| Coalbed methane,a naturally occurring gas in coal,is regarded as a relatively clean-burning and eco-friendly resource.During mining,coalbed methane may be leaked to the environment,leading to potential coal mine catastrophes such as coal and gas outbursts,and gas explosions.But there are most of lower permeability coal seams in China.It will affect gas extraction production.Nowadays,integration of hydraulic flushing and fracturing technology was an emerging measure to improve the effect of pressure relief antireflective of coal seam.The field practice of coal mine also proved it can preferably improve the effect of pressure relief antireflective in coal seam.But the theory of joint network reconstruction and corresponding optimization of technical parameters need to be improved.It takes further work to study how to effectively guide the safe and efficient production,Combined with the site of hydraulic fracturing and hydraulic punching process technology,relying on the national research platform "State Key Laboratory of Coal Mine Disaster Dynamics and Control(Chongqing University)",a new physical simulation test of integration of hydraulic punching and fracturing was presented in the laboratory.According to the new test method,the integration of hydraulic punching and fracturing system was developed.A series of physical simulation tests of hydraulic punching,hydraulic fracturing,and integration of hydraulic punching and fracturing were carried out.Combined with the theory of rock mechanics,fracture mechanics and seepage mechanics,a useful discussion on the test results are carried out.Through the research,some conclusions or progresses are made in the following aspects:1)Based on the basic test and theoretical analysis of hydraulic fracturing,the influence of geological stress on crack pressure,the propagation and the extension mechanism of hydraulic fracturing were studied in this paper.The coal seam fracture network expand space-time evolution rule and cracking mechanism were discussed with the micro shear fracture evolution test.These results were used to support the improvements of hydraulic extraction mechanism.2)A new physical simulation test of integration of hydraulic punching and fracturing was presented in the laboratory based on hydraulic fracturing,hydraulic punching and coalbed methane extraction process.According to the new test method,the integration of hydraulic punching and fracturing system was developed.Through the internal arrangement of various sensors,the quantitative treatment of the experimental results was realized.The experimental technical measures were provided for the mechanism study of coalbed methane hydraulic extraction.3)In this paper,the physical simulation test of coal seam hydraulic punching with three-dimensional stress condition was realized.The relationship between the punching water pressure,punching rotation velocity,and punching drilling velocity with punching coal output and the punching radius was established.It was shown that increasing punching rotation velocity and reducing punching drilling velocity affected the coal output.And it would enlarge the radius of the punching hole.Compared the space-time evolution of gas pressure during the gas extraction process before and after hydraulic punching,the effective influence under different punching conditions was investigated.The gas permeability after pressure relief had been evaluated,and the pressure relief scope of hydraulic punching had carried in this theory.4)The physical simulation tests of coal seam and roof virtual reservoir for hydraulic fracturing were carried out with three dimensional stress condition.The influencing factors of the joint network reconstruction in coal seam were revealed.The relationship between stress deformation of coal and rock and the joint network reconstruction was established.Through the method of internal fluid pressure sensor,the visualization of the spatiotemporal evolution of hydraulic fracturing fracture field was realized,which was consistent with the fracturing surface of hydraulic fracturing.Compared with the time-space evolution of gas pressure before and after hydraulic fracturing,the pressure relief and permeability increase of the hydraulic fracture joint network reconstruction in coal seam was realized.5)The time-space evolution of gas pressure before and after hydraulic punching,hydraulic fracturing,hydraulic punching and then fracturing and hydraulic fracturing and then punching were analyzed.The gas pressure was evaluated for coalbed methane through integration of hydraulic punching and fracturing to enhance gas extraction.The results showed that through integration of hydraulic punching and fracturing measures were better than single hydraulic punching or single hydraulic fracturing for the improvements of gas extraction obviously.It was also proved the integration of hydraulic punching and fracturing to enhance gas extraction was feasibility. |
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