Production Response to Supercritical CO2 Cyclic Injection SCCI and CO2 Sequestration Potential in a Tight Reservoir, China

Abstract CO2 based gas injection techniques for enhanced oil recovery (EOR) coupled with offsetting greenhouse gas emissions have received significant attention. In this work, a tight geological reservoir in China was focused. To further unlock the reserves after a natural depletion, the technique of SCCI was therefore suggested. The interest of this paper was to study the production response of the tight reservoir to SCCI and CO2 sequestration efficiency during this process. As a result of CO2 dissolution, the viscosity of the crude oil was gradually reduced with CO2 molar fraction and then nearly plateaued from 35 mol%. For this given reservoir, the optimal depleting pressure to implement SCCI was 20.88 MPa, which corresponded to the highest ultimate oil recovery. Moreover, the oil recovery increased linearly with CO2 slug size due to the pressurizing effect and viscosity reduction, which thus led to 11% of incremental oil recovery after a natural depletion. However, the oil production rate was found to rapidly decline with the decrease of core pressure. Due to the limited gas diffusion, the oil recovery steeply dropped with the cycle number and only 0.5% of oil was produced at the third cycle, indicating the insufficiency of SCCI to further mobilize the oil in place. During the SCCI, more than 85% of the injected CO2 species have been retained in the tight porous media.