School of Resources & Environment, Henan Polytechnic University
Collaborative Innovation Center of Coalbed Methaneand Shale Gas for Central Plains Economic Region

Fractures in coal are the main channels for the migration of coalbed methane and are the direct factor thataffects and controls the permeability of coal reservoirs. Tectonically deformed coals are generally developed in China,and the characteristics of fractures in different types of tectonically deformed coals are significantly different,and they have different effects on the permeability of coal reservoirs. Therefore,it is necessary to study the fracture andpermeability in the tectonically deformed coal. In this study,the middle and high⁃rank tectonically deformed coal sam⁃ples were selected from the Pingdingshan 13th Mine and the Jincheng Hudi Mine. Firstly,the columnar coal sampleswere made by epoxy resin to solve the problem of difficulty in the sample preparation of tectonically deformed coal. Secondly, by means of scanning electron microscopy, micro - CT scanning and digital image processingtechnology,the differences of development,distribution,morphology and structure of aperture greater than 15 μmin the two coals were analyzed. Finally,a permeability prediction model was established based on the Poiseuille’slaw,triaxial permeability experiment and fracture structure parameters of CT scanning. The mechanism of fracturestructure controlling permeability was discussed. The results show that large fractures with simple morphology are most⁃ly developed in the weak tectonically deformed coal(tend to primary structural coal) under the scale of aperture grea⁃ter than 15 μm,and the fracture connectivity and connection strength are poor,while the micro⁃fractures in thestrong tectonically deformed coal are complex in morphology,and the fracture connectivity and connection strengthare good. The fracture porosity of coal with the strong tectonic deformation is larger than that of coal with weak tecton⁃ic deformation. Permeability decreases in a negative exponential trend with the increase of effective stress. The perme⁃ability of coal reservoirs is controlled by multiple factors,including fracture aperture,number,volume,connectivityand connection strength,of which aperture has the most significant influence. In addition,considering the factorsof controlling permeability and the fractal dimension and roughness of fractures,a tubular fracture permeability modelwas established,and the accuracy and applicability of the model in predicting permeability at this scale were verified.