Numerical Analysis of CO2 and Water Displacement in Natural Rock Cores Based on a Fully Heterogeneous Model

Abstract

Based on a core flooding experiment, a multiphase flow model considering the heterogeneity of porosity, permeability, capillary pressure, and relative permeability (i.e., the fully heterogeneous model) is proposed to analyze CO2/water displacement in a natural sandstone core. Our results indicate (1) the fractal model approximately represents the porosity-permeability relationship of the core and combining it with the Leverett’s J-function, it can be used to effectively describe the heterogeneity of capillary pressure; (2) although hypothetically assuming petro-physical properties at a few locations where obviously inhomogeneous structure and significant fluctuations of CO2 saturation are observed, the fully heterogeneous model is generally applicable to model CO2/brine two-phase flow in the sandstone core and can potentially reflect the CO2 saturation buildup; (3) the heterogeneity in capillary pressure plays an important role in generating local fluctuations of CO2 saturation profile and causing the heterogeneous CO2 saturation distribution, whereas the permeability heterogeneity can only result in slight fluctuations of CO2 saturation profile and has a small effect on the heterogeneous saturation distribution; and (4) an abrupt rise of CO2 saturation in the heterogeneous downstream region of the core cannot be fully reasonably interpreted by the heterogeneity of capillary pressure and permeability. The heterogeneity in the relative permeability can also possibly play an important role in causing such rise.