Experimental Investigation of Supercritical CO2 Injection for Enhanced Gas Recovery in Tight Gas Reservoir

Abstract

ABSTRACT Tight gas reservoirs always have low natural gas recovery due to poor physical properties. However, there is still no effective means to enhance gas recovery (EGR) in tight gas reservoir. In this paper, experimental approaches were carried out to study the Supercritical CO2 (SCCO2) injection for EGR in tight gas reservoirs. Phase behavior investigation was performed to indicate the property difference between SCCO2 and natural gas under reservoir condition. Results show that SCCO2 has significantly higher density and viscosity than natural gas under reservoir condition. Gravity differentiation and near-piston displacement can be achieved in case of SCCO2 injection and thus the displacement efficiency can be improved. Gas adsorption tests show that the adsorption capacity of SCCO2 in tight sandstone is more than 50% higher than that of natural gas. Diffusion simulation show that SCCO2 shows weak diffusion capacity and slow diffusion process in natural gas, which indicates that SCCO2 and natural gas are not easy to mix and it is good for displacement and EGR. On the basis of these fundamental tests, long-core experiments of SCCO2 injection for EGR in tight gas reservoir were carried out using natural cores from DS tight gas reservoir. Results indicate that SCCO2 injection can improve gas recovery by 18.9% on the basis of gas depletion. Furthermore, the influencing factors of SCCO2 injection in tight cores were experimentally investigated. Results demonstrate that SCCO2 injection have better EGR effect in case of lower permeability, higher water saturation and greater dip angle.