Organic Geochemistry Characteristics and Resources Potential of Triassic Natural Gas in Sichuan Basin, China

The lower and middle Triassic series in the Sichuan basin are formed in marine environment, most of the sediments are carbonate rocks, and the upper Triassic series are formed from marine to land environments, the sediments are mainly clastic rocks. The natural gas produced from the lower and middle Triassic comes mainly from shale source rocks, coal and carbonate source rocks in the Permian System, partly from the shale source rock in the Silurian System, some of them come from the lower and middle Triassic itself. The gas produced in the upper Triassic comes from coal bed in itself. So the gas produced from the Triassic System belongs to two petroleum systems, the former is the Silurian to lower and middle Triassic petroleum system and the latter is the upper Triassic to Jurassic petroleum system.The hydrocarbon source quantity and its generation intensity in Triassic gas pools in Sichuan Basin have been calculated based on its thickness, richness and maturation and according to the parameters acquired from the heat simulation test for the total organic carbon. The total gas generation quantity related to the lower Triassic gas pool is relatively high in the east, south, north and middle of the Sichuan basin. The total gas generation quantity related to the middle Triassic gas pool is relatively high in the east, middle, north and west of the Sichuan basin. Among them, the areas of high total gas generation quantity of the Silurian source rock are in eastern and southern Sichuan basin, the areas of relative high total gas generation quantity of the Permian source rock are in eastern, middle and northern Sichuan basin. The total gas generation quantity of lower Triassic source rock is slight. The area of highest total gas generation quantity of upper Triassic source rock is the western Sichuan basin, followed by the northern and middle, and the lowest is the eastern. The total oil generation quantity related to lower Triassic gas pools is relatively high in the east, south, middle and north of the Sichuan basin. The relative high areas of total oil generation quantity of upper Triassic source rock are in the west and middle of the Sichuan basin.The Triassic System in the Sichuan basin is very rich in oil and gas resources and has a vast range of prospects for oil and gas exploration. Both the sides of the Kaijiang-Liangping trough are the most important gas exploration areas to the Feixianguan formation of lower Triassic, and this area is also important to organic reefs in the Upper Permian. Especially, the belts combination oolic shoal in the lower Triassic with organic reef in the upper Permian is the most likely to find large scale gas fields in this area. The most important gas exploration area to the Jialingjiang formation of the lower Triassic and the Leikoupo formation of middle Triassic is the fracture developed belts in the northern, middle, southern and eastern Sichuan basin. The upper Triassic in the Sichuan basin is widely distributed and has a good condition for gas accumulation. The main exploration area ranges from east Longmen mountain to west Huayin mountain, and from south Jiulong mountain to north Hebaochang-Jieshichang.