GB709365A - Improvements in or relating to drill assemblies - Google Patents

Abstract

709,365. Drill assemblies. STANDARD OIL DEVELOPMENT CO. Nov. 24, 1952. [Jan. 29, 1952], No. 29689/52. Class 85 A drilling assembly comprises a tubular collar 1, which is secured to the lower end of a rotatable string of drill pipe or casing and has internally formed circumferential grooves, 2, 4, and a drill unit which can pass through the bores of the drill string and collar. The drill unit consists of a tubular mandrel 6 on which are pivotally mounted spring-biased latches 22 and cutter supports 11, 12. A sleeve 9 slidably fits over the lower portion of the mandrel, being biased towards the lower end thereof by a spring 7, and has spring-biased latches 25 and a pair of downwardly extending cutter supports 15 spaced apart at the lower ends by a wedge 17. A second sleeve 20 slidably fits over the upper portion of the mandrel and in one position slots formed in said sleeve register with the latches 22 to permit outward movement of the latter. In use, the drill unit is lowered through the drill string by a wire attached to a spearhead 21 of the sleeve 20 which supports the mandrel 6, since the extensions of the latches 22 are now contained in recesses formed in the mandrel by the sleeve 20 as they engage the lower surface of the slots in said sleeve. As the drill unit reaches the collar 2 latches 25 extend outwards into the groove 4 to abut against shoulder 5 and so prevent further downward movement of the sleeve 9 which, up to this point, has been previously supported on a shoulder of the mandrel. The mandrel continues downwards until prevented on the cutter supports engaging the wedge 17 by which they are forced into a drilling position. The sleeve 20 then descends with respect to the mandrel until latches 22 project through slots in said sleeve and enter groove 2 to abut against shoulder 3, when the weight of the drill string is transferred on to the cutters. Rotary motion is transmitted from the string to the bits by lugs in the groove 2 engaging the latches 22. The tool can be removed by re-attaching the line to the spear head and hauling up the sleeve 20, so causing the withdrawal of the latches 22 from the groove 2, whilst latches 25 ensure relative movement of the mandrel and sleeve 9 to free the cutter supports 11, 12 from the wedge 17 so that the whole drill unit may now be withdrawn. A packer 38 is provided on the mandrel and is forced into contact with the collar 2 on the descent of the sleeve 20. The grooves 2 and 4 may be combined into a suitably proportioned single groove. In a modification, to permit of controlled free falling of the drill unit, the upper portion of the mandrel bore is enlarged to house a valve controlling the upward flow of fluid through the bore. If the rate of fall of the drill unit is too high the valve closes the bore and the resultant pressure build-up therein acts through ports in the mandrel to expand a resilient sleeve against the casing string to exert a braking force.