The types and evolution of platform-edge reefs in Permian Changxing Formation,eastern Sichuan Basin

Abstract：The formation, development and consumption of Kaijiang-Liangping trough have obviously controlled the distribution of Changxing Formation reefs, and thus determined the types, sizes and distribution of the reef gas reservoirs. Through the detailed study of internal structures and their development, the authors found that the platform-edge reefs have very different sedimentary characteristics in different places near the trough, and could be divided into patch reefs, mound reefs and barrier reefs according to the development scales. The platform-edge reefs and their evolutionary stages were summarized systematically. The patch reefs were mainly developed from Changxing 1st period or Changxing 2nd period to Changxing 3rd period on the southern side of Kaijiang-Liangping trough, characterized by the shortest formation time, the smallest scale, the most simple texture and three evolutionary stages. The mound reefs were mainly developed from Changxing 2nd to Changxing 3rd period on the middle to northern side of Kaijiang-Liangping trough, and their development could mostly last to the Changxing 3rd period, with the characteristics of larger scale, more complex texture relative to the patch reef, and five evolutionary stages. The barrier reefs were mainly developed from Changxing 1st to Changxing 2nd period at western Hubei trough or in east Sichuan area, and their development mostly lasted to Changxing 3rd period, with the characteristics of longest formation time, largest scale, most complex evolution and five evolutionary stages.