UK North Sea Strathspey Field Development: How Use Of A Satellite Tie-Back To A Third Party Host Created A "Win-Win" Situation
Authors: Cheifetz S.A. , Hale J.E. 
Published: October 2008

The Texaco operated Strathspey Field lies in the Northern Sector of the UK North Sell. Development option for the 150 million barrel oil equivalent field included use of a fixed platform, floating production system and sub-sea tieback to an existing platform. Decision Analysis was used to examine the risk profile of the different options. The choice of a sub-sea tieback to the Chevron operated Ninian Field (North & South Platforms) created economic benefits for partners in both fields as compared to the use of a stand-alone development for Strathspey.

STRATHSPEY DEVELOPMENT

The Strathspey Field is located ill UK North Sea Block 3/4a, approximately 110 miles east of Shetland ill a water depth of 450 feet. Following initial discovery and subsequent appraisal Fig. 1: Infrastructure Map(Available in full paper) drilling, evaluation work undertaken to identify feasible development options led to the adoption of a subsea system. The choice meant that Texaco's considerable expertise acquired developing the subsea Highlander and Petronella fields could be applied to Strathspey.

The Strathspey Reservoirs

There are two reservoirs in Strathspey, the Statfjord Formation of Triassic to Lower Jurassic in age, and the sandstones of the Brent Group which are middle Jurassic in age. The Brent Group sandstones contain a volatile oil, whereas the Statfjord formation sandstones contain a rich gas condensate underlain by a volatile oil rim. Initial shut-in wellhead pressures for the Brent & Statfjord wells are ~3,500psi and ~5,500 psi respectively. The Brent reservoir is at a depth of ~9,100 feet with the Statfjord at ~9,800 feet. Fig. 2: Oil & Gas Production Profiles(Available in full paper)

Total liquid recoverable reserves are estimated to be 89MMBbls with total recoverable gas reserves 334 BCF (Brent 66 BCF & Statfjord 268 BCF).

The Brent Reservoir is planned to be produced from eight subsea wells with pressure support from 3 downdip water injection wells. Two of the producing wells will be appraisal wells completed at a satellite location. Injection water will be supplied from the nearby Ninian Southern Platform with rates expected to peak at 88,000 bbl/d.

The Statfjord Reservoir will be produced from six subsea wells drilled from the same central location as the Brent wells. Two of the Statfjord wells are planned to use horizontal drilling technology to drain the oil rim of the reservoir. The first of the horizontal wells has been drilled with a horizontal section of approx 3,000 feet in the 85ft thick oil rim.

Development drilling commenced in October 1991 and will continue till 1996 with breaks for the installation of the subsea facilities and programmed wellwork. Initial production from the field was obtained in December 1993 and, following full commissioning, peak production of approx 43,000 BBIID liquids & 120MMSCFD gas are expected in 1995/6.

Subsea Facilities

The field will be developed using a subsea production system controlled from the Ninian Central Platform. The design of the facilities has been based on Texaco's 10 years experience with subsea production gained from the subsea wells on the Tartat1, Highlander & Petronella fields. Fig. 3: Processing Facilities on Ninian Central Platform(Available in full paper).