Review on Microemulsions for Conformance Improvement Technology: Fundamentals, Design Considerations, and Perspectives

The area of conformance improvement technology (CIT) encompasses the application of a myriad range of conventional fluids, including polymers, gels, foams, polymer-enhanced gels and foams, bacteria, and emulsions. However, these routes show operational limitations in terms of chemical degradation, thermal degradation, formation damage, susceptibility to high salinity, and segregation within pore spaces. To mitigate these problems, it is necessary to employ conformance agents that can be effectively tuned for a wide variety of reservoir conditions. Microemulsions are a promising class of fluids that exhibit thermodynamic stability, robust structure, and tunable properties. The concept of this research is to inject the optimal (correct) dosage of surfactants, which form micelles with in situ hydrocarbons to form microemulsions. Microemulsions are characterized by direct and reverse micelles, which contribute to their intermolecular interactions responsible for fluid stability and propagation under dynamic shear conditions. Design and reservoir considerations must comprise of a number of factors, namely, salinity, pH, temperature, slug concentration, and fluid activation/placement. An optimal microemulsion can be identified by understanding the flow mechanisms while accounting for mobility control, rock permeability and heterogeneity, thief zone permeabilities, and the presence of anomalies. It has been established in this review that microemulsions help plug the high permeability pore throats via a combination of the "Jamin effect" and viscosity modification. By adoption of a proper workflow design, the reservoir may be tuned via the introduction of microemulsions to suit the needs of the industry. However, considerable research is still needed to validate the design aspects and application of microemulsions for conformance improvement.