Improving the Estimation Method of Subsurface Shale Gas Capacities Based on the Amankwah Model

Accurately evaluating the in situ gas content of shale is a crucial step in achieving effective exploration and optimizing exploitation strategies, which holds significant importance for understanding resource enrichment patterns and enhancing resource utilization efficiency. In order to achieve precise evaluation of shale gas volume, a new approach for estimating in situ shale gas content based on the London dispersion potential and Polanyi adsorption potential has been optimized. Comprehensive analyses were performed on shale cores from the Shanxi Formation at 3153.03 m in the Ordos Basin, including helium-based porosity measurements, high-pressure methane adsorption isotherms, on-site canister desorption tests, and gas composition analysis. Combining the previously analyzed shale (at 1264.42 m), the modified Polanyi–London (PL) method and three previous methods were employed to calculate the on-site shale gas volume. The results indicate that the gas contents obtained by the direct and indirect methods are significantly lower than those obtained by the PL method and modified PL method, which is due to the notable uncertainties associated with the former two methods. At greater burial depths, the difference in gas content obtained by the PL method and modified PL method is larger than that at shallower burial depths, and this difference depends on the suitability of the Amankwah model used by the latter, compared to the Antoine model used by the former, for the supercritical state of gas. The modified PL method is underpinned by an established theoretical framework. Upon comparison with the other four methods, the results obtained using the modified PL method appear more perfect, and the results are more reasonable.