Design Principles For Multi-Well 'Subsea Production Equipment

ABSTRACT Use of multi-well subsea production systems has recently increased due to the early production this type of system offers for large oil fields and the economical production it offers for marginal fields. Current and future installations using equipment designed and fabricated by one manufacturer are described in this paper, as well as the design principles and philosophies resulting from these installations. Multi-well subsea production systems utilize either a floating production vessel, fixed platform or tension leg platform as the production facility. When a floating production facility is used, wells are completed with subsea trees; production is gathered at a subsea manifold and transported to the floater by a riser. Wells completed in this manner can also be produced through flowlines to a remote platform. When a fixed platform is used, wells are pre-drilled through a leveled template and tied back to surface production trees. The most recently developed production facility, the tension leg platform also utilizes some wells pre-drilled through a template, as well as some drilled from the tension leg platform, all completed at the surface. Templates, common to all three systems are manufactured in three types spacer, modular and unitized. Design principles for all three types have evolved from experience in fabrication, installation and leveling the templates. General design principles developed for mu1tiwell subsea production systems include simplicity of design, use of field-proven equipment, standard installation and operation procedures and incorporation of back-up systems. Adherence to these principles, followed by stringent quality assurance and proper training of operations and field service personnel will continually improve reliability of future subsea production equipment. INTRODUCTION For approximately ten years various oil companies and equipment suppliers have been involved in developing concepts for multi-well subsea production. These developments include methods and equipment for producing several subsea wells to floating facilities, fixed platforms and tension leg platforms. Using subsea trees and a subsea manifold, several wells can flow to either a floating production vesse1 or a tanker at a loading terminal. Using subsea templates and tie-back tools, several subsea wells, previously drilled with a floating drilling vessel, can be produced to a fixed platform. The most recently developed concept is for producing several subsea wells to a tension leg platform located over a subsea template. Some of the wells will be pre-drilled with a floating drilling vessel and the remaining wells will be drilled from the tension leg platform. The methods of producing multiple subsea wells to a fixed platform and to a floating production vessel have both been successfully used to commercially produce several oil fields. Plans are now being implemented to use these methods to produce numerous other oil fields. The method of producing multiple subsea wells to a tension leg platform has been the object of evaluation, design studies and prototype tests by numerous oil companies. Recently, it has been announced that plans are being implemented to commercially produce the Hutton Field in the North Sea using this method.