.

136

2.2.2 Dynamic light scattering (DLS).The micellar size distribution of the mixed surfactants

137

system at varying salinities were carried out by using laser diffraction method of Zetasizer

138

Ver.6.00 (Malvern Instruments Ltd., Worcestershire, UK).First, aqueous solution of the

139

chemical formulation was prepared by mixing 1wt.% of TERGITOL 15-S-9, followed by

140

addition of [P4

141

individual surfactants was chosen on the basis of their interaction parameter evaluated after

142

surface tension measurements. Salinity of the aqueous chemical formulation was varied from

143

0 -12.5 wt.% NaCl and its effect on the aggregation behaviour of the mixed micelles was

144

investigated. The corresponding hydrodynamic diameters of the mixed micelles were then

145

calculated from Stokes–Einstein relationship.

146

2.2.3 Phase behaviour scans and determination of optimal salinity. Phase behaviour tests for

147

the mixed surfactant system were carried out as follows: Aqueous solution of the chemical

148

formulation was prepared by mixing 1wt. % of TERGITOL 15-S-9and [P4 4 4 16] Br in 1:1

149

molar ratio. This accounted for a total concentration of 1.8 wt. %. From this formulation, 4ml

150

samples were taken and their salinities were varied from 0-20 wt. % NaCl. Each of them were

= 0, 0.2, 0.5, 0.8 and 1) have been prepared. CMC of each of the solutions was

4 4 16]

Br(mole fraction α =0.5). Aforementioned mole fraction of mixing


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then taken in separate 8ml stoppered vials and crude oil was then added to it such that the

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water-to-oil ratio (WOR) is 2:1. After gentle shaking, the vials were allowed to stand for a

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week. Results were drawn on the basis of visual observation. In order to find optimal salinity

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at which the chemical formulation should be injected into the packed calcite core, 6 ml of

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chemical formulation having same concentration but varying salinities (1 -10 wt.% NaCl)

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and 3ml crude oil (WOR= 2:1) were taken in graduated stoppered 10 ml test tubes. The test

157

tubes were gently shaken and allowed to stand for a week. Optimal salinity was then

158

calculated on the basis of solubilisation parameters, Vo/Vs and Vw/Vs, where Vo, Vw and

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Vs are the amount of oil, water and surfactant in the microemulsion phase respectively. After

160

determining the optimal salinity, phase behaviour of the individual SAIL (1.8 wt. %) and

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nonionic surfactant (1.8 wt. %) in the same ternary system was examined at the same salinity

162

(9.25 wt. % NaCl). It was then compared with the phase behaviour of the optimised chemical

163

formulation (containing equimolar mixture of SAIL and nonionic surfactant) under similar

164

conditions. The phase behaviour tests were carried out at room temperature.

165

2.2.4 Small-angle neutron scattering measurements (SANS). SANS method was used for

166

characterizing shape of micelles present in the optimised chemical formulation that has to be

167

injected into the artificially prepared carbonate reservoir during surfactant assisted EOR

168

process. During SANS the optimised chemical formulation containing TERGITOL 15-S-9 (1

169

wt. %) and equimolar amount of [P4 4 4 16]Br at high salinity of 9.25 wt.% NaCl, was prepared

170

in D2O instead of distilled water since it provides a better contrast between micelles and the

171

solvent. SANS diffractometer at the Dhruva reactor, BARC, Trombay was used for

172

characterization. During the experiment an incident neutron beam having mean wavelength

173

5.2Å and resolution of approximately 15% is passed through a monochromators of

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polycrystalline BeO. All the data were collected in the wave vector transfer (Q=4 π sin(θ/2)/

175

λ), where θ is the scattering angle recorded in the range of 0.02–0.24 Å-1. SANS experiment


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were carried out at room temperature. The resulting corrected intensities were normalized to

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absolute cross-sectional unit using standard procedures35.

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2.2.5 Equilibration time and stability tests using Turbiscan. In the present study, when

179

carrying out core flooding experiments, during oil drainage into the packed calcite core,

180

synthetic oil instead of crude oil was injected into the packed bed. In order to confirm that the

181

optimised chemical formulation prepared above forms WINSOR III phase with the synthetic

182

oil too, a synthetic oil/brine/chemical formulation system was prepared at that same 9.25 wt.

183

% salinity and WOR (2:1). Coalescence period required for formation of a clear and stable

184

WINSOR III phase was determined by passing light rays of 880 nm wavelength through the

185

ternary system using Turbiscan classic MA 2000 (Formulaction). The tests were carried out

186

at room temperature.

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2.2.6 Core flooding experiment. With an aim to carry out a comparative analysis of

188

percentage additional oil recovered during surfactant assisted EOR process, two chemical

189

formulations were prepared. One of them was the optimised chemical formulation

190

phosphonium based ionic liquid and nonionic surfactant at 9.25 wt. % salinity (achieved after

191

carrying out the above experiments) and the other one constituted of nonionic surfactant

192

alone at the same salinity. The two core flooding experiments were carried out at room

193

temperature. Following steps were followed during the core flooding experiments: - first the

194

core was tightly packed with washed and vacuum dried calcite powder which acts as a proxy

195

of carbonate reservoirs. The packed bed was saturated with 9.25 wt.% brine. A volume

196

balance method was used to calculate the porosity of the artificially prepared core. The

197

injection rate of brine(9.25wt.%) was then changed gradually and pressure drop across the

198

packed bed was recorded. Absolute permeability was then calculated using Darcy’s law. The

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wet packed calcite bed was flooded with synthetic at the rate of 1ml/minuntil no more water

200

was produced at the effluent end from the core holder. At this point, material balance was


of

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used to calculate Original oil in place (OOIP), initial oil (Soi) and water (Swi) saturations.

202

The calcite core bed was then allowed to remain for a day. After 24 hrs, brine (9.25 wt.%

203

NaCl) was flooded into the packed calcite core bed at the rate of 1ml/min. Approximately

204

1.25 pore volume (PV) of brine was injected into the coreholder before water breakthrough

205

occurred during the water flooding process. Henceforth same flow rate was maintained

206

during surfactant assisted EOR process and chase water flooding steps. Next during the

207

surfactant assisted EOR process, 1 PV of surfactant slug was injected into the core holder and

208

percentage of additional oil recovered (AOR%) was calculated from the effluent oil collected.

209

For waterflooding as well as surfactant assisted EOR process, pressure at the outlet end of the

210

coreholder varied from 200 - 400 psig. Hereafter 0.5 PV brine containing9.25 wt.% NaCl was

211

injected into the core during chase flooding before ending the displacement experiment.

212

3. RESULTS AND DISCUSSIONS

213

3.1.Synergism between surface active ionic liquid, [P4 4 4 16] Br and nonionic surfactant,

214

Tergitol 15-S-9 in distilled water. FIG. 1 represents surface tension v/s Log Concentration

215

of the different surfactants at room temperature. It indicates that upon addition of nonionic

216

surfactant in the binary chemical formulation, surface tension values as well as CMC values

217

of the chemical formulation reduced considerably. The CMC values for [P4

218

found to be 1.8321 mol/m3 which is consistent with the value of CMC (2 mol/m3) obtained

219

for the same SAIL by K. Cinku and B.Baysal36. Also the CMC of TERGITOL 15-S-9 was

220

found to be 0.0833 mol/m3, which match with the value of CMC obtained for the same non-

221

ionic surfactant (0.077 mol/m3) obtained by Sahu et al. in their work37. They studied

222

interactions between sodium dodecylbenzenesulfonate(SDBS) and three different nonionic

223

surfactants Tergitol 15-S-12, Tergitol 15-S-9 and Tergitol 15-S-737. A similar reduction in

224

surface tension as well as CMC on increasing the concentration of nonionic surfactant in the

225

optimised chemical formulations was observed by them. They attributed this to the


4 4 16]

Br was

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enveloping behaviour of nonionic surfactant on the charged head group of the anionic

227

surfactant resulting in a synergistic interaction among the surfactants37.

228

FIG.1: Plot of surface tension v/s surfactant concentration for TERGITOL 15-S-9 + [P4

229

4 4 16]

230

From the surface tension plot important thermodynamic parameters that govern the surface

231

activity of the surfactant solutions can be obtained. Equations used to calculate

232

thermodynamic parameters have been elaborately discussed in Supplementary Information

233

S1.Surface properties of the chemical formulation when the two surfactants are mixed in

234

different ratios in distilled water are enlisted in TABLE1. It can be seen that with increasing

235

mole fraction of TERGITOL 15-S-9 in the chemical formulation, the surface pressure value,

236

ΠCMC, increases indicating that the nonionic species reduce the surface tension values on

237

addition. Surface activity of the mixed surfactant system studied here has also been evaluated

238

in terms of surface excess concentration, Γ max. It is well established that higher the value of Γ

239

max

240

nonionic surfactant increases in the chemical formulation, its maximum surface excess

241

concentration Γ

242

molecule, Amin. Minimum area per molecule Amin provides information on the degree of

243

packing and the orientation of the adsorbed surfactant molecule. It is observed from TABLE1

244

that the Amin reduces as the concentration of nonionic surfactant in the optimised chemical

245

formulation goes on increasing. This indicates a more compact packing of the surfactant

246

molecules and increased surface activity. This might be attributed to reduction in repulsion of

247

the charged hydrophilic head of the ionic liquid molecules at the interfaces resulting in due to

248

the enveloping behaviour of nonionic species37,

249

micellisation, ΔGm, is an important thermodynamic parameter that gives an insight of the

250

micellisation taking place in the binary chemical formulation. Negative values of ΔGm

Br mixture in distilled water at 298.15 K.

higher the surface activity37. From TABLE1 it can be seen that as the concentration of

max,

increases. Further Γ

max

can be used to calculate minimum area per

38.

The standard free energy change of


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indicate that the chemical formulation favours micellisation. As the concentration of nonionic

252

surfactant increases in the binary chemical formulation, value of ΔGm decreases. Such a trend

253

has also been reported by other researchers37, 38. Such behaviour has been attributed to the

254

enveloping behaviour of nonionic surfactant on the charged hydrophilic heads of the ionic

255

surfactants37, 38.

256

TABLE 1: Surface properties of optimised chemical formulation containing

257

TERGITOL 15-S-9 &[P4 4 4 16] Br in different mole fractions in distilled water at 298.15

258

K.

259

The thermodynamic parameters evaluated in TABLE1 clearly indicate that the two

260

surfactants studied here, [P4 4 4 16] Br and TERGITOL 15-S-9 when mixed to form a chemical

261

formulation exhibit synergism by favouring micellisation and improving surface activity.

262

Although the existence of synergistic relation between the two surfactants is clearly evident,

263

in the following section investigation of synergism in quantitative terms has been done using

264

Rubingh’s theory34. Since surfactants are generally used above their CMC’s, surfactant

265

micellar structure may be a key to understanding and predicting synergism. Moreover micelle

266

formation is considered favourable in surfactant assisted EOR process. In order to determine

267

the compositional change in the mixed micelles as a result of interaction between the two

268

surfactants, micellisation behaviour of mixed surfactant species has been studied. Rubingh’s

269

theory uses the CMC values (data generated from surface tension measurements (FIG. 1)) in

270

determining the micellar mole fraction of nonionic surfactant, XM 1 in the mixed

271

micelle.Knowing micellar mole fraction XM 1 in the mixed micelle models, the molecular

272

interactions between two different surfactants in micelles can be determined in terms of the

273

interaction parameter, βM. A negative value of βMindicates that the two surfactants experience

274

less repulsion upon mixing than before mixing whereas a positive β value, greater repulsion

275

upon mixing than before mixing33.The interaction parameters for mixed micelle formation by


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two surfactants in their formulation, at an interface can be determined using equations (1) and

277

(2)33. 2

278

(XM 1 ) ln (αC12

M

M XM 1 C1 )

(1 ― XM1)2 ln [(1 ― α)C12 M

M

ln (αC12

M

M (1 ― XM 1 )C2 ]

(1)

=1

X1CM 1)

(2)

279

β =

280

M M Where, CM 1 , C2 and C12 are the CMCs of individual surfactants TERGITOL 15-S-9 and [P4

281

4 4 16]

282

nonionic surfactant in the total surfactant in the mixed micelle; and βM is a parameter that

283

measures the nature and extent of the interaction between the molecules of the surfactant,

284

TERGITOL 15-S-9 and [P4 4 4 16] Br in the mixed micelle in aqueous solution. The value of

285

XM 1 was obtained on iteratively solving Eq. (1),which may be then used to determine the

286

M interaction parameter,βM. The values of micellar composition XM 1 and interaction parameterβ

287

for binary chemical formulation s having different, 𝛼[𝑃4 4 4 16 𝐵𝑟] have been listed in TABLE2.

288

Since the values of interaction parameter is negative for all the binary chemical formulation s.

289

Hence we conclude that the mixture of nonionic surfactant TERGITOL 15-S-9 and ionic

290

liquid [P4 4 4 16]Br exhibit synergism in mixed micelle formation in aqueous medium.

291

TABLE2: Micellar properties of binary chemical formulation containing nonionic

292

surfactant TERGITOL 15-S-9 and ionic liquid [P4 4 4 16] Br at different molar ratios.

293

According to Rosen et al. when maximum reduction in CMC is desirable then at that time

294

optimised chemical formulations having largest negative βMvalues should be selected33. From

295

TABLE2 it is clearly evident that when the two surfactants are mixed in an equimolar ratio,

296

the interaction parameter has the largest negative value. It is due to this reason that henceforth

297

in the present work, chemical formulation having equimolar ratio of the two surfactants have

298

been investigated for their potential application as surfactant slug for EOR purpose.

(1 ― XM1)2

Br, and their mixture at a given value of α, respectively; XM 1 is the mole fraction of


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299

3.2 Dynamic light scattering (DLS). Changes in size of the micellar structure in the

300

optimised chemical formulation at varying salinities of aqueous medium were studied from

301

DLS measurements. In this step salinity of the optimised chemical formulation was varied

302

from 0 to 12.5 wt.% NaCl. Typical plot of % intensity v/s size distribution of the micelles

303

(d.nm) in the optimised chemical formulation at varying salinities is shown in FIG.2. It is

304

observed that size of micelles increase gradually as salinity increases. It has also been found

305

that the distribution of the dispersed micelle size is narrower for chemical formulations

306

around optimal salinity. As a result more oil is solubilised in micelles around optimal salinity

307

leading to higher oil recovery. The Z-average diameter depends on intensity % and is a good

308

indicator for presence of larger particles. In this study it has been found that salinity of the

309

surfactant solution has a profound effect on the Z-average diameter of the micelles. Z-average

310

diameter of the optimised chemical formulation were found to be 8.559, 16.06, 24.64, 32.03,

311

25.38, 21.77, 27.47 and 64.86 d.nm at 0, 5, 7, 8, 9, 10, 10.5 and 12.5 wt.% salinity

312

respectively. Similar effect of addition of NaCl salt on the size of micellar aggregates formed

313

in mixture of nonionic (polyoxyethylene dodecyl ethers) and anionic surfactant (sodium

314

dodecyl sulphate) has been reported by Patel et al.39. They had concluded that presence of

315

NaCl instigates increased intake of charged ionic surfactants into the micellar core, thus

316

facilitating accumulation of surfactant molecules and leading to an increase in the micellar

317

size39. At high salinities (>10.5 wt.% NaCl) two peaks are observed which correspond to

318

presence of micelles with widely differing average sizes. This behaviour might be attributed

319

to the presence of loosely bound clusters of micelles formed at higher salinities.

320

FIG. 2: Effect of salinity on the size of micellar aggregates formed in the optimised

321

chemical formulation containing 1 wt.% TERGITOL 15-S-9 and equimolar amount of

322

[P4 4 4 16] Br.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

323

3.3 Phase behaviour scan and determination of optimal salinity. Phase behaviour of an

324

oil-aqueous surfactant system is strongly affected by the salinity of the surfactant solution. It

325

is well known that increasing the salinity of brine reduces solubility of the surfactant present

326

in it and the surfactant eventually moves from the aqueous phase into the oil phase3, 4. In

327

other words as salinity of the surfactant solution increases, the phase behaviour of the oil-

328

surfactant system shifts from WINSOR I phase (oil in water microemulsion) to WINSOR II

329

phase(water in oil microemulsion). In WINSOR I phase, the lower phase microemulsion

330

coexists with upper excess oil phase which is free of surfactant. In WINSOR II phase, the

331

upper phase microemulsion coexists with lower clear, excess aqueous phase that is free of

332

any surfactant. However at some intermediate range of salinity a WINSOR III phase is

333

formed, wherein a middle phase microemulsion coexists with excess oil as well as excess

334

aqueous phase. This layer of middle phase microemulsion contains most of the surfactant

335

present in the system along with water and oil. Formation of WINSOR III phase is favourable

336

for EOR since it is an ideal situation when ultralow IFT is reached3, 4. In this work, phase

337

behaviour of crude oil – optimised chemical formulation at varying salinities was examined.

338

Thereby salinities of the optimised chemical formulation containing 1 wt. % TERGITOL 15-

339

S-9 and equimolar amount of [P4 4 4 16] Br was varied from 0 - 20wt.% NaCl. Phase behaviour

340

tests were performed for crude oil – optimised chemical formulation systems mixed in such a

341

way that WOR was 2:1. Photos of phase behaviour scan tests are shown in FIG.3. Pictures

342

were taken a week after the system achieved stability and no further change was observed.

343

FIG. 3: Phase behaviour of crude oil with optimised chemical formulation (1 wt. %

344

TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br) at different salinities and at

345

room temperature.

346

After visual observation it can be concluded from FIG. 3, that for salinities 0 -7.5 wt. %

347

NaCl, presence of WINSOR I phase can be marked. In this range as salinity increases the


Page 14 of 39

Page 15 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

348

lowers surfactant solution emulsifies more and more oil (darker colour is observed). Within

349

the salinity range 8 wt.% to 9.5wt.%, a clear water phase starts appearing at the bottom.

350

Presence of a WINSOR III phase was found in this salinity range. At higher salinities, 15 wt.

351

% to 20 wt. % the lower water phase becomes clear indicating formation of WINSOR II

352

phase.

353

In a Winsor III system there exists a bicontinuous microemulsion consisting of both water

354

and oil solubilised in it. The volume of oil and water solubilised in the microemulsion phase

355

is an important tool used in determining the optimal salinity of the injected surfactant slug.

356

Healy expressed the amount of oil and water solubilised by a surfactant in a microemulsion in

357

terms of solubilisation parameters (Vo/Vs and Vw/Vs)36. Vo, Vw and Vs are volume of oil,

358

water and surfactant solubilised present in the microemulsion phase respectively. Healy

359

assumed that all the surfactant in the system is confined to the microemulsion phase and not

360

in the excess oil or excess water phase40.As salinity increases, solubilisation parameter of the

361

component in the excess phase increases or decreases. However Vo/Vs is equal to Vw/Vs, at

362

some salinity in the bicontinuous microemulsion region. This salinity at which the

363

microemulsion contains equal volume of oil and water is the optimal salinity of the phase

364

behaviour and leads to high oil recovery. In the present reported work, optimal salinity

365

determination for the optimised chemical system containing 1 wt. % TERGITOL 15-S-9 and

366

equimolar amount of [P4 4 4 16] Br has been performed following the procedure mentioned in

367

the section 2.2.3. The salinity of the system had been varied 1wt.% to 10.5 wt.%. FIG. 4

368

displays plot of solubilisation parameter as a function of salinity for the optimised chemical

369

system studied in the present work. The point at which the two functions meet (intersection

370

point) is the point of optimal salinity i.e.9.28wt.%. Hence we conclude that the optimised

371

chemical system studied here has a very high optimal salinity. Such high optimal salinity


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

372

surfactant systems are suitable for flooding into high salinity reservoirs which are typical for

373

carbonate reservoirs.

374

FIG. 4: Optimal salinity at room temperature for the optimised chemical system

375

containing 1 wt.% TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br.

376

C. Huh was able to demonstrate that the solubilisation parameters and the interfacial tension

377

are inversely proportional to each other41. Moreover at optimal salinity when both the

378

solubilisation parameters are equal, a more simplified version of Huh’s calculation can be

379

used to determine IFT of the system. At optimal salinity Huh’s calculation led to the

380

equation, γ = C1 / SP*2, where γ is the IFT, SP* is the solubilisation parameter at optimal

381

salinity and C1 is a constant whose value is 0.30 ±0.05 when γ is expressed as mN/m41. The

382

equation, however, is not valid at salinities other than the optimal salinity. Using Huh’s

383

correlation IFT at the optimal salinity was found to be 2.35 *10-2 mN/m. In our previous

384

work, IFT between water and crude oil was found to be 20mN/m32. Here it can be seen that

385

addition of equimolar amount of phosphonium based SAIL and non-ionic mixture at optimal

386

salinity resulted in tremendous reduction in IFT. According to Green et al., at optimal salinity

387

solubilisation parameter must be on the order of 10 or greater in order to obtain ultralow IFT

388

suitable for EOR applications3. Though this is not the case here, reduction in IFT is quite

389

significant.

390

In the next step, comparison of the phase behaviour of individual SAIL and nonionic

391

surfactant with the optimised chemical formulation in the same ternary system and at same

392

salinity has been carried out. An image showing phase behaviour results has been presented

393

in FIG. 5. In FIG. 5(a), it can be seen that before addition of crude oil, the aqueous phase

394

(salinity 9.25 wt. %) containing SAIL(marked as P in the figure)is turbid and might contain

395

liquid crystalline structure. However aqueous solutions (salinity 9.25 wt. %) of the optimised

396

chemical formulation (marked as CF in the figure) and nonionic surfactant (marked as T in


Page 16 of 39

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Energy & Fuels

397

the figure) is clear and stable. According to J. Sheng, injection of a single phase solution is

398

important because injectable solution containing liquid crystals, precipitates or those forming

399

second liquid can lead to nonuniform distribution and different mobilities of coexisting

400

phases resulting in lower oil recovery4.After that crude oil has been added to each of the vials

401

so that WOR = 2:1. From FIG. 5(b), we observe that the individual SAIL and nonioinic

402

surfactant behave differently as compared to the optimised chemical formulation. In case of

403

ternary system containing individual nonionic surfactant (1.8 wt. %), presence of WINSOR I

404

phase indicates an oil in water microemulsion in equilibrium with the excess oil phase. In

405

case of individual SAIL, no colour change is observed in the aqueous phase which implies

406

presence of less oil-in-water microemulsions. However a clear middle phase microemulsion

407

(WINSOR III) can be seen in the ternary system containing the optimised chemical

408

formulation studied here. This study further proves efficiency of the optimised chemical

409

formulation as compared to individual SAIL and non-ionic surfactant in forming a WINSOR

410

III phase with crude oil at high salinity.

411

Fig. 5: Comparison of phase behaviour of individual SAIL (P), nonionic surfactant (T)

412

and optimised chemical formulation (CF) containing equimolar amount of TERGITOL

413

15-S-9 and equimolar amount of [P4 4 4 16] Br. (a) Aqueous solutions (9.25 wt. % salinity)

414

of individual SAIL( 1.8 wt.%), individual nonionic surfactant (1.8 wt.%) and optimised

415

chemical formulation (total concentration 1.8 wt.%)

416

crude oil and injectable surfactant solution at 9.25 wt. % salinity (WOR=2:1).

417

3.4 Small angle neutron scattering. Small angle neutron scattering is a diffraction

418

experiment, which involves scattering of a monochromatic beam of neutrons from the sample

419

and thus measuring the scattered neutron intensity as a function of the scattering angle. In

420

SANS experiments, one measures the differential scattering cross section per unit volume of

421

the sample by𝑑Σ 𝑑Ω as a function of wave vector transfer function Q. Data generated from


(b) Ternary system containing

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 39

422

the SANS experiment can then be analysed either by direct modelling of the structure with an

423

appropriate form and comparison of the calculated scattering curve for the model with the

424

experimental data or model-independent indirect Fourier transformation approach. SANS

425

experiments were carried out in order to determine the structure of the mixed micelles in the

426

optimised chemical formulation containing TERGITOL 15-S-9 (1 wt.%) and equimolar

427

amount of [P4 4 4 16]Br in 9.25 wt.% brine. FIG.6 shows the SANS data from the optimised

428

chemical formulation at 30°C. High intensity scattering and absence of peak from the

429

surfactant solution is an indication of the presence of large micellar structure. The semimajor

430

axis (Ra) and the semiminor axis (Rb) are the parameters used in analysing the SANS data.

431

The prolate model (Rb< Ra) fits the experimental data, which suggests that the mixed micellar

432

shape is prolate ellipsoidal or needle like. From the data generated in SANS experiment,

433

values of semimajor axis and the semiminor axis are 14.6 nm and 2 nm respectively. These

434

values are well in agreement with the hydrodynamic diameter of micelles (21.77 nm)

435

retrieved from DLS measurements in optimal salinity range. As discussed in section 3.2 as

436

the salinity of surfactant solution increases, increase in the hydrodynamic diameter of the

437

micelles is observed suggesting an increase in size of the micelles. The axial ratio (Ra/Rb) for

438

the prolate ellipsoidal mixed micellar shape is greater than 4. Similar results were reported by

439

Varade et al. they suggested that such a change in size might be attributed to decrease of

440

intermicellar interaction and growth of the micelles. They elucidated that a prolate ellipsoidal

441

structure of the micelles existed at high concentration of NaCl42.

442

cylindrical micelles enhance the hydrocarbon solubilisation manyfold. Tornblom et al. in

443

their study found that aggregation behaviour of dilute surfactant solution containing rodlike

444

micelles (axial ratio > 4) changes upon oil solubilisation43. They found that solubilisation of

445

small amounts of hydrocarbons results in growth of the micelles. However increasing

446

addition of hydrocarbon solubilisates causes a decrease in the aggregate size39. Joshi et al.


The ellipsoidal or

Page 19 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

447

studied the changes in micellar structure of cationic alkyltrimethylammonium bromide

448

(CnTAB) surfactants (n=12, 14, 16) in aqueous solution on the addition of hydrocarbon by

449

small-angle neutron scattering (SANS)44. They found that the size and aggregation number of

450

the prolate ellipsoidal shaped micelles increase on hydrocarbon solubilisation, and this effect

451

is more pronounced for the larger sizes of the micelles having longer chain lengths40. In the

452

present study it was also found that with water-to-crude oil ratio equal to 2, presence of

453

middle microemulsion phase was observed. However with water-to-crude oil ratio equal to 1,

454

no middle phase microemulsion phase was present. This might be attributed to growth of the

455

prolate ellipsoidal micellar structure into larger micelles thus solubilising more oil and

456

forming a WINSOR III phase at higher water-to-oil ratios.

457

FIG.6: SANS distribution from optimised chemical formulation containing TERGITOL

458

15-S-9 (1 wt. %) and equimolar amount of [P4 4 4 16]Br in 9.25 wt. % brine.

459

3.5. Equilibration time and quality of bicontinuous microemulsion formed in

460

oil/brine/optimised chemical formulation system. Time required by an oil/brine/surfactant

461

system to form a stable middle phase microemulsion (no further changes in its volume is

462

observed) is called the equilibration time. It is desirable that the phase behaviour samples

463

have fast equilibration time, preferable less than 24 hours. Longer equilibration times imply

464

formation of middle phase microemulsion with high viscosity, formation of a gel or a liquid

465

crystal structure3, 4. Presence of such viscous structures can reduce the oil recovery rates due

466

to clogging of rock pores. In contrast fast equilibration time is a good indicator of low

467

microemulsion viscosity. Not only fast equilibration time but it is also desirable to keep phase

468

behaviour between oil bank and surfactant slug in Winsor Type-III (low interfacial tension)

469

as long as possible3, 4.

470

In the present work, stability of the phase behaviour sample containing the optimised

471

chemical formulation - synthetic oil - brine at 9.25 wt. % salinity was examined by scanning


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

472

the samples in a Turbiscan for 6 days. The profile related to light transmission (%) of the

473

sample is shown in FIG.7.

474

FIG.7: Transmission profile of phase behaviour sample containing optimised chemical

475

formulation- synthetic oil and brine (at optimal salinity – 9.25 wt.%)

476

As observed from FIG.7 the equilibration time of microemulsion is less than 24 hrs which

477

means that the system rapidly coalesced to form a middle phase microemulsion. Presence of

478

three distinct phases can be seen in the sample tube. Also the middle phase microemulsion

479

remained stable for more than 7 days. Thus we can conclude that the given optimised

480

optimised chemical system forms a WINSOR III phase with synthetic oil at optimal salinity.

481

The small equilibration time and stable bicontinuous microemulsion at optimal salinity for

482

the chosen system elucidate the minimal possibility of formation of gels, liquid crystals

483

which might lower the percentage of oil recovery.

484

3.6 Core Flooding Experiments: Validation of Chemical Formulation. Two core flooding

485

experiments were performed whose details & results are summarized in TABLE 3. Core

486

flooding experiment 1 was conducted to study the performance of nonionic surfactant

487

TERGITOL 15-S-9 to recover oil from artificially prepared carbonate cores oil during

488

surfactant assisted EOR process at high salinity. In experiment 1, after waterflooding 1.25 PV

489

of 9.25 wt.% brine during the secondary oil process only 43.75 % of OOIP was recovered. In

490

the next step 1 PV of surfactant slug containing 1.8wt.% TERGITOL 15-S-9 in 9.25 wt.%

491

brine was injected into the core at the same rate. Only 4.17% of OOIP was recovered during

492

this step. FIG.8 shows the water cut, oil recovery factor and total oil recovered versus pore

493

volume injected during different injection stages of experiment 1.Bataweel in his study had

494

suggested that a sharp increase in oil recovery on the onset of chemical injection indicates

495

favourable oil displacement45. As observed in FIG.8, a discontinuous oil production indicates


Page 20 of 39

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Energy & Fuels

496

early water breakthrough and low oil recovery. The additional oil recovered during surfactant

497

assisted EOR process with the aforementioned chemical slug was 7.28 %.

498

FIG.8: Core flood history for experiment 1 for slug having 1.8wt.% TERGITOL 15-S-9

499

in 9.25 wt.% brine.

500

In core flooding experiment 2, the artificially prepared core with residual oil after

501

waterflooding was flooded with 1 PV of formulation optimised in the present work viz., the

502

optimised chemical formulation containing TERGITOL 15-S-9 and equimolar amount of [P4

503

4 4 16]Br

504

recovered versus pore volume injected during different injection stages of experiment 2. It

505

can be seen that oil production does not cease after waterflooding and tailing of oil

506

production occurs at a very later stage. 10.29% of OOIP was recovered during surfactant

507

assisted EOR process with the optimised chemical formulation. An increase in oil recovery

508

might be attributed to large size mixed micelles in the injected solution, formation of a

509

WINSOR III phase (lowering in IFT) at optimal salinity, lesser equilibration time of

510

microemulsion and favourable growth of prolate ellipsoidal shaped micelle upon addition of

511

hydrocarbon solubilizates. This recovery was better than oil recovery with the single nonionic

512

surfactant system. The additional oil recovered during surfactant assisted EOR process with

513

the optimised chemical slug at was16.68 %. Fig. 10 shows the additional oil recovered

514

during surfactant assisted EOR process for both the surfactant slugs used in this study.

515

FIG.9: Core flood history for experiment 2 for slug having optimised chemical

516

formulation of 1 wt.% TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16]Br in 9.25

517

wt.% brine.

518

Fig. 10: Additional oil recovered during surfactant assisted EOR process of artificially

519

prepared carbonate cores with two different surfactant slugs.

in 9.25 wt.% brine. FIG.9 shows the water cut, oil recovery factor and total oil


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

520

TABLE 3: Summary of core flooding experiments

521

4. CONCLUSION. In this work, chemical formulation containing phosphonium based

522

surface active ionic liquid (Tributylhexadecylphosphonium bromide) and nonionic surfactant

523

(TERGITOL 15-S-9) at varying molar ratios has been prepared. Composition of the mixed

524

micelle and interaction parameter between phosphonium based SAIL and nonionic surfactant

525

has been determined using Rubingh’s theory A negative interaction parameter obtained

526

thereby indicates synergism (attraction) between the two species when mixed in equimolar

527

ratio. In order to get a better insight of the improved surface activity a study of

528

thermodynamic parameters has been performed. DLS technique has been used to determine

529

the size of the mixed micelles in the optimised chemical formulation at varying salinity. It is

530

observed that size of micelles increase gradually as salinity increases which results in

531

solubilising more oil. SANS characterization technique has been used to determine shape of

532

the mixed micelles formed in the optimised chemical formulation that is injected in the core.

533

SANS results suggests that the mixed micellar shape is prolate ellipsoidal. It is known that

534

ellipsoidal or cylindrical micelles enhance the hydrocarbon solubilization manyfold. In order

535

to investigate the effectiveness of the proposed EOR method, phase behaviour of the ternary

536

system containing crude oil/water /optimised chemical formulation has been studied at

537

varying salinities. A clear presence of WINSOR III phase was observed at higher salinities.

538

The ternary system has optimal salinity as high as 9.28 wt. % surfactant thus making the

539

optimised chemical formulation highly suitable for surfactant assisted EOR process in highly

540

saline carbonate formations. Absence of middle phase microemulsion in case of individual

541

oil/brine/ SAIL or nonionic surfactant ternary systems further elucidated the efficiency of

542

optimised chemical formulation under high salinity conditions. Moreover the optimised

543

chemical formulation formed a WINSOR III phase microemulsion with synthetic oil used in

544

this study, taking lesser equilibration time and displaying prolonged stability. The optimised


Page 22 of 39

Page 23 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

545

formulation demonstrated high residual oil recovery in the lab-scale core flood experiments.

546

Additional oil recovered during surfactant assisted EOR process during two core flooding

547

experiment was 16.68%for the optimised chemical formulation and 7.28% for the other

548

containing individual nonionic surfactant Thus it can be concluded that the chemical

549

formulation containing phosphonium based surface active ionic liquid and nonionic

550

surfactant in equimolar ratio can be a good candidate for the chemical EOR processes even

551

under harsh conditions of salinity.”

552 553

ACKNOWLEDGEMENT

554

The authors would like to thank Dr. Vinod K. Aswal, Solid State Physics Division

555

(SSPD), BARC, Mumbai, INDIA for allowing us to use SANS facility.

556 557

REFERENCES

558

[1] Islam, M. R. Energy Sources1999, 21 (1–2), 97–111.

559

[2] Lake, L. W.; Venuto, P. B. Oilf. Rev.1992, 88 (17), 62–67.

560

[3] Green, D. W.; Willhite, G. P. Enhanced Oil Recovery; SPE Textbook Series, Vol. 6;

561

Society of Petroleum Engineers (SPE): Richardson, TX, 1998; pp. 239-289.

562

[4] Sheng, J. J. Modern Chemical Enhanced Oil Recovery Theory and Practice; Gulf

563

Professional Pub.: Amsterdam, Netherlands, 2011; 239-335.

564

[5]

565

Brazilian J. Pet. Gas2008, 2 (2), 83–95.

566

[6] Romero-zerón, L. In Introduction to Enhanced Oil Recovery (EOR) Processes and

567

Bioremediation of Oil-Contaminated Sites; Romero-zerón, L., Ed.; IntechOpen, 2012; pp. 1–

568

43.

Gurgel, A.; Moura, M. C. P. A.; Dantas, T. N. C.; Neto, E. L. B.; Neto, A. A. D.


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569

[7] Seethepalli, A.; Adibhatla, B.; Mohanty, K. SPE J.2004, 9 (4), 17–21.

570

[8] Ahmadi, M. A.; Shadizadeh, S. R. Energy Fuels2012, 26 (8), 4655–4663.

571

[9] Ahmadi, M. A.; Zendehboudi, S.; Shafiei, A.; James, L. Ind. Eng. Chem. Res.2012, 51

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(29), 9894–9905.

573

[10] Shahri, M. P.; Shadizadeh, S. R.; Jamialahmadi, M. J. Japan Pet. Inst.2012, 55 (1), 27–

574

32.

575

[11] Freemantle, M. An Introduction to Ionic Liquids; Royal Society of Chemistry:

576

Cambridge, U.K., 2010; pp 1−3.

577

[12] Rogers, R. D.; Seddon, K. R. Ionic LiquidssSolvents of the Future. Science 2003, 302,

578

792–793.

579

[13] Kadokawa, Jun-ichi. Ionic Liquids-New Aspects for the Future. InTech, 2013.

580

[14] Weingärtner, H. Angew. Chemie - Int. Ed.2008, 47 (4), 654–670.

581

[15] Murillo-Hernández, A. A.; Aburto, J. In Ionic Liquids: Applications and Perspectives;

582

Kokorin, A., Eds.; InTech: Rijeka, Croatia, 2011; pp. 439−458.

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629

338–347.

630

[45] Bataweel, M. A. Enhanced Oil Recovery in High Salinity High Temperature Reservoir

631

by Chemical Flooding. 2012 (Doctoral dissertation, Texas A & M University).

632 633 634

FIGURE CAPTIONS

635


636

4 4 16]

637


638

chemicalformulation containing 1 wt.% TERGITOL 15-S-9 and equimolar amount of

639

[P4 4 4 16] Br.



Page 26 of 39

Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

640

FIG. 3: Phase behaviour of crude oil with optimised chemicalformulation (1 wt.%

641


642

room temperature.

643


644

containing 1 wt. % TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br.

645

Fig. 5: Comparison of phase behaviour of individual SAIL (P), nonionic surfactant (T)

646


647


648


649


650

crude oil and injectable surfactant solution at 9.25 wt. % salinity(WOR=2:1).

651

FIG. 6: SANS distribution from optimised chemical formulation containing

652

TERGITOL 15-S-9 (1 wt.%) and equimolar amount of [P4 4 4 16]Br in 9.25 wt.% brine.

653


654

formulation- synthetic oil and brine (at 9.25 wt. % salinity ).

655

FIG. 8: Core flood history for experiment 1 for slug having 1.8 wt.% TERGITOL 15-S-

656

9 in 9.25 wt.% brine.

657

FIG. 9: Core flood history for experiment 2 for slug having optimised chemical

658

formulation of 1 wt.% TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br in 9.25

659

wt.% brine.

660


661


662



Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

663 664


665

4 4 16]



Page 28 of 39

Page 29 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

666 667


668

chemical formulation containing 1 wt.% TERGITOL 15-S-9 and equimolar amount of

669

[P4 4 4 16] Br.

670 671

FIG. 3: Phase behaviour of crude oil with optimised chemical formulation (1 wt.%

672


673

room temperature.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

674 675


676

containing 1 wt.% TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br.

677 678 679 680 681 682


Page 30 of 39

Page 31 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

683 684

Fig. 5: Comparison of phase behaviour of individual SAIL(P), nonionic surfactant (T)

685


686


687


688


689

crude oil and injectable surfactant solution at 9.25 wt. % salinity (WOR=2:1).



Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

690 691

FIG. 6: SANS distribution from optimised chemical formulation containing

692

TERGITOL 15-S-9 (1 wt.%) and equimolar amount of [P4 4 4 16]Br in 9.25 wt.% brine.


Page 32 of 39

Page 33 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

693 694


695

formulation/ synthetic oil / brine (at optimal salinity – 9.25 wt.%)


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

696 697

FIG. 8: Core flood history for experiment 1 for slug having 1.8 wt.% TERGITOL 15-S-

698

9 in 9.25 wt.% brine.


Page 34 of 39

Page 35 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

699 700

FIG. 9: Core flood history for experiment 2 for slug having optimised chemical

701

formulation of 1 wt.% TERGITOL 15-S-9 and equimolar amount of [P4 4 4 16] Br in 9.25

702

wt.% brine.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

703 704


705


706 707 708 709 710 711 712 713


Page 36 of 39

Page 37 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

714 715

TABLE CAPTIONS

716


717

TERGITOL 15-S-9 & [P4 4 4 16] Br in different mole fractions in distilled water at 298.15

718

K.

719

TABLE 2: Micellar properties of binary chemical formulation containing nonionic

720

surfactant TERGITOL 15-S-9 and ionic liquid [P4 4 4 16] Br at different molar ratios.

721

TABLE 3: Summary of core flooding experiments

722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 39

738


739

TERGITOL 15-S-9 & [P4 4 4 16] Br in different mole fractions in distilled water at 298.15

740

K. Mole Mole fraction of fraction

of Tergitol 15-S-9,

[P4 4 4 16] Br, 𝜶𝑷𝟒 𝟒 𝟒 𝟏𝟔 𝑩𝒓

CMCExperimental γCMC

ΠCMC

Γ max

Amin

ΔGm

(mol/m3)

(mN/m) (mN/m) (µmol/m2) (Å2)

(kJ/mol)

-6.16

𝜶𝑻𝒆𝒓𝒈𝒊𝒕𝒐𝒍 𝟏𝟓 ― 𝑺 ― 𝟗

0

1

0.0833

30.9

39.4

1.7823

93.15

0.2

0.2

0.0787

32.8

37.2

0.5748

288.85 -6.3

0.5

0.5

0.0892

34.8

35.4

0.4844

342.81 -5.99

0.8

0.2

0.3101

37.2

33

0.3770

440.49 -2.9

1

0

1.8321

37.4

32.7

0.4296

386.55 1.5

741 742 743

TABLE 2: Micellar properties of binary chemical formulation containing nonionic

744

surfactant TERGITOL 15-S-9 and ionic liquid [P4 4 4 16] Br at different molar ratios. Mole fraction of CMCExperimental

XM 1

βM

Condition

[P4 4 4 16] Br, 1-α

(mol/m3)

0

0.0833

0.2

0.0787

0.839969

-4.1465

Yes

0.5

0.0892

0.733723345

-4.4440

Yes

0.8

0.3101

0.796221

-0.6428

Yes

1

1.8321

for

synergism satisfied?

745 746


Page 39 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

747

Energy & Fuels

TABLE 3: Summary of core flooding experiments Core flooding expt. 1 Core flooding expt. 2 Porosity of packed bed (%)

35.6

38.16

Permeability (mD)

692.54

671.13

Pore volume (PV) (ml)

58

62.04

Original oil in place (OOIP)(ml)

48

17

Initial oil Saturation (Soi)

82.76

27.40

43.75

38.24

after 57.29

61.76

Oil recovered during waterflooding (% OOIP) Residual

oil

saturation

waterflooding (Sor) Binary 1.8

surfactant

mixture

wt% containing TERGITOL 15-S-9 (1

Design of surfactant slug injected TERGITOL 15-S-9

wt. %) and equimolar amount of

during EOR in 9.25 wt% brine

[P4 4 4 16]Br in 9.25 wt. % brine. Additional oil recovered during 7.28 % surfactant flooding 748 749


16.68 %

Potential of a novel surfactant slug in recovering ... - ACS Publications

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