Abstract:

By means of detailed outcrop observation, lateral formation tracking and correlation, realistic writing of typical sedimentary section, systematic sampling and laboratory experimental analysis, detailed study was performed for the first time on sedimentary system of the Late Permian Wujiaping Formation in the western Sichuan Basin.The study found that the Dongwu movement at the end of the Early Permian was uplifting of fault block under tensional background.The Dongwu movement turned the southwest Kang-Dian ancient land into a provenance under the pushing and shoving by the ancient Tethys oceanic crust.Meanwhile, a trough graben area was formed in the northwest Guangyuan-Wangcang area due to the associated tensional subsidence.The relief in the area declines at low angle from southwest to northeast and indirectly controls the formation and lithofacies distribution of Wujiaping Formation.The sedimentary facies zones feature in wide and gradual variation.The Late Permian Wujiaping Formation was resulted from an high sea level transgression from northwest to southwest above the early weathering erosion interface.A denudation area and alluvial plain-coastal plain-coastal swamps-carbonate ramp sedimentary systems are successively developed from the southwest to northwest.Among these sedimentary systems, the moderate-shallow ramp bioclast beach was the most favorable reservoir facies belt with large thickness, wide distribution and near distance to the Guangyuan-Wangcang hydrocarbon kitchen, and it is capable of trapping hydrocarbons generated nearby.Several rounds of detailed digital seismic investigation have revealed many buried structures, providing new domains for enlarged exploration of carbonate gas reservoirs in the basin.

Key words: sedimentary system, evolution model, Wujiaping Formation, Late Permian, Sichuan Basin