Use of organoclay as a stabilizer for water-in-oil emulsions under high-temperature high-salinity conditions

Accepted Manuscript Use of organoclay as a stabilizer for water-in-oil emulsions under high-temperature high-salinity conditions Abdelhalim I.A. Mohamed, Ibnelwaleed A. Hussein, Abdullah S. Sultan, Ghaithan A. Al-Muntasheri PII:

S0920-4105(17)30862-8

DOI:

10.1016/j.petrol.2017.10.077

Reference:

PETROL 4401

To appear in:

Journal of Petroleum Science and Engineering

Received Date: 23 February 2017 Revised Date:

27 August 2017

Accepted Date: 26 October 2017

Please cite this article as: Mohamed, A.I.A., Hussein, I.A., Sultan, A.S., Al-Muntasheri, G.A., Use of organoclay as a stabilizer for water-in-oil emulsions under high-temperature high-salinity conditions, Journal of Petroleum Science and Engineering (2017), doi: 10.1016/j.petrol.2017.10.077. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Formation Brine

Emulsion

Diesel

100 90

RI PT

70

600 ppm Cloisite 15A 30 % Hydrocarbon phase 70 % Formation brine o o 120 C (248 F)

60 50 40 30

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Phase volume, %

80

20

0 0

4

8

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12 20 30 46 78 98 120 146 160 190 218 240 266 305

Time, minutes

AC C

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Phase behavior for the emulsion system, 600 ppm Cloisite 15A at 120oC (248oF)

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1 2 3 4 5

Use of Organoclay as a Stabilizer for Water-in-oil Emulsions under HighTemperature High-Salinity Conditions Abdelhalim I.A. Mohamed1, Ibnelwaleed A. Hussein2*, Abdullah S. Sultan 3, 4, Ghaithan A. AlMuntasheri5 1

Petroleum Engineering Department, University of Wyoming, Laramie, WY 82071, USA Gas Processing Center, College of Engineering, Qatar University, PO Box 2713, Doha, Qatar 3 Petroleum Engineering Department, College of Petroleum & Geosciences, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia 4 Center for Integrative Petroleum Research, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia 5 EXPEC Advanced Research Center, Saudi Aramco, Dhahran 31311, PO Box 62, Saudi Arabia

13

Abstract

14

Emulsified polymer gels are used in near wellbore applications for water shut-off treatment to

15

control produced water in oil and gas reservoirs. The emulsified gels are expected to separate

16

into oil and water phases at reservoir conditions. The stability of emulsified gels, as measured by

17

the separation time, is influenced by the emulsifier type, salinity of the mixing water, and

18

temperature. Although a range of commercial surfactants is used as emulsifiers, their toxicity and

19

high cost are significant drawbacks. Nowadays, various nanomaterials have been developed for

20

quite a few applications in different fields of endeavors, due to their low cost, availability, high

21

surface area, and most prominently environmental-friendly. The proposed alternative organoclay

22

(OC) has been shown to enhance emulsion stability with increasing OC concentration. The total

23

separated volume reduced by a factor of 4.8, due to the decrease in the interfacial tension, when

24

the OC (Cloisite 15A) concentration was increased from 600 to 1000 ppm. The stability of an

25

emulsion prepared using a 6 vol.% polyethylene glycol-2 ether (PEG-2E) enhanced by a factor

26

of ~ 2 when the concentration of Cloisite 15A was increased from 300 to 1000 ppm. The

27

separation time can be controlled by controlling the OC dose, depending on the application. A

28

chelating agent can be used to reduce the effect of salts on emulsion stability. The OC materials

29

have the potential to be used as cost-effective emulsifiers for PAM/PEI at high temperature

30

(>100oC) and high salinity (>200,000 ppm). The OC materials can be used as standalone

31

emulsifiers or co-surfactants to enhance the performance of commercial emulsifiers.

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Keywords: W/O emulsion, Emulsion stability, Organoclay, High-temperature High-salinity,

33

Chelating agent

34

*Corresponding Author: [email protected]

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35 36 37

Introduction

38

fluids (Greaves et al., 2009), polymerization (Anderson and Daniels, 2003), paints (Osemeahon,

39

2011), and the food production (Friberg, 2003; McClements, 2009). Also, emulsification

40

technology is widely applied in oilfields; Emulsification technique was introduced to the oil

41

industry with the use of emulsified acids in 1933. Emulsified acids were formulated to address

42

the corrosion problems rather than improve well stimulation (De Groote, 1933). Consequently,

43

many researchers studied this technique comprehensively to further understand the advantages

44

and disadvantages of emulsified acids (Crenshaw and Flippen 1968; Sayed et al. 2013).

45

Furthermore, their flow in porous media showed a non-Newtonian characteristic, in specific the

46

shear thinning feature which makes them appealing from an operation point of view (Al-Yaari et

47

al. 2014b; Mandal and Bera, 2015). Recently, the use of the emulsification technique gained

48

momentum in the oil industry with the identification of new applications. Emulsification is used

49

in drilling fluid formulations (Lawhon et al. 1967; Patel, 1999; Ebeltoft et al. 2001; Habibnia et

50

al. 2010), well stimulation treatment (Al-Mutairi et al. 2008; Sayed et al. 2013), enhanced oil

51

recovery (Mandal et al. 2010), improved well productivity via the removal of asphaltene deposits

52

(Fattah and Near, El-Din 2010), and drag reduction in multiphase flow (Al-Yaari et al. 2014b).

53

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Emulsions are commonly used in pharmaceuticals (Nielloud and Marti-Mestres, 2000), hydraulic

Oilfield Water Shut-off

55

Water production in gas and oil reservoirs is a serious problem. The excess water stream

56

produced alongside hydrocarbons has environmental, technical and economic implications

57

(Ahmed et al. 2010; Mirzaei-Paiaman et al. 2010; Mohamed, 2014). One of the methods to

58

handle this problem is using relative permeability modifier fluid (RPM), which is effective in

59

treating reservoirs with multi-layers and coning problems (Liang et al. 1993; Stavland et al.,

60

1998; Botermans et al. 2001). Treatment based on RPM fluids are widely used in the field

61

(Schneider and Owens, 1982; Sparlin 1976; Zaitoun 1999; Liang et al. 1992, Kalfayan and

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Dawson 2004). Polymer gels are commonly used for water shut-off. However, their use leads to

63

a considerable reduction in hydrocarbons flow, together with the water. Thus, zonal-isolation

64

was proposed to optimally isolate the water and hydrocarbons layers prior the treatment

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injection, however, beside the associated high-cost, also if crossflow between layers exists, this

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effort is rendered ineffective. Thus, a selective shut-off technique was developed to handle the

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crossflow without the need for isolation means. Hence, a new oilfields application of the

68

emulsification technique is proposed recently, that is emulsified gels. In a patent, Stavland and

69

Nilsson proposed injection of a gelant, a mixture of a copolymer of acrylamide and tert-Butyl

70

acrylate (PAtBA) crosslinked with polyethyleneimine (PEI), as an emulsion for RPM based

71

treatment in the field (Stavland and Nilsson, 1999). In the work of Stavland et al. (2006) an

72

emulsified gel is expected to completely separate into its constituent oil and water phases at

73

reservoir conditions; when injected into the reservoir. The aqueous phase flows into water-wet

74

pathways, then forms gels, while the oil phase remains mobile, thus secure some open pathways

75

for oil flow. In treatment based on RPM, the gel fraction that occupies the porous media must be

76

controlled. The reduction in relative permeability is controlled by the gelled water fraction

77

(Stavland et al. 2006). In recently published work, our group studied the gelation kinetics of the

78

emulsified PAM and PEI emulsified with commercial surfactants, employing the thermal

79

analysis technique (Mohamed et al. 2015). The cross-linking between PAM and PEI was thought

80

to be through a nucleophilic substitution in which the imine nitrogen in PEI will replace the

81

amide group at the carbonyl carbon of PAM (Al-Muntasheri et al. 2007; El-Karsani et al. 2014).

82

Emulsion Physicochemical Properties

83

Emulsions consist of two or more immiscible fluids (Tadros and Vincent, 1983), such as water

84

and oil, where one fluid is dispersed in the other. Droplets are formed when two immiscible

85

fluids are mixed, and the surface of a droplet is a boundary between the hydrophilic and

86

hydrophobic phases, which is naturally unstable due to the tendency of the system to reduce its

87

interfacial free energy, through the coalescence of the dispersed phase droplets. Thus, reducing

88

the interfacial area between the two phases (Weiss, 2002; Rieger, 1976; Tamilvanan et al. 2010),

89

the coalescence process can be slowed down, and a large interface is maintained in existence of

90

so-called emulsifier.

91

Emulsifiers stabilize emulsions by the following two main mechanisms: (i) Electrostatic

92

stabilization, where the electrical charge generated on the surface of droplets by the stabilizer

93

induces repulsive forces between the droplets, and/or (ii) Steric stabilization, where a kinetic film

94

formed by the emulsifier prevents the coalescence of droplets (Becher, 1983; Urrutia, 2006; Min

95

and Akoh, 2008). A typical emulsifier either (i) a surface-active agent, so-called surfactant, a

96

surfactant molecule has a fairly long non-polar part (hydrophobic chain), which is oil-soluble,

97

and a small polar part (hydrophilic group), which is water-soluble. The ability of a surfactant to

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stabilize a particular type of emulsion lays in its hydrophilic-lipophilic balance (HLB) as given in

99

Figure 1a (Schramm, 2005; Tamilvanan et al. 2010). Alternatively, (ii) solid colloidal particles

100

(organic/ inorganic). The ability of those particles to stabilize emulsion depends on (i) inter-

101

particle interaction, (ii) particles size, must be smaller than the emulsion dispersed droplets, and

102

(iii) wettability, partial wetting properties is favorable for emulsification. Emulsion stabilized

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with solid particles known as Pickering emulsion as shown in Figure 1b (Pickering, 1907; Gelot

104

et al. 1984).

RI PT

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105

SC

106 107

O/W emulsion

W/O emulsion

108

110 111

114 115 116 117 118 119 120 121 122

Water Phase

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Oleic Phase

Oleic Phase

Water Phase

Surfactant

EP

112

Hydrophilic < Lipophilic

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Hydrophilic > Lipophilic

109

Lipophilic (Tail)

Hydrophilic (Head)

124 125 126 127

(a)

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132 133 134 135

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136 137 138

Particle wettability

139

Lipophilic Phase (Oleic)

Intermediate-

Oil-wet

141

SC

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Water-wet

143 144

o

Ѳ > 90

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o

o

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Ѳ = 90

Maximum

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Hydrophilic Phase

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TE D

148 149

Pickering O/W Emulsion

151 152 Oleic Phase

153

155 156

AC C

154

158 159

Solid particle

Water Phase

Water Phase

157

Pickering W/O Emulsion

EP

150

Oleic Phase

Oil-wet

o

Ѳ < 90

160 161 162

o

Ѳ > 90 Lipophilic particle

Water-wet Hydrophilic particle

5

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(b)

164 165

Figure 1 Emulsifier types and emulsification mechanisms, (a) classical surfactant-

166

stabilized emulsion, and (b) Pickering, particles-stabilized emulsion. When an emulsifier adsorbs at the interface, a kinetic barrier stabilizes a large interface by

168

lowering the interfacial free energy. Hence, small droplets can exist despite the overall large

169

interfacial surface contact area (Pickering, 1907, Li and Fu, 1992; Backes et al. 1990; Lyklema,

170

2005). According to the Gibbs isotherm Eq. 1 (Wang, 2013), the decrease in the interfacial free

171

energy depends on the type and concentration of the emulsifier (Dong et al. 2002; Sztukowski

172

2005). For instance, solid particles primarily reduce the interfacial free energy by minimizing the

173

interfacial area between two phases, whereas, surfactant reduces the interfacial/surface tension.

174

G

175

Where A, σ, and G are the interfacial area, interfacial/surface tension, and interfacial free

176

energy, respectively.

177

One of the advantages of Pickering emulsion is its high inclination to resist coalesce;

178

consequently, the formation of a more stable system is expected when compared with classical

179

emulsion. Furthermore, charge free emulsifier is a highly desirable propriety in applications such

180

as pharmaceutical, where classical surfactants display undesirable side effects, such as hemolytic

181

behavior and irritancy (Chevalier and Bolzinger, 2013).

182

Stability of an emulsion depends on several factors, including oil-water-ratio, emulsifier type and

183

concentration, salinity and viscosity of the continuous phase, temperature, and mixing intensity

184

(Joshi et al. 2012). The stability of an emulsion is influenced by the quantity of surfactant

185

adsorbed at the boundary. The adsorption of more surfactant molecules acts as a barrier against

186

the coalescence of droplets (Becher 1983; Joshi et al. 2012; Rai and Pandey, 2013). Moreover,

187

salinity plays a major role in the stability, for oil-in-water emulsion increase in water phase

188

salinity from 5 to 20,000 ppm led to increase in the stability, further increase > 20,000 ppm

189

significantly reduced the stability and resulted in emulsion inversion (Winsor, 1948; Al-Yaari et

190

al. 2014a). Inversely, an improvement in water-in-oil emulsion stability and viscosity at salinity

191

≥ 20,000 ppm was observed, this thought to be due to the increase in the disappeared droplets

192

phase double layer and interfacial tension (Aveyard et al. 1989; Al-Yaari et al. 2014a).

193

Macroemulsions are an inherently thermodynamically unstable system. Increase in temperature

∗A

…………………………..………………… (1)

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results in increases of droplets collision rates and reduces the interfacial viscosity due to the

195

increase in the thermal energy, which leads to high coalescence frequency of droplets. Hence, a

196

faster rate of emulsion destabilizing "separation" (Weiss, 2002; Rieger, 1976; Tamilvanan et al.

197

2010).

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Emulsifiers: Surfactant versus Organoclay

200

Typically, a commercial surfactant is used as the emulsifier in the emulsification of the water-

201

soluble material into an oleic phase in the applications reported so far. However, almost all the

202

available surfactants are expensive, a higher dose is commonly necessary to achieve a desirable

203

stability, and most of them are highly toxic (Stavland et al. 2006; Al-Yaari et al. 2014b). The use

204

of emulsifiers based on nanomaterials are promising due to their high surface area of the

205

dispersed nano-sized particles, low-price, availability, and being environment-friendly (Al-Yaari

206

et al. 2014b). Nanomaterials have been widely used in the industry in enhanced oil recovery

207

(Ogolo et al. 2012; Abdelfatah et al. 2017), drag reduction in multiphase flow (Al-Yaari et al.

208

2014b). Moreover, nano-silica, nano-clays and nano-sized Tapioca starch are used as additives in

209

improving the cuttings carrying capacity and controlling filtration properties of drilling fluids

210

(Elochukwu et al. 2017; Shakib et al. 2016; Zoveidavianpoor and Samsuri, 2016). Furthermore,

211

the extraction of nanopowders such as Titanium dioxide (TiO2) prepared from purified sulphate

212

leach liquor of red mud produced from alumina plants is of foremost importance due to its wide

213

range of applications (Tsakiridis et al. 2011). Herein, of particular interest are polymer

214

composites containing organically modified clays, which display a significant improvement of a

215

vast number of physical properties (Sinha-Ray and Bousmina, 2005). Such as, the high surface

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area of organoclays (OC) improves the properties of polymer composites containing organically

217

modified clays (Chen et al. 2002). Also, the application of (OC) for drag reduction resulted in a

218

cost-effective system (Al-Yaari et al. 2014b). Further, research in the application of OC as an

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alternative emulsifier, for potential applications such as emulsified polymeric gels and acids in

220

oilfields, can provide cost-effective and environment-friendly solutions. Hence, the objectives of

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the work reported herein are, the possibility of using OC materials a cost-effective substitute to

222

classical surfactant, stabilized water-in-oil emulsions and to explore the use of OC as a

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reinforcing agent to enhance the properties of commercial nonionic surfactants in harsh

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conditions, typical to those encountered in oilfields for the emulsification applications. Wherein

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the emulsified system encounter high-temperature and high-salinity (Al-Muntasheri et al. 2007;

226

El-Karsani et al. 2014; Al-Mutairi et al. 2008 and references within). Ionic surfactants are very

227

sensitive to electrolytes, specifically divalent cations, which are ample in hard water, thus the

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selection of nonionic surfactant. Furthermore, investigating the compatibility of OC in

229

emulsifying PAM (2 to 4 $/kg) and PEI, which is more cost-effective compared to the current

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system of PAtBA (7$/kg) crosslinked with PEI used in oilfields for water control applications.

231

Herein, the choice of PAM and PEI was attributed to their excellent thermal stability, blocking

232

effectiveness and cost considerations (El-Karsani et al. 2014).

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Materials

234

The organoclay (Cloisite 15A) was obtained from Southern Clay Products, Inc., and its chemical

235

and physical properties are shown in Table 1. The commercial surfactants (1~ 4$/gram) used in

236

this study, properties of which are listed in Tables 2 and 3, were obtained from Sigma-Aldrich®.

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Characteristics

Appearance

EP

Organic Modifier

TE D

Table1: Cloisite 15A), physical and chemical properties

238

AC C

Modifier Concentration

Dimethyl, ammonium

dihydrogenated

Cream powder 125 meq/ 100g clay

Appearance

Cream powder

Density

1.66 g/cm3

Solubility

Oil soluble

X-Ray d-Spacing (001) Price

3.63 nm > 1$/gram

239 240

8

tallow,

quaternary

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241 242 243

Table 2 Polyethylene Glycol-2 Ether (PEG-2E), physical and chemical properties

Nonionic

Molecular formula

C18H35(OCH2CH2)nOH, n~2

Molecular weight (MW)

Mn ~357

Appearance

liquid, yellow

Refractive index

n 20/D, 1.462

Relative density

0.912 g/cm3 at 25 °C

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Type

HLB

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Table 3 Polyethylene Glycol-3 Ether (PEG-3E), physical and chemical properties

Characteristics

Nonionic

EP

Type Molecular formula

C16H33(OCH2CH2)nOH, n~2

Molecular weight (MW)

Mn ~ 330

AC C

244 245 246 247 248

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Characteristics

Appearance

Solid, white

Refractive index

N 20/D 1.466 (lit.)

Relative density

0.978 g/mL at 25 °C

HLB

5

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249

Formation brine was used as the water phase: the composition of brine is given in Table 4.

251

Diesel from a local gas station was used as the oleic phase (814.6 kg.cm-3). Both polymers

252

polyacrylamide (PAM) and polyethyleneimine (PEI) were used as solutions, and PEI used as

253

cross-linker. The physical and chemical properties of the polymers are described elsewhere (El-

254

Karsani et al. 2015). ACS grade salts were also used. A Chelating agent, L-glutamic acid-N, N-di

255

acetic acid (GLDA) obtained from AkzoNobel was introduced to assess its impact on emulsion

256

stability. The stability constants of metal chelates and the protonation constant of GLDA are

257

provided by Le Page et al. (2011).

258 259 260

Equipment

261

Basic, VWR International). The homogenizer is equipped with a variable speed drive with six

262

speeds in the range 500 to 10000 rpm. A conductivity meter (HACH) with a range of 0.01 to

263

200,000 µS/cm was used to determine the emulsion type (i.e., oil-in-water or water-in-oil). High-

264

temperature disposable test tubes made of soda-lime-glass (18 x 180 mm) with an approximate

265

volume of 32 mL and an operating temperature of 180oC were used to study the stability of the

266

emulsions.

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The emulsion was formed using a high-performance dispersing instrument (Ultra–Turrax T 50

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Table 4 Chemical analysis of brine composition

Formation brine, ppm

Na

59,300

Ca

23,400

Mg

1,510

SO4

HCO3

110

M AN U

Cl

137,000

353

TE D

Total Dissolved Solids* 269

RI PT

Ion

SC

268

221,673

* Addition determined TDS. The high-temperature tubes were sealed with a screw-cap and a rubber seal case to prevent

271

evaporation during experiments. The initial and final volumes of the samples were compared at

272

the end of each experiment to verify that there is no evaporation loss. A hot oil bath was used to

273

control the temperature and study the stability of emulsions. An emulsion with a short separation

274

time is characterized as unstable. The desired separation time is about one hour as per our

275

previous calculations (El-Karsani et al. 2015). The separated volume fraction of the phases was

276

measured as a function of time. A Tensiometer was used to measure the liquid-liquid interfacial

277

tension (IFT) by the pendant drop method. The setup was calibrated prior each test, and the

278

surface tension of distilled water was measured for calibration.

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Experimental Setup and Procedure

281

Preparation of Emulsions

282

Bancroft's rule describes the type of emulsion that might be stabilized by a given emulsifier: “the

283

phase in which an emulsifier is more soluble forms the continuous phase” (McClements, 2009).

284

Hence, a water-in-oil emulsion is formed when an oil-soluble emulsifier is used and vice versa

285

(Langmuir, 1996; Min and Akoh, 2008). Several emulsion systems with a different type of

286

emulsifiers (organoclays, surfactants, and composite system of organoclays-surfactants) and at

287

varying concentration, were prepared systemically to ensure the reproducibility of water-in-oil

288

emulsions. The rate of the addition of the dispersed phase to the continuous phase and the

289

intensity of mixing are crucial, resulting in emulsions with higher stability and a smaller droplet

290

size (Al-Mutairi et al. 2008).

291

A water-in-oil emulsion was prepared by first dissolving the emulsifier (at a specific

292

concentration) in diesel and allowing it enough time to mix thoroughly by agitating the mixture

293

for 5 minutes, a specific volume of the water phase was gradually added to the hydrocarbon

294

phase (the mixture of emulsifier and diesel), then additional 5 minutes of mixing was allowed to

295

ensure the emulsion formation. The emulsification was accomplished using a high-power

296

homogenizer operated at a speed of 2000 rpm. Dilution and conductivity tests were performed to

297

confirm that the emulsion is a water-in-oil emulsion (Al-Yaari et al. 2014). More details about

298

the procedures used for the determination of the emulsion type are described elsewhere (Al-

299

Mutairi et al. 2008; Al-Yaari et al. 2014a; Mohamed, 2014).

300 301

Emulsion Stability

302

An emulsion is inherently thermodynamically unstable due to the tendency of its components to

303

separate then minimize its interfacial energy. The Stability test is one of the absolute imperative

304

measurements that provides insight about the system’s resistance to change with time, this being

305

the ease with which the water and oleic phase separate. The stability of the emulsions was

306

evaluated by monitoring the separated volume of each phase versus time at a constant

307

temperature using high-temperature test tubes. The separated volume for water and oleic phases

308

at a given time were collected, then the separated volume of each phase was calculated as a

309

percentage of the total volume, and the total separated volume was calculated as the summation

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of the separated volume of the both phases given as a percentage. Such an evaluation can provide

311

an indication of the quality of an emulsion by relating the emulsifier concentration to the thermal

312

stability.

313

A total volume of 30 mL of each emulsion evaluated in this study was prepared with 70% of the

314

water phase (brine) and 30% of the hydrocarbon phase by volume. The diesel percentage is in

315

the range of 24-28%, while the emulsifier percentage is in the range of 2%-6%. All emulsions

316

were prepared at room temperature, and their thermal stability was evaluated in bulk at 120°C

317

(248°F) for 12 hours using a heating bath.

318

Results of the Thermal Stability Tests

319

From an operational point of view, the thermal stability of the system plays a critical part in the

320

success of any treatment. For instance, when emulsified acids are used, separation should not

321

take place until the reservoir is reached to avoid exposing the metallic parts of the well to the

322

corrosiveness of the acids (De Groote, 1933; Sayed et al. 2013). Similarly, designed stability

323

(separation time) is necessary for the water shut-off applications. The emulsified polymer gel is

324

desired to have a controllable separation and gelation time (Stavland and Nilsson, 1999; Stavland

325

et al. 2006; Mohamed et al. 2015). A gelation time, longer than the separation time is favored, as

326

a weaker gel will be developed if the gelation starts before the complete separation of the

327

emulsified gel (Mohamed et al. 2015). Moreover, an adequate gelation time (longer than the

328

injection time) is necessary to avoid gel development inside the well (Stavland and Nilsson,

329

1999; Stavland et al. 2006). The time required for polymer gel placement at high salinity and

330

temperatures higher than 130°C is about 55 minutes (Albonico et al. 1993; Al-Muntasheri et al.

331

2010; El-Karsani et al. 2015). Similar gelation times, of about 1 to 2 hours, have been reported

332

for emulsified gel systems at a temperature of 120°C (Stavland et al. 2006, Mohamed et al.

333

2015). Hence, the emulsified gel system should be stable for at least one hour. De-emulsification

334

and gelation should start afterward. Therefore, the thermal stability of all formed emulsions was

335

investigated at 120oC.

336

Figure 2 shows typical results of the thermal stability of the emulsions, the emulsion phase’s

337

evolution as a function of time at a constant emulsifier concentration and temperature. The

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338

emulsion total separated volume percentage then calculated from the phase behavior results and

339

plotted against time as shown in Figures 3, 5(a-d), and 6.

Formation Brine

Emulsion

RI PT

100 90

600 ppm Cloisite 15A 30 % Hydrocarbon phase 70 % Formation brine o o 120 C (248 F)

50 40 30 20 10 0 0

4

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70

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Phase volume, %

80

60

Diesel

12 20 30 46 78 98 120 146 160 190 218 240 266 305

Time, minutes

340

342

Figure 2 Phase behavior for the emulsion system, 600 ppm Cloisite 15A at 120°C (248°F)

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341

Effect of the Organoclay Concentration

344

Three emulsions were prepared in the formation brine (TDS=221,673 ppm) with 1000, 600, and

345

300 ppm of Cloisite 15A to evaluate the effect of the OC concentration. The Cloisite 15A

346

particles thought to achieve the emulsification due to their partial wettability propriety, which

347

eases the adsorption at the hydrophilic-lipophilic interface, hence reduces the interfacial area

348

between the dispersed and the continuous phase. Although an emulsion was not formed when a

349

low dose (300 ppm) of Cloisite 15A was used, when the concentration was increased to 600 ppm

350

an emulsion was formed. Furthermore, when the Cloisite 15A concentration was increased the

351

stability of the emulsion was increased. When the Cloisite 15A concentration was increased from

352

600 to 1000 ppm, the total separated volume at 200 minutes decreases from 36% to 13% (Figure

353

3). While further separation was not observed at 1000 ppm concentration, a total volume of 62%

354

separated after 278 minutes at 600 ppm concentration. These percentages remained constant

355

(36% of the water phase and 26% of the oil phase) until the completion of the test. This behavior

AC C

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is associated with the ability of the Cloisite 15A to form an effective kinetic barrier around the

357

droplets of the dispersed phase, which delays the coalescence driven by their high surface area.

358

Figure 4 shows the effect of the Cloisite 15A concentration on IFT, with the reference sample or

359

the blank (without any Cloisite 15A) having an IFT between the diesel and the formation brine

360

phases of 26.15 mN/m. When the Cloisite 15A concentration was increased to 300, 600, and

361

1000 ppm, the IFT reduced to 17.14 (by a factor of 1.5), 14.52 (by a factor of 1.8), and 9.17 (by a

362

factor of ~2.9), respectively. When more Cloisite 15A particles are adsorbed at the interface, the

363

IFT between diesel and formation brine correspondingly reduced, leading to the formation of

364

more stable emulsions. The dependence of the interfacial tension on the Cloisite 15A was

365

modeled in the form of exponential decay as follow:

367

IFT = e

[ ]

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366

SC

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356

……………………….………………………..………………… (2)

368

Where C is the organoclay concentration, a and b are constants as shown in Figure 4.

370 371

Effect of the Polymer Loading

372

To study the effect of polymer loading on the stability, an emulsion was prepared with 1000 ppm

373

of Cloisite 15A. 7wt % of PAM and 1 wt % of PEI added to the water phase. Addition of the

374

polymers lowered the stability of the emulsion. For example, as shown in Figure 3 the total

375

separated volume at 425 minutes increased from 13% for the system without the gelant to 52%

376

for the system with the gelant. In the case where a gelant was not used, water phase did not

377

separate, and only 13% of the oil phase separated. On the other hand, in the case where a gelant

378

was used 36% of the water phase and 16% of the oil phase separated. The decrease in the

379

stability is most likely due to the adsorption of the emulsifier by the polymer as reported

380

elsewhere (Stavland et al. 2006). Another possible explanation is the change in the density of the

381

components of the emulsion. The fact that phase separation is dependent on the densities of the

382

different phases is well known. Gravitational droplet creaming or sedimentation takes place

383

when the densities of the two phases are different (Min and Akoh, 2008; McClements, 2009).

384

The dispersed phase volume fraction is 70%, and with the addition of the gelant (PAM/PEI), a

385

denser dispersed phase is produced, which is thought to lower the interfacial viscosity. Hence, a

386

higher rate of coalescence and higher phase separation (sedimentation) was observed.

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100

600 ppm Cloisite15A 1000 ppm Cloisite15A 1000ppm Cloisite15A + (7/1) wt % PAM/PEI 1000ppm Cloisite15A + 2 Vol % GLDA

90

70 60

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Separated volume, %

80

50 40

30 % Hydrocarbon Phase 70 % Formation brine 120°C (248°F)

30

SC

20 10 0 100

200

300

M AN U

0

400

500

Time, minutes

387 388

Figure 3 Volume fraction for the emulsion system at 120°C (248°F)

TE D

25 20

IFT = 25.181e-0.001[C] R² = 0.9804

EP

15 10

AC C

Interfacial Tension, mN/m

30

5

0

389 390

200

400

600

800

1000

Concentration, ppm

Figure 4 Interfacial tension (IFT) of Cloisite 15A at ambient conditions.

391

The results described above show that when Cloisite 15A is used as an emulsifier very stable or

392

less stable emulsions can be formed depending on the dose. Hence, the concentration of the OC

393

governs the formation of stable emulsions, and emulsions are not formed when the dose is very

394

low (i.e. < 300 ppm). Using Cloisite 15A by itself as the emulsifier, therefore, is not the optimum 16

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choice. As discussed earlier, an emulsified gel is designed to separate under the conditions

396

prevailing in reservoirs completely. Thus, control over the separation time is required under

397

reservoir conditions. The salinity of the water phase is one of the factors influencing the stability

398

of emulsions. The stability of an emulsion has been reported to increase when the salinity

399

increases (Al-Yaari et al. 2014). Chelating agents are known for their strong influence on

400

isolating salts (of divalent ions) in brine, thereby decreasing the salinity, consequently reducing

401

the emulsion stability. Hence, a chelating agent is proposed to control the separation time.

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395

An emulsion with 1000 ppm of Cloisite 15A and 2 vol.% GLDA was added to the water

403

phase and was used to evaluate the impact of the chelating agent on the stability. A lower

404

emulsion stability was obtained in the presence of GLDA, with the separated total volume at 390

405

minutes increasing from 13% to 83%. For a system with GLDA, 53% of the water phase

406

separated, while for the system without GLDA the water phase did not separate. The reduction in

407

the stability is due to the ability of GLDA to sequester cations (Ca2+ and Mg2+) in the brine,

408

hence reducing the stability of the emulsion.

M AN U

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402

409 410

Effect of Organoclay on Surfactant Performance

Due to the beneficial properties of OC materials such as the high surface area (Chen et al.

412

2002; Sinha Ray et al. 2005; Al-Yaari et al. 2014b), they can be added to commercial surfactants

413

to improve their performance as emulsifiers. To this end, a mixture of a surfactant and Cloisite

414

15A as a composite emulsifier was used to prepare the emulsions. Emulsions were prepared

415

using commercial surfactants PEG-2E and PEG-3E at concentrations of 2, 4 and 6 vol.% with

416

Cloisite 15A at concentrations of 300, 600, and 1000 ppm. Importantly, as shown in Figure 5

417

emulsions are formed even at a low Cloisite 15A concentration of 300 ppm at different

418

concentrations of PEG-2E tested. As presented earlier, an emulsion cannot be formed at this OC

419

concentration in the absence of the surfactants.

EP

AC C

420

TE D

411

Moreover, Addition of Cloisite 15A at this low concentration of 300 ppm to 2 vol.%

421

PEG-2E showed a slight improvement in the stability. Whereas, a major enhancement was

422

observed when PEG-2E concentration increased to 4 and 6 vol.%; complete separation shifted

423

from 20 to ~ 110 minutes when compared to the performance of PEG-2E as a standalone

424

emulsifier. A low stability and a complete separation were achieved in less than 25 minutes at all

17

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425

concentrations tested. This thought to be due to presence of enough emulsifier concentration at

426

the interface to achieve the emulsification.

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80 60 40

No Cloisite15A

30 % Hydrocarbon Phase 68 % Formation Brine 2 vol% PEG-2E 120°C (248°F)

20

300 ppm Cloisite15A

SC

Separated volume, %

100

600 ppm Cloisite15A 1000 ppm Cloisite15A

0 50

100

150

200

250

300

350

M AN U

0

400

450

Time, minutes (a)

427 428 429 430

TE D

80

40 20

30 % Hydrocarbon Phase 66 % Formation Brine 4 vol.% PEG-2E 120°C (248°F)

EP

60

AC C

Separated volume, %

100

No Cloisite15A 300 ppm Cloisite15A 600 ppm Cloisite15A 1000 ppm Cloisite15A

0

0

431 432 433

100

200

300

Time, minutes

(b)

18

400

500

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30 % Hydrocarbon Phase 64 % Formation Brine 6 vol.% PEG-2E 120°C (248°F)

80

RI PT

60

No Cloisite15A 40

300 ppm Cloisite15A 600 ppm Cloisite15A

20

1000 ppm Cloisite15A

0 0

100

500

M AN U

436

TE D

80

60

30 % Hydrocarbon Phase 70 % Formation Brine PEG-3E 120°C (248°F)

40

20

AC C

0

EP

Separated volume, %

100

0

439 440 441 442

400

(c)

435

438

300

Time, minutes

434

437

200

SC

Separated volume, %

100

50

100

2 vol% + 1000 ppm Cloisite15A 2 vol% + No Cloisite15A 4 vol% + 1000 ppm Cloisite15A 4 vol% + No Cloisite15A 150

200

250

Time, minutes

(d)

Figure 5 Volume fraction for the emulsion system, PEG-2E with the addition of Cloisite 15A of 300, 600, and 1000 ppm at 120°C (248°F). (a) 2 vol.% PEG-2E, (b) 4 vol.% PEG-2E, (c) 6 vol.% PEG-2E, and (d) PEG-3E

443 444 19

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445

Moreover, the OC particles are believed to facilitate the surfactant molecules adsorption at the

446

interface as shown in Figures 6 and 7. Improved performance, a higher stability was obtained

447

when the composite system at the low concentration of Cloisite 15A (300 ppm) and at all PEG-

448

2E concentrations used as an emulsifier when compared to PEG-2E as a standalone emulsifier.

RI PT

449 450 451 452

SC

453 454

456 457

M AN U

455

458 459

Figure 6 Chemical structure, (a) Cloisite 15A, and (b) PEG-2E

(a) Monolayer

462 463

466 467 468 469 470 471

(c) Particles network

Interface

H 2O

AC C

465

EP

464

(b) Bilayer

TE D

460 461

(b) Polyethylene Glycol-2 Ether (PEG-2E)

(a) HT: Hydrogenated Tallow (~ 65% C18, ~30% C16, ~5% C14)

472 473 474 475

Figure 7 Cloisite15A particles (red circle) and surfactant molecules (yellow circle with black line segments) synergy

476

composite system the stability was increased; notice the shift to the right in the shoulder-like

Furthermore, when Cloisite 15A was added at a high concentration above 300 ppm to the

20

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behavior. For instance, for a PEG-2E concentration of 6 vol.% and a Cloisite15A concentration

478

of 300, 600, and 1000 ppm 80% of the total separated volume was attained after 90, 146, and 190

479

minutes, respectively. The separation time doubles when the concentration was increased by a

480

factor of 3, from 300 to 1000 ppm as shown in Figure 5c. In general, when the composite

481

emulsifier is used the emulsion stability increases as the amount of the emulsifier adsorbed at the

482

interface. Albeit, the stability of the emulsions was higher when Cloisite 15A was used as a

483

standalone emulsifier compared to the case of a composite emulsifier (see Figures 3 and 5). This

484

observation holds at all PEG-3E concentrations as given in Figure 5d. This behavior is most

485

likely due to some exchange between the surfactant and Cloisite 15A molecules at the interface.

SC

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477

To further investigate the interaction between Cloisite 15A and PEG-2E, emulsions with

487

different concentrations of PEG-2E and 1000 ppm of Cloisite 15A were used to examine the

488

influence of the surfactant concentration on the stability of the emulsions. As shown in Figure 8,

489

a sharp decrease in the stability (48% total separation in 22 minutes) was observed when 2 vol.%

490

of the surfactant was used, followed by an additional separation of 17%, which is 65% in total at

491

425 minutes, 28% and 37% is oleic and water phase, respectively. On the other hand, only a

492

slight decrease in the stability was observed with 10% and 4% total separated volume obtained in

493

75 minutes for 4 and 6 vol.% of PEG-2E, respectively, followed by a sharp decrease in the

494

stability. The total separated volume after 200 minutes increased to almost 83% and 94% for the

495

4 and 6 vol.% concentrations, respectively, following which there was no significant change. The

496

emulsions became less stable with increasing the surfactant concentration as illustrated in

497

Figures 5d and 8. This behavior could be explained through the physical chemistry of the

498

emulsification, due to the wetting affinity of the nonionic surfactants, specifically their

499

hydrophilic head and lipophilic tail, those molecules may adsorb at the surface of the organoclay

500

particles, which are partially wetted as well. In that scene, there are two possible scenarios of

501

how the surfactant molecules adsorb onto the OC particles surface, the hydrophilic surfactant

502

head onto the hydrophilic OC surface and the lipophilic surfactant tail onto the lipophilic OC

503

surface as shown in Figure 9. Which in any case, results in altering the wetting characteristics of

504

the OC particles, if one phase (oleic or water) easily wetted the particles, this renders them

505

passive (neutral to the emulsification process) as efficiently hindering their transport and

506

accumulation at the interface (Gelot et al. 1984). This is explicitly evident at high surfactant

507

concentration, thus the low observed stability. Wherein, at low surfactant concentration, the

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21

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508

effect was less pronounced. This could be related to the availability of some OC particles not

509

screened out through the interaction to achieve the emulsification; therefore, more OC particles

510

adsorbed at the interface.

No Surfactant 2 vol% PEG-2E 4 vol% PEG-2E 6 vol% PEG-2E

SC

80

60

30 % Hydrocarbon Phase 64 - 68 % Formation Brine 1000 ppm Cloisite15A Heating Temperature 120oC

40

M AN U

Separated volume, %

100

20

0 0

50

100

150

TE D

515

518 519 520

300

(b) Low surfactant content, less stable emulsion.

EP

(a) No surfactant, stable emulsion.

AC C

517

250

350

400

450

Figure 8 Effect of the surfactant concentration on the composite emulsifier stability

514

516

200

Time, minutes

512 513

RI PT

511

Water Phase

Oleic Phase

Water Phase

Oleic Phase

(c) High surfactant content, unstable emulsion

Water Phase

Oleic Phase

521 522

Figure 9 Graphical representation of the surfactant (yellow circle with black line segments) and

523

Cloisite15A (brown circle) interaction at the interface 22

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524 525

Transport of nanomaterials in porous media The use of OC in the oilfields for the emulsification applications (i.e. emulsified

527

polymers and acids) is promising, due to their beneficial proprieties, especially their stability at

528

hash reservoir environment. Recently, our group studied the performance of two different

529

organoclays (a) Cloisite 15A, and (b) Cloisite 30B as friction loss reducer to flow of surfactant-

530

stabilized water-in-oil emulsion. Generally, the emulsion exhibits a shear-thinning behavior. The

531

addition of OC was found to reduce the emulsion viscosity, and this phenomenon was more

532

pronounced as the concentration increased. Pressure drop measurements were carried for W/O

533

emulsions with 0.3 (diluted) and 0.7 (concentrated) water volume fractions, in horizontal pipes

534

with different diameters. The addition of OC to the concentrated emulsions led to 25 % pressure

535

reduction. Whereas, for the diluted emulsion pressure drop only noticed in the turbulent region,

536

this behavior was evident at high OC concentration and high Reynolds number. While no

537

pressure drop was seen in the laminar region (Al-Yaari et al. 2014).

M AN U

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526

Although, OC has excellent flow behavior and drag reduction ability, which are highly

539

desirable from an operational point of view when those fluids injected into the reservoirs,

540

nevertheless, their transport in porous media involve some challenges. Albeit, that OC has a

541

small particle size, using those materials can results in a formation damage through different

542

mechanisms (Ju and Fan 2009; Abdelfatah et al. 2017). Herein, the use of oil-soluble OC can

543

lead to permeability reduction in the oil-wet pathways, (i) chemically due to adsorption, which

544

promoted through the electro-kinetics between the fluid and the rock and environment salinity,

545

which is influencing the electro-kinetics adsorption via the electric double layer (EDL) thickness

546

alteration, thicker EDL is expected at low salinity. (ii) Mechanically via pore throats entry

547

plugging by mono-particle or aggregate of small multi-particle. Recently, numerical results

548

indicate that the formation damage degree is controlled mainly by the nanomaterials injection

549

rate and concentration. High flow rate, even at a low dose was found to promote high

550

permeability reduction and multi-particle plugging due to the increase in the particle Reynolds

551

number. Whereas, at low flow rate the mono-particle plugging and adsorption are dominant.

552

Moreover, increasing the concentration resulted in an increase in all of the damage mechanisms

553

magnitude, in general. Hence, the injection rate and the dose must be augmented to minimize the

554

associated damage (Abdelfatah et al. 2017).

AC C

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23

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Fortunately, a low concentration is needed to achieve emulsification. After the emulsion

556

separation, the concentration of the Cloisite15A particles in the oleic phase is expected to be less

557

than the original, due to the portioning of some particles into the water phase (owed to OC

558

particles dual affinity), and most importantly, no aggregates were noticed in the separated oleic

559

phase. Furthermore, the high-salinity condition and Cloisite15A non-polar feature promote less

560

electro-kinetics adsorption. Moreover, emulsified gels and polymer gels treatments are usually

561

involving an injection of high molecular weight fluid. Therefore, applied for a high-permeable

562

reservoir (> 100 mD) with a high average pore size ≥ 50 µm (Sparlin, 1976; Seright et al. 2001;

563

Stavland, A. et al.

564

reservoirs. Thus, injection at a high flow rate herein is the unfavorable scenario as discussed

565

earlier.

566

Conclusions

567

The possibility of using organoclay to form stable water-in-oil emulsions and augmenting the

568

properties of commercial surfactants for applications at high temperature (>100oC) and high

569

salinity (>200,000 ppm) was investigated. Following are a summary of the findings of this study:

570

1. The stability of the emulsions increases with increasing Cloisite 15A concentration. The

571

increase in the stability is most likely due to their high surface area and excellent wetting

572

characteristics of OC, which primarily allows a formation of a rigid kinetic barrier that

573

delays the coalescence of droplets. The reduction of the IFT between the continuous

574

phase and the dispersed phase can also contribute to the stability enhancement.

RI PT

555

TE D

M AN U

SC

2006; Ahmed et al. 2010), systems are yet to be developed for tight

2. Cloisite 15A was found Compatibility with PAM/PEI at the condition of study. The

576

addition of polymers (PAM/PEI) results in a decrease in the emulsion stability. This

577

reduction may be due to the increase in the dispersed phase Interfacial viscosity upon

579 580

AC C

578

EP

575

addition of the gelant or part of the emulsifier being adsorbed by the polymer. Furthermore, organoclay particles are expected to improve the flow properties and the gel strength for the emulsified cross-linked polymer used.

581

3. A chelating agent (GLDA) may be utilized as an emulsion destabilizer. When GLDA was

582

used with OC, the separated volume increases by a factor of ~ 6.4. This is most likely due

583

to the ability of the chelating agent to sequestrate divalent cations (Ca2+, Mg2+),

584

destabilizing the emulsion of particular interest is the applications of oilfield

585

demulsification when formation brine with high divalent content is present. 24

ACCEPTED MANUSCRIPT

4. The addition of the OC to commercial surfactants improves their performance. The

587

separation time doubled (the stability was enhanced) when the concentration of the OC

588

was increased from 300 to 1000 ppm at a constant surfactant (PEG-2E) concentration.

589

5. The addition of surfactant to OC reduces the stability of emulsions. This behavior is

590

probably due to the interaction between the surfactant and OC at the interface. Tentative

591

explanations for this observation is provided. The reduction in the stability due to

592

surfactant addition is of particular interest on demulsifying or destabilizing undesirable

593

crude oil emulsions formed naturally in the oil reservoirs, due to the presence of solid

594

emulsifiers such as resins and asphaltenes.

SC

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586

6. A higher stability was achieved when Cloisite 15A was used as a standalone emulsifier.

596

For example, the emulsion prepared with 1000 ppm of Cloisite 15A was found to be very

597

stable, with only 13% of total separation taking place after about 7 hours at HTHS. These

598

formulations require further optimization for near wellbore applications. However, the

599

stability is expected to meet the desired target for deep reservoir profile modification.

600

7. The composite system (combinations of surfactants and OC) showed various behaviors,

601

at a low concentration of OC 300 ppm and different surfactants contents, an improvement

602

in the stability was attained. Wherein, at high OC concentration (> 600 ppm) with all

603

surfactants contents, a lower stability was observed, when compared to the stability

604

achieved by OC as a standalone emulsifier. Therefore, a further investigation is required

605

to understand the interaction between OC and nonionic surfactants at low and high

606

concentration, hence optimizing the concentration needed for emulsification. Likewise,

607

the interaction between ionic surfactants and nanocomposite materials are required,

608

which may result in more promising results.

610

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EP

AC C

609

M AN U

595

8. Organoclays have the potential to be used as cost effective emulsifiers to form emulsified polymeric gels or acids suitable for applications in the oilfields.

611

9. Transport of nanomaterials can cause formation damage; thus, particular attention must

612

be dedicated to optimizing their flow in porous media. Specifically, when injected at high

613

flow rate and concentrations. A Full-scale experiment studying the transport of the

614

emulsified system in the porous media under various conditions of wettability and

615

permeability is highly desirable to understand the system flow mechanism further.

616

25

ACCEPTED MANUSCRIPT

The results as discussed earlier successfully highlighted the possibility of using nanomaterials as

618

alternative emulsifiers to the classical commercial surfactants for the water-in-oil

619

emulsifications. Potential application of the proposed polymeric gel system for water shut-off

620

must be supported by coreflooding experiments to confirm the system performance. However,

621

such measurement is yet to be performed and will be a subject of future research.

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617

622 623 624

Acknowledgements

626

This research was supported by King Abdul-Aziz City for Science and Technology (KACST)

627

under project # AR-30-291. Moreover, the authors acknowledge the support of Saudi Aramco

628

and King Fahd University of Petroleum & Minerals.

629

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630

Abdelfatah, E., Pournik, M., Shiau, B. J. B., Harwell, J. 2017. Mathematical Modeling and

631

Simulation of Formation Damage Associated with Nanoparticles Transport in Porous Media.

632

Society of Petroleum Engineers. DOI:10.2118/184894-MS.

633

Ahmed, Q. A., Mohamed, A., Salah, R., & Bakhit, A. 2010. Risk Analysis and Decision Making

634

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Albonico, P., Burrafato, G., Di Lullo, A., & Lockhart, T. P. 1993. Effective Gelation-Delaying

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639

Shut-off with Polymer Gels in A High-Temperature Horizontal Gas Well: A Success Story.

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643

Concentration, and Acid-Volume Fraction on the Rheological Properties and Stability of

644

Emulsified Acids. SPE Prod & Oper 23 (4): 484–497. SPE-107741-PA. DOI: 10.2118/107741-

645

PA. 26

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646 647

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649

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651

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652 653

Anderson, C.D. and Daniels, E.S. 2003. Emulsion Polymerization and Latex Applications. ChemTec Publishing Inc.

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Backes, H. M., Ma, J. J., Bender, E., and Maurer, G. 1990. "Interfacial tensions in binary and

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656

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657

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658

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659

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Chen, J., Poliks, M., Ober, C., Zhang, Y., Wiesner, U., Giannelis, E., 2002. Study of the

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664

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665

Crenshaw, P.L. and Flippen, F.F. 1968. Stimulation of the Deep Ellenburger in the Delaware

666

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TE D

660

668

Min, D.B., Akoh, C.C. 2008. Food Lipids: Chemistry, Nutrition, and Biotechnology, Third

669

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Dong J., de Almeida V.F., Tsouris C. 2002. Effects of applied electric fields on drop—interface

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677

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678

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679

El-Karsani, K. S., Al-Muntasheri, G. A., Sultan, A. S., & Hussein, I. A. 2014. Gelation of a

680

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Organoclay is introduced as emulsifier for water-in-oil emulsions as alternative for surfactants

•

Emulsion stability is enhanced with increasing organoclay concentration

•

Total separated volume decreases by a factor of 4.8, due to the decrease in the interfacial

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tension, when Cloisite 15A concentration is increased from 600 to 1000 ppm •

A chelating agent can be used to reduce the effect of salts on emulsion stability.

•

The separation time can be controlled by controlling the organoclay dose.

•

The organoclay has the potential to be used as cost-effective emulsifiers for PAM/PEI at

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high temperature (>100oC) and high salinity (>200,000 ppm).