Quantitative characterization of micropore structure for organic-rich Lower Silurian shale in the Upper Yangtze Platform, South China: Implications for shale gas adsorption capacity

Abstract

The pores in shales are mainly of nanometer-scale, and their pore size distribution is very important for shale gas storage and adsorption capacity, especially micropores having widths less than 2 nm, which contribute to the main occurrence space for gas adsorption. This study is focused on the organic-rich Lower Silurian black shale from four wells in the Upper Yangtze Platform, and their total organic carbon (TOC), mineralogical composition and micropore characterization were investigated. Low pressure CO2 adsorption measurement was conducted at 273.15 K in the relative pressure range of 0.0001-0.03, and the micropore structure was characterized by Dubinin-Radushkevich equation and density functional theory method and then the relationship between micropore structure and shale gas adsorption capacity was discussed. The results indicated that (1) The Lower Silurian shale have high TOC content in the range of 0.92%-4.96%, high quartz content in the range of 30.6%-69.5%, and high clays content in the range of 24.1%-51.2%. The TOC content shows a strong positive relationship with the quartz content which suggests that the quartz is mainly biogenic in origin. (2) The micropore volume varies from 0.12 to 0.44 cm 3 /100g and micropore surface area varies from 4.97 to 17.94 m 2 /g. Both of them increase with increasing TOC content, indicating TOC is the key factor to control the micropore structure of the Lower Silurian shale. (3) Low pressure CO2 adsorption measurement provides the most suitable detection range (0.3-1.5 nm) and has high reliability and accuracy for micropore structure characterization. (4) The TOC content is the key factor to control gas adsorption capacity of the Lower Silurian shale in the Upper Yangtze Platform. Cited as : Chen, L., Jiang, Z., Liu, K., et al. Quantitative characterization of micropore structure for organic-rich Lower Silurian shale in the Upper Yangtze Platform, South China: Implications for shale gas adsorption capacity. Adv. Geo-Energy Res. 2017, 1(2): 112-123, doi: 10.26804/ager.2017.02.07