The Effects of Water Immersion-Induced Softening and Anisotropy of Mechanical Properties on Gas Depletion in Underground Coal Mines

Yuling Tan, Hanlei Zhang, Xiuling Chen (), Qinghe Niu and Guanglei Cui
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Yuling Tan: Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Hanlei Zhang: Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Xiuling Chen: China State Key Laboratory of Intelligent Deep Metal Mining and Equipment, Northeastern University, Shenyang 110819, China
Qinghe Niu: Key Laboratory of Roads and Railway Engineering Safety Control, Shijiazhuang Tiedao University, Ministry of Education, Shijiazhuang 050043, China
Guanglei Cui: China State Key Laboratory of Intelligent Deep Metal Mining and Equipment, Northeastern University, Shenyang 110819, China

Energies, 2025, vol. 18, issue 8, 1-27

Abstract: Coalbed methane (CBM), a highly efficient and clean energy source with substantial reserves, holds significant development potential. Permeability is a crucial factor in CBM recovery in underground coal mines. Hydraulic fracturing technology causes water to enter the coal reservoir, which will change mechanical properties, affecting permeability changes and gas depletion trends. This study combines theoretical analysis with numerical simulation techniques to create a coupling model for fluid flow and reservoir deformation. The numerical model is established by referring to the geological conditions of the Wangpo coal mine, Shanxi province. Specifically, the impact of water immersion-induced softening and changes in the anisotropic mechanical properties on the directional permeability and gas flow rate is examined through parametric analysis. The dominant role in controlling the evolution of permeability varies depending on the orientation. Horizontal deformation primarily affects vertical permeability, which is subsequently influenced by the gas adsorption effect. In contrast, horizontal permeability is mainly determined by vertical deformation. Water immersion-induced softening significantly reduces the permeability and gas flow rate. Young’s modulus, which is dependent on water saturation, alters the permeability trend under water-rich conditions. Vertical permeability evolution is more sensitive to water-induced softening and changes in the anisotropic mechanical properties. When S w 0 is 0.7, the vertical permeability decreases by 60%, while the horizontal permeability decreases by 43%. Ultimately, the vertical permeability ratio stabilizes between 0.9 and 1.0, while the horizontal permeability ratio stabilizes in the range of 0.6 to 0.7. The influence of permeability on gas production characteristics is dependent on the water saturation conditions. In water-scarce conditions, variations in the fracture permeability greatly influence production flow rates. Conversely, in water-rich conditions, a higher permeability facilitates a quicker return to original levels and also enhances gas production flow rates. The research findings from this study provide important insights for fully understanding the mechanical properties of coal and ensuring the sustainable production of CBM.

Keywords: coal permeability; water saturation; mechanical parameters; anisotropy (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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