STUDY ON THE INFLUENCE OF RESERVOIR TIME-VARYING PERMEABILITY ON DEVELOPMENT PERFORMANCE IN HIGH-SHALE AND LOW-PERMEABILITY, UNCONSOLIDATED SANDSTONE RESERVOIR

Currently being at an early stage of water injection development, the W loose sandstone reservoir exhibits high shale content and low permeability. The impact of water injection on the reservoir remains unknown, which poses implications for subsequent development. Hence, this study aims to conduct time-varying experimental tests on the permeability of unconsolidated sandstone reservoirs characterized by high shale content and low permeability. Through the integration of numerical simulation methods, the objective is to establish the permeability evolution pattern of such reservoirs during water injection. The findings indicate the following: (1) The quality of injected water in high-shale, low-permeability, unconsolidated sandstone reservoirs has a discernible influence on permeability. As the oil content and suspended solids in the injected water increase, permeability gradually decreases, accompanied by an expanding range of change. (2) The experimental conclusions are further substantiated through numerical simulation, demonstrating that the influence of permeability variation in a 50 mD reservoir can be disregarded, regardless of the impact of injected water quality or the magnitude of the loss rate. On the other hand, the influence of injected water quality on permeability variation in a 10 mD reservoir becomes more apparent, with lower permeability exhibiting a greater susceptibility to water quality. (3) As the permeability of the high-shale, low-permeability, loose sandstone reservoir decreases, the impact of injected water quality on development becomes more pronounced. A doubling of suspended solids and oil content in the injected water quality corresponds to an amplified decrease in cumulative oil production. Thus, the influence of injected water quality must be taken into consideration during the water injection development process for such reservoirs.