Fire-Resistant Wellhead Equipment for Statfjord B Platform
Authors: Millmaker Allan B. , Leiser Manfred E. , Rowe Frederick G. 
Published: December 2007

While fire-resistant wellhead equipment has been of interest to the industry for many years, the application of the technology has been limited and the basic concepts are not known widely.

In this work we review the existing knowledge on the subject and the rationalization for taking a fire-resistant approach when designing for Stat fjord B. A comparison is made between conventional and fire-resistant equipment with particular reference to the design features of the Stat fjord B hardware.

Introduction

The Stat ford field is located on the Norwegian/U.K. boundary between latitudes 610 and 61030 north and was discovered in 1974. It is the largest oil field in the North Sea, extending over 15 miles (24 km) from northeast to southwest and averaging 2 1/2 miles (4 km) in width. The field will be developed from three fixed platforms of the Condeep-TM design. platforms of the Condeep-TM design. Stat fjord B platform, the second in the development of the Stat fjord field, combines in a single structure the production process, utility and auxiliary functions, along production process, utility and auxiliary functions, along with drilling facilities and domestic accommodations. This type of combined activity, production, drilling, and quarters platform is known as a ‘PDQ platform." The normal production rate will be 180,000 STB/D (28 603 stock-tank m3/d) of crude oil with individual well rates as high as 50,000 STB/D (7945 stock-tank m3/d). The platform is equipped with a single drilling rig operating platform is equipped with a single drilling rig operating between two well shafts, each containing 21 slots. Wells will be completed with 7-in. (177.8-mm) production tubing and 6%-in. (161 .9-mm) nominal bore Christmas trees.

During the design phase, there was concern for the overall risk level of the platform. The principal concern was that many personnel would be living on a facility containing producing wells, a drilling rig, and a complex process plant handling large volumes of hydrocarbons. process plant handling large volumes of hydrocarbons. An in-depth safety study was initiated to evaluate potential hazards and to design a platform that would reduce potential hazards and to design a platform that would reduce these hazards to a level well below normal acceptable limits. The resulting design was a PDQ platform with safety features unique in their extent and application.

A prime objective in preparing the wellhead specifications for this facility was to ensure that they were compatible with the platform design concept. In this regard, fire resistance for the wellhead valves was considered a desirable feature since other valves in hazardous areas were specified fire tested to API RP 6F and BS 5146. However, as no standards or specifications were available for the wellhead/Christmas tree assembly as a whole, a review of advances in wellhead technology was undertaken to determine the state of the art. Concurrently, the platform design criteria and assumptions made in the safety study were investigated to evaluate the requirements for wellhead fire resistance. A decision then was made to incorporate fire-resistant wellhead equipment on the Statfjord B platform.

JPT

P. 472