Shale gas reservoir characteristics of Ordovician-Silurian formations in the central Yangtze area, China

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• 作者：Chang’an Shan ; Tingshan Zhang ; Yong Wei ; Zhao Zhang
• 关键词：reservoir characteristic ; shale gas ; Upper Ordovician ; Lower Silurian ; central Yangtze area
• 刊名：Frontiers of Earth Science
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：11
• 期：1
• 页码：184-201
• 全文大小：
• 刊物主题：Earth Sciences, general;
• 出版者：Higher Education Press
• ISSN：2095-0209
• 卷排序：11

文摘

The characteristics of a shale gas reservoir and the potential of a shale gas resource of Ordovician–Silurian age in the north of the central Yangtze area were determined. Core samples from three wells in the study area were subjected to thin-section examination, scanning electron microscopy, nuclear magnetic resonance testing, X-ray diffraction mineral analysis, total organic carbon (TOC) testing, maturity testing, gas-bearing analysis, and gas component and isothermal adsorption experiments. A favorable segment of the gas shale reservoir was found in both the Wufeng Formation and the lower part of the Longmaxi Formation; these formations were formed from the late Katian to early Rhuddanian. The high-quality shale layers in wells J1, J2, and J3 featured thicknesses of 54.88 m, 48.49 m, and 52.00 m, respectively, and mainly comprised carbonaceous and siliceous shales. Clay and brittle minerals showed average contents of 37.5% and 62.5% (48.9% quartz), respectively. The shale exhibited type II₁ kerogens with a vitrinite reflectance ranging from 1.94% to 3.51%. TOC contents of 0.22%–6.05% (average, 2.39%) were also observed. The reservoir spaces mainly included micropores and microfractures and were characterized by low porosity and permeability. Well J3 showed generally high gas contents, i.e., 1.12–3.16 m3/t (average 2.15 m3/t), and its gas was primarily methane. The relatively thick black shale reservoir featured high TOC content, high organic material maturity, high brittle mineral content, high gas content, low porosity, and low permeability. Shale gas adsorption was positively correlated with TOC content and organic maturity, weakly positive correlated with quartz content, and weakly negatively correlated with clay content. Therefore, the Wufeng and Longmaxi formations in the north of the central Yangtze area have a good potential for shale gas exploration.