Role of basement faults in gas accumulation of Xujiahe Formation, Sichuan Basin

The Xujiahe Formation is characterized by a large gas-bearing area, low reserve abundance, low yield, and dominantly lithologic gas pools because sandstone reservoirs are tight and low permeable, structures have gentle relief, and faults and fractures are undeveloped. Searching sweet-spots is the key step in gas exploration. The basement heterogeneity in the Sichuan basin has led to the activity of basement faults in NE and NW directions since Meso-Cenozoic, which influences the evolution of sub-structure zones and causes the occurrence of fractures and minor normal faults in Xujiahe Formation reservoirs. These fractures and minor faults improved the reservoirs quality, provided the path for gas migration, and contributed to the formation of local gas-rich trends. Meanwhile, later activity of basement faults caused an abnormally high geothermal field, accelerating the thermal evolution of source rock. The area of basement faults has the most favorable conditions for gas accumulation and is the main target for gas exploration.