Research and Application of Jet Assisted Drilling Technology

Drilling forepumping is the main form of gas drainage,and the drilling depth is the key factor to affect the effect of gas drainage.Common drilling can form high confining pressure area,which can limit the drilling depth.In view of this,a new jet assisted drilling concept was developed,the drilling depth can be increased through eliminating confining pressure by jet cutting.On this basis,the effect on mechanic character of coal under confining pressure area was studied,and the theory of eliminating confining pressure in jet assisted drilling process was analyzed;The new jet drilling was designed,and the industrial application in the scene was put on.Studies show that confining pressure can increase the ultimate breaking strength of coal significantly,which enhance the difficulty of drilling;jet drilling can eliminate confining pressure area effectively and reduce the drilling resistance;The jet drilling depth is deeper than the normal one,the average depth increased by 25%,which do benefit to gas drainage.