Experimental Study On Similar Materials Of Ductile Surrounding Rock In Pressure Relief During The Coalbed Methane Development

The research and development of similar materials for surrounding rocks of tectonically-deformed coal is the premise of physical simulation experiment of pressure relief of tectonically-deformed coal during the coalbed methane development.Taking the huaibei mining area,a typical tectonic coal development area in China,as the research area,the paper collected the original rock samples of Ductile surrounding rocks of tectonically-deformed coal and studied their mineral petrology,permeability and rock mechanics characteristics.The similarity requirements of similar materials were determined by combining the research results of similarity theory and the experimental conditions of large-scale simulation equipment.The experimental scheme design of material optimization,proportion of similar materials and optimization of molding was carried out,the permeability and mechanical property parameters of similar materials were tested,and the material selection,proportion optimization and molding scheme of similar materials were determined.The research of this work has mainly achieved the following understandings and achievements:(1)Ductile rock surrounding the tectonic coal in the study area is mainly sandy mudstone,silty mudstone and mudstone.Their main minerals are quartz and illite-based clay minerals.Protolith is simulated under 15 MPa of formation pressure,the tri-axial compressive strength of ductile rock is 90.85 MPa on average;the elasticity modulus is 7.16×10~3 MPa on average;the Poisson’s ratio is 0.135 on average.(2)Based on similar conditions of the ductile rock prototype and stress condition,the similarity principle and ratio of analogous material are confirmed.Specifically,it includes:1 lower original permeability in samples of analogous material;2 the tri-axial compressive strength is 1/5 of protolith without breaking under the condition of 5MPa in the simulation test device,and;3 the elasticity modulus of analogous material is 1/5 of protolith(3)Based on the optimization experiment of analogous material,80 mesh quartz sand was selected as the aggregate,high-strength construction gypsum and 1250 mesh talcum powder were used as cementing materials,and pure borax was analyzed as retarder to carry out research and development of analogous material of ductile rock.Considering the effects of sand-cement ratio,gypsum:talcum powder,water-to-solids ratio,molding pressure and molding time on the permeability and rock mechanics of analogous material,an orthogonal test of 5 factors and 4 levels was designed.(4)The ratio of sand to cement has a significant effect on the permeability of samples of analogous material.As the ratio increases,the permeability of samples increases significantly.In addition,when ratio of gypsum to talc powder<1:2 in the cement,the permeability of sample increased significantly.(5)The ratio of sand to cement,gypsum:talc powder,water to solid ratio,and forming pressure have an effect on the mechanical properties of analogous material.Among them,the ratio of sand to cement and gypsum:talc has a significant influence on the rock mechanical parameters of analogous material.As the ratio of sand to cement increases,the tri-axial compressive strength and elastic modulus of analogous material show a decreasing trend.In the cement materials,as the proportion of gypsum increases,the tri-axial compressive strength and elastic modulus of analogous material show an increasing trend.(6)Based on the analysis of orthogonal test results,it is considered that the optimal ratio of the analogous material of the ductile rock in the study area and the forming project are:The ratio of sand to cement is 1:1,the ratio of gypsum to talc powder is 1:1,The ratio of water to solids is 25%,the molding pressure is 16.26 MPa(3t exerts on a cylindrical surface with a diameter of 48 mm),and the forming time is6 hours.