Study On Hard Rock Drilling Efficiency For Underground Cross Measure Borehole In Huainan Mining Area

In order to effectively prevent the disasters caused by gas in the mine production process,Huainan mining area adopts cross measure borehole for treatment.However,the drilling efficiency is low in hard rock or soft-hard interactive strata when drilling through strata in the top and bottom of coal seam.Based on this problem,the research on hard rock drilling technology for underground cross measure borehole in Huainan mining area is carried out to achieve the goal of efficient drilling.After consults the research status of hard rock drilling at home and abroad,and understands the geological conditions,lithology of coal measures and coal seams,the existing equipment and drilling technology in Huainan mining area,this paper analyzed the influencing factors of hard rock drilling efficiency of underground cross measure borehole in the research area,and concluded that the key factors affecting hard rock drilling are axial load and bit.According to the key factors,the rock breaking mechanism of the drilling tool is analyzed,and the simulation model of bit-rock interaction is established.The displacement,stress and plastic zone of the bit increase with the increase of the axial load in the simulation process.And model calculation shows that the axial load effect of three-wing arc-angle carcass PDC bit and four-wing flat-angle carcass PDC bit are pressed by the model to be significantly higher than the drill bit.Finally,the high-efficiency drilling test of underground cross measure borehole hard rock was carried out in Huainan mining area to verify the previous research results.Through the statistical analysis and grey correlation analysis of the test results,it is concluded that the drilling efficiency of rotary drilling in hard rock drilling is lower than that of percussive rotary drilling,and the drilling parameters of pneumatic percussive rotary drilling are lower than those of hydraulic percussive rotary drilling;there is a big difference in drilling efficiency between different structure bits in medium and hard rock formations;with the increase of rock hardness coefficient,the pump pressure of drilling parameters increases,the drilling pressure decreases,and the rotational speed increases;the bit is more suitable for combination with pneumatic DTH hammer;the footage,the use of screw drill pipe and the drilling pressure are the most important factors for drilling efficiency of downhole drilling in hard rock.The correlation degree between drilling parameters and drilling efficiency is the greatest,and the BHA is the influencing factor of the drilling parameters.The above research results have been verified in the engineering practice of cross measure borehole for gas drainage in Huainan mining area,which provides an example for high-efficiency hard rock drilling of cross measure borehole in Huainan mining area and other mining areas.