A New Configuration for Steel Risers in Ultra Deep Waters

In the last years, the design of risers to allow the exploitation of oil and gas in ultra deep waters has been a major concern to the oil industry. The main challenges related to this task are the risers’ top connections, where high stresses are a consequence of the combination of high tensions and bending due to platform rotation movements, and the TDZ (touchdown zone), where fatigue is one of the key issues. Possible solutions to these problems include production units insensible to the action of environmental loads, both in terms of offset and dynamic motions, or risers that do not develop high stresses due to these loads. Considering PETROBRAS option for FPSOs, Brazilian riser designers shall focus on the last alternative. In this way, the objective of this paper is to propose a new riser configuration, called RSAA (riser suspended and moored by chains, in Portuguese), composed by chain segments, a steel riser and jumpers. In this configuration, the top connection problem is solved by dissociating the maximum tension from the platform rotation movements, and the TDZ problem is solved by a compliant flexible structure. The obtained results indicate that this configuration can positively contribute to the exploitation of oil and gas in ultra deep waters, especially in Santos Basin, making feasible even the utilization of large diameter steel risers in FPSOs.