A Comparative Analysis of Ultra Deep Water Catenary Rigid Risers

Abstract

The ever increase of global demand for petroleum and natural gas brings needs to discover new petroleum fields. Particularly in the Brazilian coast, these discoveries are located on more and more remote areas combined with harsh and aggressive petroleum fluid production, such as the case of recently announced pre-salt petroleum fields. Development of offshore systems for field production in this scenario demands sophisticated and innovative technological solutions. It brings the necessity for developments of frontier technologies to make viable design of oil and gas production systems to be applied for ultra deep water depth applications. Production riser is a very critical component of most offshore petroleum production systems. Riser acts as a physical connection between subsea wells and floating production facility at the sea surface. It conducts the oil and gas production, and sometimes, fluid or gas for injection into the petroleum reservoir. Wellhead control commands are also guided between the floating platform and the subsea system throughout the riser system. In the literature, many different riser systems have been proposed and extensively discussed for ultra deep water applications. Among others configurations, Steel Catenary Riser (SCR) appears as a technically feasible and economically viable solution. This system is comprised with a free hanging steel pipe, suspended from the platform directed to the wellhead in a catenary shape. In ultra deep water, the riser weight itself commonly is the limitation for application of this type of riser system. Once it requires a much more expensive floating production platform with larger capacity. Furthermore, it also can cause high concentrated stresses in some regions along the riser structure. Catenary shaped risers with lighter material such as Aluminum seem to be a very attractive alternative due to the great riser weight reduction observed. The present paper describes and proposes procedures for the design and operation of petroleum production riser system for ultra deep water application to produce high flow rate of oil and gas in a typical pre-salt petroleum field offshore Brazil condition. Results and discussions are shown through comparisons for catenary riser systems composed by steel pipe and other kind of lighter material. Case studies are conducted for water depth up to 3000 meters by parametric analysis. Current and waves effects along with floating platform motions and riser geometries are analyzed in order to identify critical conditions and to depict feasible solutions.