Patent GB-1473799-A (GB)
Title: Device for guiding a drilling string during underwater drilling
IPC: E21B19/00
Filed: 1975-06-25
Abstract: 1473799 Boring earth &c ENTREPRISE DE RECHERCHES ET D'ACTIVITES PETROLIERES (ELF) 25 June 1975 [26 June 1974] 26962/75 Heading E1F A device for guiding drill strings for use in a floating platform having a well for the passage of the drill string 2 includes a flexible guide tube 1 whose internal diameter is constant over most of its length, the thickness of the tube 1 diminishing progressively from its median zone to each of its two ends, and means for mounting the guide tube 1 in the platform. The internal diameter of the guide tube 1 is constant (except for the flared end regions s) and lies within the range of 1.1 to 1.4 times the external diameter of the joints 3 of the drill string 2. The minimum thickness e of the guide tube 1 at its ends is at least 4mm and the ratio E/e of the thickness E at the median zone to the minimum thickness e lies   between 4 and 25, whilst the ratio E/L of the thickness E in the median zone to the overall length L of the tube lies between 0.002 and 0.010. The guide tube 1 preferably has a ball and socket swivel joint 4 which is connected to the platform by lateral and longitudinal connections. In a first embodiment (Fig. 4) the outer part 4a of the swivel joint 4 is connected by jacks 6 to the walls 5 of the well in the platform and is supported longitudinally by rods 7 pivoted to the joint 4 and to the platform beneath rotary table 8. The jacks 6 permit the tube 1 to move sideways in the well and exert a force tending to return the tube to the centre of the well. In a modification (not shown) the swivel joint 4 is supported by three pairs of jacks, the jacks of each pair being inclined in opposite directions to the horizontal. In a second embodiment (Fig. 7) the swivel joint 4 is supported longitudinally by a tube 10 connected to the platform by a second swivel joint 11 and is supported laterally by cables 6<SP>1</SP> passing round pulleys 6<SP>11</SP> and connected to jacks 6. In a third embodiment (Fig. 8) the swivel joint 4 is supported laterally by jacks 6 and longitudinally by a tube 12 connected to the platform by straps 13. The tube 12 is connected by swivel joint 17 to marine riser 14, 14<SP>1</SP> and has a mud outlet 15, the swivel joint 4 being provided with ducts (not shown) for the passage of the mud. To allow for rapid assembly or removal of the tube 1 the outer part 4a of the swivel joint 4 may consist of two parts 4<SP>1</SP>a and 4<SP>11</SP>a (Fig. 11) locked together by spring loaded fingers 20. The fingers 20 may be retracted by a ring 21 having an inclined surface 21b which engages corresponding inclines 20b on the fingers 20. The dividing surface between the parts 4<SP>1</SP>a, 4<SP>11</SP>a may be frusto-conical as shown in Fig. 11 or cylindrical (not shown) with a conical seat at the bottom. Alternatively the inner part 4b of the swivel joint may be divided in a similar way. In a fourth embodiment (Fig: 9) the guide tube 1 is supported longitudinally by a tube 10a connected to the platform by swivel joint 18 and to the top of the guide tube 1 by swivel joint 19. The guide tube 1 is located laterally by an annular tube 16 containing compressed air which bears against the platform or a marine riser (not shown).