Patent ID: 6164392
Filing Date: 2000-12-26
Classification: E21B

Abstract:
A percussive drilling apparatus for extension drilling comprising:a drill bit having a rear section possessing a female screw thread;a tube including a rear end having a female screw thread, and a front end having a male screw thread, the male screw thread being larger in diameter than the female screw thread of the tube, the male screw thread being connected to the female screw thread of the drill bit, the tube having a first central fluid passage extending therethrough for conducting flushing fluid to the drill bit; anda rod including a front end having a male screw thread connected to the female screw thread of the tube, the rod having a smaller outer diameter than the tube, and the rod including a second central fluid passage extending therethrough for conducting flushing fluid to the first fluid passage, the second fluid passage being of smaller diameter than the first fluid passage;the drill bit sized to drill a hole having a diameter in the range of 60-170 mm which is at least twice an outer diameter of the rod;a total area of a cross-sectional surface of the tube being within 100-125% of a total area of a cross-sectional surface of the rod.