Challenges Faced in the Design of SLWR Configuration for the Pre-Salt Area

Abstract

With the recent discoveries of the pre-salt reservoir, new areas of the Brazilian coast rose to prominence, especially for the Santos Basin. This area is adjacent to the Campos Basin, which now accounts for around 80% of Brazilian production. In this new area, in addition to the difficulties of drilling in salt rock, the deployment of subsea production systems have also to overcome new challenges, since environmental conditions are more severe than those in the Campos Basin. Other important issues are: the water depth of about 2200 meters; the high pressure for gas injection riser; and the high CO2 content, requiring special attention to the materials that will be in contact with the production fluid. At this new production frontier, priority was given to the use of floating units with storage capacity like VLCC hulls, in order to export oil production through shuttle tankers, as no pipeline grid is available. Depending on the motions level of these VLCC vessels, the selection of a viable configuration of riser becomes crucial. Thus, some alternatives have been studied and the Steel Lazy Wave Riser (SLWR) configuration was one of the options considered to be used for production and gas injection riser functions, besides being possibly used for risers with large diameters. As this area of the Santos Basin presents more severe conditions, the free-hanging configuration (SCR) was not feasible, even with the use of VLCCs with optimized motions. In this case, the SLWR configuration was better suited to overcome the problems faced by free-hanging configuration. This paper aims to present a set of variables and its right combination involved in SLWR configuration to make it feasible, considering some key points in the design of SLWRs, for example: motions level of the floating unit, thermal insulation required for the flow assurance of production risers; difficulties faced during the installation process and the need of using clad pipes or lined pipes due to the high level of corrosion imposed by CO2 fluid content.