To investigate the permeability characteristics of coal under different confining pressures and hydraulic loads, SEM micro-scan images and a binary analysis system were used. Based on the fractal characteristics of pore and fracture networks, a model was developed to simulate the porosity and static permeability of the coal rock. Dynamic permeability tests under different water pressures and confining pressures were conducted using a GDS-DYNTTS soft rock rheometer. The research results show that by using reasonable fractal dimensions based on the microstructure images and permeability model, realistic static permeability values can be obtained. Under the coupling of fixed water pressure and different confining pressures, the coal exhibite three different stages of permeability: the stage of pore compression closure, the stage of slow pore deformation release, and the stage of rapid pore deformation recovery. When the confining pressure exceeds 6 MPa, the sensitivity of permeability to water pressure was relatively low. However, when the confining pressure was below 4 MPa, the permeability increase exponentially with increasing water pressure. Under dynamic coupling conditions, the overall trend of coal permeability showed two distinct features: a plateau period and a rapid increase period. The research results provide references for understanding water inflow paths, estimating water quantities in coal seams after mining-induced stress relief, and predicting water inrush risks.
XIEHeping.Research review of the state key research development program of China:deep rock mechanics and mining theory[J].Journal of China Coal Society,2019,44(5):1283-1305.
ZOUGuanghua, WANGChongzhi, MALong,et al.Mechanism of slurry fracture seepage and pore seepage based on mud sand media[J].Journal of Liaoning Technical University(Natural Science),2023,42(2):152-159.
[5]
WANGL C, CARDENASM B, SLOTTKED T,et al.Modification of the Local Cubic Law of fracture flow for weak inertia,tortuosity,and roughness[J].Water Resources Research,2015,51(4):2064-2080.
PANYongliang, JIANWenxing, YANGGuanghui,et al.Damage and evolution characteristics of Jurassic soft rock in Three Gorges Reservoir area under water pressure[J].Journal of Engineering Geology, 2021,29(3):693-701.
YEPingping, LIBobo, WUXuehai,et al.Study on coal seepage evolution mechanism under cyclic loading and unloading of pore pressure[J].Journal of China University of Mining & Technology,2023,52(4): 739-749.
ZHANGYing, LIPeng, GUOQifeng,et al.Research progress of deformation and failure mechanism in fractured rock mass under hydromechanical coupling[J].Journal of Harbin Institute of Technology,2020,52(6):21-41.
[12]
GANL, CHENG Y, SHENZ Z,et al.Modification method of seepage parameters for rough fractures based on digital image technique[J]. Journal of Petroleum Science and Engineering,2022,209:109967.
ZHANGPeisen, ZHAOChengye, HOUJiqun,et al.Experimental study on seepage characteristics of deep sandstone under high temperature and different hydraulic pressures[J].Chinese Journal of Rock Mechanics and Engineering,2020,39(6):1117-1128.
GUOBaohua, CHENGTan, CHENYan,et al.Seepage characteristic of marble fracture and effect of filling sands[J].Journal of Hydraulic Engineering,2019,50(4):463-474.
YANGXiurong, JIANGAnnan, ZHANGFengrui,et al.Seepage characteristics of fractured limestone under osmotic pressure-stress coupling[J].Journal of China Coal Society,2019,44():101-109.
[19]
TIANZ X, ZHANGW S, DAIC Q,et al.Permeability model analysis of combined rock mass with different lithology[J].Arabian Journal of Geosciences,2019,12:755.
WANGHuanling, WANGTingchao, HUMingtao,et al.Experimental study on the rheological properties of red-bed soft rock under the effect of hydraulic and constitutive model[J].Journal of China Three Gorges University (Natural Sciences),2023,45(5): 31-37.
CAOXulou, LIUJiangfeng, NIHongyang,et al.Simulation study on effect of crack opening degree of coalbed methane seepage based on SEM image[J].Safety in Coal Mines,2020,51(5):173-176.
[24]
ZHAOY, WANGC L, BIJ.Analysis of fractured rock permeability evolution under unloading conditions by the model of elastoplastic contact between rough surfaces[J].Rock Mechanics and Rock Engineering,2020, 53(12):5795-5808.
DUANLingling, DENGHuafeng, QIYu,et al.Study on the evolution of seepage characteristics of single-fractured limestone under water-rock interaction[J].Rock and Soil Mechanics,2020,41(11): 3671-3679, 3768.
JIANGTao, XUWei, SUZhuangzhuang.Calculation and analysis of permeability of sandstone SEM image by small island method[J]. Journal of North China Institute of Science and Technology,2018, 15(5): 54-59.
LIBobo, WANGBin, YANGKang,et al.Study on fractal characteristics of coal pore fissure structure and permeability model[J].Coal Science and Technology,2021,49(2):226-231.
LIZhihao, CHENShijiang, DUGuangsheng,et al.Research on coal and rock seepage laws under different confining pressures and hydraulic pressures[J].Coal Science and Technology,2020,48(12):101-108.
[33]
GANL, LIUY, XUT,et al.Experimental investigation of the seepage characteristics of a single fracture in limestone with different roughness and seepage fluids[J].Journal of Hydrology,2023,622:129699.
[34]
WANGP F, ZHANGX Y.Experimental study on seepage characteristics of a soil-rock mixture in a fault zone[J].Fluid Dynamics and Materials Processing,2021,18(2):271-283.