Laboratory Study of Stress Sensitivity Characterization and Reservoir Quality Evaluation of Yingxiongling Shale in Qaidam Basin

Yingxiongling shale is characterized by high-frequency cyclic deposition, and the rocks in the area are classified into five rock types, which means that this area has complex geological features. Different types of rocks have nonhomogeneity and unclear stress sensitivity characteristics, which are important for reservoir stimulation and production. In this paper, the permeability stress sensitivity characteristics of different types of rocks are evaluated based on the elastic parameter stress sensitivity results, and the stress sensitivity parameters of rocks in the in situ stress state are proposed. The reservoir engineering quality of different types of rocks is evaluated by combining their microscopic pore characteristics with stress sensitivity characteristics. The results show that the stress sensitivity characteristics of different types of rocks are affected by the number of laminae and clay mineral content, the elastic parameter stress sensitivity of laminated rocks is stronger than that of layered rocks, and that of argillaceous rocks is stronger than that of limy rocks in layered shale. The permeability stress sensitivity of layered rocks is stronger than that of laminated rocks, that of argillaceous rocks is stronger than that of limy rocks in layered shale, and that of sandstone is the strongest. The laminated rocks are more capable of forming cracks and have better pore connectivity than the layered rocks. Finally, based on the elastic parameter stress sensitivity coefficient, a new coefficient is proposed to improve the permeability stress sensitivity, and the improved permeability stress sensitivity coefficient is used to evaluate the permeability characteristics of the reservoir under the in situ stress. Then, the quality of the main reservoirs was evaluated by the new parameters; the reservoir quality of laminated limy shale was the best and that of layered argillaceous shale was the worst. This study provides theoretical support for the target layer preference of Yingxiongling shale and highly efficient development.