Bentley Field, North Sea, United Kingdom

The Bentley oil discovery is located in block 9/3b in the North Sea, 160km east of the Shetland Islands on the western edge of the Viking Graben. Xcite Energy Resources (XER) has a 100% interest in the block, which covers an area of over 200km². The block was awarded to XER in October 2003.

As per the 2D seismic study, two structures within the block - 9/3-1 and 9/3-4 - established accumulations of heavy oil: these make up the Bentley field.

The reprocessed 3D seismic survey was interpreted by the company in 2009. First production from the field will take place in the first half of 2012.

BP signed a contract with XER in January 2010 to market and distribute the crude oil extracted from the Bentley field.

Bentley field geology and reserves

The Bentley field's oil is found in the Dornoch Formation of the late Palaeocene age. Block 9/3b is located at the eastern margin of the Palaeocene Shelf.

The formation within the block consists of rough clastics, which further lead to the formation of a prograding delta compound across the eastern boundary of the east Shetland Platform. The main rock is the Upper Jurassic Kimmeridge Clay formation and is encountered within Viking Graben to the east of the block.

The reservoir contains approximately 160 million barrels of recoverable oil. The stock tank oil initially in place reached 690 million barrels of oil, with the upside at 890 million barrels of oil in June 2009.

Bentley field drilling

The Bentley field was discovered through the drilling of three wells, 9/3-1, 9/3-2A and 9/3-4; however, due to the uncertainty of fluid properties, the impact on flow rates and commerciality, another appraisal well was drilled in 2007 to identify the commercial prospects of the field. Five wells have been drilled in the field since 2003.

The 9/3b-5 appraisal well was spudded in December 2007 and drilled to a total depth of 4,105ft. The well found heavy oil-bearing Palaeocene Upper Dornoch Formation sands at 3,712ft, with an 87ft gross hydrocarbons column. During drill stem testing, 100% crude oil was reported at rates of up to 150 barrels of oil per day from a 50ft section of the oil column that had been successfully penetrated. The reservoir found was of high porosity and permeability unconsolidated sandstone.

In September 2010, the 9/3b-R well was spudded by the Ocean Nomad semi-submersible drilling rig. XER completed the pilot section of the 9/3b-6 appraisal well in October 2010. The well encountered a 113ft oil column in the Dornoch Reservoir. The pilot section was plugged and abandoned, and work on the horizontal side track, 9/3b-6z, began. In December 2010, the side track was suspended for use as a future production well.

Development of the Bentley field

XER will develop the field in a phased manner, with the initial phase involving the early production system. As per the production plan, four horizontal production wells and two vertical water injection wells will be drilled from the jack-up rig.

Fluid processing and water separation process will be carried onboard the jack-up rig by the production module, which was purposefully developed.

Extraction of the heavy oil requires special skills and equipment. The oil produced will be transferred to and stored in a moored tanker for further offloading to a shuttle tanker. It will then be transferred to large cargoes for transporting to specialised heavy oil refineries such as Humberside, Mongstadt and Rotterdam.

Bentley field contractors

Fugro Services carried out the drilling and testing of a horizontal production well as part of a contract signed in October 2009.

Applied Drilling Technology International was given the letter of intent in February 2010 to provide the Ocean Nomad semi-submersible drilling rig for drilling and testing of the 9/3b-R well.

Under a contract signed in February 2010, AMEC facilitates the operator in demonstrating the reserve potential of the field and bringing the field into production.

AMEC provided technical expertise, engineering and project management skills for the well test programme.

In December 2010, XER signed a letter of intent with British American Offshore (part of Rowan Companies) to supply a deepwater jack-up unit called Rowan Norway for the field's development. The vessel was delivered to Rowan Companies by Keppel FELS shipyard in July 2011.