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Shale Composition and Pore Structure Controls on Gas Storage Potential of Silurian Marine Shale and Jurassic Lacustrine Shale, Central China

Hou, Yuguang; He, Sheng; Harris, Nicholas B.; Wang, Yi; Zhang, Jiankun; Cheng, Chunyang

The Silurian Longmaxi Formation (marine) and Jurassic Ziliujing Formation (lacustrine) are gas-prospective shale formations in the central Yangtze area of China. In this study, we investigate possible controls by shale composition and fabric on pore structure and CH4 sorption. The total organic carbon (TOC) content of the Longmaxi Formation is between 0.12 and 4.85 wt% at thermal maturity from 1.92 to 3.9%VRo. TOC content of the Ziliujing Formation ranges from 0.54 to 2.10 wt% at maturity of 1.25 to 1.45%VRo.

The Silurian shales are mainly microporous (<2nm) with complex, heterogeneous pore size distributions as identified by low pressure N2 sorption BET surface areas of 9.9-34.5m2/g. The mesoporous (2nm~50nm) in Jurassic shales have typically N2 BET surface areas in the range of 5.3-12.3 m2/g, indicative of larger pore sizes. The surface area of Jurassic shales increases only with detrital mineral, in particular the abundance of quartz, which implies that porosity associated with the inorganic mineral component may be the primary controls.

The methane sorption capacity of Silurian shales ranges between 0.49 to 5.85 cm3/t with temperature at 55 degrees Celsius and pressure at 10.5 MPa and the corresponding. The sorption capacity of Jurassic shales is 1.03 and 3.26 cm3/g. Methane sorption in Silurian shales increases with increasing TOC and micropore volume, indicating that microporosity associated with the organic fraction is a primary control. For Jurassic shales, high TOC and lower surface area correlate with methane capacity. We suggest that sorption capacities for these shales are unrelated to thermal maturity. The different correlations between gas sorption with TOC content and detrital mineral content in Silurian and Jurassic shales is in part attributed to the different depositional environments.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013