Comparison of the impact of moisture on methane adsorption and nanoporosity for over mature shales and their kerogens

Li, Wei; Stevens, Lee A.; Uguna, Clement N.; Vane, Christopher H.; Meredith, Will; Tang, Ling; Li, Qianwen; Snape, Colin E.

Abstract

© 2021 Elsevier B.V. Moisture in shales under reservoir conditions adversely affects gas adsorption and nanoporosity and is also likely to impact on the contribution that kerogen makes to the methane adsorption capacity. To investigate these phenomena, two over mature shales from the Wufeng-Longmaxi Formation, south of the Sichuan basin, and their kerogens isolated by demineralisation were investigated dry and at 95% relative humidity (R.H.) by high-pressure methane adsorption, and low-pressure nitrogen (N2) and carbon dioxide (CO2) sorption. The kerogen concentrates account for 68–97% and 50–64% of the methane adsorption capacities for the shales dry and at 95% R.H. respectively. However, the isolated kerogens could adsorb more methane than the organic matter in the shales because their shallower adsorption isotherms indicate large micropores and small mesopores not evident for the shales. Methane adsorption capacities of the kerogens and shales reduced by 46–72% at 95% R.H. This compares with the reductions in surface area (SA) and pore volume of 81% and 48–59%, respectively, for the kerogens and 98–99% for both SA and pore volume of the shales at 95% R.H. Water can block most micropores less than 1.3 nm reducing the micropores volume and blocking the micropore necks connecting the larger pores, and vastly reducing accessible pores for gas transport. The greater proportional losses in SA and pore volume compared to the methane adsorption capacities is probably due to ice forming at −196 °C in the low-pressure N2 analysis. Failure to take moisture into account for free and adsorbed methane overestimates the total gas in place (GIP) by 36–45% for the shales investigated.

Citation

Li, W., Stevens, L. A., Uguna, C. N., Vane, C. H., Meredith, W., Tang, L., Li, Q., & Snape, C. E. (2021). Comparison of the impact of moisture on methane adsorption and nanoporosity for over mature shales and their kerogens. International Journal of Coal Geology, 237, Article 103705. https://doi.org/10.1016/j.coal.2021.103705

• Journal Article Type: Article
• Acceptance Date: Feb 1, 2021
• Online Publication Date: Feb 6, 2021
• Publication Date: Mar 15, 2021
• Deposit Date: Feb 19, 2021
• Publicly Available Date: Feb 7, 2022
• Journal: International Journal of Coal Geology
• Print ISSN: 0166-5162
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 237
• Article Number: 103705
• DOI: https://doi.org/10.1016/j.coal.2021.103705
• Keywords: Kerogen, Moisture, Methane adsorption capacity, Nanoporosity.
• Public URL: https://nottingham-repository.worktribe.com/output/5334763
• Publisher URL: https://www.sciencedirect.com/science/article/abs/pii/S0166516221000318
• Additional Information: This article is maintained by: Elsevier; Article Title: Comparison of the impact of moisture on methane adsorption and nanoporosity for over mature shales and their kerogens; Journal Title: International Journal of Coal Geology; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.coal.2021.103705; Content Type: article; Copyright: © 2021 Elsevier B.V. All rights reserved.