Variations in Gas Content in Organic Matter-Rich Low Maturity Shale; Example from the New Albany Shale in the Illinois Basin

Abstract

This paper investigates controls on gas content in the Upper Devonian to Lower Mississippian New Albany Shale, specifically addressing the influence of organic matter content and porosity on the desorbed and residual gas contents. The shale samples studied come from Daviess County, Indiana, where the entire New Albany Shale thickness of 40 m (~120 ft) was cored. Gas content was measured by canister desorption and volumetric displacement apparatus, and porosimetric techniques included He adsorption (total porosity) and low-pressure N2 (mesopore characteristics) and CO2 (micropore characteristics) adsorption techniques. Other techniques included organic petrographic analysis, TOC and S analysis, and SEM. Total porosity of the shales ranges from 2.9 to 10.3 %, BET surface area from 4.1 to 9.1 m2/g, BJH mesopore volume 0.0125 to 0.0243 cm3/g, and micropore volume 0.0080 to 0.0197 cm3/g. Our data demonstrate that organic matter content is a good predictor of gas content, and micro-pores present in organic matter are the main storage sites not only for residual but also desorbed gas. The role of larger pores in gas storage in these shales is limited.