Water in Oil Emulsion Stability that is used in Oil Drilling

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Water in Oil Emulsion Stability that is used in Oil Drilling

Background

The water-in-oil emulsion formation plays a vital role on the industry of oil. The activity of water-in-oil (W/O) emulsion occurs at different phases in the course of drilling, processing, production, as well as transportation of crude oil. Crude oil refers to a blend of aromatic hydrocarbons, aliphatic, oxygen, nitrogen, and sulfur that has compounds of asphaltenes and resins. In some cases, water-in-oil emulsions are the products of oil spillage. Spill workers often refer the emulsions to as “mousse” or “chocolate mousse,” because cleaning up the spilt oil appear to be challenging. During the formation of the emulsion of this nature, a dramatic change occurs in the physical characteristics of oil. It is worth to realize that asphaltenes and resins of crude oil produces the components that are interfacially active. Numerous studies have confirmed that the core mechanism of W/O emulsions’ asphaltenes is via the creation of the viscous film network that is cross-connected with an elevated mechanical rigidity (Nour & Yunus, 2006; Fingas & Fieldhouse, 2015). The oil viscosity often shifts from some few hundred mPa.s to 100,000mPa.s, and rise by a factor of between 500 and 1000 (Fingas & Fieldhouse, 2015). This scenario indicates the liquid product changing from a heavy and semisolid material. This foundational background results in the need to carry out this study that investigates the W/O emulsion stability that is used in oil drilling, focusing on how to get a stable water in oil emulsion and how to make a stable water in oil emulsion using mineral oil, SPAN 80, and oil EDC 95/11.

Problem Statement

The formation of water in oil emulsion has emerged to be an interesting activity in today’s oil industry because of the environmental and economic issues that come with it. The fact that the emulsions take place at different stages results in an increase in the production cost as well as the costs of transporting oil. There have been environmental issues that have occurred as a result of the hectic process of cleaning up the surrounding after the oil has spilled using methods like pumping, burning, use of sorbants, as well as the use of dispersants (Nour & Yunus, 2006). This problem has made emulsions hard to recover using the traditional recovery equipment of spillage, which has, in turn, made the process of drilling difficult. Undoubtedly, drilling is presently occurring in the environments that are harsh, associated with weather conditions that cannot be predicted as well as the complex geographical structures. The fields that have heavier deposits present further environmental issues when it comes to the extraction of oil.

Contamination resulting in drilling have also presented another problem that the oil refineries needs to deal with to have quality oil. Drilling of the wells into the ground is necessary prior to reaching the actual layer that contains oil. The product of this process is always contaminated oil, making it not suitable for transportation via pipelines. The solution to this issue called for the invention of oil-in-water (O/W) emulsions to get the pure oil for easy transportation (Saad et al., 2019). The most commonly used types of emulsions in the oil industry to clean oil comprise inverted and direct emulsions. While direct emulsions have been popular with extremely deviated wells and horizontal wells, stabilized indirect emulsions have gained wider applications in oil industry. Such emulsions have the features of enormous volumes of surfactants, which can cause destructions in the well. The solution to this problem has been the use of direct emulsion, though they have a limitation when it comes to drilling horizontal sections moving for distances that are longer. It also a drawback of having the difficulty in controlling the shales’ stability. These varied issues have compelled the majority of the oil refinery firms to consider changing from oil-in-water (O/W) emulsion methods to better techniques such as W/O emulsions to achieve the desired quality of oil during the drilling process.

The General Theory of the Formation of Emulsions

There are numerous theories that have explained the creations of emulsions. The most prominent theory argue that emulsion occurs when the fluid droplets completely disperse in the other fluid that acts as a phase, and the two liquids must be immiscible under normal circumstances (Abdulredha et al., 2018). The emulsification of water and oil occurs successfully via shear motion. This process produces pure emulsification that is unstable and temporary because the liquids begins to form nearly immediately once the motion is halted. The prior researcher has suggested two distinct techniques for emulsification of oil and water, O/W and W/O, which rely on the phase of emulsion (Abdulredha et al., 2018). O/W arises when emulsion takes place in water where the droplets of oils are dispersed in water phases, while W/O is the product of the emulsion occurring in oil, with the molecules of water being dispersed in oil phase. The process of emulsion has helped in the generation of complex mixtures of emulsion such as oil-water-oil (O/W/O) or water oil water (W/O/W) emulsions.

Some theories have established the different types of emulsions in their investigations of the creation of W/O emulsions. Fingas and Fieldhouse (2014) established there are four W/O types resulting from the mixture of crude oil with water. They name these forms of emulsions as stable, unstable, meso-stable, and entrained W/O emulsions. These types came about after water resolution that was conducted over time with several rheological measurements. They were also discovered by the visual appearance of W/O products, both on the day during which the emulsions are formed and a week later (Fingas, 2014). The four types are extremely different from each other based on two or more measurements of water content, as well as the five rheological measurements.

The formation of emulsions have been studied based on the roles of the asphaltenes. Several researchers have noted that asphaltenes are the primary factors for the creation of W/O emulsions over four decades ago (Fingas, 2014). Undoubtedly, it was until recently that the specific asphaltenes roles in emulsions were defined. At the present, the basic concepts of W/O emulsions can be understood clearly because of the existence of numerous studies that have suggested numerous roles of asphaltenes. Fingas and Fieldhouse (2015) argue that the stabilization of W/O emulsions is paramount during the formation process. Research assert that the films of high-strength visco-elastic asphaltene form around the droplets of water in oil. It has also been evident that resins can also help in the formation of emulsions, though resins do not give the emulsions that are stable. Resins are used to increase the stability of asphaltene emulsion, where it serves as solvents of asphaltene and offers temporary stability when slow migration of asphaltene occurs. In general, numerous scientists have confirmed that the composition of oil forms a core factor in the formation of emulsion of W/O, which comprise the types as well as the amounts of resin, asphaltenes, together with the contents of the saturate.

High quantity of water that accompanies the crude oil extraction is among the key issues affecting the oil industry. The formation of emulsions has an immense contribution to some theories that regulate the cost of pumping, production, and transportation of crude oil. Abdulredha et al. (2018) argue that emulsions are formed three primary reasons. They name the first reason as to bring about diffusion of a liquid into the other liquid because of the existence of mixing energy or turbulent flow. The second reason could be the enhancement of the interactions between two liquids that are immiscible, including water and oil. Moreover, the emulsifying agents present in the crude oil such as resins and asphaltenes calls for the formation of emulsions. Therefore, understanding the different reasons for forming emulsions is necessary in the development of the appropriate method than can help in cleansing the unpolished oil.

The aspect of turbulence plays a significant role in the emulsion formation. Notably, the mixing energy or disturbance as the initial factor that led to the creation of emulsions. According to Abdulredha et al. (2018), the existence of turbulence in the pipeline flow assists in the formation of emulsion because of the two flow system that is similar to that of the fluid, where crude oil mixes with water. The authors point out that turbulence influences break-up as well as coalescence of emulsions (Abdulredha et al., 2018). During the flow of the oil in the pipeline, the suppression of turbulence also takes place as a result of the contact between the droplets of emulsion and other fluids at a constant stage. In scientific perspective, turbulence suspension arises as a result of the kinetic energy of one fluid, which has a single stage, turns out to be higher as compared to other two-phase liquid at the flow rate of the fluid. Moreover, there is the transfer of part of the kinetic energy to emulsions from the stream that is two-phased, making this kind of energy less as opposed to single-phased kinetic energy. Similarly, the turbulent strength decreases when the kinetic energy or power flows from single-phased to the particle. This article is relevant in this research because it provides an understanding of the impact of turbulence on emulsion to help in the selection of the method that can match it to solve the issues associated with oil in the course of drilling.

Resins and asphaltenes and other elements, which are also known as functional molecules, have an influence on the creation of emulsions. The molecules of this nature have heteroatoms, like oxygen, sulfur, and nitrogen. According to Subramanian et al. (2017), these components lead to basic and acidic characteristics in the fluids that petroleum-based, which result in the stabilized W/O emulsions. This article regards alphaltenes as the components with the strongest stability of W/O emulsion since they possess polycyclic aromatic and aromatic hydrocarbons. The knowledge of the fact that alphaltenes contribute to the stability of W/O emulsions begun more than four decades ago (Abdulredha et al., 2018). In general, this argument explains the reason for the increased usage of the W/O emulsions as compared to the traditional techniques such as O/W.

Stability of Water in Oil Emulsion

The study of rheology of emulsions seek to examine the stability in W/O. As argued earlier, asphaltenes and resins have been established as the strongest stabilizers of emulsions (Abdulredha et al., 2018). According to Fingas and Fieldhouse (2014), the emulsions that have stabilized using surfactant films, including and asphaltenes and resins act in a similar manner as the hard-sphere dispersions, depicting viscoelastic behavior. In the formation of emulsion, the relaxation time is determined, which appears to be increasing as the volume fraction of the discontinuous stage increases. The authors observed that the stability of emulsion heavily relies on the rheological features of the interface of water–oil, where an elevated elasticity also leads to an increase in the stability level (Fingas & Fieldhouse, 2014). These findings resonate with the previous studies suggesting that the W/O emulsions are stabilized using both resins and asphaltenes, though there is a need for ensuring that the content of resin slightly exceeds the asphaltene content for greater stability.

The emulsions that have proved to be stable are the semi-solid substances (reddish to brown type).  The stable emulsions have an average content of water of between 70 percent and 80 percent on the day during which they are formed and nearly one week later (Fingas, 2014).  Notably, steady emulsions continue being in stable state for four or more weeks under conditions of the laboratory. The stable emulsions that have been previously studied have remained to be stable of over one year (Fingas, 2014). On the other hand, Meso-stable emulsions, start at almost 65 percent, but they lose a larger amount of this water within a short periods (in days). The entrained types of W/O then collect only approximately 40 percent of water, which merely loses this water at a slow rate in at least 12 months. However, the W/O types that are not stable pick up only a small water percentage, where no much variation occurs within a year. In this case, the viscosity of stable emulsion rises within one year, while others decrease or can only grow by small amounts. Fingas (2014) further argue that the unstable W/O types products undergo change and turn out to be more viscous as compared to being elastic. The research evidence indicate that the unchanging emulsion possesses the viscous similar to the elastic components within one year. Furthermore, all other types of W/O depict a higher component of viscosity as compared to the element of elasticity.

The study also establishes the characteristics of W/O types in providing the understanding the stability of emulsions. Research has identified a variety of properties when using oil in the formation of W/O types of emulsion during the start as compared to other three W/O forms. As an illustration, viscosities may be extremely high or low. The light fuels such as diesel fuel while heavy and viscous oil products include heavy residual oils. The entrained W/O types are black viscous liquids, having the water content of averagely between 40 percent and 50 percent on the first day when the formation starts, with the content of below 28 percent one week later (Fingas, 2014). The viscosity of this type of emulsions rise in a day of formation, with averages obtained in of two weeks and the other week later. Unstable W/O types of emulsions, on the other hand, have the oil that does not contain large amounts of water because of blending with water.

Destabilization of Emulsion

The theory explaining the concept of destabilization focuses on coalescence, which means the process through emulsions are completely disintegrated. It splits emulsified fluids into initial immiscible water and oil as suggested by Fingas (2014). This process works under the mechanism of destabilization, comprising creaming and aggregation. The process of aggregation relates to flocculation. Creaming, on the other hand, is regarded as sedimentation, which is the product of the density variations between the emulsified liquids. In this scenario, the lighter liquid settles on top of the liquid that is denser, resulting in the layers of liquids that are immiscible (Fingas, 2014). The researcher also makes an observation that flocculation occurs when clumping of at least two droplets of immiscible liquids is done together with no occurrence of coalescence, and thus all droplets maintaining their integrity. As the coalescence process takes place, there is fusion of at least droplets of liquids together to form one droplet that bigger as compared to the first droplet, and losing their integrity. Therefore, all these processes of sedimentation, coalescence, and flocculation lead to destabilization of emulsions.

Models of Water-in-Oil Emulsion Formations
Old Frameworks

The processes of emulsification examined above were not in existence until the past one and a half decades, which have since been transformed into equations of modelling. The diverse W/O types determine that one simple equation does not sufficiently forecast the formation of emulsions. In earlier years, the data on the kinetics of creation at the sea, among other modeling information was not adequate (Fingas, 2014). Today, the formation of emulsion stems from surfactant-like activity of the resin compounds and polar asphaltene. The old models depict that asphaltenes formed much more stable emulsions as the similar compounds behaved like surfactants when not in solution. It was realized that the emulsions start forming when the desired viscosity and chemical conditions were achieved and sea energy was sufficient. It was further observed that the formation of three different water-in-oil types occur based on the type of oil together with its constituents. Nevertheless, some oils canton form any W/O types, resulting in a fourth type of W/O that has called for further exploration.

In ancient days, the emulsion formation rate was presumed to be of the first-order nature as time advanced. The logarithmic or exponential curve was used to approximate this rate (Fingas, 2014). One of the assumptions was the physical one, stating that all oils pick up water on a basis of the first-order. This assumption was widely employed in oil spill frameworks despite not being consistent with the knowledge of how formation of emulsions takes place. The study reveals that the old models proved not to be reliable and offer the formation predictions that are not accurate.

New Frameworks

The new models were invented to address the limitations that were encountered in the old models. Current researchers have recently developed some latest models to predict the formation of W/O emulsions. These frameworks have proved to be efficient since they utilize empirical data in the formation prediction of emulsions by use of a nonstop function, which also utilize the chemical and physical characteristics of oil (Fingas, 2014). The properties of emulsifications of more oils were also determined, while the properties of some oils in the current set of oil measured once again. This series of measurements resulted in the recalculations of the old models with because of obtaining reliable data on a given set of discrete samples.

The latest models have resulted in the formation of stabilized W/O emulsions using asphaltenes, where the resin participation also occurs. Fingas (2014) present the evidence of this type and other types which indicate that the whole distribution effects of Saturates, Aromatic, Resins, and Asphaltene (SARA) on the emulsions of formation. Asphaltenes have been used as prime stabilizers while resins are the secondary agents in the emulsion formation, especially where the concentration of the aromatics and saturates occur at some level and when the accurate viscosity and density are used. Most importantly, the empirical information that encompasses the data on the oil content, density, viscosity, as well as the W/O type stability that is formed were utilized in the development of mathematical correlation.

The current models suggest the need for a transformation for the adjustment of the information to one decreasing or increasing role. The model suggested by Fingas (2014) show that regression techniques do not respond rightly to a function that change both inversely and directly with the parameter that is targeted. The majority of parameters possess an optimal value associated with class, implying that the values possess a peak function based on class or stability. The new model has made the rectifications in the values of the old models leading to an increase in the regression coefficient. The framework also employs arithmetic approach which helps in the conversion of the values ahead of the peak to the values that appear at the back of the peak, leading a simple decreasing function (Fingas, 2014). These adjustments has made the optimal value to utilize a peak function, where the fit of the peak function fit is obtained from software called TableCurve.

The transformed values have immensely contributed to the development of new model proceeding where a multiple linear equation has been fit to the information. The model has been able to attain the functionalities of logarithmic, exponential or square curves through the correlation to the actual value of the input features in addition to their expanded values. In this case, the functionalities are treated as the exponential of the initial figure, together with their expanded values, using ln (the natural log). Every parameter relates to the index of stability in five different sets of mathematical accounts, which resembles the method of standard Gaussian expansion regression (Fingas, 2014). This technique involves the expansion of the regression to functionalities below and above the linear relationship until the whole unit is optimized. As an illustration, there would be an inclusion of a linear function, followed by a square and a square root, etc. These steps are followed until the complete regression tests indicate that no more gains occurs in the expansions that have increased. The method results in six input parameters, which omprise ln (natural log) of viscosity, density exponential, content of resin, content of the saturate, the asphaltene/resin ratio (A/R), and content of asphaltene.

This study employed a qualitative research method where the secondary data was collected from the sources such as journal articles and books that have been published on the topic of W/O emulsion stability used in drilling. The review of the literature from the secondary sources was conducted based on the technique that Gupta et al (2018) recommended, though with some small adjustments. The adjustments on the review of literature entailed searches for the keywords, the selection of the journals to be used, abstract reviews, as well as full-text reviews in accordance with the approach proposed by Saad et al. (2019). During the search, there was a keen selection of the keywords to shun the unintentional restriction of the research sources that the investigator sought to retrieve. Some of the keywords included crude oil, emulsifications, emulsions, emulsion stability, oil-in-water emulsions, and water-in-oil emulsions, among others. The qualitative data collected from the secondary sources was thematically analyzed. This section, thus presents the comprehensive approaches to the preparation of emulsions; emulsion type determination; calculation of stability; and measurement of stability.

In the preparation of emulsions, material selection was a crucial activity. The experiment used in this study was performed by Fateev (2014). It utilized Tween 80 and Span 80 as emulsifiers to prepare both O/W and W/O emulsions, though this study has made some modifications to include mineral oil, and oil EDC 95/11. Tween 80 was soluble in water but insoluble in oil. The modifications occurred as a result of the preparation of various emulsifiers in different proportions of weight of Tween 80 and Span 80 by blending them. At this stage, it was necessary to determine the average HLB (Hydrophilic-lipophilic Balance) number using the following equitation suggested by Shrestha (2011):

…………………………………. Eq.1.

The description of the parameters used in the equation are as follows:

: The compound value of HLB

, : The surfactants’ HLB values.

: The surfactants’ weight fractions.

The HLB numbers obtained were as shown in Table 1 below:

Table 1: HLB Number obtained.

Number
Span 80: Tween 80
HLB

 

1
1:00
4,3

2
4:01
6,4

3
2:01
7,8

4
4:03
8,9

5
2:03
10,7

6
1:04
12,9

7
0:01
15,0

 

The preparation of emulsions entailed the mixture of 0.01% of emulsifier with either proportion of weight of 80% (65 ml) of oil/20% (17 ml) of water or 80% of water/20% of oil. Surfactants were pre-blended with one of phase, with the other phase added later to obtain the full picture of how emulsion behaves. Homogenization of all phases took place continuously for a period of 5 minutes at a speed of 400 rpm by use of Silverson L4RT-A mixer as represented in Figure 1. The emulsified liquid was left to settle for 2 hours. The emulsions were named S1-28) based on the weight proportions of W/O as indicated in Figure 2.

 

Figure 1: The setup of the experiment

Figure 2: Water-based and EDC 95/11 mineral oil emulsions: a) S1-S4 (HLB 4.3); (b) S5-S8 (HLB 6.4); (c) S9-S12 (HLB 7.8); (d) S13-S16 (HLB 8.9); (e) S17-S20 (HLB 10.7); (f) S21-S24 (HLB 12.9); (g) S25-S28 (HLB 15)

The formed emulsions were observed for two hours at room temperature. The any of the formed emulsions failed to reveal any destabilization sign, the emulsions were then as stable. The prepared emulsions were also observed nonstop for the next 3 days to see if destabilization occurred. Also, if destabilization never took place after this long time, the formed emulsion was stable. Therefore, emulsions that were resistance to destabilization within the initial two hours were viewed as short-term stable, while long-term stability was realized when this condition took longer period, at least 72 hours.

During the preparation of the emulsion, EDC 95/11 base-oil was also used as described in the experiment performed Rismanto and van der Zwaag (2007). This base-oil had the viscosity 2.65 cp at the temperature of 40. At 35°C, the viscosity computed through extrapolation to obtain 2.96 cp, where 35° C was the working temperature of the magnet in the Nuclear Magnetic Resonance (NMR) instrument. In a study that Fateev (2014) carried out, he selected the mineral oil EDC 95/11 as oil phase with having some properties. These features included the density of 815 kg/m³ and viscosity of 3.4 mm²/s. The creation of stable emulsion utilized Versavert SE and Versavert PE as the emulsifier (Rismanto & van der Zwaag, 2007). EDC 95/11 was measured at the beginning of the process without emulsifying water. The emulsions of different samples of varying rations of water/oil were used as shown in Table 2 below:

Table 2: Data for different samples of emulsions

Sample
Mean T2 (ms)

EDC 95/11 – 100/0
504

EDC 95/11 – 85/15
612

EDC 95/11 – 80/20
633

EDC 95/11 – 75/25
747

EDC 95/11 – 70/30
750

 

The process utilized the water drawn directly from the tap. The investigators chose to premix Lisamine red with water in dying the water because of the transparence of both of phases, and thus helping in differentiating the phases.

The tests on dye solubility were carried out by Fateev (2014) on the long-term stable emulsified liquids with the aim of establishing the type of an emulsion, where Lisamine red as a dye indicator was used. The W/O type emulsion was expected to float on the surface of the emulsion when Lisamine red was used. If this observation did not occur, it could mean that the dye had dissolve, resulting in a shift in the emulsion color from white to purple.

 

Determination of Stability

The calculations of stability were based of the indices of stability. Fingas and Fieldhouse (2011) conducted a series of tests stability indices, which referred to a single value that could give the desired separation between the types of W/O even on the first day the formations started to take place. It was crucial to perform these tests because the r content of water alone could not lead completely lead to separation since some of the water was lost in hours or days, and particularly where meso-stable emulsions were formed. All of the indices were used to a certain extent to distinguish the four types of W/O emulsions. The steps and equations used to compute the stability index are as follows:

The first step was to conduct rheological research on the W/O product to determine the complex modulus as well as the modulus of elasticity. Then, the cross product (Xpr) of the elastic modulus and complex modulus was calculated by dividing them with the viscosity of the initial oil as indicated in the equation below:

…………………….. Eq.2.

The cross product (Xpr) was then rectified to obtain stability, also known as Stability C based on the following equation:

……………………………. Eq.3.

The literature on emulsions indicated that stabilization of droplets as a result of agitation of the systems of two liquids by the viscous forces of surface as well as dispersed-phase, which are then broken by forces that result from incessant phase turbulence. Fateev (2014) performed the rotational method tests on the emulsified liquids to establish rheological properties of the W/O type emulsions. He tested all samples under the rate of shear between the speed of 400 rpm and 1400 rpm, with incremental intervals of 200 rpm. During the experiment, several issues of rheological measurement occurred as a result of phase discrimination, making the measurements to be non-reproductive. Therefore, it was necessary to keenly observe the behavior of this phenomenon to establish such problems.

It was also vital to measure the pH of the formed emulsions during the study. A digital pH meter (Orion Research Model 201) was used to determine the changes in the pH values of the created emulsions (Fateev, 2014). The values were measured within the time intervals of 12 hours for three consecutive days (72 hours). The pH meter used is shown in Figure 1 below:

Figure 3: Orion Research 201type pH meter

Methods of PVM and FBRM measurement

Fateev (2014) used PVM and FBRM measurement probes in the experiment he conducted. The selection of the probes was based on the fact that they are of the latest equipment that makes it possible to measure real-time distribution, as well as the microstructure of droplets of the emulsions.

Emulsion Formation

The compositions of the emulsions were as recorded in Table 3 below:

Table 3: Results of the compositions of emulsions

 

Figure 2 and Table 3 reveal that all the emulsions having the weight fractions of water to mineral oil of 80%:20% were S3,4,7,8,11,12,13,15,16,20,23, and 24, which did not form emulsions of long-term stability and discriminated immediately once stirring was complete. It was also observed that the emulsified liquids S1, 5, 10, 14, 18, 22, and 25 having weight proportion of the water to mineral oil of 20%:80% underwent destabilization instantly after stirring. The emulsions that involved the all HLB number indicated no formation of O/W emulsions. The occurrence of destabilization of emulsions may have resulted from the emulsion separations. The reason behind this situation could be the merging of the small droplets merge to procreate bigger species, leading to the discrimination of the unceasing phase from the emulsified liquid. This happening led to the surfactant barrier breaking with incessant coalescence of the droplets that were smaller in size. The destabilization of this nature was viewed as such small amounts of surfactant failing to form a physical barrier that was sufficiently strong near the droplets that prevented the droplet from coming close to each other to merge (Fateev, 2014). The presence of destabilized emulsion indicated the occurrence of short-term stable emulsions. Only four emulsified liquids appeared to be stable for 2 hours, and were subsequently remained settled at room temperature for up to at least 72 hours (3 days). These results resonate with the evidence in the earlier research explaining that coalescence is a likely mechanism that led to the destruction of the emulsified liquids (Nour & Yunus, 2006). The destabilization has taken place because the larger adhesive energy between two droplets as opposed to the turbulent energy that causes the separations of emulsions.

During the tests, it was observed that a combination of low and high HLB emulsifiers gave better results as opposed to the use of only one emulsifier. Thus, the mixtures of Span 80 and Tween products, such as mineral oil, formed stable W/O emulsions of different types. The stability of emulsions was an indicator of the presence of the components like asphaltenes and resins, which were obtained from the crude oil. It was also realized that the temperature change affected the stability of the W/O emulsions. Substantial temperature changes lead to the shift in the interfacial tensions, the nature of HLB of the surfactant, viscosities, molecule thermal integrations, and the pressures of vapor the liquid phases. Stable emulsions were found where the temperatures approached the point of the least solubility of emulsions. Therefore, a combination of Span 80, mineral oil EDC 95/11 could be best suggestion for formation of stable W/O emulsions in drilling.

Water stability was determined using the percentage of the separated water, expressed in percentage. The determination of the amount of water separation was calculated using the following relationship:

………………. Eq.4.

The water content obtained in one week after the creation of emulsions was used as the basis of the determining the stability index of the emulsions. The component was different among all the four types of W/O emulsions (Fingas & Fieldhouse, 2011). The results of the calculated stability were recorded in Table 4 below based on different types of W/O emulsion. The findings indicate that the index of stability could be simply computed based on the rheological information, which can also be employed together with certain primary property data like viscosity and density in pursuit of classifying the W/O type emulsions.

Table 4: Computed Stability of W/O type emulsions

 

Figure 4: Stability indices of different W/O type emulsions

The minimum, average, as well as the maximum indices of stability for every type of W/O emulsion have been presents in Figure 4 and Table 4. It was observed that the averages varied based on the W/O type, with a small overlap between the peak and minimum values.

 

Emulsion Type Determination

 

pH Determination

The data obtained from the measurement of the changes in the pH of emulsified liquids was used to construct the plots as shown in Figures 5 below:

Figure 5: The values of pH of emulsions: (a) short-term stable emulsion, and (b) long-term stable emulsion

The data of the values of pH of emulsions taken for 3 days was used to draw the graphs as indicated in Figure 5(a) and (b). The long-term stable emulsion (S9, 13, 17, and 21) had the pH values that slightly fluctuated near the starting point of pH value, where a small rise was noted in the value of pH after one and a half days (36 hours). The short-stable emulsions (S1, 5, and 25), on the other hand, depicted pH values that were continuously declining. Fingas (2014) provided similar results indicting that long-stable emulsions are associated with an increase in pH values leading to an increase in coalescence. After 36 hours, the pH values begun to slightly rise, resulting in an increase in coalescence as well as the more separation of the emulsions.

Viscosity of Emulsions

The data on the viscosity of emulsions was analyzed as shown in Figures 6 and 7.

Figure 6: The relationship between the viscosity of the blend and the rate of shear (a) water proportion of 20% (b) Water fraction of 80%

Figure 7: The association between the viscosity of the apparent combination and the rate of shear (a) water proportion of 20% (b) water proportion of 80%

The Figures 6 (a) and (b) present the viscosity of plastic mixture in relation to the shear rate. The results reveal that all emulsions were formed under rotational tests of the measurements of viscosity, which helped in the determination of the association between the shear rate and plastic mixture viscosity. The figures show that the rate of shear rises with an increase in mixture viscosity. According to Fingas (2014), such behavior may have occurred as a result of the emulsion systems being shear-thickening or dilatants. It was further noted that the emulsions with high content of water (80%) possessed lower values of viscosity as compared to those with low water content (20%). This phenomenon indicated the occurrence of phase inversion occurrenc in the water proportion from 20% to 80% (Fateev, 2014). These results were also consistent with other studies, which demonstrated the HLB values increase with the emulsions’ viscosity. Therefore, this evidence indicates the existence of adequately firm barrier to coalescence, leading to stable emulsion emulsions.

Limitations

This study had several limitations that are worth to mention. First, it was impossible to perform all the test because of inadequate availability of these units. Despite this limitation, the key emulsion behavior states were also verified and thus utilized as the states of reference for the whole work. This study also relied on the secondary data, which was obtained from the studies conducted by other researchers for the analysis of W/O emulsions stability.

Conclusion

The study performed on the stability of W/O emulsions has used the secondary data to analyze the several methods and features for getting stable emulsions. The experiments utilized Span 80 and the mineral oil EDC 95/11, where the emulsions where left undisturbed for at least three days and results taken. The study has established both short- and long-term emulsions. The most stable emulsions were formed by the combination of Span 80 and EDC 95/11, indicating that the objective of this study was successfully attained. Therefore, the stable W/O emulsions have been suitable for use in the drilling industry cleanse crude oil.

Recommendations

Several recommendations were made on how the limitations associated with this study would be addressed in the future study. The first suggestion is that the researcher needs to ensure that the he increases the units used in the research to attain reliability and validity of the data. It was also observed that the studied used purely secondary data. This problem would be addressed by conducting a survey to collect the primary data that is up-to-date. This step would in getting the results and analysis that are effective in determining the methods to get stable W/O emulsions utilized in drilling.

References

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