A preliminary study on the characterization and controlling factors of porosity and pore structure of the Permian shales in Lower Yangtze region, Eastern China

• Permian shales in the Lower Yangtze region contain mainly gas-prone kerogen.
• Porosity increases with TOC when TOC < 12 wt.%, but decreases for higher TOC samples.
• Positive correlation exists between TOC and micropore volume for all samples.
• Permian shales with TOC > 4 wt.% are suggested to have shale gas potential.

Permian organic-rich shales occur throughout the Lower Yangtze region in Eastern China and are potentially a future target for shale gas exploration. Due to the lack of data, the gas potential of these Permian shales is difficult to evaluate. In this study, a total of 22 Permian shale samples were collected from two wells and their geochemical and rock property (porosity) characteristics were investigated. The results show that the samples have a total organic carbon (TOC) content of 0.6–17.4 wt.% derived from mainly gas-prone kerogen with a vitrinite reflectance (Ro) value ranging from 2.3 to 2.7%. Total porosity of the samples ranges between 1 and 5.5%. The micropore and mesopore surface areas range between 5.41–35.69 m2/g and 3.59–11.23 m2/g, respectively. Micropore and mesopore volumes range between 0.22–1.44 cm3/100 g and 0.67–1.76 cm3/100 g, respectively. Total porosity and pore structure data of these samples show a correlation with TOC. For samples with TOC < 12 wt.%, their total porosity has a positive correlation with TOC, while for samples with TOC > 12 wt.%, negative correlation relationships were observed. TOC content strongly impacts gas storage capacity of the Permian shales in the Lower Yangtze region, and the preliminary results of the present study have important implications for the shale gas play evaluation in this area.