Early Paleozoic shale properties and gas potential evaluation in Xiuwu Basin, western Lower Yangtze Platform

Abstract

From 2012, China has produced significant amount of shale gas from Wufeng–Longmaxi Shale of Late Ordovician–Early Silurian and Qiongzhusi Shale of Early Cambrian in the Sichuan Basin and its southern and eastern surrounding area, Upper–Middle Yangtze Platform. The Wufeng–Longmaxi Shale and Qiongzhusi Shale, covering the most area of the Yangtze Platform, have become the primary target formations for shale gas exploration in the South China. The current studies mainly focused on Sichuan Basin and its surrounding areas in Upper–Middle Yangtze Platform with a few studies in the eastern Lower Yangtze Platform. Therefore, we implemented this research, on the one hand, to evaluate the shale gas potential of Early Paleozoic formations in Xiuwu Basin in the western Lower Yangtze Platform, and on the other hand, to contribute to the comprehensive studies of shale gas exploration in the entire Yangtze Platform. Mineral composition by X–ray diffraction (XRD), organic matter features by total organic carbon (TOC) analysis, Rock–Eval pyrolysis, and vitrine reflection (Ro), pore structure by mercury intrusion and low–temperature/low–pressure N2 physisorption, and sorption capability by methane isothermal adsorption were implemented to estimate the geological characteristics of organic shale in Xiuwu Basin. The results indicated that the heterogeneity of Early Cambrian shale is serious, but in general, its fracability is strong, mesopores and micropores are well-developed, and the capacity of gas generation and adsorption are strong. These analyses indicate the Early Cambrian shale in Xiuwu Basin to be a promising play of shale gas development.