Geological characterization of a lower Cambrian marine shale: implications for shale gas potential in North-Western Hunan, South China

In this study, geological features of the lower Cambrian-aged Niutitang Shale in
north-western Hunan province of South China are investigated. Results indicate that the Niutitang Shale has abundant and highly mature algal kerogen, with total organic carbon (TOC) content ranging from 0.6% to 18.2%. The equivalent vitrinite reflectance (equal-Ro) value is between 2.5% and 4.3%. Mineral constituents are dominated by quartz and clay. The average quartz content (62.8%) is much higher than that of clay minerals (26.1%) and suggests a high brittleness index. Organic-matter pores, inter-particle pores, intra-particle
pores, interlaminated fractures, and structural fractures are all well developed. Porosity ranges from 0.6% to 8.8%, with an average of 4.8%, while permeability varies from 0.0018 μD (microdarcy) to 0.0600 μD (averaging 0.0182 μD). The porosity of TOC- and clay-rich shale samples is generally higher than that of quartz-rich shale samples. The gas adsorption capacity of the Niutitang Shale varies from 2.26 cm3 /g to 4.53 cm3 /g, with a mean value of 3.11 cm3
/g. The TOC content appears to significantly influence gas adsorption capacity. In
general, TOC-rich samples exhibit much higher adsorption capacity than TOC-poor samples.