Ensign offshore gas and condensate field is located 80km away from the English coastline and 78km away from the UK / Dutch median line at a water depth of 28m (92ft) in the southern North Sea.
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The field lies in blocks 48/14a and 48/15a of the United Kingdom Continental Shelf (UKCS).
Centrica Energy Upstream, a production and exploration arm of the UK-based company Centrica, owns and operates the field. First gas from the field was produced in May 2012.
Ensign gas field discovery, geology and development
The Ensign Gas field was discovered by Shell / Esso in 1986 with the drilling well 48/14-2. The field was further apprised by Conoco in 1988 with the drilling well 48/15a-6. The field was later acquired by Venture North Sea Gas and NSGP, which drilled two additional appraisal wells namely 48/14-5 and 48/14-6.
Centrica gained ownership of the field upon acquiring Venture North Sea Gas and NSGP in 2009. The field development approvals were received from the Department of Energy and Climate Change (DECC) in 2011. Centrica invested about £150m ($237m) on the field development.
The appraisal wells were drilled through hydraulic well fracturing techniques to improve the gas recoverability. The process involved pumping high pressure fluids into reservoir rock formations for creating fractures and opening up the rock to allow the flow of gas.
Infrastructure of the North Sea field
The gas field has been developed by the installation of a Not Permanently Attended Installation (NPAI).
The production and processing infrastructure at the field comprises of three production wells, including two platform wells and one subsea well tied back to a 24km long ten-inch export pipeline connected to the Audrey A platform.
Gas from the Audrey platform is exported via a 20in pipeline to the Lincolnshire Offshore Gas Gathering System (LOGGS) operated by ConocoPhillips, and further exported to Theddlethorpe Gas terminal.
The topside of the platform weighs 500t and measures 16m long, 12m wide and 8.5m high. It features a cellar deck, mezzanine deck and weather deck, as well as a helideck.
The well head jacket of the platform, weighing 500t, has length and width of 20m and height of 48m.
Production and reserves of the UK’s Ensign gas field
The initial gas production from the field is enough to power about 225,000 households. The field has estimated gas reserves of about 97bcf. The field is expected to produce about 2.3 million metric standard cubic metres (MMSm3) of gas a day.
Contractors involved with the offshore development
Heerema Fabrication Group was awarded with a contract to provide engineering, procurement and construction of the wellhead platform and jacket for the field in August 2010.
The construction of both topside and well head jacket was completed in August 2011.
The topside was constructed at Victoria Dock facility in Hartlepool. The well head jacket was constructed at Greenland road facility in Hartlepool.
Subsea 7 was awarded with the engineering, procurement, installation and commissioning (EPIC) contract for the flow lines and subsea works at the field in February 2011. The contract was worth about $60m. The scope included installation of 24km of 10in gas and 2in methanol pipelines that connected the Ensign platform and the existing subsea pipelines at the Audrey A platform.
Other contractors involved in the field development included Noble Julie Robertson (NJR), which drilled the production wells, and Petrofac, which provided the front end engineering design (FEED) and execution of topside modifications.
Aker Solutions was contracted to supply subsea controls for the wells. Dril-Quip supplied production trees and Seaway Heavy Lifting provided transport and installation services.
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