Clair
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The Clair reservoir was discovered in 1977 with the 206/8-1a exploration discovery well penetrating a 568 metre oil column in a thick (>700m) sequence of Devonian to Carboniferous continental sandstones overlying Pre-Cambrian basement. A well test flow of 1500 Stb/d of 25 API oil was recorded from the best quality reservoir unit. Between the discovery well and the late 1980's, some 10 appraisal wells were drilled in several periods of competitive E&A activity by the four Clair licence groups. This activity covered the entire accumulation, demonstrating that the structure extended to an area of some 400km2 with static oil-in-place. Although this is comparable to some of the larger North Sea fields, the programme failed to confirm the presence of economically recoverable reserves.
In early 1990, the Clair licensees pooled their resources and through a 'Joint Appraisal Agreement' agreed to share future appraisal activity with BP appointed as the Operator. |
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Interpretation of a 3D seismic data survey, together with an integrated study of core data, provided crucial insights into the influence and understanding of fractures on reservoir productivity. With this understanding came the drilling of two wells in 1991 followed by a further two wells and an extension to the 3D seismic in 1992. The two wells drilled in the 'Core' area of the field, the 206/8-8 well in 1991 and the 206/8-9z well in 1995, demonstrated the potential for commercial flow rates but were not produced for long enough to give any confidence in long term reservoir deliverability. This programme did however identify the Core area as a potential development 'sweet spot' in the field.
In 1996, a breakthrough occurred in the drilling and extended well testing (EWT) of 206/8-10z well in the Core area. A total of 525 MStb of oil was extracted from the Core area without encountering boundaries to the reservoir. The EWT was immediately followed by the side-tracking of an offset well, 206/8-9y, using the suspended 1992 well, 206/8-9z, directly into the pressure sink created by the EWT. The 1996 well test results proved considerable vertical connectivity in the Devonian sequences of the Core area. This data set the scope for the 1997 drilling activities and triggered interest in a first phase of development of the Clair field, termed the 'Phase 1 Development'.
Two further wells were drilled in 1997 to appraise the 'Graben' and '3A' segments of the reservoir to reduce uncertainty in these areas adjacent to the Core area.
In May 1997 it was agreed by the Clair partners to jointly develop the field. BP as the major stakeholder, was appointed as the Operator and programme coordinator. The Clair Partnership now comprises 5 Partners each with the following fixed equity interests:
BP 28.6%
ConocoPhillips 24.0%
Chevron Texaco 19.4%
Enterprise 18.7%
Amerada Hess 9.3%
Field & Reservoir Description
The Clair field is the largest discovered, but not yet producing, hydrocarbon resource on the UKCS.
The field is located 75 km West of Shetland in water depths of up to 150m and extends over an area of some 220km2.
It is divided into 9 fault-bounded segments, which have a common free water level and a maximum oil column of some 600m. A gas cap is present in the structurally elevated Ridge segments.
The reservoir is made up of fractured sandstones of Devonian to Carboniferous age with current interpretations suggesting a total volume of oil in place of excess of 410 million metric tonnes of 22 - 23 API oil.
However, there is significant uncertainty both in terms of reserves and the ability to commercially produce the highly fractured reservoir.
The field comprises an extensively layered and fractured sandstone reservoir with significant open fractures and variable matrix quality. The successful commercial development of Clair is dependent on:
- Understanding the productivity of the fractured reservoir.
- Covering static reservoir description.
- Reservoir performance prediction.
- Drilling and well engineering.
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Field Development
Development of the Clair reservoir will be a 'phased development'. The first phase - 'Clair Phase 1 Development' - will target the Core, Graben and Horst segments of the southern area of the reservoir. This first development phase is laterally extensive and relatively shallow, requiring high step-out extended reach wells for maximum drainage from single well access points.
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Phase 1 of the Clair development has recoverable reserves of around 250 million barrels of oil. Plateau production is expected to be around 60 thousand barrels of oil a day and 20 million cubic feet of gas per day. Further development phases will be dependent on the performance and success of the Phase 1 Development.
Concept Development
The development concept for Clair Phase 1 Development has been selected and agreed by the Clair Partnership, in full consultation with the Health and Safety Executive. A comprehensive formal safety assessment process ensures that safety visits are kept as low as reasonably practicable.
The concept has been demonstrated as reducing risks to a level as low as reasonably practicable (ALARP) based on information available at the time. As the selected development concept is further defined, the concept selection decision will require ongoing testing to provide assurance it remains the 'ALARP' solution.
The design comprises a single steel jacketed platform with integrated topsides deck, incorporating the following key elements and features:
- Design life 25 years,
- Single steel jacket structure.
- Platform location over 206/8-10z well.
- Integrated topsides deck (include. Accommodation) with separate modular drilling rig.
- Maximum 10,500 metric tonnes single lift installation for topsides deck.
- Jacket lift(s) to be within single lift capability of installation vessels.
- All platform development wells with dry wellhead trees (ie. No subsea development wells).
- Full offshore processing to tanker export crude quality (ie. 'dead' and 'dry' oil export).
- Additional processing facilities for offshore power generation, water injection, produced water and cuttings re-injection, surplus gas disposal (export or re-injection), and flare gas recovery.
- High angle and horizontal production wells.
- Artificial lift provided for all producing wells with option of Electrical Submersible Pumps (ESPs) for future wells intervention.
- Simultaneous drilling and coil tubing well intervention operations (SIMOPS).
The Environment
One of the key aspects of the environmental assessment process is to ensure that the project has a clear understanding of the environment upon which the proposed activities may have an impact.
Consultation with many diverse groups and individuals has been key to the development of the Clair project. Between November 2000 and March 2001, widespread consultation was undertaken with our stakeholders specifically to listen to concerns and issues raised with respect to the Clair project. The consultation process included a Q&A and a questionnaire as well as face-to-face discussions and meetings. The feedback from this process has been incorporated into the project plan and the decision making processes of the project.
The key studies completed to date, which have contributed to the decision making for the current conceptual design are of two basic types:
- Those which increase our understanding of the environment at and around Clair.
- Those which predict the potential impact of planned activities on the environment.
- Environmental assessment process.
One of the main objectives of the environmental assessment process is the identification of key issues in order to design out or minimise any potential impacts.
The importance of potential issues is determined by a number of factors:
- Impact on the environment.
- Regulatory requirements.
- BP corporate requirements.
Stakeholder views
Stakeholder views are gained in a number of ways:
- Through the experience gained from other projects West of Shetland (Foinaven and Schiehallion).
- Through ongoing consultation between the oil industry and its stakeholders.
- Through consultation specific to this project.
Clair HSE Principles
The design and development of Clair will be undertaken in a responsible manner. Decisions have been made with full consideration of relevant economic, safety and environmental factors and address the views of all stakeholders. The objectives in developing and subsequently operating Clair are:
- No harm to people.
- Minimise emissions and waste generation.
- Improve on current best industry performance.
- Maximise efficiency of resource and energy usage.
Avoid significant biodiversity impact
Anticipate the impact of future legislation. Once all issues have been considered and environmental impacts designed out or mitigated through design, those remaining issues ('residual issues') are reassessed, and minimised through operational procedures. In addition environmental monitoring will take place throughout the life of the development to ensure continuous assessment of potential impacts.
The Clair project is regarded as a groundbreaker for the UKCS. The project has excellent HSE results, set new benchmarks for performance metrics and has opened the door for future development and growth for the EU offshore industry.
