Experimental investigation of CO2 huff-n-puff process for enhancing oil recovery in tight reservoirs

Abstract

Due to the feature of tight formation, the primary oil recovery is usually very low and leaves substantial oil still in place. This fact results in a strong motivation of applying an enhancing oil recovery (EOR) method to further increase the oil recovery. In the present work, CO2 huff-n-puff process as a potential EOR method for tight oils was experimentally investigated in 0.3md cores. The visual tests proved that the oil swelling factor and CO2 solubility increased with pressure. The core tests indicated that CO2 huff-puff process is a viable technique to promote tight oil recovery. The magnitude of oil recovery is strongly dependent on CO2 pressure, the oil recovery can reach 30.9% at 16MPa in our experiment. Compared multi- to single-cyclic operation, the oil recovery is further increased by 10% by a four-cycle operation. However, after two cycles, the oil recovery significantly dropped. Differential production pressure (ΔP) is the dominant parameter for tight oil recovery in CO2 huff-puff process. This work is supposed to provide some necessary clues for pilot design.