| Based on outcrop, core, thin section and geochemical data, the development characteristics and formation stages of natural fractures of Leikoupo Formation in Pengzhou area of Western Sichuan Depression, Sichuan Basin were studied. The macro fractures in the study area can be divided into structural fractures and non-structural fractures according to their genesis. The structural fractures include tensile fractures, shear fractures and broken fractures, while the non-structural fractures are mainly weathering fractures. The macro fractures are mainly structural fractures (shear fractures and tensile fractures), in which the vertical fractures and high angle fractures have higher development density and effectiveness. Micro fracture has high filling degree, poor effectiveness and so has little influence on reservoir. The Leikoupo Formation in the study area mainly developed four stages of structural fractures and one stage of weathering fractures. The structural fractures were formed in the middle to late Indosinian, early to middle Yanshanian, late Yanshanian and Himalayan, and the weathering fractures were developed in the early Indosinian. The Indosinian fractures have been filled with calcite and gypsum before the large-scale expulsion of hydrocarbon from the source rocks in the middle and late Yanshanian, which is of little significance to the enrichment of oil and gas. The vertical fractures and high angle fractures formed in the middle and late Yanshanian and Himalayan are of great significance to the gas development of Leikoupo Formation in Pengzhou area. This study provides a basis for further comprehensive evaluation of reservoir characteristics and gas enrichment in the study area. |
