GB842190A - Improvements in drilling boreholes - Google Patents

Abstract

842,190. Boring earth &c. IMPERIAL CHEMICAL INDUSTRIES Ltd. Dec. 15, 1958 [Dec. 18, 1937], No. 39309/57. Class 85. Deviations of a cutting head in a borehole are detected and corrected by means within the head operable from ground level. In Fig. 1, the cutting head 3 is connected to the drill pipe string 1 by a member 2 having some flexibility, and a sensing-means 8 rotatable in a ball and needle roller bearing 15, 7 is projectable, into a frusto-conical cavity 12 of the head, by an axially movable string 5. Passages 4 in the bearing 9 admit drilling fluid to passages 60 and 61. If the'cutting head deviates radially to the bore axis, the direction and extent of the deviation may be detected by stopping the drill and probing the cavity with the sensing device 8 which is moved around as well as vertically, in the cavity, the results being shown by indicators 10, 11. The deviation is corrected by applying resilient, e.g., spring or pneumatic pressure, by means of the sensing means 8, to the appropriate side of the cavity. The cutting head is then rotated without downward pressure, the means 8, 5 remaining static until the deviation is eliminated, when the drilling again proceeds with the means 8, 5 rotating with the drilling assembly. In a modification, the cutting head is driven by a dog-clutch connection with the end of the drill string which, with a ball-andsocket mounting on the string, permits slight radial deviations of the head. Such a deviation is detected by a roller-ended sensing device on the cutting head ball-andsocket mounting which projects upwardly into a canted cylindrical recess in a plunger-like end of the axially movable string 5. The nature of deviation is detected by probing the canted recess with the roller-ended sensing device which latter is positioned to bring the head back into alignment. In a further modification, the deviation is detected hydraulically, the drilling fluid, issuing into the cavity 59 from a nozzle 58, remaining at constant pressure as long as the cutting head is concentric with the nozzle tube 53. The nozzle is rotated at a speed different from that of the cutter 3 and eccentricity is detected by variations in hydraulic pressure. The pressure builds up at the side which needs internal pressure from the nozzle to correct the alignment. In a modification of the hydraulic embodiment, the nozzle 58 is used only as a sensing device and is vertically movable by a string corresponding with 5 of Fig. 1. The cutter 3 is driven by a dog-clutch arrangement from the bottom of the drill pipe. When the string 5 is raised, steep pitched helical grooves in the bottom of the string engage pins projecting inwardly from thrust collar bearing members which turn in opposite directions when the string 5 is moved axially. The bearing members have sloping end faces which act cam-wise to cant the cutter 3 in the required direction.