Patent GB-1451542-A (GB)
Title: Core-sampling device for obtaining a core sample from a loose ground layer
IPC: E21B25/00
Filed: 1974-02-19
Abstract: 1451542 Core samplers INSTITUT FRANCAIS DU PETROLE 19 Feb 1974 [20 Feb 1973] 7496/74 Heading E1F A down hole core sampler includes an outer body 1 adapted for connection to. a downhole motor and accommodating a fixed. liner 5 in which is located a massive piston 9, initially retained by detent balls 21 in an upper position in which a cutting shoe 8 on the end of a core barrel 7 carried by the piston is engaged via a key 16 and a groove 18 with a bit 2 on the end of the body. During preliminary drilling operations, when no core sample is required to be taken, a plug 13 closes the lower end of the core barrel, the plug having cutting teeth 14 and a groove 17 receiving the key 16. The plug is connected by a rod 19 to a dashpot piston 27 working in a chamber 28 of a fitting 25 secured to the body 1, the fitting 25 having passages 47 through which drilling fluid can pass when balls 49 shift radially under centrifugal force, the fluid reaching the bit via passages 6 formed in the liner 5. When a core sample is to be taken, rotation of the body is interrupted to allow the balls 49 to close passages 47, and then the drilling fluid pressure is increased to depress a piston 44 against spring 46 to shift a keeper 43 from behind a latch 42 which can, then retract and allow piston 38 to be raised against spring 40 by gas under pressure in chamber 31, the piston 38 thereby raising valve piston 36 to an open position in which it allows the gas in chamber 31 to pass to the space above the piston 9 which is thus depressed to drive the core barrel through the bit to obtain a core sample. The sample is received in a protective plastics sheath 10, any fluid between the plug 13 and the piston 9 escaping via valves 11. If the piston 9 actually impacts against the plug 13, the force of the impact depresses piston 27 against spring 29 and gas under pressure in chamber 28, . any excess gas pressure being relieved via valve 35. The piston 9 uncovers a groove 54 at the bottom limit of its travel to allow the drive gas to escape, the spring 40 serving to return valve piston 36 to its closed position, trapping gas at a desired lower pres sure in chamber 31 to prevent drilling fluid intrusion. The core barrel can remain in its exposed position during retrieval of the sampler or it can be retracted into the body, as in the Fig. 3 embodiment, where the rod 19 is slidable in piston 27 and carries a piston 61. In this case, as the pressure in chamber 31 falls a pair of pistons 57 are retracted clear of collar 60 of rod 19, and after the piston has driven the core barrel into bottom of the hole and the piston 27 has absorbed any impact, pressure equalizes across piston 27 via restricted orifice 56 and piston 61 is raised and via the rod 19, lifts the plug 13 which in turn lifts the piston 9 and thereby retracts the core barrel. The space above piston 61 is via air passages 66, 68, and the piston 61 is subsequently reset by pressure admitted via valve 72. The retraction of the core barrel in a third embodiment is effected using the dashpot piston 27.