A center in the present paper is referred to as an area or region which may include one or more hydrocarbon accumulations. A hydrocarbon generation center is referred to as an area containing high quality source rock which was subjected to thermal maturation. A gas generation center is an area in which an oil pool or accumulation was present, and oil was thermally cracked to generate gas. A gas accumulation center is referred to as an area in which natural gas generated from cracked oil accumulated. A gas preservation center is referred to as an area or region where the present natural gas pool/pools is/are located.As one of the oldest petroleum reservoir rocks in the world, the upper Sinian Dengying Formation (Upper Proterozoic) in the Sichuan basin was deeply buried, and its paleo-oil pools (gas generation centers) underwent complex transformation into paleo-gas pools (gas accumulation centers ) and the present gas pools (gas preservation centers) as a result of multiphase tectonic activities. The paleo oil pools (gas generation centers) were the main hydrocarbon sources of the paleo gas pools (gas accumulation centers), which were in turn the main sources of hydrocarbons for today's (remaining) gas pools (gas preservation centers). The key factor in the oil accumulation was the presence of rich hydrocarbon source rocks (hydrocarbon generation centers) in the Early Cambrian strata and a good seal development. Being controlled by the early tectonics and sedimentary development of the basin, the hydrocarbon generation centers appeared to have been stationary in space, while in time the other three centers (gas generation centers, gas accumulation centers and gas preservation centers) migrated as result of tectonic events in the basin. Therefore, * Author for corresponding. E-mail: 287671077@qq.com the time-spatial relationships between these "three centers" (gas generation centers, gas accumulation centers and gas preservation centers) decides the final distribution of natural gas in the Sichuan basin.Relationship between generation, accumulation and preservation of hydrocarbons in the marine carbonates buried deeper than 4500 m in the Sichuan basin, can be separated into: (1) an accumulation mode with the "three centers" being superimposed; (2) an accumulation mode with "the preservation center" disintegrated; (3) an accumulation mode with the "three centers" migrated for a short distance; (4) a destruction mode with the preservation center lost. The natural gas exploration of the upper Sinian carbonate rocks in the Sichuan basin can be most successful where the "three centers" overlap, such as at the front area of the Micang Mountains, which could be the most promising area for the future gas exploration.
The only major breakthrough in the exploration of the Sinian of the Sichuan Basin has been track simulation was applied to constrain the thermal evolutionary history of the source rocks in this study. Combined with trap formation and evolution, the formation, destruction, and accumulation history of the Sinian reservoirs were analyzed from a dynamic perspective. The Sinian reservoirs underwent several primary stages: the paleo-reservoir formation and destruction in the late Silurian, hydrocarbon Jurassic, and the exsolution and accumulation of dissolved-gas as a result of episodic uplift since the Late gas. The formation of the Weiyuan gas field is also related to this process. The Sinian in the Sichuan Basin has a broad exploration prospect, and exploration targets focused on the Leshan-Longnüsi Paleotransformation.
The lower Cambrian Niutitang Formation hydrocarbon source rocks at the DingshanLintanchang structure in the southeast Sichuan Basin were of medium-good quality with two excellent hydrocarbon-generating centers developed in the periphery areas, with a possibility of forming a medium to large-sized oil-gas fi eld. Good reservoir rocks were the upper Sinian (Dengying Formation) dolomites. The mudstone in the lower Cambrian Niutitang Formation with a good sealing capacity was the cap rock. The widely occurring bitumen in the Dengying Formation indicates that a paleo oil pool was once formed in the study area. The fi rst stage of paleo oil pool formation was maturation of the lower Cambrian source rocks during the late Ordovician. Hydrocarbon generation from the lower Cambrian source rocks stopped due to the Devonian-Carboniferous uplifting. The lower Cambrian source rocks then restarted generation of large quantities of hydrocarbons after deposition of the middle Permian sediments. This was the second stage of the paleo oil pool formation. The oil in the paleo oil pool began to crack during the late Triassic and a paleo gas pool was formed. This paleo gas pool was destroyed during the Yanshan-Himalayan folding, uplifting and denudation. Bitumen can be widely seen in the Dengying Formation in wells and outcrops in the Sichuan Basin and its periphery areas. This provides strong evidence that the Dengying Formation in the Sichuan Basin and its periphery areas was once an ultra-large structural-lithologic oil-gas fi eld, which was damaged during the Yanshan-Himalayan period.
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