This paper details the methodology and knowledge obtained from a recent riser concept study for a deepwater development in the Gulf of Mexico. The proposed development is a wet tree development tied back to a floating facility with sour production service. Semi submersibles, Spars and Tensioned Leg Platforms are considered in combination with steel catenary riser, lazy wave riser and single vertical import riser (SVIR). The riser design is challenging due to the requirement of artificial lift, resistance to high production pressures, accommodation of sour service upon onset of water injection and the need for large diameter export lines. It is prudent to be conservative in the initial phase of design in order to account for the possibility of detrimental design changes in the later phases of the project. A review of the conservatism involved in the preliminary riser concepts study is conducted in this paper. The demands made by such conservatism for exotic and novel strength and fatigue mitigation concepts such as lumped masses on the SCRs, titanium touch down zones and light weight coating is discussed. It is observed that fatigue knockdown due to sour service on steel, titanium or clad pipes is the most contributing factor in driving production riser design towards the requirement for novel technology. The need for knowledge of accurate sour service knockdown is highlighted. In this paper, the relative performances of the aforementioned vessel riser combinations are presented. The effectiveness and previous track record of the fatigue mitigation technologies for sour service are reviewed. Finally, the benefits and limitations of each vessel and riser system are compiled and the factors considered by the operator in selecting one particular system are discussed. Introduction Subsea riser design is one of the most challenging engineering aspects of a deepwater field development. Risers constitute the conduit that connects the floaters at the surface to the subsea wellhead. The primary challenge in riser design emanates from the fact that these are dynamic structures highly susceptible to environmental and operational loads. As the global demand for hydrocarbons has increased, offshore projects have moved deeper and deeper and riser design has become more challenging than ever before, involving novel technologies and materials. The latest field developments in the GoM are often in the order of 5,000 ft water depth or more; requiring extensive engineering in order to come up with an optimum riser design. This paper describes a case study of a GoM deepwater riser design in the pre-FEED stage. The water depth at this location is greater than 5,000 ft and a variety of riser-vessel combinations are assessed. The technical performances of the range of riser designs are presented with a summary of benefits and limitations of each type. Design data and constraints such as sour production are highlighted and the demand for unconventional technologies driven by the harsh environment and pre-FEED robustness requirements is demonstrated. The commercial feasibility and track record of the different riser solutions are also discussed. Finally, the recommendations and learnings from this study are summarized. The material presented in this paper provides ample insight on how deepwater risers behave in the harsh GoM environment. It is understood that not many project analysis findings are presented in the public domain. In that light, the sections herein are indeed valuable guidance to a designer in the preliminary stages of project development. Certain riser technologies presented herein are considered novel and to date have not been implemented in the field. It is expected that offshore projects will utilize more of these technologies in the coming years. The work conducted in this paper is a stepping stone for such technologies to be realized.

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Various computational methods that have been developed in the past are combined in this paper to predict: (a) the performance of podded propulsors, and (b) the sheet cavitation on a rudder which is subject to the flow of an upstream propeller. An 3-D Euler-based finite volume method (GBFLOW-3D) is used to predict the flow around a pod with a strut, and is coupled with MPUF-3A, a lifting surface vortex-lattice method, which is applied to the propeller(s) of the pod. The propellers are modeled via body forces in GB FLOW. The 3-D effective wake for each of the propellers of the pod is evaluated by subtracting from the total inflow (determined in GBFLOW-3D) the velocities induced by the same propeller ( determined in MPUF-3A). Several iterations between GBFLOW-3D and MPUF-3A are performed until convergence is reached. The three-way interaction among the pod/strut and the two propellers is fully accounted for at the end of the iterative process. The inflow to the rudder is determined by applying GBFLOW-3DIMPUF-3A on the propeller upstream. Once the propeller-induced flow to the rudder is evaluated, PROPCAV (a potential-based boundary element method), is used to predict the cavitation patterns on the rudder. The effects of the hull are considered by using the image model in PROPCAV. Several validation studies with other methods, some analytical solutions, and experiments are presented.

Top tensioned risers (TTRs) have been used for deepwater applications in the Gulf of Mexico, offshore West Africa, and offshore Southeast Asia. Dry tree riser systems attached to floating production units such as spars, tension leg platforms (TLPs), and deep‐draft semisubmersibles are continually being considered for future developments, and designs have been developed for ultradeepwater. TTRs are complex dynamic structures, and the design of these riser systems is primarily governed by loading from the environment and the floater motions. This article presents the TTR system configuration for production and drilling applications and briefly describes the different components that comprise the TTR stack‐up. The design and functionality of different tensioner systems used to provide top tension is presented in detail. Aspects of TTR design, fabrication, installation, and commissioning are discussed to highlight the key considerations in progressing TTR design from concept to service.

An iterative technique for the prediction of the performance of two-component propulsors, includ­ing the effects of sheet cavitation, is presented. A vortex-lattice method, originally developed for the prediction of the performance of cavitating single propellers in non-axisymmetric inflow, is applied to each one of the components. The "effective" wake for each component is determined via an Euler solver, based on a finite volume method, in which both components· are represented via body forces. The axisymmetric version of the method is used to predict the mean performance of a contra-rotating propulsor and of a pre-swirl stator/rotor combination. The non-axisymmetric version of the method is used to predict the non-axisymmetric flow-field in the wake of a pre-swirl stator, and the unsteady cavitating flow performance of the rotor subject to that flow-field.