Research Laws Of Seepage Characteristics Of Coal Under Hydraulic Fracturing Condition And Its Application In Project

Research on laws of seepage characteristics of coal under hydraulic fracturing condition is an important part of the technology of hydraulic fracturing for underground coal seam.The 1307 coal-seam face of Guojiahe coal mine was researched in this paper,theoretical analysis,laboratory experiment,numerical modeling and field test was adopted to reveal laws of damage deformation and seepage characteristics of coal under hydraulic fracturing condition.Results showed that when coal under different loading conditions,there have different damage behavior,and the statistical damage constitutive of coal model has been established on this basis.Besides,fluid-structure coupled model of the coal was revised which could describe under hydraulic fracturing condition through damage variable,and the model was verified by numerical simulation.The paper has obtained the following results:(1)The permeability of the coal was decrease at first and then increase in pace with axial strain at the full stress-strain process,and the size of permeability presented “U” shape,the permeability of coal had been low before its reach the yield point,there was a period of calm,and the permeability were increased quickly after the yield point.At the same time,the pore water pressure had good correlation with permeability of the coal,that is with the pore water pressure increased,the damage to the coal specimen were more severe,high water pressure could promote the functions of the permeability.The relationship between permeability and volume strain before and after permeability mutation was corrected by experimental data.Based on the theory of damage mechanics,through the statistical microscopic damage mechanics derived constitutive relations with damage.(2)Under hydraulic fracturing condition,there were supported by the change of effective stress of coal,and through S-D model,the paper used damage variable revise permeability and porosity model.Further,the gas transport was divided into two phases under hydraulic fracturing condition,there were water and gas replacing and depressurization of gas flow,furthermore,we inferred seepage field and stress field deformation equation,the definite solution condition was given.(3)we used the COMSOL Multiphysic software to simulate above equations,from the simulate results,good agreement was found between the experimental results and numeric simulate values,the applicability of the theory was proved.Meanwhile,based on the back ground of 1307 coal-seam face of Guojiahe coal mine,the process of hydraulic fracturing of coal seam and drainage and depressurizing gas extraction was simulated.On that basis,it had shown that the flowing rule of gas in coal bed and the evolution law of gas permeability of coal seam.From the simulation results,In line with the general law of hydraulic fracturing.(4)We carried out the Industrial field test of hydraulic fracturing in 1307 coalseam face of Guojiahe coal mine,and used numerical simulation results layout the hole construction on site,and examined the range of the coverage in hydraulic fracturing,quantity and concentration of gas extraction,the results agree with the simulation results.