Abstract
The adsorption characteristics of methane in shales play a critical role in the assessment of shale gas resources. The microscopic adsorption mechanism of methane considering the effect of moisture and especially salinity remains to be explored. In this work, combined molecular dynamics and grand canonical Monte Carlo simulations are conducted to investigate the adsorption behaviors of methane in the realistic kerogen matrixes containing different moisture contents (0–6 wt %) and various salinities (0–6 mol/L NaCl). Adsorption processes are simulated under realistic reservoir conditions at four temperatures in the range from 298.15 to 358.15 K and pressures up to 40 MPa. Effects of the moisture content on methane adsorption capacities are analyzed in detail. Simulation results show that the methane adsorption capacity declines as the moisture content increases. In comparison to the dry kerogen matrix, the reduction in the maximum CH4 adsorption capacity is as high as 42.5% in moist kerogen, with a moisture content of 6.0 wt % at 338.15 K. The overlap observed in the density distributions of water molecules and decrease in adsorbed methane indicates that the water molecules occupy the adsorption sites and, thus, lead to the reduction in methane adsorption capacity. Besides, the effects of salinity on CH4 adsorption isotherms are discussed. The salinity is found to have a negative influence on the methane adsorption capacity. The maximum CH4 adsorption capacity reduces around 6.0% under the salinity of 6 mol/L at 338.15 K. Adsorption of methane in kerogens of constant salinity but different moisture contents are further discussed. Results from the present study show that the moisture content has a greater impact on the adsorption of methane compared to that of salinity. The findings of this study have important implications for more accurate estimation of shale gas in place.
Highlights
Natural gas, shale gas, is identified as a relatively clean energy source that helps reduce greenhouse gas emissions
In 2017, the U.S Energy Information Administration (EIA) reported that the dry natural gas production in the United States was slightly greater than natural gas consumption, in which shale gas wells served as the largest source of total natural gas production, providing 57% of total natural gas production.[3]
A reduction of 42.5% is observed in CH4 maximum adsorption capacity of kerogen matrixes at 6.0 wt % moisture content
Summary
Shale gas, is identified as a relatively clean energy source that helps reduce greenhouse gas emissions. Shale formations consist of two parts: inorganic and organic. Kerogen makes up the predominant component of the organic matter in most shales[5] and is considered as a most favorable place for the occurrence of shale gas.[6] Generally, there are three modes of shale gas occurrence in reservoirs, including adsorbed gas, free gas, and dissolved gas, among which adsorbed gas (up to 85%) and free gas are the main shale gas modes of occurrence.[7] Understanding the methane storage, especially the adsorption mechanism in kerogen, is important for the accurate assessment of the storage potential and the effective design for exploitation of shale gas
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
