Experimental and analytical study of oxygen consumption during air injection in shale oil reservoirs

Abstract

AIP (air injection process) is applied as an EOR (Enhanced oil recovery) method in conventional oil reservoirs, while the implementation of AIP in shale oil reservoirs has rarely been studied. The thermal effect of AIP in shale oil reservoirs is insignificant considering its low air injectivity, and the main challenge is whether the produced oxygen concentration at the production well can be reduced below 10% to avoid the potential safety hazards. In this paper, an analytical method was proposed to estimate the produced oxygen concentration during AIP, where the oxygen reaction rate was measured by the SBR (small batch reactor) experiments. In the SBR tests, a constant oxygen reaction rate was observed at a corresponding reservoir temperature. A higher reservoir temperature resulted with greater oxygen consumption. The air flooding tests were conducted with shale core and the proposed analytical method was validated by the air flooding tests. The analytical method was further applied to investigate the AIP feasibility in the air flooding tests. The results indicate that a core needs to be a longer than 0.132 m, or the injection pressure is lower than 2.68E + 06 Pa (388.70 psi), to satisfy the produced oxygen concentration requirement for AIP. This study can explore the potential of air injection in developing shale oil reservoirs and provide insights to the AIP projects in field level.