An Experimental Study of Cyclic CO2 Injection to Improve Shale Oil Recovery

Abstract The low recovery and high oil volume remaining in shale oil reservoirs are a strong motivation to investigate the application of enhanced oil recovery methods in these reservoirs. This paper presents the potential of applying cyclic CO2 injection to improve the recovery factors of shale oil reservoirs. Cyclic CO2 injection could be an effective technique to improve the oil recovery of this type of reservoirs for several reasons. It is a single-well process; well-to-well connectivity is not required, the hydraulic and natural fractures provide a large contact area for the injected gas to penetrate and diffuse into the low-permeability matrix; and the payback period of the cyclic CO2 injection process is short compared with the other flooding process. Very limited numerical and laboratory studies are available to study the feasibility of CO2 huff-n-puff for shale oil reservoirs. Latest numerical studies have revealed that CO2 huff-n-puff technique could be an effective method to increase recovery factors of shale oil reservoirs. In order to support the numerical studies results, a laboratory study was conducted using shale cores from Mancos and Eagle Ford. The aim of this study is to evaluate the potential of cyclic CO2 injection. Many design parameters such as soaking period, soaking pressure, and numbers of cycles were considered to evaluate the feasibility of cyclic CO2 injection. The laboratory results indicate that cyclic CO2 injection improved recovery of shale oil cores from 33% to 85% depending on the shale core type and the other operating parameters. These results have shown that cyclic CO2 injection is a promising method to improve the recovery of shale oil reservoirs. Also this study aided to develop a better understanding of the performance of cyclic CO2 in shale oil reservoirs.