OTC-OTC-26399-MS-MS

Rheology and Temperature Dependency Study of Saraline-Based Super Lightweight Completion Fluid Zulhelmi Amir, Badrul Mohamed Jan, Ahmad Khairi Abdul Wahab, Munawar Khalil, Chong Wen Tong, Faculty of Engineering, University of Malaya

Copyright 2016, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference Asia held in Kuala Lumpur, Malaysia, 22–25 March 2016. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract One of the effective alternatives to minimize this perforation-induced formation damage is by application of underbalanced perforation. Fluid systems with very low density could be used to perforate reservoirs in underbalanced pressure conditions that virtually eliminate or minimize fluid invasion and damage along perforation tunnels. To respond in the need such fluid, Saraline-based super lightweight completion fluid (SLWCF) has been formulated from glass bubble, stabilizing and homogeneity agent. This paper focuses on a rheological and statistical evaluation of Saraline-based SLWCF and its effect on operating temperature. Eight rheological models, namely the Bingham plastic, Ostwald-de Waele, Herschel-Bulkley, Casson, Sisko, Robertson-Stiff, Heinz-Casson, and Mizrahi-Berk, were used to describe the rheological behavior of the fluid. Based on the results, rheology of the fluid was best represented by both the Sisko and the Mizrahi-Berk models. Furthermore, it is also found that the viscosity of Saraline-based SLWCF was more dependent to temperature changes at low shear rate. The Arrhenius activation energy for the fluid to flow was also found to be decreasing with shear rate and their relationship can be expressed with a power law equation. 1. Introduction

Perforating is an important process in completing and prepares a well for hydrocarbon production. The created perforation tunnels are the only paths that connected reservoir and wellbores that are cemented with steel casing. Oil and gas well is perforated to allow hydrocarbon flowing through the casing in controlled means, when final depth has been reached. Clean and optimal perforation path is considered as the vital element in determining the productivity of a well (Mustafa et. al, 2009). To create perforation tunnels, a shaped charge perforation gun is the most commonly used method (Papamichos et al., 1993). However the pressure from shaped charge impairs and shatters the rock properties and responsible for permeability reduction, which leads to reduction of flow potential at the crushed zone during perforating activity (King et al., 1986; Bartusiak et al., 1997). This rock property impairment is referred to as “perforation-induced formation damage” (Walton, 2000; Karacan and Halleck, 2003).

One of the effective completion practices to establish clean and undamaged perforation tunnels between wellbore and reservoir rock is through underbalanced perforation (King et al., 1986; Behrmann, 1996). Underbalanced perforation refers to perforation job conducted in condition where wellbore pressure is maintained lower than reservoir pressure prior to gun detonation (King et al., 1986; Karacan

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and Halleck, 2003). The mechanism is the surge flow of reservoir fluids created due to dynamic forces, differential pressure and drag erodes out shattered rock grains and perforation debris out resulting in the clean perforation tunnels (Bolchover and Walton, 2006). Fig. 1 shows the effect of underbalanced perforation compared to balanced perforation in which the former clearly created cleaner perforation tunnels.

Fig. 1 Comparison of balanced and underbalanced perforations (Behrmann et al., 2000).

Generally, underbalanced perforation could be performed through several ways. Conventionally,

gas-based compressible fluid mixtures, such as air-, gas-, mist-, or natural gas-based completion fluids have been applied to achieve an underbalanced condition during perforation (Al-Riyamy, 2000). In recent years, one of the oil and gas service providers has developed the system which the transient underbalance of the well was used and optimized without applying the equivalent static initial underbalance, which occurs instantaneously after the creation of the perforation cavity (Behrmann et al., 2002). In order to improve the performance of the system, it has been strengthened with a new deep-penetrating shaped charge (Bruyere et al., 2006).

Eventhough the mentioned practices have some benefits such as good hole cleaning capability and the ability to handle considerable formation water, they also have some drawbacks. They are not always promising since they usually require additional work, time, special equipment, cost and safety considerations. For instance, the holes could be eroded if formation is loosely consolidated by utilizing compressible gas-based completion fluid. In addition, there is also possibility of downhole fire if hydrocarbons are encountered. This is not very ideal because of dealing with these type completion fluids, especially high pressure gas or air is considered dangerous and extra safety precautions is necessary. Hence, the industry is anticipated the application low- to very low-density and non-compressible completion fluid to perform underbalanced perforation.

In response to the challenge, Badrul et al. (2009) has introduced a significantly lower density (0.60 g/cm3 [5.0 lbm/gal]) novel completion fluid with the application of 3M Scotchlite glass bubbles referred to as Super Lightweight Completion Fluid (SLWCF). Low density fluid systems reduce the volume of fluid invasion into a producing reservoir (Alsobrook and Jones, 2007). More importantly, the use of SLWCF in a very low density liquid form, underbalanced perforation could easily be achieved, thus minimize damage on perforation tunnels. In addition, post perforation wellbore treatment, such as acidizing and skin fracturing, may not be necessary (Al-Riyamy, 2000). SLWCF is also applicable in various reservoirs, including a pressure-depleted reservoir or matured well, in which the wellbore is always in an overbalance or balance condition.

The use of SLWCF has become one the most attractive ways to achieve an underbalance condition. Based on the field test, well BKC-18 of Bunga Raya field located at a joint-development area between Malaysia and Vietnam, at the center of Block PM3 CAA that was perforated by application of

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SLWCF, produced approximately an additional 1,000 barrels of oil daily compared to the neighbouring well with similar properties but perforated with conventional completion fluid (Badrul et al., 2009).

In earlier study, SLWCF was formulated using Sarapar oil as the continuous phase (Khalil et al., 2010; Khalil et al., 2011). Then, the next study by Muhammad et al. (2011) was formulated SLWCF using Saraline oil. Based on the results, SLWCF with a density value of 0.50 g/cm3 (4.17 lbm/gal) was formulated with a Saraline to glass bubbles ratio of 60:40, and homogenizing and stabilizing agent content of 3 and 9 %w/w, respectively (Muhammad et al., 2011). However, no work has been continued on the investigation of flow behavior of Saraline-based SLWCF. Therefore, the rheological behavior of Saraline-based SLWCF is presented in this study.

In the upstream oil and gas industry, an accurate understanding of the fluid rheological behavior as a function of formation transient temperature and pressure during, before, and after the operations is important (Davison et al., 1999; Tehrani, 2007). Information on fluid rheology could be used not only to ensure that the fluid meets the requirement of the operation but also to select the correct operational practice. Rheological behavior can be described as the relationship between an applied shear stress and the resultant shear rate in a laminar flow condition. This usually can be obtained by curve fitting of experimental viscometric data (Livescu, 2012).

In this article, flow properties and viscosity dependence on temperature were carried out for Saraline-based SLWCF. Eight different rheological models, namely the Bingham plastic, Ostwald-de Waele, Herschel-Bulkley, Casson, Sisko, Robertson-Stiff, Heinz-Casson, and Mizrahi-Berk, were used to fit the experimental data. These models were used to predict the rheological behavior of Saraline-based SLWCF. Furthermore, the viscosity-temperature relationship was also studied, in which the Arrhenius equation was used to evaluate the fluid viscosity dependency on temperature. 2. Materials and methodology 2.1. Materials and formulation

In this study, Shell Saraline 185 V synthetic oil was used as the new continuous phase to formulate Saraline-based SLWCF. Saraline oil is derived from natural gas, thus it does not contain any aromatic hydrocarbons, sulfur compounds, or amines. The density of Saraline oil is 0.778 g/cm3 [6.49 lbm/gal] (Shell MDS, 2014). Meanwhile, to reduce the density of Saraline oil in formulation, glass bubbles (HGS4000) were used as a density-reducing agent. Finally, to improve fluid stability, bentonite clay and hydrocarbon based emulsifier were used as homogenizing and stabilizing agent, respectively.

In this study, Saraline-based SLWCF was prepared based on our previous work’s formulation (Muhammad et al., 2011). The fluid was prepared by mixing 60 %wt of Saraline and 40 %wt of glass bubbles. To improve the stability of the fluid, 3 %wt of clay and 9 %wt of emulsifier were added. The mixture was then agitated by using IKA T25 digital ultra-turrax disperser at 6000 rpm for an hour. The readily prepared fluids were then placed in a sealed-cap container for further tests. 2.2 Rheological and temperature dependency measurement

Shear rate and shear stress of the SLWCF were measured using a rotational Haake Viscometer model VT550 equipped with MV2P spindle (repeatability and accuracy, ±1%; comparability, ±2). Measurements were carried out by measuring the shear stress at various applied shear rate, which ranged from 2.639 s–1 to 264 s–1. To investigate fluid dependency on temperature, fluid viscosity was measured at different temperatures by using a rotational viscometer. The temperature was controlled by a thermostatic water bath (Haake CH bath reservoir with Haake F3 temperature controller) connected to the viscometer. The volume of the sample was approximately 100 mL, and the volume of the water bath

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was approximately 3500 mL. In addition, the sample was always stirred by the viscometer spindle in the sample cup. These two conditions ensured that the temperature throughout the sample was the same. 2.3 Statistical evaluation

After measurement, the experimental data of SLWCF shear rate and shear stress were fitted to eight different rheological models to investigate the rheological behavior of the Saraline-based SLWCF. The eight rheological models were the Bingham plastic, Ostwald-de Waele or Power Law, Herschel-Bulkley, Casson, Heinz-Casson, Robertson-Stiff, Sisko and Mizrahi-Berk. These rheological models are shown in Table 1.

Table 1 Rheological models and equations (Kelessidis & Maglione, 2006).

Models Equations

1 Bingham plastic γµ+τ=τ !BB

2 Ostwald-de Waele plnplK γ=τ !

3 Herschel-Bulkley ( ) HBnHBHB K γ+τ=τ !

4 Casson 5.05.05.0 γµ+τ=τ !CC ( 5.0Cτ = Ck0 )

5 Sisko Snba γ+γ=τ !!

6 Robertson-Stiff ( ) RSnRSK γ+γ=τ !! 0

7 Heinz-Casson ( )nHCn

HCn K γ+τ=τ !

8 Mizrahi-Berk ( ) MnMM Kk γ+=τ !05.0

Furthermore, to determine the effect of temperature on the viscosity of SLWCF, the Arrhenius

equation was used (Alderman et al., 1988). The relationship between viscosity and temperature according to the Arrhenius law was expressed as the following:

⎟⎠

⎞⎜⎝

⎛ Εµ=µ

RTexp0

a (1)

A linear relationship plot of ln ( )µ against 1/T was plotted to evaluate the relationship between viscosity and temperature. The measured viscosities data over the interest temperature range were fitted to the Arrhenius equation. All the fitting works were carried out by using a commercial statistical toolbox on Matlab R2015A. 3. Results and discussion 3.1. Rheological behavior of SLWCF

The measured shear stress as a function of the applied shear rates of Saraline-based SLWCF is given in Table 2. In Table 2, the higher shear stress can be observed when the higher shear rate was applied. Then, the measured shear stress data were fitted to the eight proposed rheological models in order to assess the rheological behavior of SLWCF. The results of the data fitting along with the corresponding calculated model and statistical parameters, which are R-squared, sum of square error (SSE), and root mean square error (RMSE) are summarized in Table 3.

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Table 2 The measured shear stress of Saraline-based SLWCF at different applied shear rates.

Shear rate (s-1) Shear stress (Pa) 2.639 0.998 5.279 1.446 26.4 4.659

52.71 8.627 79.28 12.563 88.17 13.873 158.3 23.01 176 25.16 264 37.983

Table 3 Rheological models of Saraline-based Super Lightweight Completion Fluid with their calculated model's parameters and statistical parameters.

Flow models Parameters R-squared SSE RMSE

Bingham-plastic Bτ = 0.9966 0.99916 1.0351 0.3845

Bµ = 0.14

Ostwald-de Waele plK = 0.2218

0.99891 1.3324 0.4363 pln = 0.9199

Herschel-Bulkley HBτ = 0.6461

0.99943 0.6927 0.3398 HBK = 0.1747

HBn = 0.9605

Casson Ck0 = 0.349 0.99946 0.6663 0.3085

Cµ = 0.3559

Sisko

a = 0.1333

0.99952 0.588 0.313 b = 0.4901

Sn = 0.2904

Robertson-Stiff RSK = 0.178

0.99942 0.7051 0.3428 0γ! = 4.041

RSn = 0.9577

Heinz-Casson HCτ = 0.3533

0.99951 0.5972 0.3155 HCK = 0.268 n = 0.6511

Mizrahi-Berk Mk0 = 0.5225

0.99955 0.5476 0.3021 MK = 0.2987

Mn = 0.5263

Firstly, the data of Saraline-based SLWCF were fitted to the Bingham-plastic and Ostwald-de

Waele models that their rheogram are shown in Fig. 2. The results show that the neither Bingham-plastic nor Ostwald-de Waele models gave a good prediction for Saraline-based fluids. The SSE and RMSE were considerably very low (1.03 and 1.33, respectively). Meanwhile, in term R-squared values, these two models were giving a considerably high value. However, compared to the SSE and RMSE values of all the models, these two models seemed to give less accurate rheological predictions for Saraline-based SLWCF. The magnitude of the SSE and RMSE values of these two models are considerably higher than other models. Low SSE and RMSE values indicate better prediction.

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Fig. 2 Shear stress versus shear rate experimental data and fitting plots for Saraline-based SLWCF based on Bingham-plastic

and Ostwald-de Waele models.

As can be observed in Fig. 2, the prediction of Bingham-plastic seems good at both high and low shear rates. The model performs satisfactorily and is able to estimate the experimental data accurately because the shear stress is directly proportional to shear rate. Meanwhile, the Ostwald-de Waele model seems to give a less satisfactory prediction of fluid behavior than the Bingham-plastic model since the Ostwald-de Waele model gave a greater error (SSE and RMSE) (Table 3). The reasons for this poor prediction of the Ostwald-de Waele model are, first, the shear rate versus shear stress behaves linearly at a lower shear rate, and, second, it is due to the nonexistence of a yield point parameter in the model; this explains the poor prediction of the Ostwald-de Waele model (Nasiri and Ashrafizadeh, 2010).

The Herschel-Bulkley, Casson, Robertson-Stiff, and Heinz-Casson models have been proven to be appropriate in describing the behavior of fluid, especially with dispersing particles. In a number of studies (Khataniar et al., 1994; Gücüyener and Mehmetoğlu, 1996; Al-Zahrani, 1997; Bailey and Weir, 1998; Kelessidis and Maglione, 2006; Park and Song, 2010), these four models have widely been used in the upstream oil and gas application, such as in the prediction of completion fluids, drilling fluids, and cement slurries.

As shown in Table 3 and Fig 3, it is apparent that these four models gave a good reliable prediction for Saraline-based SLWCF, when these four models gave almost similar high values of R-squared and low magnitudes of SSE and RMSE values. This good prediction is because of the ability of these four models to satisfactorily accommodate the existence of equation parameters. Hamed and Belhadri (2009) reported that the increment of solid suspension increases the consistency index and decreases the flow behavior index. Saraline-based SLWCF seems to follow this behavior when, a high concentration of glass bubbles led to a low value for the consistency index and a high value for the flow behavior index. In addition, the power relationship between shear stress and shear rate, and yield point parameters demonstrated good performance. Thus, the four models are appropriate for the prediction of fluid behavior of Saraline-based SLWCF.

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Fig. 3 Shear stress versus shear rate experimental data and fitting plots for Saraline-based SLWCF based on Herschel-

Bulkley, Casson, Robertson-Stiff and Heinz-Casson models.

These two models gave the most reliable performance in quantitative and qualitative estimation of the Saraline-based SLWCF as shown in Table 3. Fig. 4 and Fig. 5 illustrate the rheogram of the Sisko and Mizrahi-Berk models.

Fig. 4 Shear stress versus shear rate experimental data and fitting plots for Saraline-based SLWCF based on Sisko model.

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Fig. 5 Shear stress versus shear rate experimental data and fitting plots for Saraline-based SLWCF based on Mizrahi-Berk

model.

The Sisko model gave a high value of R-squared (0.99952) and very low values of SEE and RMSE (0.5880 and 0.3130, respectively). Sisko (1958) found during work on lubricating greases that lubricating grease could be characterized by two flow units; Newtonian and non-Newtonian. In Saraline-based SLWCF (Fig. 4), the fluid seems to behave in almost in a similar manner as lubricating grease: Newtonian at a higher shear rate and non-Newtonian at an extremely low shear rate. Hence, Saraline-based SLWCF can be predicted by the Sisko model.

Meanwhile, the Mizrahi-Berk model seems to produce a high value of R-squared (0.99955), and very low values of SEE and RMSE (0.5476 and 0.3021, respectively). The Mizrahi-Berk model was developed when working on concentrated orange juices that used to describe the rheological behavior of fluid with dispersing particles within the system (Mizrahi and Berk, 1972). A high concentration of glass bubbles that act as dispersing particles provides the best performance of Mizrahi-Berk model in predicting flow properties of Saraline-based SLWCF. It can be concluded that these two models, Sisko and Mizrahi-Berk could represent the qualitative and quantitative rheological behavior of Saraline-based SLWCF. 3.2. Temperature dependency on the fluid flow properties

To investigate the effect of temperature on fluid properties, the viscosity of Saraline-based SLWCF was measured at different various temperatures, which ranged from 25°C to 85°C, and at nine different shear rates, which ranged from 2.693 to 264.0 s–1. The results of the viscosity measurement are given in Table 4. Meanwhile, the plot of Saraline-based SLWCF viscosity against shear rates at various temperatures is shown in Fig. 6.

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Fig. 6 Plot of experimental viscosities against temperature of Saraline-based SLWCF at various shear rates.

As shown in Fig. 6, the measured data showed that the viscosity of Saraline-based SLWCF

decreased hugely with temperature changes when shear rates were increased. This is due to the additional thermal energy increases the intermolecular distance and weakens the attraction forces. In addition, Saraline-based SLWCF viscosities have lost their dependency on temperature especially at a low shear rate. The viscosity of Saraline at 25°C measured at 2.6 s–1 was approximately 420 mPa·s. As the temperature and shear rate increased to 80°C and 264 s–1, respectively, Saraline-based SLWCF viscosity reduced in double magnitude to approximately 150 mPa·s. This low rate of viscosity changes for Saraline-based SLWCF because of the high content of glass bubbles in the fluid.

The Arrhenius equation was used to investigate the dependence of the viscosity of Saraline-based SLWCF on temperature. The calculated parameters of the Arrhenius equation for the Saraline-based SLWCF are shown in Table 5.

Table 4 Experimental viscosity values of Saraline-based SLWCF at different temperatures and shear rates.

T (°C) Shear rate (s-1)

2.693 5.279 26.4 52.71 79.28 88.17 158.3 176 264 25 429 349 195.3 172.3 169 165.3 159.7 157 156 35 349 266 171 160.7 148.3 141.7 138 135 132.7 45 261 190.8 133 120 115 111.3 108 107.3 104 55 218.3 174.3 116 102.7 99 96.2 90.1 88.5 83.9 65 193.7 123.7 87.2 84.6 81 78.9 74.5 73.1 72.6 75 151 113.3 85.7 78.4 75.7 74.8 73.2 72.4 71.3 80 145.3 95 78.1 72.1 73.1 71.7 70.2 68.9 68.3 85 116 116 76.5 70.4 69.3 67.8 66.2 64.7 63.1

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Table 5 Arrhenius equation parameters for predicting the dependency of Saraline based-SLWCF flow properties on temperature.

Shear rate (s-1) Arrhenius parameters

R-squared 0µ (Pa.s) aΕ (kcal.mol-1)

2.639 0.2735 4.3451 0.988 5.279 0.1096 4.744 0.9892 52.71 0.5614 3.3941 0.9827 79.28 0.665 3.2623 0.9841 88.17 0.7053 3.2069 0.9341 158.3 0.7094 3.18 0.9719 176 0.6896 3.1877 0.9734 264 0.6732 3.1899 0.9672

From the results, the Saraline-based SLWCF seems to give a high value of aΕ at a low shear

rate. Activation energy tends to decrease hugely at lower shear rate (<100 s–1) and remains at the same magnitude with small fluctuation when the shear rate was increased to higher than 100 s–1. The plot between the calculated aΕ at each particular shear rates for Saraline-based SLWCF is presented in Fig. 7.

Fig. 7 Fitting plots of activation energy against shear rate for Saraline-based SLWCF.

A significant pattern of aΕ was obvious in the plot of aΕ against shear rate. The plot shows that

aΕ decreased when the higher shear rates was applied. High activation energy value indicates that the fluid viscosity is highly dependent on temperature (Falcone et al., 2007). In this case, Saraline-based SLWCF has less temperature effects at a higher shear rate than at a lower shear rate. This phenomenon may be due to low flash point of Saraline oil, which is lower than 362.15 K (Shell MDS, 2014). A lower flash point tended to give a high value of aΕ at a low shear rate before it decreased dramatically towards moderate and high shear rates.

Power relationship could be used to describe aΕ of Saraline-based SLWCF behavior as the effect of shear rate. The power equation of Saraline-based SLWCF for these two variables is y = 3.114x-

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0.2028 + 2.054, where y is the aΕ and x is the shear rate (R-squared: 0.8686). The negative exponent from

the power equation (–0.2028) is an indication that aΕ decreases with shear rate. Thereafter, aΕ remains constant at a higher shear rate that indicated by the intercept at 2.054. This also explains that Saraline-based SLWCF is slightly dependent on temperature. This is shown by high activation energy value of Saraline-based SLWCF. 4. Conclusions

1. Based on the results, two models, Sisko and Mizrahi-Berk, were determined to be the most-appropriate models to describe the rheological properties of Saraline-based SLWCF.

2. The two models yielded the highest statistical value, accommodating the Saraline-based SLWCF characteristic theory.

3. The Arrhenius equation seems to satisfactorily describe the variation effect of temperature on Saraline-based SLWCF viscosity.

4. The activation energy of the formulated fluid seemed to decrease with shear rate, and it tended to follow a power law equation, which indicated that the viscosity of Saraline-based SLWCF was more dependent to temperature changes at low shear rate.

Nomenclature Latin letters

aΕ Activation energy (ML2T−2M−1)

HBK Herschel-Bulkley fluid consistency index (M/LT2−n)

HCK Heinz-Casson fluid consistency index (M/LT2−n)

MK Mizrahi-Berk fluid consistency index (M/LT2−n)

plK Power law fluid consistency index (M/LT2−n)

RSK Robertson-Stiff fluid consistency index (M/LT2−n)

R Gas constant (ML2T−2 θ−1M−1) =1.987 × 10-3 kcal K-1mol-1 T Temperature (θ) Greek letters γ! Shear rate (T-1)

0γ! Shear rate correction factor (T-1) η Heinz-Casson fluid flow behavior index (-)

HBη Herschel-Bulkley fluid flow behavior index (-)

Mη Mizrahi-Berk fluid flow behavior index (-)

plη Power law fluid flow behavior index (-)

RSη Robertson-Stiff fluid flow behavior index (-)

Sη Sisko fluid flow behavior index (-)

Ck0 Square root of Casson fluid yield stress (M1/2/L1/2T)

Mk0 Square root of Mizrahi-Berk fluid yield stress (M1/2/L1/2T) τ Shear stress (M/LT2)

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Bτ Bingham plastic fluid yield stress (M/LT2)

Cτ Casson fluid yield stress (M/LT2)

HBτ Herschel-Bulkley fluid yield stress (M/LT2)

HCτ Heinz-Casson fluid yield stress (M/LT2)

µ Viscosity (M/LT)

0µ Viscosity under reference condition (M/LT)

Bµ Bingham plastic fluid plastic viscosity (M/LT)

Cµ Casson fluid plastic viscosity (M/LT)

5. Acknowledgements The authors would like thank to the Shell MDS (Malaysia) Sdn. Bhd., 3M Asia Pacific, Pte. Ltd., Scomi Oil and Gas (Malaysia) Sdn. Bhd. for their contribution in providing the materials for this work. The authors also appreciate the contributions of UMRG Programme-AFR Frontier Science, project RP031B-15AFR, the support of University of Malaya IPPP grant, project PG0040-2015A, High Impact Research Grant, HIR-D000006-16001, University of Malaya Fellowship Scheme, Center for Energy Science, University of Malaya and Department of Chemical Engineering, Faculty of Engineering, University of Malaya. 6. References Al-Riyamy, K.M. (2000). Synthesis and characterization of reversible emulsions: Application to Completion

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