New perspectives on supercritical methane adsorption in shales and associated thermodynamics

Tang, Xu; Ripepi, Nino; Rigby, Sean; Mokaya, Robert; Gilliland, Ellen

Abstract

Understanding methane adsorption behavior in shales is fundamental for optimizing shale gas development as the adsorbed methane is a large portion of the subsurface shale gas resource. However, the adsorption mechanism of supercritical methane in shales and associated thermodynamics are poorly understood because the equation of state of the adsorbed methane is unmeasurable. This work analyzed adsorption equilibria (up to 32 MPa and 393.15 K) using a rigorous framework that can account for non-ideal gas properties and accurately extrapolate absolute adsorption uptakes from measured adsorption isotherms. The framework also allows a straightforward calculation of thermodynamic potentials relevant to adsorption such as enthalpy and entropy. Modelling results show that methane adsorption isotherms in shale under different pressures and temperatures are represented by a two dimensional adsorption isotherm surface. The density of the adsorbed methane in shales depends on temperature and pressure, which is always lower than the liquid methane density but higher than the corresponding gaseous methane density. The temperature-dependent and pressure-dependent characteristics of adsorbed methane density leads to the corresponding temperature-dependent and pressure-dependent measured/absolute adsorption isotherms. The maximum adsorption uptake of shales is independent of temperature and pressure. The isosteric enthalpy/entropy of adsorption and enthalpy/entropy of adsorbed methane are found to be temperature- and surface coverage-dependent. These new findings therefore not only clarify some historical misunderstandings of methane adsorption in shales for engineering application, but also provide a novel framework for interpreting methane adsorption behavior in shales and for determining the associated thermodynamics.

Citation

Tang, X., Ripepi, N., Rigby, S., Mokaya, R., & Gilliland, E. (2019). New perspectives on supercritical methane adsorption in shales and associated thermodynamics. Journal of Industrial and Engineering Chemistry, 78, 186-197. https://doi.org/10.1016/j.jiec.2019.06.015

• Journal Article Type: Article
• Acceptance Date: Jun 8, 2019
• Online Publication Date: Jun 15, 2019
• Publication Date: Oct 25, 2019
• Deposit Date: Oct 31, 2019
• Publicly Available Date: Jun 16, 2020
• Journal: Journal of Industrial and Engineering Chemistry
• Print ISSN: 1226-086X
• Electronic ISSN: 2234-5957
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 78
• Pages: 186-197
• DOI: https://doi.org/10.1016/j.jiec.2019.06.015
• Keywords: Shale; Methane; Adsorption; Enthalpy; Adsorbed density
• Public URL: https://nottingham-repository.worktribe.com/output/2471267
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S1226086X19303053?via%3Dihub
• Additional Information: This article is maintained by: Elsevier; Article Title: New perspectives on supercritical methane adsorption in shales and associated thermodynamics; Journal Title: Journal of Industrial and Engineering Chemistry; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.jiec.2019.06.015; Content Type: article; Copyright: © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.