Microfracturing in the Upper Triassic Sichuan Basin tight-gas sandstones: Tectonic, overpressure, and diagenetic origins

摘要: The western Sichuan Basin located at the front of Longmen Mountain in Province China is a foreland basin formed Late Triassic. Upper Triassic Xujiahe Formation an ultralow-permeability and low-porosity tight-gas sandstone reservoir. Microfractures, such as intragranular microfractures, grain-edge transgranular are abundant tight sandstones. Microfractures improve storage permeability impact distribution natural gas. reflect tectonic, overpressure, diagenetic origins. Using quartz calcite fluid inclusions burial history, tectonic microfractures were determined to be end Triassic, Cretaceous, Neogene–early Pleistocene. related being tension commonly filled with bitumen middle Cretaceous when maximum pressure coefficients 1.6 2.1. In late Neogene, coefficient was reduced less than 1.3 because fault activity uplift southwestern Basin, these closed calcite. transition stress state from compression by overpressure reason that setting. Diagenetic fractures Jurassic. Under intense compaction, grain-crushing crackle cleavage feldspar microfractures. Some caused diagenesis along bedding plane parallel directional mineral grains.