Shared Actuator Manifold - An Innovative Conception to MInimize Costs
Authors: Moreira C.C. , Ribeiro L.P. , Cerqueira M.B. , Garcia A. , Cosentino L.G. 
Published: October 2008

Subsea Manifold has been used as a very attractive alternative in the development of subsea fields. The discover of giant fields in deep waters and the completion of marginal fields very far from the production unit, increased the complexity of the manifolds considering the Control System and the diverless intervention method. The analysis of the conception of existent manifolds indicated that some simplification could be made without loss of reliability or functionality. This paper describes the development of the MAC Manifold, a monogram in Portuguese of Shared Actuator Manifold. A conception that use manual valves operated by a unique retrievable actuator that is able to walk over the manifold to operate all the valves.

Introduction

Considered as a technical and economical solution for subsea completion due to production anticipation and to minimize the number of risers connected to surface facilities, a very important issue in deepwater fields, Subsea Manifolds have been used in Campos Basin since 1979, in a total of 46 production and/or injection manifolds installed. Although the majority of those manifolds are very simple with direct hydraulic actuated valves and maintenance by diver assistance, the discover of giant fields, in water depths deeper than 300 m. limit to work with divers, and the completion of fields very far from the production unit, increased the size and complexity of the manifolds considering the control system and the diverless intervention methods. As a consequence of complexity the costs related to subsea manifold also increased. Looking for an optimized design and cost reduction, a study was performed resulting in the conception of the Shared Actuator Manifold (MACManifold).

Typical Manifold

Different types of manifolds have been used in Campos Basin since the atmospheric chambers to the complex diverless systems for deep waters (fig. I), but the majority of these manifolds use diver assisted philosophy with direct hydraulic control system with the following characteristics:–inspection, repair and maintenance are diver operated;–flowline connections are diver operated;–resident positive chokes installed and replaced by divers;–direct hydraulic control system with no data acquisition;–all the components are resident;–smaller dimensions and weight (less than 80 ton) with easier installation normally using cranes from conventional Diving Support Vessels (DSV).

Considering the subsea diverless manifold 3 generations are in use since 1990. The first generation of subsea diverless manifolds was installed in Albacora Field Campos Basin in December 95, in 620 m of water depth. The main characteristics are:–vertical flowline connection system: 1st end connection type for exporting lines and 2nd end one for well collecting lines:–guidelineless retrievable valve and choke modules;–multiplexed control system for functions actuation and data acquisition from the manifold and its 8 satellite subsea trees with guidelineless retrievable control pods.–sub-base used as a shallow foundation(gravity base) compensating the 50 sea bed slope. An additional leveling system revealed not being necessary during installation;–20 × 14 × 7m envelope dimensions and 450 ton of total weight. Installation was done by a crane barge;