Sensitivity Study of Foam Diversion Processes for Matrix Acidization

Abstract

ABSTRACTFactors key to the success of foam diversion processes for matrix acidization were measured in Berea cores. Foam mobility was low in high-permeability (847-md) Berea and higher in low-permeability (92 md) Berea, suggesting effective foam diversion. Injection of surfactant solution, emulating foam-compatible acid injected following foam, trapped some of the foam in place, but imputed diversion of acid was not as complete as diversion of foam itself. After a period of injection of liquid, more gas was displaced, starting from the core inlet, and mobility rose further. Using these coreflood results, fractional-flow methods predict effective acid diversion between layers differing in permeability in field application. A sensitivity study indicates that the size of the preflush and the propagation rates of foam within rock are secondary factors in the success of foam diversion in the field. Foam strength and especially gas trapping following foam injection are the keys to successful application. In a process in which gas trapping following foam injection is ineffective, or is less effective in high-permeability layers, a continuous-injection foamed-acid process would outperform a process of alternating slugs of foam and acid. Further data, especially in field cores, are needed to confirm these conclusions.