**Abstract**

Hydrocarbons are produced and transported in a form of mixtures containing oil, gas, and water plus organic and inorganic contaminants. The flow presence of these contaminants (emulsifiers) with the continuous agitation from reservoirs up to surface facilities leads to formation of tight emulsions that need to be dealt with carefully to treat and process them adequately. Emulsions, in the other hand, are sometimes intentionally formed for using in enhanced oil recovery (EOR) and well stimulation. In EOR, emulsions are formed and injected into the reservoirs for the objective of improving both the microscopic displacement efficiency and the macroscopic sweep efficiency, which leads to higher recovery factor. In well stimulation emulsified acids are used during matrix acidizing and acid fracturing to retard acid reaction with rocks, to generate deeper penetration inside the reservoir. Microemulsion is a form of emulsion with less droplet size, and hence higher stability, that occasionally used during EOR and hydraulic fracturing to further improve the reservoir recovery and well production rate. This chapter discusses the application of emulsions and microemulsions in petroleum industry. The chapter discusses emulsions, microemulsions, emulsification processes, application of emulsions and microemulsions in enhanced oil recovery and well stimulations, and ended with conclusions.

**Keywords:** emulsion, microemulsion, enhanced oil recovery (EOR), microemulsion flooding, microscopic displacement, macroscopic displacement, interfacial tension, surfactant injection, phase behavior, physical stability

## **1. Introduction**

According to Khan et al. [1] "An emulsion may be defined as a biphasic system consisting of two immiscible liquids, one of which (the dispersed phase) is finely and uniformly dispersed as globules throughout the second phase (the continuous phase)." In other words, an emulsion is an insoluble mixture composed of two different types of liquid in which one liquid, i.e., dispersed phase, is spreading in the other liquid, which is in a continuous phase. Emulsions are widely used in our daily lives, examples of the most frequently used emulsions are milk, lotion, and creams. Emulsions in different industries can be formed intentionally to meet required applications, but emulsions occurrence in many cases is undesired and may cause


#### **Table 1.**

*Emulsions as problems and solutions in petroleum industry.*

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 considered as problems and solutions in petroleum industry.
