Subsea Manifolds Design Based on Life Cycle Cost
Authors: Paula M.T.R. , Labanca E.L. , Childs Paulo 
Published: June 2014

Subsea manifolds are very attractive due to the reduction on the capital expenditure (CAPEX) obtained by reducing the number of flowlines and umbilicals, weight cut on the floating production platform due to reduction in the number of risers and reduction in the time required to connect the subsea wells to the platform, allowing for first oil anticipation. These advantages are more evident when a FPSO is used as a production platform.

Petrobras has been using subsea manifolds for a long time, ranging from one-atmosphere chambers in shallow waters in the Garoupa field to deepwater guidelineless subsea manifolds in Albacora, Marlim and MarimbÃ¡ fields. With the experience acquired along these developments, thus, it has been possible the optimization of the technical requirements aiming subsea equipment that can contribute not only for CAPEX reduction, but also for reduced operational costs, in a life cycle cost approach.

The new generation of subsea manifolds are being designed for easy maintenance and reduced impact of subsea interventions in production loss, through system modularization, usage of reliable components and also by transferring some critical equipment to the subsea trees. These optimized manifolds are the best, promising alternatives for deepwater developments.

This paper describes the possibilities of enhancing the design of subsea manifolds and presents a comparison among different generations of such equipment that is being used through the life of Campos Basin oilfields.

Introduction:

With respect to the economy, it its very important to evaluate all available options for the development of an offshore field. To enhance cost attractiveness of subsea production systems, it is imperative that the designed facility addresses all opportunities to reduce capital and operating expenditures.

Subsea manifolds have been used in the development of oil and gas field and the driving aspects that normally are used to select this alternative are:Minimum use of subsea flowlines and production risers;Simplification of floating production system configuration by reducing the number of riser's hookup's;Anticipation of production.

The use of subsea manifolds to develop subsea fields has been applied extensively by Petrobras and by now we have 60 subsea manifolds installed in water depths up to 950 meters and among these figures, 11 of them are diverless/guidelineless manifolds with electro-hydraulic multiplexed control systems and vertical connection systems.

This type of manifold is a very complex equipment with high technology involved and normally with a high acquisition cost. Installation and maintenance costs of such equipment are very expensive too, due to the daily rates of the resources involved. It is essential to have, therefore, a high performance and reliability during its operational lifetime, otherwise the use of subsea manifold cannot be considered an economically feasible solution.

Considering the analysis based on a life cycle cost, the results are strongly dependent on the initial capital expenditures, the maintenance costs and the losses caused by production interruption. In this way, Petrobras has been making tremendous efforts to ensure the highest standard of fabrication and installation of the deepwater manifolds, as well as special procedures for maintenance and spare parts acquisition philosophy.