GB847769A - Method and apparatus for conducting offshore drilling operations - Google Patents

Abstract

847,769. Drilling wells. JERSEY PRODUCTION RESEARCH CO. Jan. 27, 1959 [Jan. 30, 1958], No. 2891/59. Class 85. In off-shore drilling operations, the re-entry of a drill string into the bore is ensured by suspending an outer conductor pipe, a casing pipe and the drill pipe concentrically from the off-shore structure, the lower end of the casing pipe being positioned above the site of the borehole, drilling and maintaining at least one of the pipes in the borehole when manipulating said pipes for continued drilling. As described, the conductor pipe 17 is suspended in the cellar 12 of a barge 10 by cables 19 and hoists 20, and, if desired, by turnbuckles 21; the casing pipe string 22 is landed with its elevators 23 on the top of the pipe 17, and the drill pipe string 31 with kelly 34 engaging the rotary 30 is lowered through the casing 22 to make a bore with bit 32 and underreamer 33. When it is necessary to extend the drill string, the pipes 17, 22 are lowered until the pipe 22 projects into the borehole, after which the drill pipe string is raised until its upper end is above the rotary 30 to enable a new length of pipe to be added. The drill string is then lowered, the casing 22 guiding it into the borehole. When sections of casing 22 must be added, the drill pipe is raised by disconnecting the kelly and screwing on a lifting eye 41, the lower end of the drill pipe being maintained in the borehole, in which position it is held by slips 36, Fig. 9, in the rotary 30, after removal of the cable from the lifting eye. The new sections of casing pipe 22 may now be threaded over the drill string; the weight of the drill string is again taken by the lifting eye and the slips 36 are removed allowing the drill string to be lowered into the borehole. The extended casing string 22 now projects into the borehole and the conductor pipe 17 descends into the borehole until its cable-bracket 18 rests on the sea-bed. The drill string may now be completely removed from the borehole for 'replacing the under-reamer 33 by a smaller one which produces a bore of diameter to receive further lengths of casing pipe 22. The drill string is again removed and controlling equipment 60, including conventional remotely operated ram type blow-out preventer 61, sleeve type blow-out preventer 62, a drilling head 63 provided with locking means and a mudreturning line 64, a locking sub 65, flexible joint 66, slip joint 67, drilling head 68 with a funnel guide 69, is connected to the upper end of the casing string 22 which is then lowered to the position shown in Fig. 13. The open ended drill pipe is then lowered through the controlling equipment 60 until the lower end is near the lower end of the casing pipe 22, cement slurry being flowed down the drill pipe and up the annulus surrounding the casing pipe 22 to cement the same in position. Drilling is now continued to the required depth, the drill fluid passing through the outlet 70 for recirculation. After drilling, the control equipment 60 and attached casing pipe 22 is removed, and the conductor pipe 17 is pulled up by the cables 19. In a modified arrangement, the conductor pipe 17 and the casing pipes 22 are independently suspended from the barge.