Design and Installation of the Na Kika Export Pipelines, Flowlines and Risers

Abstract

Abstract This paper describes the design and installation of the export pipeline and subsea flowline systems for the Na Kika Floating Development System (FDS). These systems are in record water depths and several significant "worlds-firsts" were achieved during installation. The 74-mile-long 18-inch oil export pipeline to Shell's Main Pass 69 pump station is the deepest pipeline ever installed in the flooded condition, thereby achieving significant reductions in wall thickness and associated costs. The 74-mile-long dual diameter 20"/24" gas export pipeline, from the host to Main Pass 260 is the deepest and largest pipeline installed by the S-lay method. In addition, a large 24"x20" in-line Wye assembly was installed by J-lay. This gas export pipeline forms part of the Okeanos pipeline system, which connects not only Na Kika but also the future Thunder Horse facility to the Destin pipeline system. The subsea flowline system design posed significant flow assurance challenges that were solved by a combination of pipe-in-pipe insulation, an electric-heating-ready hydrate remediation system, and an innovative gas lift riser system. In total approximately 100 miles of intra-field flowlines were installed. All flowlines, including pipe-in-pipe flowlines and risers on the South side fields were installed by the reel method-an industry first for reeled pipe-in-pipe risers. The pipe-in-pipe flowlines on the North side were installed by the J-lay method. Because the 10 wells that comprise the Na Kika subsea system (12 wells including the Coulomb field) were all dispersed, no subsea manifolds were installed. Instead some 23 sleds, many with multiple well connection hubs, were installed. The sleds connected flowlines and wells with jumpers. A total of 11 Steel Catenary risers were installed, for which a special bridge equipped with a 1.5 million pound chain jack had to be constructed across the open area in the center of the semi-submersible host. Total cost of the export pipeline, flowline and riser system, including subsea sleds and jumpers exceeded $ 350 MM. Introduction The Na Kika development actually comprises five separate fields (Kepler, Ariel, Herschel, Fourier and East Anstey) that were developed as one system. The fields are roughly spread out West to East, with the two furthest wells being roughly 25 miles apart. In addition, the Coulomb field, South East of the Na Kika FDS is tied back to the Na Kika FDS with a single flowline that is 27 miles in length. With exception of the Coulomb field, Shell and BP own an equal interest in the development. The fields were discovered as early as 1986, and in 1996 a systems selection effort commenced to first determine the technical feasibility of systems in water depths over 6000 ft and then develop a commercially viable solution. With regard to the pipelines, flowlines and risers, thetechnical challenges were many. The maximum water depth in the Na Kika field was 7000 ft (with the water depth at the Coulomb field being even greater at 7600 ft). With pipe sizes being considered, the installation tensions could exceed 600- 700 tons, well beyond the capability of the capacity of existing pipelay vessels.