Deepwater Production Riser

ABSTRACT A deepwater production riser design developed by Mobil Research and Development Corporation is presented. The riser consists of a lower rigid section terminated about 200 feet below the sea surface with a tensioning buoy assembly and a flexible upper section made of a bundle of flexible pipes. It is designed to be compliant to waves, currents and vessel motions and applicable to both mild and severe environments. Design, analysis, testing, and installation method are discussed. INTRODUCTION A deepwater production system developed by Mobil Research and Development Corporation consists of clustered well production manifolds on the seafloor, a floating production facility at the sea surface and a production riser to link the two. The system, shown in Fig. 1, contains five major component s:Subsea Atmospheric System (SAS), which consists of a multiwell template through which peripheral wells are directionally drilled, split trees in the wet consisting of master valve and wellhead connector assemblies and a dry subsea work enclosure housing the control valves, chokes, piping and instrumentation required for automated producing operations.l, 2Flowline bundle which connects SAS units to a central riser manifold, the special installation method of which was the subject of a paper presented at the OTC last year. 3The central riser manifold or Subsea Atmospheric Riser Manifold (SARM), designed to manifold production from several SAS units and interface with the production riser.Production riser, which is the subject of this paper.Floating Production Facility (FPF) which accommodates producing facilities and the equipment for injection of gas and water, and also provides storage and offloading capability. In this system the production riser serves to transfer the produced fluids from the seafloor to the surface and injection fluids from the surface to the seafloor. It is a bundle of pipes that in addition to production and injection, includes conduits for communication, control, power, and habitat life support. The flexibility needed for production requirements and withstanding waves and currents for continuous service through weather extremes makes the deepwater production riser development a technological challenge. The design developed by Mobil over the past several years is known as the "Mobil Compliant Riser" and is described. DESCRIPTION OF THE COMPLIANT RISER The Compliant Riser shown in Fig. 2 consists of two sections:the lower rigid section of steel pipes and subsurface buoy andthe upper compliant section of a flexible pipe bundle The lower section stays relatively un disturbed requiring minimal maintenance, although each line is individually retrievable. The upper section, being compliant, is continuously in motion and is considered the most vulnerable section. Also, each pipe is individually replaceable from the floating production facility.