Sensitivity Analysis on Technical Parameters of Foam Assisted Water Alternating Gas (FAWAG) for Heavy and High Viscosity Oil Case

Abstrak

The use of gas injection for oil recovery is challenging for heavy and high viscosity oil case. The difference between gas and heavy oil density allows the occurrence of gravity segregation of the gas phase, and the high oil viscosity creates viscous instability  which results poor mobility ratio of the fluids. This increase the possibility of early gas breakthrough, hence decreasing effectivity of oil recovery. Foaming surfactant has been used to improve the mobility ratio of gas phase and liquid phase, therefore delaying gas breakthrough and improving sweep efficiency.

Foam Assisted Water Alternating Gas (FAWAG) is known as one of the foam injection methods, in which the gas and surfactant solutions are injected in separate slugs from a single well. FAWAG is favored as a foam injection method due to the improvement in injectivity and the reduced risk of corrosion and material compatibility. This study used CMG STARS to simulate the field scale application of FAWAG. The local-equilibrium foam model introduced a function FM: the effect of foam on gas mobility is represented as modification of gas relative permeability.

This study conducted sensitivity analysis on technical parameters of FAWAG: foam quality, slug injections duration, injection rates, and feasibility on different reservoir permeabilities. This study also analyzed the impact of FAWAG in improving oil recovery and production performance in comparison to other EOR methods: water flooding, CO2 flooding, and Water-Alternating-Gas. The results proved that with oil recovery factor of 43.47%, the application of FAWAG significantly improved oil recovery; more than 10% gain of recovery factor in comparison to the former methods. The results also showed that FAWAG is only effective when applied on reservoir with high permeability; as for reservoir with permeability lower than 600 mD, FAWAG is not able to significantly improve oil recovery compared to WAG.