| In view of the energy structure of rich coal,lack of oil and less gas in China,it has been proved that coal and rock contain a large amount of combustible gas.Therefore,it is an important trend of mineral energy development to exploit coal and rock gas through minimal radius radial drilling technology.Water jet technology is applied to coal and rock gas mining,in which the direct rotating mixed jet meets its needs because of its good drilling effect,mining efficiency and strong stability.However,further research is needed for the performance research and optimization of its core component bit and the specific research of drilling and rock breaking.In this paper,the combination of theoretical analysis,numerical simulation and jet drilling experiment is used to carry out the bit design,bit optimization design,flow field characteristics analysis and cement mortar specimen drilling analysis of the application of direct rotating mixed jet bit in rock breaking and mining technology.The main achievements are as follows:1)Through theoretical analysis and calculation,the main process of damage and fracture of coal and rock impacted by jet is revealed:stress concentration caused by water hammer pressure stage,initial fracture pit and microcrack are generated.Under the mixed action of rotating jet and direct flow,microcrack expands and finally forms macro fracture.Three kinds of jet erosion tests were carried out:the energy of direct flow is concentrated,the hole is deep but the hole diameter is small,which directly affects the continuous drilling of jet;The rotary jet has a large erosion area,but due to the weak energy of the jet axis position,there is a central low-speed area,and the central boss phenomenon appears in the erosion process,which affects the drilling of the bit;The direct rotating mixed jet not only eliminates the central boss,but also has a good aperture,which meets the requirements of drilling and improves the drilling efficiency.The erosion drilling test and the above simulation results verify each other.2)The optimization design of the direct rotating mixed jet bit is carried out,and the impeller and mixing cavity in the bit body are analyzed by numerical simulation.The velocity of the jet in space after ejection is taken as the evaluation index.Through the comparison and analysis of the simulation results,some parameters in the impeller and mixing chamber are preliminarily optimized:the impeller groove width is d_s=0.7mm(width diameter ratio d_s/d_y=0.068);The radial length of the impeller is d_r=3.5mm(length diameter ratio d_r/d_y=0.32);Impeller length:4.5mm;Impeller inclination 45°;Central hole diameter:1.2mm;The mixing chamber is 6mm long.3)Through specific erosion and drilling experiments,the influence of six parameters changed by jet bit on erosion and crushing results is analyzed.The slot width,radial length and central hole diameter mainly affect the direct rotation flux ratio.The direct rotation mixed jet has the respective advantages of two single jet forms.When the ratio is 0.54,the impact rock breaking performance of the mixed jet can be better released;The angle of inclination directly affects the diffusion degree of jet flow field.The greater the angle of inclination,the stronger the diffusion ability of jet flow field;The length of mixing chamber affects the mixing uniformity of direct rotating jet,then affects the energy dissipation of jet,and finally leads to the change of jet velocity;The length of the impeller directly affects the length of the rotating channel.The longer the channel,the stronger the swirling capacity of the jet,but the more intense the momentum and energy exchange with the surrounding medium,and finally affect the jet speed.4)Through the grey correlation analysis method,the importance ranking of the influencing parameters of the jet is determined.The order from high to low is:center hole diameter,impeller groove width,impeller radial length,mixing cavity length,impeller inclination and impeller length.The research results of this paper provide some theoretical guidance for water jet radial drilling technology,enrich the research on its flow field characteristics,rock breaking mechanism and optimization criteria,and have certain significance.Figure[59]Table[8]Reference[91]... |
PDF Full Text Request