Petroleum Reservoir Evaluation and Development >
2023 , Vol. 13 >Issue 5: 636 - 646
DOI: https://doi.org/10.13809/j.cnki.cn32-1825/te.2023.05.011
Primary research on expression of kerogen in Longmaxi Shale and its adsorption characteristics
Received date: 2022-08-10
Online published: 2023-11-01
Adsorbed gas represents a primary mode of shale gas occurrence and is a major source of shale gas production in the later stages of development. It primarily resides within the organic kerogen and clay minerals of shale formations, with organic kerogen being the dominant host. Consequently, the study of organic kerogen characteristics and its adsorption mechanisms is crucial for understanding shale gas development. In this paper, the kerogen of Longmaxi Shale in the Sichuan Basin is taken as the research object. The microstructure of kerogen is expressed by combining methods through the solid-state NMR experiment, Fourier transform infrared spectroscopy experiment, X-ray photoelectron spectroscopy experiment, and the molecular structure model of kerogen is constructed. The adsorption mechanism and characteristics of CH4 in kerogen of Longmaxi Shale are analyzed by magnetic levitation weight experiment, molecular simulation methods of the Grand Canonical Monte Carlo（GCMC）, and Molecular Dynamics（MD）. The results show that the molecular formula of the kerogen of shale experimental sample of Longmaxi Formation is C237H219O21N5S4. The excess adsorption gas volume of CH4 in kerogen increase first and then decreased with the increase of pressure. Under the same pore size and pressure, the excess adsorption gas volume and total gas volume of CH4 decrease with the increase in temperature. The C and S atoms in kerogen are the main cause of CH4 adsorption. The CH4 near the kerogen pore wall presents an adsorption state, while the CH4 far from the kerogen pore wall presents a free state. As the pore size increase, the distance between the two peaks of CH4 density gradually increases, and the peak value decreases gradually.
Dali HOU , Xin HAN , Hongming TANG , Jianchun GUO , Fengming GONG , Lei SUN , Xianyu QIANG . Primary research on expression of kerogen in Longmaxi Shale and its adsorption characteristics[J]. Petroleum Reservoir Evaluation and Development, 2023 , 13(5) : 636 -646 . DOI: 10.13809/j.cnki.cn32-1825/te.2023.05.011
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