Characteristics and significance of supergene karst of the Upper Permian Changxing Formation in Puguang Gasfield,Sichuan Basin
Yang Fei1, Zhang Hong-An1, Wang Xue-Jun1, Peng Jun1, Mo Jian-Wu1, Zhuo Se-Qiang1, Zeng Zheng-Qing1, Zhou Kai1, Wang Yun-Suo1, Wei Ming-Yang2, Li Zong-Feng2, Lu Kai2
1 Exploration and Development Research Institute,Sinopec Zhongyuan Oilfield Company,Zhengzhou 450046,China; 2 College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;
Abstract：There is a great dispute in understanding the contact relationship between the Permian and Triassic, and origins of the karst of Changxing Formation in Sichuan Basin for a long time. Through the analysis of field outcrops, drilling, cores, imaging logging, C-O isotope and other data, this paper finds that large-scale karst gullies, karst caves, cystic karst caves and karst breccias occurred in Changxing Formation of Puguang Gasfield. The carbon isotopes of the dissolved limestone in Changxing Formation were negatively excursed near the Permian-Triassic boundary. The top of Changxing Formation is an obvious unconformity, and the karst facies variations are obvious on the imaging logging map. Furthermore, at the top of Changxing Formation, some strata is missing. According to the comprehensive analysis, the results reveal that the supergene karst had occurred in the Changxing Formation of Puguang Gasfield, and that the major factor causing the supergene karst is the great regression event at late Changxing Stage. Changxing Formation had been modified by the supergene karst for a long time. In addition to the reef-bank reservoirs at the edge of the platform, the interior of the platform and the up-slope at the front of the platform where the reef-bank is not occurred are also the favourable areas to search for the unconformity karst reservoirs.
Yang Fei,Zhang Hong-An,Wang Xue-Jun et al. Characteristics and significance of supergene karst of the Upper Permian Changxing Formation in Puguang Gasfield,Sichuan Basin[J]. JOPC, 2019, 21(6): 901-912.
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