Three-dimensional numerical simulation for estimating subsidence and stress evolution in coal seams during coalbed methane recovery
ZHU Yuxun1，LIU Jinfeng1，2，3
(1. School of Earth Science and Engineering，Sun Yat-Sen University，Guangzhou，Guangdong 510275，China；2. Guangdong Provincial Key Lab of Geodynamics and Geohazards，Sun Yat-Sen University，Zhuhai，Guangdong 519082，China；3. Southern Marine Science and Engineering Guangdong Laboratory，Zhuhai，Guangdong 519082，China)
Abstract：In this contribution，we developed a numerical model for describing a coupled effect of stress-strain-sorption-diffusion-permeability on evolution of deformation and internal stress in coal seams during coalbed methane(CBM) recovery，assuming that coal behaves as a poroelastic media. Three-dimensional discrete fracture network of a coal seam was first constructed using COMSOL，consisting of natural and hydraulic fractures. On this basis，we quantitatively determined the development of subsidence and internal stress of the constructed coal seam，using our proposed numerical model，given proper parameter values. The results indicate，that：(1) subsidence mainly occurred on the top of the coal seam，which was located near the both sides of fractures，resulting in a vertical dislocation along the natural fractures and the dislocation rate can be up to 2 mm per year. (2) Both the intermediate and minimum principal stresses in the area near the natural fractures decreased significantly，while the minimum principal stress exhibited a transition from compression to tensile，which can reach to 3 MPa. In addition，parameter sensitive analysis was performed to determine the main factors controlling CBM recovery induced dislocation and stress evolution. By the research we suggests that during CBM recovery，deformation and stress drops around the natural fractures should be paid more attentions as it may cause local damage and even earthquake，though the CBM recovery induced subsidence is relatively small.
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2023, Vol. 42 
