Research On Sedimentary Characteristics Of Changxing (Dalong) Formation Of Upper Permian In Jiangyou And Jiange, Northwest Sichuan Basin

In this paper, the Changxing (Dalong) formation's stratigraphy, lithology, sedimentary diagenesis and reservoir characteristics in upper Permian, have been painstaking researched in northwest region of Sichuan. The research by the theoretical guidance of carbonate sedimentology and petroleum geology, reservoir geology, and the latest research progress at home and abroad, with the research object to profiles and thinsections. Focusing on the sedimentary facies of the main features, the main role of diagenetic reservoir. Finally, I made a summary on Changxing reef, beach development and distribution regular pattern, predicted the oil and gas prospects of reef body too.In our research area, the lithology of the Changxing formation is dominated by bioclastic pack-stone which contains many organisms, such as sponges, crinoideas, gastropods, brachiopodas, foraminiferas and so on. The Dalong formation is different from Changxing formation by sedimentary facies but identical in time. It is marked by a deep water sediments which are formed by black mud-stone and have many kinds of organisms dominated by sponge spicules. The reservoir of the Changxing formation has different types of the pore space which mainly includes intergranular pore, biologic framework pore and fracture. While the quality of the reservoir in the Dalong formation is bad because the silication.Research shows that since from the initial deposition stage of Late Permian Changxing formation, Guangyuan–Liangping area is a gulf which formed by the rift-type synsedimentary fault in Upper Yangtze Platform. Tidal flat and open platform (with bioclastic shoal)have developed on profiles of Jiangyou Changxing Yudongliang and Pingshan Changxing formation. Immature sponge reefs have been also developed on Pingshang profile. Jiange Changjianggou profile have developed deep water deposits (rich in sponge spicules and radiolarians) on Dalong Formation, whose age is same to Changxing formation. Main types of storage space are intergranular dissolution pores, intergranular pore, fracture-type caves, structural fratures and dissolution fratures. In a word, reefs on the edge of Guangyuan - wangcang Gulf located on the Guangyuan Erlangmiao in Jiangyou and Xiasi in Guangyuan where Changxing Formation is deep buried, are a favorable layer for exploration of underground reef -beach combination.