History matching of CO_2 core flooding CT scan saturation profiles with porosity dependent capillary pressure

摘要

This paper presents a numerical simulation study of a CO_2 core flooding test performed on a Tako sandstone sample,which measured 14.5 cm long and 3.68 cm in diameter. During the test,supercritical CO_2 (at 10 MPa and 40oC) was injected into one end of the horizontal core and a Xray CT scanner (with a resolution of 0.35mm x 0.35mm) was employed to monitor and record changes in the fluid saturations at 70 sections evenly spaced along the core length to enable 3D mapping of the saturation profiles throughout the core during the course of CO_2 flooding and imbibition. Analysis of the mean saturation profiles along the core length (obtained by averaging the CT values over each cross-section) revealed a strong influence by the (mean) porosity distribution,though this influence became gradually less pronounced after CO_2 breakthrough. A 1D model of the core was first constructed to simulate the CO_2 injection process and in particular to history match the evolution of the CT scan CO_2 saturation profiles along the core length with time. It was found that a reasonably match could be achieved by using a porosity-dependent capillary pressure multiplier. The multiplier was also dependent on injection time (CO_2 saturation level). In order to match the saturation profiles,it needs to be gradually scaled down as more CO_2 is injected.