Characterization of the Lower Cambrian Shale in the Northwestern Guizhou Province, South China: Implications for Shale-Gas Potential

The Lower Cambrian shale in the Northwest part of the Guizhou Province (NWG), South China, has recently been considered as a potential shale gas reservoir because of its large distribution and high total organic carbon (TOC) content. An integrated characterization about this shale succession is provided in this study to illustrate its shale gas potential. The shale in the NWG area is characterized by high TOC content and high thermal maturity. The mineralogical composition and lithofacies assemblage of the NWG shale are compared with hot shales for analogy and found to be greatly similar to the Barnett shales. Five different genetic types of pores have been identified by scanning electron microscopy. The porosity shows no correlation with the quartz and clay ratios, but it correlates well with the TOC content, suggesting that organic matter pores have contributed a lot to the total porosity. The pore size distribution is evaluated by pore volume and surface area based on diameter, indicating that the micropores and mesopores are the major pore sizes. The methane sorption isotherms conducted on representative samples with different TOC and clay contents certify the assumption that microporous organic matter in high-maturity shales provides a large internal surface area for the adsorbed gas. After comprehensive analysis, the lower part of the studied shale in the NWG, with high TOC contents, is proposed as a target for shale-gas production.