Methane Adsorption on Shale under Simulated Geological Temperature and Pressure Conditions

TLDR

Shale gas is becoming an increasingly important energy resource. The study examined methane adsorption on a dry, organic‑rich Alum shale sample at pressures up to ~14 MPa and temperatures 300–473 K, conditions relevant to geological gas storage. Supercritical adsorption was modeled with modified Dubinin–Radushkevich and Langmuir equations and compared to absolute isotherms derived from surface excess and pore volumes measured by subcritical gas adsorption of N₂, CO₂, and CH₄. Methane excess uptake ranged from 0.176 to 0.042 mmol g⁻¹ (125–30 scf t⁻¹) as temperature rose, following a linear trend, with an isosteric enthalpy of 19.2 ± 0.1 kJ mol⁻¹, and the combined subcritical and surface‑excess data set an upper limit on gas retained by adsorption during petroleum source‑rock generation.

Abstract

Shale gas is becoming an increasingly important energy resource. In this study, the adsorption of methane on a dry, organic-rich Alum shale sample was studied at pressures up to ∼14 MPa and temperatures in the range 300–473 K, which are relevant to gas storage under geological conditions. Maximum methane excess uptake was 0.176–0.042 mmol g–1 (125–30 scf t–1) for the temperature range of 300–473 K. The decrease in maximum methane surface excess with increasing temperature can be described with a linear model. An isosteric enthalpy of adsorption 19.2 ± 0.1 kJ mol–1 was determined at 0.025 mmol g–1 using the van't Hoff equation. Supercritical adsorption was modeled using the modified Dubinin–Radushkevich and the Langmuir equations. The results are compared with absolute isotherms calculated from surface excess and the pore volumes obtained from subcritical gas adsorption (nitrogen (78 K), carbon dioxide (273 and 195 K), and CH4 (112 K)). The subcritical adsorption and the surface excess results allow an upper limit to be put on the amount of gas that can be retained by adsorption during gas generation from petroleum source rocks.