Subsea Manifolds Optimization - The combination of Mature and New Technologies

Abstract

Abstract Subsea equipments can be considered nowadays a mature option for offshore field developments. In Brazil, since the first oil in Campos Basin, different concepts ranging from one atmosphere chambers to deepwater guidelineless x-mas trees, have been tested, contributing for this development. @The experience acquired during these years makes it possible to combine the proven systems to the new technologies being developed, for the design of subsea manifolds The main target is more etllciency and cost reduction. When choosing a manifold concept. a usual rule is applicable: the simpler the better. The maturity, confidence and reliability obtained, allow the usage of resident hydraulically actuated valves, simplifying considerably the manifold arrangement. Other contributions come from: the reduction of piping bend radius allowed by the new pigs; the increased reliability of subsea instrumentation and chokes, allowing elimination of the gas-lift-test flowline, and the development of the direct vertical connection, that turns subsea tie-ins very fast and easy operations. Combining all that with the new technology of multiphase meter (to eliminate the test flowline and even the test separator on the platform), we can achieve a cost effective solution. This paper describes the possibilities of simplifying the subsea manifolds and presents a comparison of different designs. The usage of mature technology combined with the new developments, can help the industry to make deep water developments profitable, worldwide. Introduction Aiming cost reduction, efficiency and reliable solutions for future deepwater developments, PETROBRAS has carried out a study for comparison of different manifold concepts to identify the potential more attractive ones. For a more realistic analysis, [he manifold was not studied as an isolated item, but, using a system approach, all the subsea components were considered trees - flowlines - connections - controls - manifold - export lines and umbilicals. @In this comparative study, mature technologies of subsea valves, chokes, controls and instrumentation were combined with the new developments of flowline connection systems and multiphase meters to achieve cost effective alternatives. Base Case and Technical Parameters Set-Up The base case used for this comparative work was a system composed of 8 subsea wells that produce crude oil (3000 BOPD each) during the life time of 20 years, using gas-lift as the artificial lift method. The production is commingled in a diverless guidelineless subsea manifold, located 400 m (1,312ft) away from the wellheads. The export lines (production outlet and lift gas inlet) are connected through flexible lines to the floating process unit 3.2 km (2 miles) away from the manifold, Flexible lines are also used for the subsea trees to manifoId connections. Electro-hydraulic multiplexed control system is considered.