Seabed Processing - Enabling Technology
Authors: Appleford David E. , Smith Ronald G. 
Published: October 2008

This paper will show that seabed processing offers multiple advantages and also that the technology for implementing it is available now. The paper will describe typical field applications and the enabling technology. Future technology, based on ongoing development programmes, will also be addressed.

The utilisation of seabed processing has been limited to date because of deficiencies in enabling technology. Fortunately, this situation no longer exists; seabed systems are now available for the development and enhancement of major as well as marginal fields. The difficulties presented by deep water and long tie-backs are effectively overcome as seabed processing gives extra drawdown and can incorporate boosting. However, the maximum advantage is only attained when the most appropriate seabed processing technology is employed.

The only two systems actually available at present utilise either insert-retrievable equipment or system-integrated modular designs. These systems will be compared and contrasted; the latter type of system being described in some detail. The enabling technology includes high voltage, high power, underwater-mateable connectors, subsea pumps, underwater electric actuators and diverless flowline connection systems.

Ongoing development engineering will provide 33 kV underwater-mateable connectors, in order to deliver higher power. Future technology will include rotary, expanding plug, double block and bleed valves principally for multi-ported fluid connectors. All-electric power and field control systems are envisaged.

Market conditions indicate that the advantages of seabed processing are particularly appropriate at the present time. Modular systems have particular advantages in terms of field development and operation.

Introduction

Traditionally, subsea field developments have been undertaken by the use of standardised Xmas trees for the wells combined with bespoke seabed manifolds. The power and controls for field developments have progressed to the use of electro/hydraulic systems utilising standardised communication protocols.

More recently, the need to develop fields in deeper water with longer tiebacks has exposed the limitations of the existing systems. This has led to the progressive development of the technology necessary to enable these fields to be produced back to a host facility. The technological advances have been made in multiphase pumps and multiphase meters. These items of equipment are now finding favour in some field developments.

Generally, the benefit of electrically powered equipment has only recently been recognised by the Oil and Gas Industry as a part of the solution to the deep-water fields with long tiebacks. As such, the Industry has now begun R&D studies for the enabling electrical equipment. It is fair to say that the enabling equipment being developed as a result of these studies, will take between one and three years before it is ready for field application.

However, this progressive approach to traditional field development has not allowed fresh thinking to emerge. Indeed, if this route is followed for future field developments, they will be unnecessarily expensive, excessively heavy and will not have the level of flexibility that can be achieved by addressing the problems with a fresh perspective. In fact, such empirically designed developments will be inferior to the system-modular solutions that are available today.