Abstract
Reservoir heterogeneity and permeability contrast are some of the factors that affect the efficiency of EOR applications in the field. The main issues of current secondary and tertiary recovery methods such as water, gas, or water-alternating-gas (WAG) injections in the field are poor mobility control, gravity segregation, and viscous fingering, among others. Displacement conformance needs to be improved as to ensure that target regions are properly swept. To address these issues, foam has been proposed to complement the existing EOR applications, with the target to improve overall sweep efficiency through the reduction of gas mobility. However, very limited data of this effect are available on the actual reservoir rocks under field conditions. In this paper, laboratory research work was conducted to capture the effect of heterogeneity on foam using actual reservoir rocks of varied permeabilities. It is observed that foam is more stable in high permeability cores compared to low permeability cores. Our finding in actual reservoir rocks is consistent with the literature observations conducted in outcrop core samples. Moreover, we used a texture-implicit-local-equilibrium model to parameterize our foam system. Mobility reduction of the gas phase by foam was found to be selectively higher in cores of higher permeabilities. Another finding from the model is that, in all cases, the parameter epcap, which regulates the significance of shear-dependent rheological behavior, approximately equals to 1. Foam exhibit Bingham-like fluid properties where pressure gradient is irrelevant to the shear rates. We also simulated our foam system in a hypothetical two-layered model reservoir using MoReS. We systematically compared the oil displacement by water-alternating-gas (WAG, no foam) process and by surfactant-alternating-gas (foam) process. It is concluded that foam can effectively improve the conformance of the oil displacement in presence of reservoir heterogeneity. The permeability-dependent foam rheology can divert the displacing fluids from the high-permeability region to the low-permeability region and therefore enhancing the overall oil recovery efficiency.
