Stress sensitivity of shale fracture network reservoirs and its impact on seepage

To address the issues of low experimental pressure and the difficulty in accurately reflecting reservoir conditions in studies on the stress sensitivity of shale fracture network reservoirs, this study employed a whole-process simulation experiment method from low pressure to actual reservoir stress to systematically evaluate the stress sensitivity of shale fracture network reservoirs and quantify its impact on fracture seepage through theoretical analysis. The stress sensitivity curve of shale fracture networks exhibited four-stage characteristics, which became more pronounced as permeability decreased. The overall permeability retention rate increased with the increase of fracture core permeability, reaching a maximum of 25.46%. Shale fracture network cores under compression underwent four stress response stages successively: plastic deformation, pseudo-plastic deformation, elastic deformation, and rigid deformation. The most significant reduction in fracture core permeability occurred in the first stage, with a maximum decrease of 73.63%. The fracture cores exhibited a stress hysteresis effect. Cores with higher fracture permeability demonstrated greater compressibility and required higher initial net stress to enter the same stress stage.Under actual reservoir stress conditions, most cores were in the elastic deformation stage, while a small portion entered the rigid deformation stage during later development phases. The actual reservoir stress sensitivity curves could be divided into two types: "L"-shaped type and quasi-linear type. Under actual reservoir conditions, the permeability loss of shale fracture cores was generally less than 25%, indicating weak stress sensitivity. In actual production, under low pressure difference conditions, the impact of stress sensitivity on flow rate was less than 5% and could be considered negligible. However, under high pressure difference production, its degree of impact exceeded 10%, with a peak of 17.59%. If stress sensitivity was neglected in the productivity evaluation of shale fracture network reservoirs, the results would be significantly overestimated. These findings provide a technical basis for the efficient development of unconventional oil and gas resources.