| The paper takes the coal sample of a coal mine of Furong Company of Sichuan Coal Industry Group and the shale sample of the Lower Silurian Longmaxi Formation outcrop section of southeastern Sichuan as the research object.In the physical experiment,preliminary analysis of pores of coal samples and shale samples by mercury intrusion method and low temperature nitrogen method;The "?CT225kVFCB high-precision CT experimental analysis system" was used to scan the coal samples and shale samples under different water conditions,and the structural characteristics of the pores and fractures under different water conditions were analyzed.Relying on "US MTS815 rock mechanics experimental device","PCI-2 acoustic emission device",“triaxial servo-controlled seepage equipment for thermo-hydro-mechanical coupling of coal containing methane(THM-2)” independently developed by Chongqing University and the SOMATOM Scope CT machine carried out experiments under different stress conditions on coal samples and shale samples.The mechanical properties,seepage characteristics and fracture evolution of coal samples and shale samples under different stress conditions were analyzed.In the numerical simulation experiment,the three-dimensional model of pores and fractures in coal sample and shale sample was established by Avizo software and the flow of methane gas in the pores and fractures was simulated.The permeability value of CT scan was calculated and the physical experiment results were compared and verified.Based on the above experimental and numerical simulation results,the following main conclusions can be obtained:(1)The results of the mercury intrusion method and the low temperature nitrogen method show that the pore size of the coal sample is about 300?1200 nm,and the pore size of the shale sample is about 50?650 nm.It is indicated that the pores of coal samples and shale samples are mainly composed of mesopores.(2)The radius of pores and fractures in the coal sample under the natural water-containing condition is mainly concentrated in the range of 0?200 ?m,and the average rate of pores and fractures is in the range of 2%?5%.The radius of pores and fractures in the shale sample under the natural water-containing condition is mainly concentrated in the interval of 0?100 ?m,and the average rate of pores and fractures is in the range of 1%?2.5%.In the saturated water and dry state,the number of pores and fractures in the coal sample and shale sample distributed in 0?300 ?m increased sharply.The saturated water treatment and drying treatment promoted the expansion and development of pore cracks in coal rock.(3)During the triaxial loading experiment,as the stress increases,the acoustic emission signals of coal samples and shale samples increase,and the pores and fractures also increase.According to the experimental results,three stages of fracture evolution under the stress conditions of coal sample and shale sample are defined: initial fracture stage,fracture expansion stage and fracture penetration stage.The difference between the coal sample and the shale sample is that the shale sample has a shorter crack penetration period,indicating that the shale damage is more rapid than the coal damage.(4)During the triaxial stress-seepage experiment,the evolution law of the permeability of the coal sample shows that it first decreases and then increases.As the permeability increases,the pores and fractures increases linearly.The reconstructed model was simulated by CT scan to simulate the flow of methane gas,and the streamline distribution of methane percolation was obtained.The comparison of permeability between the numerical simulation and the physical experiment found that the permeability value of the numerical simulation is roughly consistent with the permeability measured by the physical experiment,indicating that the numerical simulation results are more accurate. |
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