Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China.

The capacity and deliverability of shale gas are closely linked to the presence of multi-scale fractures, including fractures and faults, within organic-rich shales. This study aims to investigate the fracture system of the Longmaxi Formation shale in the Changning Block of the southern Sichuan Basin and quantify the influence of multi-scale fractures on shale gas capacity and deliverability. The fracture system was analyzed through outcrop, core observations, and 3D seismic interpretation. Criteria for fault classification were established based on the horizon, throw, azimuth (phase), extension, and dip angle. The Longmaxi Formation shale mainly comprises shear fractures that form under multi-phase tectonic stress, characterized by large dip angles, small extensions, small apertures, and high density. The high content of organic matter and brittle minerals in the Long 1-1 Member facilitates the occurrence of natural fractures, which somewhat enhance shale gas capacity. Reverse faults with a dip angle of 45-70° exist vertically, while laterally, there are early-stage nearly E-W faults, middle-stage NE faults, and late-stage NW faults. Based on the established criteria, faults that cut upward through the strata in and above the Permian with a throw greater than 200 m and a dip angle greater than 60° have the greatest influence on shale gas preservation and deliverability. These results provide important guidance for shale gas exploration and development in the Changning Block and contribute to our understanding of the relationship between multi-scale fractures and shale gas capacity and deliverability.