The Cladhan facilities are tied-back to TAQA's Tern Alpha platform. Credit: TAQA.
BASF subsidiary Wintershall divested its entire share in the Cladhan field to MOL Group in March 2014. Credit: BASF.
Proserve supplied the control systems for Cladhan field's subsea wells. Credit: Proserve.

Cladhan field is located approximately 100km north-east of the Shetland Islands, UK. It extends across blocks 210/29A and 210/30A of the Northern North Sea, at a water depth of approximately 500ft.

The offshore oil field is operated by TAQA Bratani (64.5%), and other development partners include Sterling Resources (2%) and MOL Group (33.5%). The field development plan (FDP) for Cladhan was approved by the UK Department of Energy and Climate Change in April 2013.

The first oil production from the field was achieved in December 2015. The initial production capacity of the field is 10,000 barrels of oil equivalent a day (boe/d).

Cladhan field discovery and appraisal

The Cladhan field was discovered by Sterling Resources in November 2008. The discovery well 210/29A-4, drilled to a total depth of 9,734ft, confirmed the presence of 31ft of net pay hydrocarbon bearing in Upper Jurassic stratigraphic trap sandstones with 35.6°API oil.

The first appraisal well 210/29A-4Z was a sidetrack well drilled to a total depth of 11,215ft in September 2010. It encountered a gross hydrocarbon column of 159ft with 102ft of net hydrocarbon-bearing sandstones.

The subsequent successful drilling of the 210/29A-4Y and 210/30A-4 wells in 2010 and 2011 further gave impetus to the field development.

Cladhan field development details

The development plan primarily involved the drilling of two producer wells and a water injection well, which is tied back to TAQA’s Tern Alpha platform, located approximately 17.5km north-east of the Cladhan field.

The tie-back facility comprises a 10in-diameter oil line, a 4in-diameter gas lift line, a 10in-diameter water injection line and an umbilical for injecting chemicals. Brownfield modifications were performed on the platform to accommodate production from the Cladhan field.

Crude oil from the northern North Sea field is blended with oil produced from neighbouring fields at the Tern platform, before being exported to Sullom Voe via the existing Brent Oil Line. Associated gas is used as fuel on the Tern Platform.

Tern Alpha platform details

The Tern Alpha is a fixed platform located at the Tern field, within Block 210/25. It is supported by a four-legged steel jacket sub-structure that is anchored by piles to the seabed. The platform provides accommodation facilities for 175 people and is equipped with production, gas lift and water injection facilities. It also serves as a production facility for the Hudson, Kestrel and Falcon fields.

Contractors involved with the Cladhan field development

The brownfield modifications to the Tern Platform were performed by AMEC, who also performed the front-end engineering design (FEED) study for the project.

Butting supplied more than 17,000m of duplex stainless steel pipes for the project, whereas Godwin International supplied its dual plate check valves for the topside modifications of the Tern Platform.

Harkand provided its diving support vessel, Da Vinci, to perform the caisson clamp installation works at the project site. Conductor Installation Services (CIS) was subcontracted by Subsea 7 to drive the piles to secure a subsea manifold to the seabed, deploying its remotely operated subsea piling system.

The subsea control and communication systems for the field were supplied and installed by Proserve, using its proprietary open communications controller (OCC) technology. The subsea project management services were rendered by Ingen.