Critical factors controlling adsorption capacity of shale gas in Wufeng-Longmaxi formation, Sichuan Basin: Evidences from both experiments and molecular simulations

The quantitative determination of the influence of the critical factors on the adsorption capacity of the shale is important for accurately evaluating its adsorption capacity under the geological conditions. The adsorption experiments are performed on both the dry and the water-saturated shale samples, and the Grand Canonical Monte Carlo (GCMC) simulations are carried out on both the organic and inorganic structures. It is found that the organic matters (OM), with strong intensity and high distribution density of the adsorption sites and large specific surface area, are the most important adsorbent in the shale, accounting for 53%similar to 92% of the adsorption capacity, and the clay minerals take the second place. For most of the adsorption sites on the clay minerals, the adsorption capacity will be impeded by the formation water because of their hydrophilicity, while only the adsorption capacity of the polar group (with hydrophilicity) on the organic surface will be hindered by the formation water. For the shale in the study area, the TOC increases with the depth, causing the increasing of the adsorption amount under the geological conditions, at the same time, the clay mineral content decreases with the depth, causing the descent of the impede effect of the formation water. The quantitative investigation of the influence of the critical factors on the adsorption behaviors of the shale gas is hopeful to provide some helpful insights and references when evaluating the adsorption amount of shale gas under the geological conditions.

Automated summary

The study confirmed that organic matters are the most important adsorbents in shale, accounting for majority of the adsorption capacity, while clay minerals come second. As the depth increases, the organic carbon content in shale rises, leading to an increase in adsorption capacity, while the content of clay minerals decreases, reducing the hindrance effect of formation water.