Research and application of high-pressure water jets drilling and repairing failure drainage borehole for enhancing coalbed methane recovery in underground coal mines

• Published in: Geomechanics and geophysics for geo-energy and geo-resources. Vol. 8; no. 6
• Main Authors: Xiao, Songqiang, Ren, Qingyang, Cheng, Yugang, Wang, Haiyang, Zhang, Liang, Liao, Yin, Chen, Bin, Jin, Honghua, Meng, Xin, Qin, Haoxin
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2022; Springer Nature B.V
• Subjects: Boreholes; Bottom trawling; Breaking; Coal; Coal mines; Coal mining; Coalbed methane; Critical pressure; Debris; Detritus; Discharge; Drainage; Drainage effects; Dredging; Drilling; Dynamic loads; Efficiency; Energy; Engineering; Environmental Science and Engineering; Exploitation; Failure; Foundations; Geoengineering; Geophysics/Geodesy; Geotechnical Engineering & Applied Earth Sciences; High pressure; Hydraulic jets; Hydraulics; Jets; Methane; Original Article; Pressure; Recovery; Rock; Rocks; Underground mines; Velocity; Velocity distribution; Water; Coal rock breakage; Gas drainage borehole; Water jets; Coalbed methane
• ISSN: 2363-8419; 2363-8427
• DOI: 10.1007/s40948-022-00500-4

Draining gas from coal seams in underground coal mines is the main method of the coalbed methane exploitation in China. When the gas drainage boreholes are located at soft, fractured coal rock seams, phenomena such as borehole collapse and blockage occur frequently, resulting in the significant decrease of gas drainage efficiency. To recover the gas drainage effect of failure boreholes, this study proposed a drilling and repairing failure drainage borehole technique by utilizing high-velocity water jets to break blockage to dredge borehole. The technical principles and key equipment compositions were described, including water jets breaking rock and discharging debris, high-pressure pipeline transport and recovery, hydraulic parameters adjustment and operation control. Based on the jet velocity distribution laws, rock breakage criterions under dynamic loading and debris movement laws in borehole, the critical pressure and flow of water jet for breaking coal rock and discharging debris during drilling were calculated. And the limit drilling and borehole-dredging length model was established. The field applications indicate that the drilling velocity in coal seams varied from 0.42 m/min to 0.76 m/min with a maximum drilling length of 43.5 m under the field conditions. Increasing the drilling angle within a certain range could improve the drilling efficiency due to the smoother debris discharge. Moreover, after the blockages in boreholes were removed, the gas drainage concentrations of all boreholes increased by 33–85%, and the average gas drainage flow of single borehole maintained 99.3 m 3 /d, increasing by 83.5 m 3 /d. Thus, the proposed technique has a good drilling performance and can significantly improve the gas drainage efficiency of the blocked failure boreholes. Article highlights A drilling and repairing failure drainage borehole technique was proposed by utilizing water jets to break blockage to dredge borehole. The critical pressure and flow of water jets for breaking rock and discharging debris were calculated. The limit drilling and borehole-dredging length model was established. The proposed technique can achieve the long-distance drilling and effectively recover the gas drainage effect of the blocked boreholes.