Chapter 13 - CO2 foams for enhanced oil recovery

Abstract

This chapter discusses the role of CO2 foams in providing mobility and conformance control during CO2 flooding applications. During the foam flow through the reservoir rock pore spaces, lamellae creation and decaying, which are important aspects of foam propagation, are explained along with the mechanism of foam flow. Foams are thermodynamically unstable; this work also explains how foam stability is affected by different factors such as capillary drainage, gravity drainage, disjoining pressure, gas diffusion, and surface elasticity. The pioneering works, date back to the late 1950s, on the practicing foam as mobility control agents of gas-phase. Since then, notable developments have been reported on this subject. A comprehensive review of the works carried out by various researchers is also presented in this chapter. Different mechanisms responsible for incremental oil recovery by CO2 foam flooding, including stabilization of the displacement process, increase in the apparent gas viscosity, and decrease in the oil–water interfacial tension, are also explained briefly. The optimum performance of CO2 foam flooding in a particular reservoir is dependent on various key parameters which are needed to be examined are also included as part of the chapter. CO2 foam is thermally unstable, and maintaining its stability in the reservoir has been a concern for petroleum engineers. An alternative solution for the generation of highly stable CO2 foams utilizing nanoparticles is also briefly discussed. An approach for providing stability is the use of colloidal gas aphrons (CGA). CGA are CO2 microbubbles formed by the combination of surfactant, gas, and polymers. CGA fluid enhances the stability of the solution, in addition to reducing the CO2 gas mobility, due to its gas-blocking ability. Efforts to increase the performance of CO2 foam flooding have led to the development of the hybrid foam flooding method. One such method that is gaining popularity is the alkaline-surfactant-alternating-gas/CO2 (ASAG) flooding. ASAG involves the injection of alkali-surfactant slug and gas/CO2 alternatively into the reservoir. ASAG flooding generates in situ foam in the reservoir domain and controls the gas mobility. A discussion on the hybrid foam method also forms a part of this chapter.