Study On The Law Of Coal Rock Mass With Different Structure Caused By Water Shock Wave Under Triaxial Pressure

With the development of human civilization,coal and oil can not meet people's increasing demand for energy.Coalbed methane(CBM),as a new type of unconventional natural gas,has been widely accepted by people for its high quality and high efficiency.However,the permeability of most of the coal bed methane reservoir in China is not good,so it is necessary to transform the stratum and increase the broken degree of coal seam.Water high voltage pulse discharge cracking and permeability increasing technology is a new technology,with its advantages of convenience and environmental protection,has been widely recognized in the industry,but due to its late start,its research content is not perfect and full.Through theoretical analysis,numerical simulation and experiment,the technique of high voltage pulse discharge to crack and increase permeability in water is studied in this paper.First in the theoretical level of high voltage electrical pulse discharge in water crack mechanism of the crack increased infiltration technique for the analysis of the system,then using PFC2 D discrete element numerical simulation software test stand and high voltage electrical pulse discharge synchronous the crack test,the crack heterogeneity and coal and rock containing different types of cracks,cracks and extension rule,Finally,the field anti-reflection test of coalbed methane well is carried out to further verify the significance and reference of the research content in this paper.The main research results are as follows:(1)The wave enters from a strong medium to a weak medium.Under the single impact of equal energy,the damage degree of the weak dielectric layer is inversely correlated with its intensity,and positively correlated with the peak pulse pressure.The curve of "pulse peak pressure-crack number" increases first and then decreases with the increase of the strength of weak medium,and then becomes a trend of constant increase.Under repeated impact,the crack develops fully and the crack extends the longest when the pulse peak pressure is the smallest.The stronger the weak layer is,the smaller the crack propagation and development degree.(2)The wave enters from the weak medium to the strong medium.Under a single impact of equal energy,the crack propagation is impeded,and the curve of "peak pulse pressure-crack number" increases continuously with the increase of the strength of the medium.Under repeated impact,the crack expands to some extent,and the greater the strength of the strong medium layer,the smaller the degree of expansion.(3)There are all kinds of cracks in the coal rock,and the wave superposition effect is the strongest when the crack is not filled,and the crack density and width are both larger after cracking.When the lime is filled,the crack can penetrate the lime,and more energy is transmitted beyond the filler crack.Relatively small when the lime is filled,more energy is transferred along the water in the crack.(4)contains a single crack parallel to the horizontal maximum energy,the main stress direction of native coal and rock crack,crack number increases with the increase of pulse peak stress,crack perpendicular to the horizontal maximum and minimum principal stress and the tilt native crack of coal rock mass,number of cracks with the increase of pulse peak pressure presents the first increase after the decrease trend.Under repeated impact,the cracks develop fully in different trends.With the increase of confining pressure and confining pressure difference,the number of cracks decreases.(5)There are weak backfill in primary cracks in coal rock.Under the single impact of equal energy,the number of cracks in the backfill is inversely correlated with its strength,and positively correlated with the peak pulse pressure.Under repeated impact,the cracks develop fully,but when the filling body strength is the lowest,the smaller pulse peak pressure can penetrate the filling body,and the peak pressure causes the filling body to break.With the increase of the strength of the filling body,the failure degree and the number of cracks decrease,but the crack length increases.(6)There are strong backfill bodies in primary cracks in coal rock.Under the single impact of equal energy,the crack development is hindered.Under repeated impact,the cracks extend to some extent and all the cracks pass through the filling body.With the increase of the strength of filling body,the crack elongation length decreases slightly.(7)Through the field experiment of CBM well anti-reflection,the crack density in the inner wall of CBM well is increased,the original blocked cracks are also dredged,and the CBM output of the abandoned extraction well is increased by nearly 30%.