Lithofacies palaeogeography of the Late Permian Wujiaping Age in the Middle and Upper Yangtze Region,China

The lithofacies palaeogeography of the Late Permian Wujiaping Age in Middle and Upper Yangtze Region was studied based on petrography and the ＂single factor analysis and multifactor comprehensive mapping＂ method. The Upper Permian Wujiaping Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks and clastic rocks, with lesser amounts of siliceous rocks, pyroclastic rocks, volcanic rocks and coal. The rocks can be divided into three types, including clastic rock, clastic rock-limestone and limestone-siliceous rock, and four fundamental ecological types and four fossil assemblages are recognized in the Wujiaping Stage. Based on a petrological and palaeoecological study, six single factors were selected, namely, thickness （m）, content （%） of marine rocks, content （%） of shallow water carbonate rocks, content （%） of biograins with limemud, content （%） of thinbedded siliceous rocks and content （%） of deep water sedimentary rocks. Six single factors maps of the Wujiaping Stage and one lithofacies palaeogeography map of the Wujiaping Age were composed. Palaeogeographic units from west to east include an eroded area, an alluvial plain, a clastic rock platform, a carbonate rock platform where biocrowds developed, a slope and a basin. In addition, a clastic rock platform exists in the southeast of the study area. Hydro- carbon source rock and reservoir conditions were preliminarily analyzed based on lithofacies palaeogeography. Sedimentary environments have obvious controls over the development of the resource rocks. With regard to the abundance of organic matter, the hydrocarbon potential of the coastal swamp environment is the best, followed by the basin environment and the carbonate rock platform. The gas reservoir types of the Wujiaping Stage can be classified as conventional and unconventional gas reservoirs, like coal bed gas and shale gas; all of them have well exploration prospects.

Lithofacies palaeogeography of the Upper Permian Changxing Stage in the Middle and Upper Yangtze Region,China

Based on the petrological study,according to single factor analysis and multifactor comprehensive mapping method,the quantitative lithofacies palaeogeography of the Upper Permian Changxing Stage of the Middle and Upper Yangtze Region was studied.The Changxing Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks;in addition,clastic and siliceous rocks occur with rare coals and pyroclastic rocks.Lithofacies can be divided into five types,including clastic rock assemblage,clastic rock-limestone assemblage,limestone assemblage,limestone-siliceous rock assemblage,and siliceous rock-clastic rock assemblage.Four fundamental ecological types and five fossil assemblages were recognized in the Changxing Stage.On the basis of the petrological and palaeoecological study,eight single factors were chosen including thickness,content of marine rocks,content of shallow water carbonate rocks,content of bioclasts with limemud matrix,content of bioclasts with sparry cement,distribution of reefs,content of thin bedded siliceous rocks and content of deep water sedimentary rocks.And eight single factor maps and one lithofacies paleogeographic map of the Changxing Stage were compiled.Paleoenvironments from west to east include an erosional area,fluvial plain,clastic platform,carbonate platform and reefs that developed there,slope and basin,low energy organic banks,and high energy organic banks.Sedimentary environments have an obvious control on the development of the source rocks,and the excellent source rocks are developed in the Dalong Formation.Changxing Stage reservoirs should be dominated by the reef and platform surrounding the GuangyuanLiangping Basin rim area,and is the most favorable exploration area of the reef petroleum reservoirs of the Changxing Formation.