Geochemical and Geological Characteristics of the Upper Ordovician-Lower Silurian Shales in the Upper Yangtze Basin, South China: Implication for the Shale Gas Exploration.

ABSTRACT

Shale gas exploration in the Upper Yangtze Basin has been conducted for over ten years. The successful drillings in the region suggest that well-planned geological survey and reservoir evaluation are indispensable for the success of these drillings. In this study, the shale gas potential of Late Ordovician to Early Silurian mudstones/shales of the Wufeng-Longmaxi formations in the Upper Yangtze Basin was evaluated. First, all of the available geochemical and petrological data from Late Ordovician to Early Silurian mudstones/shales in the region were compiled. Distributional patterns of total organic carbon (TOC) values, thickness, thermal maturity, and burial depth of organic-rich mudstones/shales from the targeted formations were then analyzed. Our results show that TOC values range from 1.20 to 5.12%; R o values range from 1.92 to 2.86%; porosity varies from 0.77 to 9.2%; permeability varies from 0.015 to 1.99 md; the composition of quartz group of mineral component ranges from 18 to 85%, 59% in average; and clay mineral component ranges from 7 to 56%, 31% in average. Finally, based on these comprehensive analysis, three areas with great potential, that is, Luzhou-Xishui, western Chongqing, and Wulong-Shizhu, were selected as targets for further shale gas exploration and exploitation.