GB693379A - Improvements relating to pressure core takers - Google Patents

Abstract

693,379. Core drills. ANGLO-IRANIAN OIL CO., Ltd., and OTWAY, C. W. Oct. 2, 1951 [Oct. 19, 1950], No. 25460/50. Class 85 A core-taker, so designed that the captured core is brought to the surface at the same pressure as occurred at the bottom of the bore, comprises a core bit carrying outer barrel 10 secured to the drill rod, and fixedly positioned therein is a pressure retaining barrel 11 provided at the lower end thereof with a spring- biased flap valve 24 that can close the bore of said barrel 4 but which is held open by a core barrel 12 slidably located within said barrel. In the core drilling position, the core barrel 12 is held stationary, against the action or a spring 33, with respect to the barrel 11 by spring biased clawed arms 21 engaging a plate 28 mounted on an extension 26 of the barrel 12. When sufficient core has been drilled, the string is raised and the catchers 62 engage the core as the barrel 11 rises with respect to the barrel 12 as the latter is held stationary by the core so that the arms 21 on the barrel 11 disengage from the plate 28 of the barrel 12 with the result that the spring 33 now forces the barrel 12 upwards into the barrel 11 past the flap valve 34 which closes to retain said barrel 12 in a chamber at the pressure ocurring at the bottom of the bore, the barrel 11 being sealed at the upper portion by mutual engagement of shoulders 46, 45 on barrels 11, 12 on a packer ring 47. The three concentrically disposed barrels are now withdrawn to the top of the bore. If the core is soft so that the catchers do not lock therein, the arms 21 can be tripped by dropping a heavy weight down the bore on to the end of the core barrel to force it downwards, relative to the barrel 11, or the rate of pumping is increased, so that differential pressure occurs on adjustable flow resisting baffle plates 55, 56 secured to the upper end of the barrel 12. To maintain the pressure in the barrel 12 aproximately constant to that existing at the bottom of the bore during withdrawal of the tool compensating means are provided and consist of a chamber 54 leading to the core-receiving chamber of the barrel 12, the chamber 54 having therein a piston 48.' Before lowering the tool into the bore the chamber 54 is pressurized through needle valves 53, 52 to a pressure approximately equal to that existing at the bottom of the bore and the valve 53 closed. On the tool being brought to the surface the bit is removed from the drill barrel and spacer member 19 replaced by a plug and pump and the pressure in the core barrel maintained by pumping fluid past valve 34, whilst the pressure in the compensating chamber is reduced to atmospheric so that portions 11c and 12d can be removed to allow opening of the valve 51 and the reduction of pressure within the core barrel.