Clair oilfield

Scottish offshore oil field

The Clair oilfield is an offshore oil field in Scottish territorial waters west of Shetland in water depths of up to The field is the largest oilfield on the UK Continental Shelf with an estimated 8 billion barrels of oil in place, according to the BP Plc's website. It extends over an area of some , covering five licence blocks.

The Clair reservoir was discovered in 1977, with exploration well #206/8 1a penetrating a oil column in a thick sequence of Devonian to Carboniferous continental sandstone. In the 1980s ten appraisal wells were drilled. This activity demonstrated that the structure extended to an area of some with static oil in place, although it failed to confirm the presence of economically recoverable reserves. Two further wells were drilled in 1991, two in 1992 and one in 1995. Two of these wells (206/8 8 and 206/8 9z) demonstrated the potential for commercial flow rates but were not produced for long enough to give confidence in long term reservoir deliverability. In 1996 there was a breakthrough in the drilling and extended well testing (EWT) of well #206/8 10z. The EWT was followed by the side tracking of an offset well into the pressure sink created by the EWT. The 1996 well test results set the scope for the 1997 drilling programme and triggered interest in a first phase of development. Two further wells were drilled in 1997 to appraise the 'Graben' and '3A' segments 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 was appointed as the operator and programme coordinator. A development plan was approved in 2001, representing an investment of £650m by BP and its four partners in the project – ConocoPhilips, Chevron, Enterprise, and Amerada Hess. The production facilities were installed in 2004. The first stage of the development was inaugurated on February 23th 2005.

The first phase of development targets the 'Core', 'Graben' and 'Horst' segments of the southern area of the reservoir, which have , of which can be recovered. After heating the well fluids are separated into three phases (oil, gas and produced water) in the two parallel High Pressure (HP) Separators. Oil from the HP Separators is further heated and passes to the two parallel 3 phase Low Pressure (LP) Separators. Oil then flows to the two parallel Electrostatic Coalescers which further separates water from the oil streams. The oil is cooled and flows to the oil export pumps, then through the oil metering skid and to the oil export pipeline. Although there are two separation trains there is only one common gas compression train. Gas from the LP separators is compressed in the vapour recovery unit and mixed with the gas from the HP separators. The combined stream is compressed in the LP and then the MP (medium pressure) compressors. Gas is dehydrated by counter current contact with glycol in the Glycol Contactor. The dry gas stream is used as fuel gas on the platform. The remaining gas is further compressed in the HP compressor, it is used as gas lift on the oil production wells or, after gas metering, is exported via the export pipeline. Produced water from the separation train is treated and flows to the water injection wellheads. The UK government approved the £4.5billion Clair Ridge development in October 2011 and production is scheduled to begin in 2016 and continue until 2050. The project involves the construction of a drilling & production platform bridge linked to a living quarters & utilities platform, with pipelines to transport the oil and gas produced to Sullom Voe Terminal. BP and its partners awarded AMEC the contract for the engineering and project management for the main platform design, with Kværner constructing the platform jackets and Hyundai Heavy Industries constructing the topsides. Subsea 7 fabricated and installed the pipelines, Alphastrut designed and supplied a weight saving aluminium raised access flooring and ceiling cable containment system, Gordon Engineering designed and manufactured the helicopter refuelling system and Bifab fabricated the flare boom. External blast walls, fire walls and blast rated HVAC ductwork system were designed and fabricated by MTE (Mech Tool Engineering Limited)

In June 2013, the Clair Ridge platform jackets left Kværner's Verdal Yard in Norway and they were successfully installed in August 2013. First oil was announced on November 23th 2018. In March 2013 BP announced that the partnership will begin a two year appraisal program to explore a third phase of Clair field development. A contract was awarded to Aker Solutions in November 2018 for engineering services associated with this project which is now known as Clair South.