The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales

Li, Wei; Stevens, Lee A.; Meredith, Will; Uguna, Clement N.; Vane, Christopher H.; Zhang, Bo; Carr, Andrew D.; Zheng, Dingye; Snape, Colin E.

Abstract

The porosity and methane adsorption capacity of shale used to estimate gas in place (GIP) are affected both by moisture and oil residing in the pore structure, as well as oil naturally present from maturation, which can include contaminant drilling mud fluids used for drilling. To demonstrate the impact of extractable oil on methane adsorption capacity for both dry and moisture-equilibrated shales, two overmature shales from China (SH1, SH2) and two lower mature shales from UK (BS3, GH4) have been investigated. The oils extracted from the overmature shales (<0.5 wt% TOC) are in low yield and arise from oil-based drilling mud, while the much higher yields from the lower maturity UK shales (1.1–2.5 wt% TOC) is mainly from oil generated by maturation. After extraction, minimal changes (<5%) in total nanopore volume (<100 nm) were observed for the dry over mature shales, but significant increases (95 and 176%) were observed for the dry lower maturity shales. More than 60% of the extracted oil resides in micro and mesopores, and removal could unblock the micropore necks and enlarge the accessible meso and macropore volume. Moisture contents are lower for extracted shales, with reductions of 7–37% observed. Methane equilibrium adsorption capacities increased after oil extraction for both the dry and wet shales, especially for lower maturity shales, where increases were over 200% for the wet shales. Henry's Law was used to show that there were not significant amounts of dissolved methane in oils for the dry shales. Extracting oil from shales prior to determining the porosity and methane adsorption capacity can lead to the GIP being over-estimated for moisture equilibrated shales, particularly for oil-window shales where an overestimation of 22% was obtained for the shale investigated in this study. These findings provide a better understanding of the combined impacts of residual oil and water on GIP and avoid its overestimation.

Citation

Li, W., Stevens, L. A., Meredith, W., Uguna, C. N., Vane, C. H., Zhang, B., …Snape, C. E. (2022). The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales. Fuel, 316, Article 123304. https://doi.org/10.1016/j.fuel.2022.123304

• Journal Article Type: Article
• Acceptance Date: Jan 14, 2022
• Online Publication Date: Jan 25, 2022
• Publication Date: May 15, 2022
• Deposit Date: Feb 3, 2022
• Publicly Available Date: Jan 26, 2023
• Journal: Fuel
• Print ISSN: 0016-2361
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 316
• Article Number: 123304
• DOI: https://doi.org/10.1016/j.fuel.2022.123304
• Keywords: Organic Chemistry; Energy Engineering and Power Technology; Fuel Technology; General Chemical Engineering
• Public URL: https://nottingham-repository.worktribe.com/output/7375100
• Publisher URL: https://www.sciencedirect.com/science/article/abs/pii/S0016236122001739?via%3Dihub
• Additional Information: This article is maintained by: Elsevier; Article Title: The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales; Journal Title: Fuel; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.fuel.2022.123304; Content Type: article; Copyright: © 2022 Elsevier Ltd. All rights reserved.