GB1262940A - Method of and apparatus for setting an underwater structure - Google Patents

Abstract

1,262,940. Subaqueous boring. A-Z INTERNATIONAL TOOL CO. 22 April, 1969 [22 April, 1968], No. 20526/69. Heading E1F. A method of setting an underwater tubular structure A comprises lowering the structure on a drill string D in a body of water, rotating the drill string within and relative to the structure to drill a hole 24 and simultaneously lowering the structure into the hole as it is drilled, cementing the structure in the hole, and retrieving the drill string. In one arrangement, Fig. 2, the drill string comprises a collar 26, a swivel 46, Figure 6, rotatable under control of a ratchet assembly 72 in one direction relative to the drill string, a stabilizer 28, an underreamer 16 and a bit 14. The structure A which may be an underwater anchor is releasably attached to the swivel by pins 58 engaging in H slots 60, Fig. 8. In operation the circulation of drilling fluid is commenced as the bit 14 nears the floor 12. The anchor enters the hole behind the bit 14 until a perforated stop plate 20 rests on the floor. After the cuttings have been flushed from the hole, and with the collar 26 seating against the top of the anchor, cement is pumped down the drill string and enters the annular space between the anchor and the hole. The drill string is then rotated in reverse, i.e. against the ratchet and lifted to release the swivel pins from the H slots. Alternatively this could be done before cementing is commenced. Pumping of cement is continued to fill the central cavity of the anchor. In an alternative arrangement, for setting a conductor pipe 84, Fig. 10, having a landing base L slidable thereon and supported by guide lines 90, the drill string comprises a swivel 100 similar to the swivel 46, a spacer latch 102 associated with a packer 104, a stabilizer 106, releasing dogs 108, a retrieving latch 110, an underreamer 112 and a bit 114. Projections on the swivel engage with H slots in a housing 94, Fig. 14, releasably connected to the conductor pipe and comprising sleeves 96, 98 and a collar 118 threaded at 92 to a landing head 116 on the conductor pipe. The threaded connection is prevented from unscrewing when the swivel is engaged in the H slot housing by a pawl 122 which is forced outwardly by the swivel against a spring 124 into a hole in the landing head. The assembly is lowered and the hole drilled as before, the conductor pipe entering the hole until a stop plate 86 abuts the top of the landing base. The swivel is disengaged from the H slots as described above and the drill string lifted while the cuttings are flushed from the bore. The drill string is lowered until the spacer latch 102 engages with the top of the conductor pipe to set the associated packer. Cement is pumped down the drill string to enter the annular space between the conductor pipe and the bore, followed by a quantity of heavy weight mud to ensure the annular space is completely filled. The drill string is lifted releasing the packer so that the releasing dogs 108 engage in the H slots, Fig. 12 (not shown). The drill string is rotated in reverse to unscrew the connection 92 with the conductor pipe, and then raised so that the retrieving latch 110 engages the H slot housing and lifts it clear of the conductor pipe for retrieval together with the drill string.