Prediction of geomechanical sweet spots in a tight gas sandstone reservoir: A case study of lower Permian strata in the southern Qinshui Basin, China

Using the tight sandstone of the lower Permian Shanxi Formation in the southern Qinshui Basin as an example, we have developed the concept of “geomechanical sweet spots” in a strongly deformed strike-slip fault zone. The evaluation elements for geomechanical sweet spots include current tectonics, paleotectonics, fractures, and rock brittleness. The high-angle basement-surface strike-slip faults that developed in the study area control the formation and development of the descending plane (upper plate) positive traction folds and the ascending plane (lower plate) isopach folds. The current tectonics and the paleotectonics in the mid-Himalayan tectonic period have a certain adjustment effect on the distribution of natural gas. We predicted the fracture development area of the target layer in the main episode of the Himalayan period based on the 3D finite-element method. The regions with a higher fracture development degree are mainly distributed in the Sitou-Houchengyao strike-slip fault zone and the northwestern and eastern parts of the study area. We also divide the brittleness index of sand group II into four grades. Based on a single-factor evaluation of the current tectonics, paleotectonics, fractures, and rock brittleness, we established a standard parameter system for evaluating the geomechanical sweet spots of tight gas sandstone reservoirs.