**2. Emulsion**

#### **2.1 Type of emulsion**

The two most common types of emulsion are oil-in-water (O/W) emulsion and water-in-oil (W/O) emulsion. There are also multiple emulsions in a complex system. Various types of emulsion can exist in the form of W/O, O/W, O/W/O, and W/O/W, however the most familiar ones are the first two [3]. In oil-in-water emulsions tiny nonpolar droplets of oil spread in a polar water phase [4]. As shown in **Figure 1**, the O/W system appears as a heterogeneous emulsion in which oil is dispersed in a form of bubbles of different sizes in the continuous water phase. In contrary, in water-in-oil emulsions oil forms the primary (continuous) phase in which water droplets disperse with different sizes.

W/O emulsions can further be categorized into stable, entrained, meso-stable, and unstable based on visual appearance, elasticity, and viscosity difference [6]. Nevertheless, in practice only stable and meso-stable states can be considered as real emulsions. The four types of water-in-oil emulsions have been clearly described by Fingas and others [6, 7] as follow:


**115**

**Figure 2.**

**Figure 1.**

*Application of Emulsions and Microemulsions in Enhanced Oil Recovery and Well Stimulation*

• Entrained emulsions: the entrained emulsions have less water cut and less viscosity increment than that of meso-stable emulsions. The water cut at the date of formation is in the range 40–50% and drops to 28% after 1

• Unstable emulsions: contains very little amount of water which almost remain

In petroleum industry, both W/O and O/W emulsions can be recognized in different locations starting from the reservoir and up to refinery and terminal stations. W/O emulsion is frequently recognized at down-hole and downstream to the choke because at these points the flow stream is mainly hydrocarbon (oil and gas) with lesser volume fraction of water. Due to the continuous turbulence and agitation of the stream while it flows through tubing and passing through wellhead and choke, the water phase breaks down into small droplets and scatters

Unlike the stable emulsions, the initial value of water content in meso-stable emulsions is in the range 60–65% but the water cut declines to less than 30% after 1 week of formation. The viscosity of meso-stable emulsions also increases with time but the increment rate is not as high as that of stable

*DOI: http://dx.doi.org/10.5772/intechopen.84538*

constant with time [7] (**Figure 2**).

*Water-oil (W/O) emulsion (left) and oil-water (O/W) emulsion (right) [5].*

*A photograph of stable emulsion (A) and unstable emulsion (B) [6].*

emulsions [7].

week [6].

*Application of Emulsions and Microemulsions in Enhanced Oil Recovery and Well Stimulation DOI: http://dx.doi.org/10.5772/intechopen.84538*

Unlike the stable emulsions, the initial value of water content in meso-stable emulsions is in the range 60–65% but the water cut declines to less than 30% after 1 week of formation. The viscosity of meso-stable emulsions also increases with time but the increment rate is not as high as that of stable emulsions [7].


In petroleum industry, both W/O and O/W emulsions can be recognized in different locations starting from the reservoir and up to refinery and terminal stations. W/O emulsion is frequently recognized at down-hole and downstream to the choke because at these points the flow stream is mainly hydrocarbon (oil and gas) with lesser volume fraction of water. Due to the continuous turbulence and agitation of the stream while it flows through tubing and passing through wellhead and choke, the water phase breaks down into small droplets and scatters

**Figure 1.**

*Microemulsion - A Chemical Nanoreactor*

More retention time (larger required separator), gas bow-by, formation of rag layer will affect level control system, additional cost (chemical/heating).

Equipment upsets, piping corrosion and scaling, affecting design throughput, single phase correlations become inaccurate when dealing with emulsions.

*Emulsions as problems and solutions in petroleum industry.*

Oil treatment

Oil transportation

**Table 1.**

serious problems. In petroleum industry, for instance, emulsions can intentionally be formed for application in some upstream operations such as enhanced oil recovery (EOR), hydraulic fracturing, and emulsified acids. Nevertheless, negative impact due undesired emulsion is also encountered downstream operations. If the produced oil/water streams reach surface facilities in form of stabilized emulsions then more time, money, and technical knowhow are needed to separate the produced streams into distinct phases and make them ready to subsequent treatments. When crude oil is extracted from a well, it frequently leaves the wellhead in a form of mixture containing water phase. This will make it difficult to deal with in surface facilities and transportation areas [2]. **Table 1** introduces where emulsions is

Enhance oil recovery

properties.

Well stimulation

The injection of emulsions and/or microemulsion into oil reservoirs is believed to enhance oil recovery due to their favorable rheological, and thermodynamical

Emulsified acids are frequently applied to retard acids-rock reaction and hence increase penetration. Microemulsions also are used in hydraulic fracturing

**Emulsions as problems Emulsions as solutions**

The two most common types of emulsion are oil-in-water (O/W) emulsion and water-in-oil (W/O) emulsion. There are also multiple emulsions in a complex system. Various types of emulsion can exist in the form of W/O, O/W, O/W/O, and W/O/W, however the most familiar ones are the first two [3]. In oil-in-water emulsions tiny nonpolar droplets of oil spread in a polar water phase [4]. As shown in **Figure 1**, the O/W system appears as a heterogeneous emulsion in which oil is dispersed in a form of bubbles of different sizes in the continuous water phase. In contrary, in water-in-oil emulsions oil forms the primary (continuous) phase in

W/O emulsions can further be categorized into stable, entrained, meso-stable, and unstable based on visual appearance, elasticity, and viscosity difference [6]. Nevertheless, in practice only stable and meso-stable states can be considered as real emulsions. The four types of water-in-oil emulsions have been clearly described

• Stable emulsions are described as reddish brown semi-solid substances having 70–80% water cut. Experimental examinations conducted by [6] indicated that stable emulsions can remain stable for more than 4 weeks and the stability can extend to more than least 1 year. They also pointed out a dramatical viscosity

• Meso-stable emulsions the meso-stable water in oil emulsions are viscous liquids and similar in color with the stable emulsions (reddish brown).

considered as problems and solutions in petroleum industry.

which water droplets disperse with different sizes.

increase to more than 800 folds after 1 week.

by Fingas and others [6, 7] as follow:

**114**

**2. Emulsion**

**2.1 Type of emulsion**

*Water-oil (W/O) emulsion (left) and oil-water (O/W) emulsion (right) [5].*

**Figure 2.** *A photograph of stable emulsion (A) and unstable emulsion (B) [6].*

inside the primary oil phase. The presence of impurities in the oil phases, which act as emulsifiers, will increase the possibility of forming W/O emulsion with stability proportional to the degree of turbulence and the concentration of the emulsifiers. O/W emulsion, from the other hand, is more frequently recognized at water outlets downstream to two phase separators and at the inlet of three phase separators and free water knock out (FWKO) facilities. This type of emulsions should be treated properly before it reaches the first pump station for long distance transportation. The main problem arise from flowing of this type of emulsions in pipelines is the corrosion of internal wall of the pipeline due to presence of water. However, presence of emulsions inside pipeline may also be useful as it facilitates smooth transportation of high viscous crude. Because of that heavy and waxy crude oils may intentionally emulsified with water to form (O/W) emulsion.
