Adsorption–desorption characteristics of coal-bearing shale gas under three-dimensional stress state studied by low field nuclear magnetic resonance spectrum experiments

• Published in: Scientific reports Vol. 14; no. 1; pp. 5566 - 13
• Main Authors: Tian, Hunan, Tang, Jupeng, Zhang, Shipeng, Zhang, Xin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.03.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/4077/4082; 639/4077/4082/4059; Adsorption; Adsorption–desorption; Average effective stress; Coal; Coal mines; Coal-bearing shale; Desorption; Humanities and Social Sciences; multidisciplinary; NMR; Nuclear magnetic resonance; Nuclear magnetic resonance T 2 spectrum; Quantitative analysis; Science; Science (multidisciplinary); Shale; Shale gas; Shales; Stress; Stress state; Coal-bearing shale; Nuclear magnetic resonance; spectrum; Adsorption–desorption; Average effective stress; Nuclear magnetic resonance T 2 spectrum
• DOI: 10.1038/s41598-024-54532-9
• ISSN: 2045-2322

The micro-scale gas adsorption–desorption characteristics determine the macro-scale gas transport and production behavior. To reveal the three-dimensional stress state-induced gas adsorption–desorption characteristics in coal-bearing shale reservoirs from a micro-scale perspective, the coal-bearing shale samples from the Dongbaowei Coal Mine in the Shuangyashan Basin were chosen as the research subject. Isothermal adsorption–desorption experiments under three-dimensional stress state were conducted using the low field nuclear magnetic resonance (L-NMR) T 2 spectrum method to simulate the in-situ coal-bearing shale gas adsorption–desorption process. The average effective stress was used as the equivalent stress indicator for coal-bearing shale, and the integral of nuclear magnetic resonance T 2 spectrum amplitude was employed as the gas characterization indicator for coal-bearing shale. A quantitative analysis was performed to examine the relationship between gas adsorption in coal-bearing shale and the average effective stress. And a quantitative analysis was performed to examine the relationship between the macroscopic and microscopic gas quantities of coal-bearing shale. Experimental findings: (1) The adsorption–desorption process of coal-bearing shale gas follows the L-F function model and the D-A-d function model respectively with respect to the amount of gas and the average effective stress. (2) There is a logarithmic relationship between the macroscopic and microscopic gas quantities of coal-bearing shale during the adsorption–desorption process. This quantitatively characterizes the differences in the curves, which may be related to the elastic–plastic deformation, damage and fracture of the micropores in coal-bearing shale, as well as the hysteresis of gas desorption and the stress field of the gas occurrence state.