Effect of N2 on CO2-foam assisted enhanced oil recovery in sandstone reservoir

The global need for CO2 sequestration and associated advantages made CO2 gas injection as one of the important enhanced oil recovery (EOR) technique. The higher solubility of CO2 in oil, less injection pressure and miscibility makes it a favorable choice for EOR processes, but it suffers from high mobility and gravity override results in lower ultimate recovery. The high mobility and gravity override can be minimized by generating the CO2 foam with the aid of a surfactant. However, CO2 is unable to generate the foam/stable foam above its supercritical point (1100 psi, 31 ^o C). These difficulties with CO2 foam is overcome by adding N2 in a small fraction to enhance the foam generation of CO2 at supercritical conditions. This study shows how the addition of small quantity of N2 helps in generating the CO2 foam and performance of the novel CO2/N2 mixture foam in enhanced oil recovery. To investigate the performance of CO2/N2 foam, core-flooding experiments were conducted at elevated pressure and temperature condition (higher than supercritical CO2 - 50 ^o C and 1500 psi) in sandstone cores. Fluorosurfactant (FS-51) was used as a foaming agent and n-decane was used as model oil in all the experiments. The selection of foam quality and N2 fraction was optimized based on foam generation and stability tests. Every gas or foam flooding was preceded by seawater injection to simulate the behavior in the reservoir. The results from the core-flood experiments showed that the CO2 and CO2/N2 foam flooding recovered an additional 34-40% of Original Initial Oil in Place (OIIP) indicating that foam flooding succeeded in producing more oil than pure CO2 gas injection processes. Additionally, the performance CO2/N2 foam injection was better than CO2 foam injection for delaying the breakthrough.