| Coal has long occupied the dominant position in China's energy structure,but there are still many disaster causing factors in deep coal mining,and the safe and efficient mining of coal still needs the cooperation of industry,University and Research Institute.Hydraulic fracturing is commonly used in coal seam permeability increasing technology,which can effectively improve coal seam permeability and reduce gas content.However,as the structural plane widely exists in coal measure strata,the influence mechanism of structural plane on hydraulic fracture extension is not clear,which makes it difficult to control the effect of hydraulic fracture.Therefore,it is urgent to carry out the research on the rule of structural plane type on hydraulic fracture extension.This paper focuses on the simulation of coal rock material with structural plane in model test.Based on the orthogonal experimental design,the similar material ratio suitable for simulation of coal rock is optimized,and the hard structural plane without filling and the soft structural plane with filling with different strength are simulated,and four kinds of coal rock material with structural plane are obtained.Combined with mechanical test and numerical simulation test,the mechanical properties of different types of discontinuities and the deformation and failure characteristics of coal like rock materials with discontinuities are analyzed.Through the hydraulic fracturing physical experiment of coal and rock materials containing discontinuities,the influence of different types of discontinuities and different flow rates on the hydraulic fracture extension is studied,and the joint action mechanism of the types of discontinuities and injection flow rates on the hydraulic fracture extension is obtained.The main research results are as follows:(1)The similar material ratio in accordance with the mechanical properties of coal and rock is obtained: the sand binder ratio is 2:1,the water paste ratio is 1:1,and the curing time is 21 days;the interval of making structural plane and the type of filling material are adjusted,and the non filling hard structural plane and filling soft structural plane with different strength are simulated,and four kinds of coal and rock like materials with different types of structural plane are obtained.(2)The deformation laws of coal bearing rock under different types of uniaxial compression and shear failure are revealed.The results show that the shear resistance of coal rock material with discontinuities increases with the increase of filling material strength;the shear failure surface becomes rougher with the increase of filling material strength;the shear failure surface of hard discontinuities without filling is rougher and more undulating than that of soft discontinuities with filling;under the same axial stress level,the strain level of specimens with longer interval is more significant The strain level of the specimens filled with mica is more significant.The stress barrier effect of unfilled hard structure surface is more significant during uniaxial compression.(3)The joint action mechanism of structural plane type and injection flow rate on hydraulic fracture extension is explored.The influence mechanism of stress state on hydraulic fracture when hydraulic fracture extends to structural plane is analyzed theoretically.The physical experiments of hydraulic fracture with different types of structural plane and different injection flow rate are carried out.The results show that the influence of structural plane type and injection flow rate on the extension mode of hydraulic fracture at structural plane is mainly due to the change of structure when hydraulic fracture extends to structural plane The joint action mechanism of structural plane type and injection flow rate on hydraulic fracture extension is obtained;the cross extension mode of hydraulic fracture and structural plane can be predicted through theoretical analysis,and the injection flow rate and the extension direction of hydraulic fracture can be adjusted according to the stress condition of structural plane. |
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