A Combination of N2 and CO2 Adsorption to Characterize Nanopore Structure of Organic-rich Lower Silurian Shale in the Upper Yangtze Platform, South China: Implications for Shale Gas Sorption Capacity

Abstract

The pores in shales are mainly of nanometer-scale, and their pore size distribution is very important for the preservation and exploitation of shale gas. This study is focused on the organic-rich Lower Silurian black shale from four wells in the Upper Yangtze Platform, and their TOC, mineralogical composition and pore characterization were investigated. Low pressure N2 and CO2 adsorption were conducted at 77.35 K and 273.15 K, respectively, and the pore structures were characterized by modified Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR), t-plot, Barrett-Joyner-Halenda (BJH) and density functional theory (DFT) methods and then the relationship between pore structure and shale gas sorption capacity was discussed. The results indicate 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 total specific surface area varies from 6.60 m2/g to 24.35 m2/g. Both the total specific surface area and quartz content are positively associated with the TOC content. (2) Shale samples with higher TOC content have more micropores, which results in more complex nanopore structure. Micropore volumes/surface areas and non-micropore surface areas all increase with increasing TOC content. (3) A combination of N2 and CO2 adsorption provides the most suitable detection range (~0.3-60 nm) and has high reliability and accuracy for nanopore structure characterization. (4) The TOC content is the key factor to control gas sorption capacity of the Lower Silurian shale in the Upper Yangtze Platform. Our studies are of great significance for the assessment and exploitation of natural gas in the shale reservoirs.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017