GB881358A - Retrievable drilling apparatus for bore holes - Google Patents

Abstract

881,358. Boring earth &c. KAMMERER, A. W. Feb. 12, 1960, No. 5160/60. Class 85. A retrievable drilling bit for bore-holes is lowered within a string of pipe and is coupled to the lower end thereof, the bit body carrying retractable cutters which are expandable radially to project beyond the pipe and to make driving engagement therewith, the bit being removable from and replaceable in the pipe without removing the pipe string from the well. The pipe string may be left in the well, and cemented, to act as a casing. The bit comprises a body 12, a number of arms 17, two as described, pivoted at 18 in the body and carrying cutter wheels 11, a lower part 13 of the body 12 and a pilot cutter 14 screwed thereinto at 15. The body 12 lands on a flange 78 on the lower pipe 10 and the arms 17 are swung outwardly by a tension spring 100 which pulls a mandrel 19 with a revoluble central spill 24 downwardly relatively to the body 12, the expander 34 being thus cammed over the contours of the arms 17 to stop in engagement with the locking surfaces 37. If the spring 100 is unable to complete this movement, the pressure of the drilling mud on the piston 20 finishes it. The spring 100 is screwed, top and bottom, into helical grooves 102 in the piston skirt and in the body 12. The mandrel 19 is integral with a member 43 which is guided in a spider 47 and has a central bore which receives a plunger 57 surmounted by a retrieving head 120 engageable by an overshot on a sand line. The plunger 57 is located by a flange 59 and is slotted to receive a latch plate 54 which is pivoted, with play, at 55 in a slot in the member 43. A pin 68, bridging the slot in the plunger 57 and slidable in axial guide slots 69 in the member 43, is disposed in a cam slot 70 in the plate 54, so that when the mandrel 19 is moved down by the spring 100, or by fluid pressure, the spring 60 projects the shoulder 62 of the plate 54 under one of the ribs of the spider 47, the hinge pin 55 being relieved from strain by the play which allows the latch 54 to bear on the bottom 67 of the slot. When the cutters are to be retracted and removed, the retrieving head 120 is pulled up, which pulls up the pin 68 to cam back the shoulder 62 from the spider rib. The pin 68 reaches the top of the slots 69 and then pulls up the member 43 and mandrel 19 against the tension of the spring 100. The expander 34 is removed from the locking surfaces 37 and the arms 17 are free to swing inwardly, this being positively ensured by a shoulder 75 engaging projections 76 on the arms 17. The drilling bit is now free for removal through the pipe string. When the bit is in operative position, the driving force is transmitted to the arms 17 by square faces 82 on the leading sides of slots 79 in the pipe 10, the opposite faces of the slots being chamfered at 88 to guide the arms 17 into correct operative position if they are misaligned with the slots whilst being projected. The drilling mud passes through passages 48, 106, 107 and nozzle 108 to the cutters 11 and to the passages 113, 115 supplying the pilot cutter 14. Also mud passes through ports 116 to the space between the pipe 10 and the bodv 12. In a modification, the latch plate 54 is omitted.