Nansen / Boomvang Field Development - Riser Systems
Authors: Wald G.M. , Carter R.H. , Beattie S.M. 
Published: October 2008

This paper presents the background and processes leading to the supply of 14 Top Tension Riser (TTR) assemblies for the Nansen and Boomvang Spar developments in the Gulf of Mexico. The observations presented will identify critical issues related to the design, analysis, procurement and installation of the world's first Top Tension Risers (TTR) to incorporate compliant guides.

Introduction

The Nansen and Boomvang developments are located in the Gulf of Mexico in water depths of 3,675' and 3,450', respectively. Nansen includes East Breaks blocks 602 and 646. Boomvang includes East Breaks blocks 642, 643 and 688. The fields are being developed using two independent Spars. Each Spar utilizes a number of Top Tension Risers (TTR) for tying back vertically produced wells. In addition, a number of satellite wells will be tied back to each Spar using flexible flowlines and risers. Steel Catenary Risers (SCR) and pipelines provide for export from each Spar. The production capacity of each facility is 40,000 BOPD and 200 MMSCFD of natural gas and 40,000 BWPD. The partners for the Nansen development are Kerr-McGee Oil & Gas Corporation (Kerr-McGee) and Ocean Energy, Inc. (Ocean Energy). The Boomvang partners are Enterprise Oil Gulf of Mexico, Inc. (Enterprise), Kerr-McGee and Ocean Energy, Inc. Kerr-McGee is the operator for both developments. Additional background information is contained in OTC 14089 (Thibodeaux, et al, 2002).

From the beginning of the project the design premise was for the TTRs for both Spars to be identical wherever possible since the well characteristics for both fields were very similar. Variations between the TTRs for the two developments were essentially limited to water depth and completion fluid density. Differences in the operating requirements for the dry trees were based on tree service - not the platform the tree was to be used on. Consequently, Nansen's greater water depth wasused to set the net buoyancy requirements. Boomvang became the driver for the riser string design due to its offset being a larger percentage of water depth with the ensuing influence on stress joint and keel joint loads. A common dry tree design was identified and incorporated into the early planning to satisfy the needs of both installations. This approach, using a standardized riser system design to be shared between the two developments, yielded several benefits. They included common equipment designs, simplified spare parts planning and commonality of installation and operating procedures. Simplifying and standardizing procedures will provide Kerr-McGee with benefits for enhanced personnel training and enhanced installation and operational safety resulting from equipment familiarity.

It is true that all offshore developments present the operator and contractor with a unique set of requirements and challenges. While the design and procurement of the Top Tensioned Risers (TTR) for the Nansen and Boomvang projects initially appeared relatively straightforward, a series of events led to a reevaluation of the design methodology for the buoyancy cans and hull mounted guides.