CO_2 flooding enhanced oil recovery evaluated using magnetic resonance imaging technique

摘要

CO_2 flooding is an efficient enhanced oil recovery method, especially for waterflooding depleted reservoirs. In this work, waterflooding and CO_2 flooding were evaluated in a coreflooding experiment using MRI to clarify the multiphase flow and oil recovery behavior in porous rock at a typical reservoir temperature-pressure condition. A series of in situ spatially and temporally resolved MR images revealed dynamic distribution information of oil, water, and SC-CO_2 during coreflooding process. For water-flooding, the phenomenon of water viscous fingering and channelling were obvious, which affected the volumetric sweep efficiency, higher water injection rate may appropriately improve oil recovery but the EOR efficiency was lower. CO_2 diffused and migrated into some regions where was not efficiently swept by waterflooding, and a CO_2-oil-miscible phase was formed. The formed local 'oil bank' before SC-CO_2 front restrained effectively CO_2 channelling and fingering, and enhanced oil recovery by 13.2% and generated more homogeneous residual oil saturation distribution in porous media compared to water-flooding. The relative permeability and capillary pressure were determined simultaneously based on the capillary end oil saturation profiles, these quantitative results demonstrated that CO_2 flooding expanded fluids mobility range of the wetting and nonwetting phases and improved the displacement efficiency about 10% than waterflooding.