| Efficient development of coal-bed methane can not only utilize coal-bed methane,but also eliminate gas disasters,which is of great significance for achieving safe coal production and ensuring national energy development strategies.Efficient mining of gas in complex coal seams must transform the coal seam in a large-scale balanced anti-reflection process.Traditional coal mine underground anti-reflection technologies such as dense drilling and hydraulic slitting have a limited anti-reflection range,which is prone to drainage blanks and poses major safety hazards.In response to the above problems,the team proposed a new idea of networked enhanced permeability drainage for self-advancing hydraulic jet drilling in deep mines,that is,using self-advancing drill bits to achieve steering drilling into coal holes in rock tunnel penetration holes and constructing in coal seams.The tree-shaped drainage hole network realizes a large-scale balanced penetration of coal seams.How to design and optimize a small size self-advancing drill bit with strong rock breaking ability and good drilling stability under the conditions of coal mine underground tunnel space and limited drilling diameter is the key to this method.Therefore,this paper uses a combination of experiment and theory to analyze the characteristics of the self-advancing bit jet flow field of the"tree-like"borehole,revealing the characteristics of self-rotating jet rock breaking,and optimizing the self-advancing bit structure.The main research results obtained are as follows(1)Based on the high-speed camera test technology,the characteristics of the self-rotatory jet flow field were revealed,and the effects of jet pressure and rotation speed on the flow field characteristics were analyzed.Compared with the conventional fixed jet,the energy density of the self-rotatory jet is lower,the atomization range of the jet is wider and the divergence angle is larger,the axial velocity of the jet decays faster;In addition,the atomization range and divergence angle of the self-rotating jet vary with the jet pressure.And the rotation speed increase gradually,the axial velocity attenuation of the self-rotatory jet at a jet pressure of 6 MPa and a target distance of 5 cm increases by 19%.(2)The rock breaking test of the spin jet under different working conditions was carried out,and the influence rule of the bit structure and the rotation speed on the rock breaking efficiency of the self-rotatory jet was obtained.The self-rotatory jet can greatly improve the rock-breaking efficiency of the jet.The 6 MPa self-rotatory jet's rock-breaking volume is 17.2 times that of the conventional fixed jet under the same conditions;the self-rotatory jet's rock-breaking volume increases first and then decreases with the jet rotation speed.The optimal rock-breaking rotation speed,and the optimal rock-breaking speed are positively correlated with the jet pressure;as the nozzle outlet angle increases,the self-rotatory jet rock-breaking volume increases exponentially,and the growth rate gradually slows as the nozzle outlet angle increases.(3)The effect of hydraulic parameters on the rock-breaking efficiency of the self-rotatory jet was obtained.Compared with the rock-breaking diameter,the contribution of rock-breaking depth to the rock-breaking volume of the self-rotatory jet dominates.The self-rotatory jet rock breaking efficiency increases with a quadratic function as the jet pressure and erosion time increase,but its growth rate shows an increasing trend and a decreasing trend respectively;with the increase of the rock breaking target distance,the rock breaking efficiency takes precedence After increasing,there is a decreasing trend,and there is an optimal rock breaking target distance.When the target distance is 1.0 cm,the rock breaking volume is the largest,which is 4.05 cm~3.The research results in this paper can provide reference and guidance for the optimal design and determination of reasonable parameters of the self-rotating drill bit,which has certain engineering significance. |
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