Geological Constraints And Improved Models Of Coal Seam Reconstruction With Controllable Shock Wave

Controllable shock wave(CSW)reconstruction is a developing and popularizing used coal reservoir stimulation technology,but the cracking process,mechanism and constraining geological conditions still need to be deeply understood.In response to this scientific problem,physical simulation experiments were carried out using the split hopkinson pressure bar(SHPB)experimental platform based on the in-situ stress state.Combined with the characterization of the impact-induced pore and fracture evolution law,to analyze the dynamic characteristics,energy distribution,pore and fracture evolution characteristics of coal with CSW.Discussing the mechanism of geological constraints,establishing a damage constitutive model of CSW,and obtaining four innovative understandings.First,coal seam shows obvious anisotropic characteristics in reconstruction with CSW.When the impact direction is parallel to the layering surface of coal seam,the main failure mode is the tensile failure along the layering surface.With the increase of the included angle,the failure mode changes to the combination of shear and tension failure.The elastoplasticity of coal changes with the increase of CSW impact distance.There is a critical distance,and the degree of fragmentation is lower when the distance is smaller.The peak stress,the first deformation modulus and the proportion of transmission energy all gradually decrease with the increase of the number of impact cycles.The peak stress degradation coefficients(?_f)are45°,0°and 90°in descending order.The average?_f of coal rock combination is 21.95%,which is 6.86%lower than that of pure coal rock.The cumulative specific energy increases with the increase of the number of cycles,and the pure coal rock has a higher cumulative specific energy absorption value than the coal rock combination.Second,CSW can significantly improve the pore structure of coal samples.With the increase of the number of impacts,the micropores peak value of NMR first rises and then falls.The peaks of medium and large pores,micro-fractures gradually increase and the growth rate increases significantly.The properties of surrounding rock in the incident direction have a significant influence on the change of coal pore structure.The newly formed fractures mainly develop on the interface where the wave impedance changes.There are many fractures around the clustered minerals.The original and early formed fractures will limit the development range of the newly formed fractures.The development characteristics of fractures are controlled by the initial fracture porosity and the distribution of weak surfaces of the original structure.With the increase of the number of impacts,the damage degree of coal samples showed a two-stage growth characteristic of rapid first and then slower.The damage degree before crushing was between 0.165 and 0.795,with an average of 0.584.Third,the adjustment of pore-fracture system is restricted by geological conditions.Pore-fracture system shows obvious anisotropic characteristics.The NMR porosity increases with the decrease of the peak stress in a power function.The improvement of porosity and permeability in the direction of the angle between 45°and 0°is better than 90°.The degree of porosity improvement is closely related to the surrounding rock properties,and the proportion of coal seam thickness in the combination has a greater impact on the CSW impact effect.The study showed that the mechanical properties of coal-rock,the layer included angle and the combination are the key geological constraints.When the layer included angle changed,the original porosity and permeability characteristics are the main controlling factors that affect the adjustment of the pore-fracture system.The influence of acoustic wave and proximate analysis parameters increases with the increase of the difference between coal and surrounding rock properties.Fourth,a damage constitutive model of CSW is established with triaxial stress state,and the model fits well with the experimental data.The porosity increase value decreases with the increase of the model parameter F₀.The effect of CSW can be judged according to the F₀ value when the impact condition does not change much.Further,it also can be used to guide the optimization of on-site operations.There are 117 figures,16 tables and 231 references in this thesis.