The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1]. That paper describes a “basic” classic, uncoupled methodology, and comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented in the companion paper [1], and these issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The present paper proceeds describing some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

The interest in the application of a SCR connected to a FPSO for exploration and production in deep water, has motivated the need to carefully study this concept due to the high offsets and vertical motions imposed by the vessel at the top of the riser. Petrobras has developed through its Research Center the study of different steel riser configurations. For bow turret-moored and spread-moored FPSOs based on VLCC converted hulls, the steel lazy-wave riser (SLWR) has been considered as an adequate solution due to its structural dynamic behavior and costs when compared to other configurations. Although the SLWR furnishes acceptable results for fatigue and extreme environmental conditions, the search for the best configuration is very demanding as any changes to a geometric parameter affect its whole structural dynamic behaviour. The search for configurations that meet all the code criteria for the riser project required meticulous detail that has not always lead to the best results because the number of variables involved is quite significant. Another important aspect is the installation procedure that can also influence the final configuration. In order to reduce the engineering time in generating and analyzing several configurations, optimization tools were studied and used in association with Petrobras in-house software to help define a model that could achieve all design verification phases more easily. This paper presents the experience with the use of an optimization procedure applied to facilitate the design of a SLWR connected to a FPSO unit offshore Brazil. The process of optimization begins with a set of preliminary geometric variables and constraints that are associated with multiple objectives related to economic, construction and safety factors. The result of the optimization process is a set of feasible configurations from which, through careful selection, the "one of the best" configuration is chosen.

Nowadays, coupled analysis tools that allow the simultaneous modelling of the hydrodynamic behaviour of the hull and the structural behaviour of the lines of floating production platforms have been increasingly used. The use of such tools is gradually allowing the introduction of some feedback between the design of risers and mooring systems. In the current practice, that comprises the so-called “hybrid” methodologies, mooring designers have been using these tools to consider the influence of the risers on the platform motions. On the other hand, riser designers can use motions that result from coupled simulations for the analysis of each riser. Such integration is already being implemented in the design practice of Petrobras; however, elsewhere the design of risers and mooring systems may still be performed separately, by different teams, therefore not fully exploiting the benefits that the coupled analysis tools can provide. In this context, this work describes an innovative, fully integrated methodology for the design of mooring systems and risers of floating production systems (FPS). This methodology considers different design stages (from preliminary to advanced), integrating the design activities of mooring lines and risers in a single spiral, allowing gains in efficiency and cost reduction. The initial design stages already include a feedback between riser and mooring analyses. The integrity of the risers can be considered in the mooring design by determining their safe operational zones, and therefore, mooring line pretensions can be modified to improve its structural performance. Then, in advanced stages critical design cases for both mooring and risers systems can be identified and rigorously verified by using fully coupled models. The application of the proposed methodology is illustrated with a case study of a typical FPS, representative of the platforms that have been recently considered for deepwater applications. It should be stressed that the methodology described here does not reflect the current design practice of Petrobras. Presently it is merely a proposal that is being studied and assessed; this work comprises the first draft of the methodology, which will be enhanced and consolidated as the result of current and future studies.

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.