The Unitized Well Cluster: A Low-Cost Alternative To Large Multi-Well Templates and Clustered Satellite Wells
Authors: Parks W.C. , Going W.S. , Beebe D.C. 
Published: October 2008

Traditional subsea production systems have been based upon large templates ystems with integral manifolds, or more recently individual satellite wells clustered around a central manifold. This paper describes the Unitized Well Cluster (UWC), a low-cost alternative to large multi-well templates and clustered satellite wells.

The UWC utilizes existing technology to combine the benefits of individual wells with those of a unitized structure into a fully integrated subsea drilling and production system. It is comprised of two main components, a drilling template and a production template, which are installed in a stacked (piggy-back) fashion.

The UWC provides the capability to drill and produce several wells from a common structure that can be installed by a semisubmersible drilling vessel using standard equipment and procedures. Three 3-we/l UWCS have been successfully installed in the Gulf of Mexico in water depths ranging from 860? to 1,520?. Other available configurations and options make the UWC readily adaptable to a wide range of development scenarios.

The primary benefits of the Unitized Well Cluster are (1) reduced operator risk, (2) reduced lead time, (3) lower capital and installation costs, and (4) improved cash flow.

INTRODUCTION

Subsea drilling and production systems have become an increasingly important and accepted means of developing offshore oil and gas reserves, especially in deep water. At the same time, the cost of developing these reserves has increased while the size of recoverable reserves has decreased. Reducing the costs associated with subseaproduction systems is therefore essential if they are to continue to play a key role in offshore developments.

Traditionally, subsea production systems have been based upon large, multi-well templates with integral manifolds. These multi-well template systems are typically large, heavy structures requiring significant up-front capital investments and long lead time, and expensive, heavy-lift crane barges for installation.

More recently, subsea production systems based upon individual satellite wells clustered around a central manifold have been developed. These "cluster" systems reduce up-front capital investment requirements and eliminate the need for a crane barge for installation, but have additional costs associated with the large number of connections between the subsea trees and the manifold.

The Unitized Well Cluster (UWC) is a unique subsea drilling and production system which provides a low-cost alternative to large multi-well templates and clustered satellite wells. The UWC combines the benefits of individual wells with those of a unitized structure into a fully integrated subsea drilling and production system, The UWC provides the capability to drill and produce two or more subsea wells from a common structure, yet it can be installed by a semisubmersible drilling vessel using standard equipment and operating procedures. This eliminates the need for a crane barge or other large support vessel normally required for installation of a subsea template. It also eliminates the need for flowline and umbilical jumpers between the subsea trees and manifold, as is required with a cluster system.

The primary benefits of the UWC are (1) reduced operator risk, both financial and technical, (2) reduced lead time, which correlates into shorter project schedules.