Adsorption Models for Shale Gas: A Mini-Review

Abstract

Clarifying shale gas adsorption mechanism and establishing a reliable shale gas adsorption model are the basis of evaluating shale gas geological reserve and studying flow theory, so rich research on shale gas adsorption has been reported recently. However, with the development of shale gas reservoirs, the reservoir depth is deeper, and the environment is more complicated, especially the characteristic of high temperature and high pressure. These bring a new challenge to reveal the deep shale gas adsorption characteristics by using existing shale gas adsorption theoretical models established based on the middle and shallow shale gas reservoirs. Therefore, the popular methods of experiments, simulation, and models on shale gas adsorption are summarized in detail, and their advantages and disadvantages are clarified. The results show that the isothermal adsorption experiment of shale gas is still the basis method to study shale gas adsorption, but the experimental pressure should be further increased to meet the conditions of deep shale gas reservoir. Molecular simulation can reveal the shale gas adsorption microcosmic mechanisms, but the simulation results have multiple solutions, and the simulation scale is small, difficult to truly reflect the adsorption characteristics of shale gas in a larger scale. Shale gas adsorption models are established mostly based on classical adsorption models or their modifications, and hence they are difficult to reflect shale reservoir characteristics, such as total organic carbon (TOC), primary water, and desorption hysteresis. Therefore, it is important to establish a set of shale gas adsorption−desorption model which can fully consider the shale reservoir characteristics in the future.

Molecular Insights into CO2-Rich Industrial Waste Gas Enhanced Shale Gas Recovery and Sequestration in Real Shale Gas Reservoirs

“…Real shale reservoirs have temperature and pressure gradient variations with depth, which have a great influence on gas adsorption. − Previous results showed that the gas adsorption capacity decreases with increasing temperature, while the adsorption capacity increases with rising pressure and its growth rate decreases gradually. , Thus, the shale gas displacement by CO 2 -rich industrial waste gas components at shale reservoir depths of 0.25–4.0 km is shown in Figure . In all of the simulations, the concentration of each gas injection was the same as the CH 4 concentration at all reservoir depths.…”

Gas-In-Place Content of Deep Shales and Its Main Controlling Factors: A Case Study on the Wufeng-Longmaxi Shales in the Middle Luzhou Block of the Southern Sichuan Basin, China

“…The pore water of shales has a significant effect on the GIP content. It not only occupies some pore space, affecting the free gas content but also adsorbs on some hydrophilic pore walls, reducing the adsorbed gas content. − In addition, pore water may completely occupy or block some nanopores, such as OM and IM micropores with pore widths less than 0.5 nm, , which is adverse to the accumulation of shale gas. Although deep shales generally have a low C PW , the water-bearing characteristics of the shales remarkably affect their GIP contents.…”

A Review of Swelling Effect on Shale Permeability: Assessments and Perspectives

“…Porous matrixes can be further divided into organic matter and inorganic matter. As nanopores inside the organic matter have extremely large internal surface area with strong affinity to methane, up to 20–85% of total shale gas initially in place could be adsorbed gas. − The production of this gas in place is strongly influenced by shale permeability. During the gas extraction process, reservoir pressure gradually declines, leading to an effective stress increase, rock compaction, and intrinsic permeability change.…”