Molecular simulation of shale gas adsorption in type III kerogen organic matter

Abstract

Type III kerogen play an important role in coal-bearing shale gas generation and occurrence. The physical and structural properties and the adsorption mechanism of kerogen are difficult to be analyzed comprehensively by experiments. Molecular simulation provides technical support to the investigation of the adsorption and enrichment mechanisms of shale gas at molecular level. Using the Grand Canonical Monte Carlo (GCMC) and Molecular Dynamic (MD) methods, type III kerogen model was constructed, and the adsorption behaviors of methane were investigated. The effects of temperature and gas composition on shale gas adsorption, and the adsorption selectivity of mixed gas C₂H₆/CH₄ and the radial distribution function (RDF) were also discussed. The results show that the adsorption capacity of C₂H₆ decreases with the increase of temperature and pressure. The adsorption capacity of C₂H₆ increases first, then decreases, and finally tends to be stable. The adsorption experiment and molecular simulation results show that Type III kerogen has a stronger adsorption capacity for C₂H₆ than CH₄. C₂H₆ in smaller nano-scale pores are more difficult to desorption under the lower pressure. The carbon atoms in kerogen interact strongly with the gas molecule of CH₄ and C₂H₆.

Keywords:

• adsorption
• kerogen
• methane
• molecular simulation
• shale gas

Acknowledgments

The authors would like to thank various organizations for the financial support. The research was supported by the Natural Science Foundation of Hubei Province, China (Grant No. 2020CFB370), the Scientific Research Project of Department of Education of Hubei Province, China (Grant No. Q20201310), the Open Foundation of Cooperative Innovation Center of Unconventional Oil and Gas (Ministry of Education & Hubei Province), Yangtze University (Grant No. UOG2020-13), and the Open Foundation of Top Disciplines in Yangtze University (Grant No. 2019KFJJ0818023). All the editors and anonymous reviewers are gratefully acknowledged.

Additional information

Funding

The research was supported by the Natural Science Foundation of Hubei Province, China (Grant No. 2020CFB370), the Scientific Research Project of Department of Education of Hubei Province, China (Grant No. Q20201310), the Open Foundation of Cooperative Innovation Center of Unconventional Oil and Gas (Ministry of Education & Hubei Province), Yangtze University (Grant No. UOG2020-13), and the Open Foundation of Top Disciplines in Yangtze University (Grant No. 2019KFJJ0818023).