Pressure Drop Reduction of Stable Water-in-Oil Emulsion Flow: Role of Water Fraction and Pipe Diameter

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Research paper

Pressure drop reduction of stable water-in-oil emulsionsusing organoclays

M. Al-Yaari a, I.A. Hussein b,⁎, A. Al-Sarkhi c

a Chemical Engineering Department, King Faisal University, Saudi Arabiab Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Saudi Arabiac Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, Saudi Arabia

a b s t r a c ta r t i c l e i n f o

Article history:Received 6 May 2013Received in revised form 22 April 2014Accepted 25 April 2014Available online 16 May 2014

Keywords:Emulsified acidWater-in-oil emulsionOrganoclaysPressure drop reduction

In this study, the influence of organoclays (OC) on the pressure drop of surfactant-stabilized water-in-oil (W/O)emulsions was studied. OC were tested as pressure loss reducing agents for stable W/O emulsions with 0.7(concentrated) and 0.3 (diluted) water volume fractions. Pressure drop measurements were conducted inhorizontal pipes with inside diameters (ID) of 0.0254-m and 0.0127-m. The results showed a significantreduction in the emulsion viscosity with the addition of OC and this effect was enhanced as the concentrationincreased. In addition, for the case of concentratedW/O emulsions, the addition of OC resulted in 25% reductionin the emulsion pressure drop in both test sections. For dilutedW/O emulsion with only 0.3 water fraction, whileno pressure drop reduction was observed in the laminar region, it was detected in the turbulent region and sucheffect was pronounced at high Reynolds numbers and high OC concentration. The observed results were ex-plained in terms of emulsion dispersed phase droplet size. In the laminar regime, the friction factor for stableW/O emulsions was in a good agreement with single phase predictions. However, in the turbulent regime thefriction factor for the multiphase system was below the predictions of single phase flow. OC proved to have agood potential as drag reducing agents by producing smaller and stable emulsion droplets hence suppressingthe Reynolds' stresses.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Emulsified acids provide significant benefits in stimulating oil andgaswells by slowing the reaction ratewith carbonates and reducing cor-rosion in the tubular goods. The emulsified acid is essentially a mixtureof up to 70% acid emulsified in a 30% continuous diesel phase. However,pumping emulsified acids can result in high friction losses. Such losseslimit the matrix acidizing job efficiency by reducing the penetrationdepth. Therefore, reducing friction pressure loss is an important factorin extending the application of emulsified acids to deeper targets.

Friction reducing agents, or drag reducing additives, have been usedto increase the throughput of oil and gas pipelines. Typically a dilutepolymer solution is continuously injected into the pipelines resultingin a drag reduction of up to 70% (Al-Yaari et al., 2008, 2009, 2012). Forstimulations, water based gels or oil based gels are used not only to in-crease viscosity for fracture width creation, leak-off prevention,proppant suspension, and diversion, but also are used because of theirfriction reduction capability. The macro-structure of the polymersdampens the development of turbulence at high pumping rate such

that the friction loss is reduced and Reynolds stresses at the wall godown to zero or close to zero.

It is known that the addition of drag reducing polymers (DRP); suchas polyethylene oxide (PEO), reduces eddies viscosity; hence reducesturbulence, in highwater flow rate (typical to those used in firefighting).Addition of less than 0.5% of PEO to water under turbulent conditionscould result in a significant reduction in friction factor. In addition, theuse of DRP is a well-known practice in oil transportation.

For surfactant-stabilized emulsions, it has been proved that oilsoluble polymers as well as water soluble polymers can be used asdrag reducing agents for W/O and oil-in-water (O/W) emulsions athigh pumping rates, respectively (Al-Yaari et al., 2013). In addition,pressure drop reduction of stable emulsions can be achievedbydecreas-ing the dispersed phase fraction (Al-Yaari et al., 2014).

New nanomaterials showed high performance in polymer nano-composites due to their high aspect ratio and the high surface area ofthe dispersed nano-sized particles. Various nanomaterials are currentlybeing developed; however, clay minerals are the most popular due totheir availability (natural source), low cost and more importantly theirbeing environmentally friendly. Of particular interest, organicallymodified clay mineral showed significant enhancement of a large num-ber of physical properties (Sinha Ray et al., 2005; Sinha-Ray andBousmina, 2005). The main reason for these improved properties in clay

Applied Clay Science 95 (2014) 303–309

⁎ Corresponding author. Tel.: +966 13 860 2235; fax: +966 13 860 4234.E-mail address: [email protected] (I.A. Hussein).

http://dx.doi.org/10.1016/j.clay.2014.04.0290169-1317/© 2014 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Applied Clay Science

j ourna l homepage: www.e lsev ie r .com/ locate /c lay

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polymer nanocomposites (CPN) is the high surface area of the organicallymodified clay mineral particles as opposed to conventional fillers (Chenet al., 2002). Clay minerals generally have layer thickness in the order of1 nm and very high aspect ratios (length over thickness) in the range10–1000.

Most of the polymer literature has focusedmainly on improvement inmechanical properties of CPN. However, known instabilities associatedwith polymer flow such as sharkskin and melt fracture (Binding,1991; Binding and Walters, 1988; Boger, 1987; White et al., 1987)have been significantly reduced and flow rates have increased by theaddition of clay minerals.

The impact of nanomaterials on polymer flow was limited torheological tests. However, Hatzikiriakos et al. (2005) found that claymineral additives had a significant effect on the extrudate appearanceof polyethylene. It eliminated surface instabilities and postponed thecritical shear rate for the onset of gross melt fracture to significantlyhigher values depending on resin type, temperature, and additive con-centration (typically 0.05 to 0.5 mass%). The authors observed that thepresence of clay minerals suppressed the development of extensionalstresses to such high levels that can cause a shift in melt fracturephenomena. Also, it was reported that the combination of claymineralswith traditional processing aids such as fluoro-polymers produces anenhanced processing aid that can increase the critical shear rates forthe onset ofmelt fracture to levelsmuch higher than the individual con-stituents when they are used independently.

Adesina and Hussein (2012) studied the effect of OC on high densitypolyethylene (HDPE) rheology and extrusion. It was reported that theaddition of ≤0.1 mass% of clay resulted in reduction in extensionalstrain and stress growth of HDPE. Also, the addition of such smallamount of OC eliminated the gross melt fracture in HDPE and reducedthe extrusion pressure; hence more throughputs were reported. There-fore, they concluded that the addition of platy-like OC can result in meltflow streamlining. They reported that the transient stress overshoot,normal stress difference, zero shear viscosity, onset of shear thinning,and extrusion pressure of polyethylene were reduced by the additionof only 0.05 mass% of the OC and such reduction was for both shearand extensional flows.

Research and experimentation into the application of OC for emulsi-fied acid system may result in a cost-effective solution for reduction ofsurface treating pressures. Potential applications extend from stimula-tion treatments to downhole or surface chemical injection whereveremulsified oil–water solutions can exist. For example, in downhole elec-tric submersible pumps or gas lifted well applications, the additionalfluid flow friction from emulsion causes excessive back pressure to thesystem. It is known that the addition of a long molecule reduces singlephase turbulence in the flow of a small molecule. Therefore, it is expect-ed to behave like the classical DRP.

This paper aims at exploring the possibility of using OC, for the firsttime, as drag reducing agents. Here, one can look for reduction of

pressure drop in stable W/O emulsions using different pipe diameters.The influence of OC type and concentration on emulsion viscosity andfrictional losses was investigated.

2. Materials and methods

All tested surfactant stabilized W/O emulsions were prepared usingbrine (with 2 mass% NaCl) as the aqueous phase. A type of kerosene,with 780 kg/m3 density and dynamic viscosity of 1.57 mPa·s, wasused as the oil phase. ARMAC T, fromAkzoNobel, was used as the emul-sifying agent and its physical properties are presented in Table 1. Fortymass% of the emulsifying agent (solid) was dissolved in naphtha toform the liquid phase. In addition, Cloisite 15A (OC1) and Cloisite 30B(OC2) were used as surface active OC and their physical properties aregiven in Table 2.

A schematic representation of the flow loop is shown in Fig. 1. Theflow loop consists of two small 0.07 m3 PVC tanks. Two centrifugalpumps were used for low- and high-pump rates. The test sectionswere made of two acrylic resin horizontal pipes with different ID(0.0254-m and 0.0127-m) that allow visual observation. Flow rate wasmeasured by two OMEGA magnetic flowmeters. The total length ofthe flow loop was 11 m. Emulsion pressure drop was measured bytwo smart Rosemount differential pressure transducers manufacturedby Emerson Process Management GmbH & Co. The first pressure tapof each pipe was located 8 m away from the entrance, ensuring thatthe flow is fully developed. In addition, the flow loop contained a con-ductivity measurement cell that was used to detect the emulsion typeand to measure emulsion conductivity while flow takes place in the0.0254-m ID pipe test section. The conductivity measurements weremonitored by a PC through a data-acquisition system. Furthermore,emulsion temperature was maintained at 25 °C by the cooling systemillustrated in Fig. 1.

The flowmeters and differential pressure transmitters' informationand accuracies are presented in Table 3. All uncertainties were calculat-ed within the 95% confidence level using a method described by Dieck(2007). The uncertainty values summarized in Table 3 represent thecombined uncertainties of random and systematic uncertainties.

0.036m3 of surfactant stabilizedW/O emulsionswith 70/30water tooil volume ratio was prepared by adding the internal phase (water) tothe emulsified external phase (oil with 0.6 vol.% emulsifier) at a rateof 0.001 m3/min (while mixing at 8000 RPM (for 30 min) by usinghigh power homogenizer (Ultra Turrax T 50 basic, WERKE IKA,Germany)). Emulsion type was tested by stability drop test whereemulsion droplets were injected in a pure phase. If emulsion dropletsdisperse, the emulsion external phase is the same as the used phasefor the test and such results were confirmed by conductivity measure-ments. Emulsions were then transferred to one of the flowloop tanks.The same procedure was followed for stable W/O with 0.3 dispersedphase volume fraction.

All rheological measurements were conducted using RheologicaStress Tech rheometer. Steady pressure drop measurements of the pre-pared emulsion were performed first in both test sections. Then, OCwere added to the prepared emulsion in one of the flowloop tanks toproduce a specific concentration. After that, emulsion with OC wasremixed to get a homogeneous distribution of the OC within the

Table 1Properties of the emulsifying agent.

Commercial name ARMAC TCommon name Tallowalkylamine acetatesAppearance at 25 °C SolidHydropile–lipophile balance (HLB) 6.8

Table 2Physical properties of used OC.

Commercial name Cloisite 15A Cloisite 30BProduct name Ditallowdimethylammonium salts with bentonite Alkyl quaternary ammonium salts with bentoniteSupplier Southern Clay Products, Inc. Southern Clay Products, Inc.Description Cream powder Cream powderSpecific gravity 1.6–1.8 1.9–2.1Solubility Oil soluble Oil soluble

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emulsion system. Finally, pressure drop measurements of the emulsionwith OC were conducted in both test sections.

Pressure drop for all emulsions wasmeasured at different flow ratesin both test sections. All measurements were conducted at steady stateconditions. Emulsion temperature was maintained at 25 °C. Based onthe pipe flow shear rate (Eq. (1)), emulsion viscosity (η) was extractedfrom rheological measurements and used to calculate Reynolds number(Re) for emulsion. The term in brackets in Eq. (1) is the Robinowitschcorrection for non-Newtonian fluids. In addition, emulsion friction fac-tor (f) was calculated using Eq. (2) and the pressure drop reduction(PDR) was defined by Eq. (3).

γ̇w ¼ 4 QπR3

34þ 14

d lnQð Þd lnτwð Þ

� �ð1Þ

where

γ̇w True wall shear rate (s−1)Q Volumetric flowrate (m3/s)R Pipe radius (m)τw Wall shear stress (Pa);η τw=γ̇w

f ¼ΔPΔL

� 2 D

ρ u2 ð2Þ

where

f Darcy friction factorΔPΔL Pressure gradient (Pa/m)D Pipe diameter (m)ρ Emulsion density (kg/m3)u Emulsion average velocity (m/s)

PDR ¼ ΔPwithout organoclays−ΔPwith organoclays

ΔPwithout organoclaysð3Þ

where

ΔPwithout organoclays Emulsion pressure drop before the addition of OCΔPwith organoclays Emulsion pressure drop after the addition of OC.

3. Results

3.1. Emulsion rheology

Effect of OC onW/Oemulsion viscositywas studied usingRheologicaStress Tech rheometer. The Bob and Cup setup was used. Two differentOC, having physical properties tabulated in Table 2, with different

Fig. 1. Flow loop schematic layout.

Table 3Instruments information and accuracies.

Parameter Test section inside diameter (ID) Instrument Supplier Range Uncertainty

Flow rate 0.0127-m Magnetic flowmeter OMEGA 0–30 gal/min (0–6.3 × 10−5 m3/s) 0.001%0.0254-m 0.584%

Pressure Drop 0.0127-m Smart rosemount pressure transmitter Emerson 0–1.8 psi (0–12.4 kPa) 0.391%0.0254-m 0–0.8 psi (0–5.52 kPa) 0.732%

0.01

0.10

1,000100

Em

ulsi

on V

isco

sity

, Pa.

s

Shear Rate, s-1

(a)

(b)

(c)

(d)

Fig. 2. Viscosity curve of stable W/O emulsion at 25 °C with OC1 at different loadings;(a) 0%, (b) 0.005 mass%, (c) 0.02 mass% and (d) 0.04 mass%.

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concentrations (0.005, 0.02 and 0.04 mass%) were added to the emul-sion with 0.7 water fraction. This test was performed to determine theoptimum loading that can produce a pressure drop reduction in theflowloop experiments. The results are given in Figs. 2 and 3.

Adding 0.005mass% of all OC showed no effect on emulsion viscosity[see Figs. 2 and 3(b)]. However, as the loading increased, emulsion vis-cosity decreased for all samples as illustrated in Figs. 2 and 3(c and d).To explain these observations, it should be recalled that all used OCare soluble in both phases. Therefore, they behave like surfactants. Asa result, they may produce stable emulsions and end up with smallerdroplets (see next section) and hence lower viscosity. Also, they may

reduce transverse flow (Adesina and Hussein, 2012; Adesina et al.,2012; Arumugam et al., 2011; Hatzikiriakos et al., 2005). Based onthese results, 0.04 mass% concentration was the minimum loading tobe tested for the flowloop emulsion flow. In addition, although OC1and OC2 showed almost the same performance in terms of emulsionviscosity reduction, OC1 showed better dispersion in oil and thus itwas recommended for the flowloop tests.

3.2. Pressure drop measurements

3.2.1. Stable W/O emulsion with 0.7 water volume fractionPressure drop measurements of surfactant stabilized W/O emulsion

were conducted in the two flowloop test sections. The internal phase(water) constitutes 70% of the emulsion volume. For each flow rate,true shear ratewas calculated by Eq. (1) and then the corresponding ap-parent viscositywas used to calculate Re. However, Darcy fraction factorwas calculated using Eq. (2).

Since oil is the external phase of the produced W/O emulsions,0.04 mass% of OC1 was added to the emulsion and mixed outside theflowloop tank. Then, it was mixed with the emulsion in the flowlooptank. Pressure drop in both test sections was measured for the concen-trated emulsion flow at 25 °C. The relationship between Re and the trueshear rate for the emulsion flow in both test sections before and afterthe addition of 0.04 mass% of OC1 is illustrated in Figs. 4 and 5, respec-tively. At the same shear rate, Re number in the test section having0.0254-m ID is almost 4 times that for the flow in the test section with0.0127-m ID. In other words, at the same Re number, the shear rate inthe 0.0127-m pipe test section is about 4 times that in the 0.0254-mpipe test section. Pressure drop measurements of before and after the

0.01

0.10

1,000100

Em

ulsi

on V

isco

sity

, Pa.

s

Shear Reate, s-1

(a)

(b)

(c)

(d)

Fig. 3. Viscosity curve of stable W/O emulsion at 25 °C with OC2 at different loadings;(a) 0%, (b) 0.005 mass%, (c) 0.02 mass% and (d) 0.04 mass%.

a b

Fig. 4. Viscosity curve of concentrated W/O emulsion without OC and the corresponding Re at both test sections with ID of: (a) 0.0127-m and (b) 0.0254-m.

a b

Fig. 5. Viscosity curve of concentrated W/O emulsion with 0.04 mass% of OC1 and the corresponding Re at both test sections with ID of: a) 0.0127-m and (b) 0.0254-m.

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addition of 0.04 mass% of OC1 in the flowloop are illustrated in Figs. 6and 7. Due to emulsion viscosity, pump power and flowloop design,the maximum Re reached was about 1800 and 2000 for the flow inthe 0.0127-m and 0.0254-m ID pipes, respectively.

In addition, introducing 0.04 mass% of OC1 resulted in a reduction of25% in emulsion friction factor. Most likely, OC has worked as a surfac-tant where the OC part is expected to be in the oil phase and the clay

part inwater. Thus, theOC emulsifier has the capability to reduce the in-terfacial tension; and hence reduces the average droplet size as shownin Fig. 8. As a result, emulsion friction factor was reduced due to theaddition of only 0.04 mass% of OC1 and a better performance is believedto be achieved when an optimum concentration is used.

Furthermore, stableW/O emulsions showed a decrease in the emul-sion friction factor (f) with decreasing pipe diameter (see Fig. 9). At thesame Re number, the true shear rate in the 0.0127-m ID pipe is almostfour times that in the 0.0254-m ID pipe (see Figs. 4 and 5); as a resultthe emulsion dispersed phase droplets are smaller in the smallerdiameter pipe as proved by microscopic images shown in Fig. 10.

Although these results are limited to laminar flow regime (as per thecriterion for single phase), it is believed that at high Re, OCmay orient inthe direction of flow leading to more reduction in fluid friction. Inmultiphase flow, the OC is expected to work as a surfactant to reduceemulsion droplet size. In addition, the platy-like surface of the claypart will help in reducing drag at high Re.

3.2.2. Stable W/O emulsion with 0.3 water volume fractionW/O emulsion with 0.3 volume fraction of water (brine with

2 mass% NaCl) was prepared following the same procedure mentionedearlier. OC1 performance, as a pressure drop reducing agent for thismultiphase system, at different concentrations (0.04, 0.06, 0.08 and0.1 mass%) was measured. The required mass of OC1 was mixed withthe prepared emulsion which is available in one of the flowloop tanks.

Emulsion pressure drop measurements, before and after the addi-tion of OC1, in bothpipe test sections are illustrated in Figs. 11–14. Slightreduction in the emulsion pressure drop was observed after the addi-tion of 0.04 and 0.06 mass% of OC1 and such reduction became clearer

0.01

0.1

1

2,000200

Fri

ctio

n F

acto

r, f

Reynolds Number , Re

Emulsion

Emulsion + 0.04 mass% OC1

Fig. 6. Effect of OC1 on theW/O emulsion friction factor while flowing in the 0.0127-m IDpipe test section.

0.1

1

2,000200

Fri

ctio

n F

acto

r, f

Reynolds Number, Re

Emulsion

Emulsion + 0.04 mass% OC1

Fig. 7. Effect of OC1 on theW/O emulsion friction factor while flowing in the 0.0254-m IDpipe test section.

a b

Fig. 8. Droplet size distribution of W/O emulsion with 0.7 water fraction; (a): without organoclays and (b): with 0.04 mass% OC1.

0.01

0.1

1

10

100 1,000

Fri

ctio

n F

acto

r, f

Reynolds Number, Re

Emulsion + 0.04 mass% OC1 in 0.0254-m ID

Emulsion + 0.04 mass% OC1 in 0.0127-m ID

Fig. 9. Effect of pipe diameter on the W/O emulsion friction factor.

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as OC1 concentration increased (see Figs. 11 and 12). At low concentra-tions, the effect of the OC is so small and difficult to detect. However, athigh concentrations such molecules might work as emulsifiers leadingto a decrease in the droplet size and the pressure drop.

In addition, as shown in Figs. 12 and 14, it is interesting to observethat themeasured friction factors of stable emulsions, in laminar region,with and without OC were in a good agreement with the single phasefriction factor calculated from Hagen–Poiseuille equation (Eq. (4)).However, in turbulent region, the emulsion friction factors, with andwithout OC, fell below the single phase theoretical values calculatedfrom Blasius equation (Eq. (5)).

For unstable emulsions (oil/water mixtures without surfactant), dif-ferent mechanisms were proposed. Omer and Pal (2010) claimed thatthe size of the droplets was bigger than the length scale of turbulence.Furthermore, it was attributed to the turbulent viscosity reduction dueto the stretching and elongation of droplets (Pal, 2007) or due to the dis-persed phase droplet effect on the turbulence characteristics of the sin-gle external phase when droplets are introduced (Pal, 1993). However,for stable emulsion, in some literatures Re numbers were calculatedbased on the laminar flow viscosity using Eq. (4) and thus it was report-ed that emulsion friction factor (in laminar and turbulent regions) couldbe predicted reasonably well by the usual single phase equation (Omerand Pal, 2010; Pal, 1993). It is believed that such approach was not cor-rect since viscosity is changing with flow rate (shear rate or Re) ratherthan constant.

f ¼ 64Re

ð4Þ

f ¼ 0:316Re0:25

ð5Þ

4. Conclusions

The application of OC for friction reduction and particularly in emul-sified acid solutions has a potential in extending the capabilities of stim-ulation treatment applications. This paper aimedmainly to investigate apossible pressure drop reduction of stable water-in-oil (W/O) emulsionusing OC. The influence of OC type and concentration on emulsion vis-cosity was reported. OC were tested as pressure drop reducing agentsfor stableW/O emulsionswith 0.7 and 0.3water volume fractions. Pres-sure dropmeasurements were conducted in horizontal pipes with ID of0.0254-m and 0.0127-m.

Fig. 10. Droplet size distribution of W/O emulsion with 0.7 water fraction while flowing at the same Re number (Re = 1000) at different pipe ID; (A): flow in 0.0254-m and (B): flow in0.0127-m.

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80

Pre

ssur

e D

rop,

kP

a/m

Flow Rate, x105 m3/s

0 mass% 0.04 mass% 0.06 mass% 0.08 mass% 0.1 mass%

Fig. 11. Pressure dropmeasurements of stableW/Oemulsion (with 0.3water volume frac-tion) in the 0.0127-m ID pipe test section at different OC1 loadings.

0.01

0.1

1

10,0001,000100

Dar

cy F

rict

ion

Fac

tor,

f

Reynolds Number, Re

0 mass% 0.04 mass% 0.06 mass%0.08 mass% 0.1 mass% Hagen-Poiseuille

Fig. 12. Stable W/O emulsion friction factor in the 0.0127-m pipe test section at differentOC1 loadings.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 50 100 150

Pre

ssur

e D

rop,

kP

a/m

Flow Rate x 10^5, m3/s

0 mass% 0.04 mass% 0.06 mass% 0.08 mass% 0.1 mass%

Fig. 13. Pressure drop measurements of stable W/O emulsion (with 0.3 water volumefraction) in the 0.0254-m pipe test section at different OC1 loadings.

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The results showed a significant reduction in the emulsion viscosityby adding OC and this effect was enhanced as the concentrationincreased. In addition, for the case of concentrated W/O emulsions, theaddition of OC resulted in a reduction of ~25% in the emulsion pressuredrop. Also, for the stable W/O emulsion with only 0.3 water volumefraction, although no pressure drop reduction was reported in thelaminar region, it was detected in the turbulent region and such effectbecame pronounced at high Re number and OC concentration. Such re-sults were explained in terms of emulsion dispersed phase droplet size.

In addition, for stableW/O emulsionswith 0.3 volume fraction of thedispersed phase, all laminar friction factor data (with and without OC)was in a good agreement with single phase predictions. However, themeasured emulsion friction factors fell below the single phase predic-tions in the turbulent regime. Finally, OC proved to work as drag reduc-ing agents. However, further research is needed to explain suchobservation in detail and highlight the mechanisms of drag reductionin multiphase flow.

Acknowledgments

The authors would like to acknowledge the support provided byKing Abdulaziz City for Science and Technology (KACST) through theScience & Technology Unit at King Fahd University of Petroleum&Min-erals (KFUPM) for funding thiswork through project No. 09-OIL 788-04,as part of the National Science, Technology and Innovation Plan. In

addition, the technical support provided by Schlumberger Dhahran cen-ter for Carbonate Research (SDCR), Saudi Arabia, is highly appreciated.

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cy F

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f

Reynolds Number, Re

0 mass% 0.04 mass% 0.06 mass%0.08 mass% 0.1 mass% Hagen-Poiseuille

Fig. 14. Stable W/O emulsion friction factor in the 0.0254-m pipe test section at differentOC1 loadings.

309M. Al-Yaari et al. / Applied Clay Science 95 (2014) 303–309