Abstract:
Industrial gas flow of shale gas was recently achieved in Doushantuo Formation of Sinian in the western Hubei Province. The organic-rich shale of Doushantuo Formation was predominantly found in Deyang-Anyue rift of the upper Yangtze region and the western Hubei rift of the middle Yangtze region, and its sedimentary characteristics and petroleum geological conditions were critical for further exploration and development of shale gas and oil resources. A comparative analysis of the sedimentary characteristics and environment of these two rifts was conducted through the analysis of the outcrops, drilling, and geophysical data of Doushantuo Formation. The results are as follows. ① The paleogeographic pattern exhibited a terrain that was higher in the west and lower in the east in the middle-upper Yangtze region during the deposition of Doushantuo Formation. ② A significant area of ancient land persisted in the upper Yangtze region during the early deposition stage of Doushantuo Formation, with a relatively thin layer or missing layer, which has mass deposition in the middle-later stage. While the middle Yangtze region features sedimentary environment such as platform, lagoon, continental shelf, and basin, with well-developed strata, substantial sediment thickness, and development of organic-rich shales. ③ Doushantuo Formation is a product of an extensional environment, and the aulacogen in the middle-upper Yangtze region all formed graben basin with in the platform. The formation of Deyang-Anyue fault depression in the upper Yangtze region occurred late, and Doushantuo Formation primarily deposited in carbonate rock. Conversely, the western Hubei rift of the middle Yangtze region formed earlier, with shale and carbonate intercalations depositing. ④ In the western Hubei Province, Doushantuo Formation depositing in the rift trough contains abundant organic matter. The well-preserved structural units are anticipated to lead to breakthroughs in shale gas exploration, which could potentially serve as the natural gas source rock of Dengying Formation, and present opportunities for conventional oil and gas discoveries within the matching area of source-reservoir-cap conditions. This research could provide some references for the oil and gas investigation work in Sinian-Cambrian rifts.