A Comparative Study On The Mechanical Strength And Pressure Pore Permeability Of Different Coal Ranks

In order to compare and study the mechanical properties of different coal rank coals,the characteristics of overburden porosity and the relationship between the two,this paper uses the MTS815.02 servo test machine to carry out conventional triaxial mechanical experiments on 9 groups of coal samples of different coal ranks.AP-608Overburden Permeability Tester conducted overburden permeation experiments on 4groups of coal samples of different coal ranks.Combined with 3 groups of mechanical experimental data and 18 groups of overburden permeation experimental data of the tutor group,the mechanics of different coal rank coal Comparative analysis of strength,porosity and their relationship.The results show that:1)With the increase of confining pressure,the elastic modulus of coals of different ranks increases exponentially,the Poisson’s ratio decreases negatively,and the peak strength,residual strength,peak strain,and residual strain increase linearly;2)The elastic modulus and peak strength of low-rank coals increase with the increase of R_o,max,and the mid-rank coals decrease first and then increase.The inflection point is around R_o,max=1.50%.The high-rank coals There is a decreasing trend;3)The coal elastic modulus sensitivity coefficient shows a rapid decrease-slow decrease-gradual stabilization three-stage change with the increase of confining pressure,and the inflection points are about 8MPa and 20MPa respectively,of which the elasticity of low-rank coal and high-rank coal The modulus sensitivity coefficient decreases with the increase of R_o,max,and the middle coal rank increases;4)The elastic energy of the coal base block decreases first and then increases with the increase of R_o,max,and confining pressure,and the inflection point Both are located at R_o,max=1.70%;5)Coal ash yield and vitrinite content and inertinite content are the main factors affecting the change of coal peak strength and elastic modulus and Poisson ratio;6)Coal porosity and permeability decrease rapidly with the increase of effective stress-slow down-gradually stabilize Three-stage change,the inflection points are about 7MPa and 12.5MPa,respectively.The relationship between porosity,permeability and effective stress is the highest fitting degree using an exponential model;7)The sensitivity of coal porosity stress performance is low coal rank>high coal rank>Medium coal rank,the permeability stress sensitivity is shown as high coal rank>low coal rank>medium coal rank;8)coal sample permeability and porosity have a positive exponential function relationship,the difference of permeability is greatly Pore relationship is close;9)The elastic modulus and peak strength of coal are negatively correlated with porosity and permeability,and positively correlated with Poisson’s ratio.The research results provide mechanical parameters for hydraulic fracturing of different coal rank reservoirs,and also have a guiding role in increasing the permeability of coal reservoirs and the drainage of coalbed methane.