HPHT Platform Wellheads & Christmas Trees- Performance Testing to Installation
Authors: Thomson Kenny , Adamek Frank C. 
Published: October 2008

Abstract
Reservoir depths, pressures and temperatures are continuing to increase. New terms such as HPHT are being coined to reflect the special class of UK North sea wells that reflect production temperatures of 300°F and higher and production pressures of at least 10,000 psi. This paper examines two HPHT platform production equipment scenarios including the qualification testing and installation. These include the:Erskine Field: 350°F & 15,000 psi. and theElgin-Franklin Field: 400°F & 15,000 psi.
Previous HPHT wells in the USA (Brazos, Mobile Bay and Norphlet) have been drilled and are producing as special projects focusing on the equipment technology development needs to produce these extreme temperature (&lt;350°F) and pressure (shut in pressures as high as 19,000 psi) wells. Production wellhead and trees were developed in the 1970's for 15, 20 and 30,000 psi and temperatures to 300°F. In the 1980's fire resistant equipment incorporating a new class of metal seal technology was developed. In the 90's, the addition of extreme temperatures approaching 450°F required requalification efforts by several equipment manufacturers. Today the HPHT class of equipment focuses on qualification of complete equipment design families.

Introduction
As drilling in the North Sea reaches deeper geological zones, a number of High Pressure/High Temperature (HPHT) developments are planned or underway in the gas condensate reservoirs of the Central Graben region. Fixed leg platforms are being used on three of the fields currently being developed in the region; Texaco Erskine, Elf Elgin and Elf Franklin. The combined effects of high pressure and elevated temperature have challenged the designs of the surface wellhead and tree equipment and spawned the development and testing of NT-2tm wellhead connector technology used on these installations. 1.2 The sub components of a wellhead and tree system that are most affected by the HPHT conditions are the non metallic elements used for casing annulus, tubing hanger and tree valve seals. The extreme temperatures subject almost all non metals to premature aging, and the high pressures can lead to failure of these components by deterioration, extrusion and explosive decompression. Wellhead and tree systems are made up of many components that require sealing interfaces between them. These are the sealing interfaces that often have non metallic primary, or secondary components, that are unsuitable for use in long term HPHT production applications. The use of all metal sealing virtually eliminates the problems associated with long term system degradation, caused by deterioration of the non metal items. This paper reviews the design and performance verification testing of the metal-to-metal sealing technology developed for use in HPHT surface wellhead and tree applications. The wellhead and tree system discussed are qualified for use in extreme service conditions with a service pressure of 15,000 psi and at operating temperatures of 350°F to 400°F.

HPHT Field Examples

Texaco Erskine.
The Texaco Erskine Project is the first commercial development of an HPHT field in the Central Graben area of the North Sea. The field is located 160 miles east of Aberdeen in blocks 23/26A & B and is being developed on a joint venture basis with British Petroleum.