The Bentley Field, located on the UK continental shelf in block 9/3b in 110 m of water, contains approximately 900 MMstb in-place of heavy (10 to 12 oAPI) viscous (1500 cP) crude. The field is four-way dip closed at uppermost Palaeocene, lowermost Eocene, Dornoch sandstone level, and covers an area of about 16 Km by 5 Km.

An appraisal programme culminating in the 2012, 9/03b-7, 7Z extended well test (EWT), has addressed the key technical concerns associated with developing the viscous crude in an offshore environment. The programme demonstrated how sustainable commercial flow-rates can be achieved through the selection of a suitable completion design, including a downhole electrical submersible pump (ESP), a downhole diluent injection strategy, and through keeping within an appropriate operating pressure and temperature envelope. It further demonstrated that the movement of water from the underlying aquifer into the production bore proceeds in a predictable and manageable way, that produced water and oil can be separated even though emulsions are created in the ESP, and that water can act as a carrier fluid within the export pipeline.

The information from the EWT has been used to define and de-risk the field development design which is currently estimated to deliver 257 MMstb of 2P Reserves over a 35 year production period. In addition it is estimated that 48 MMstb of 2C Contingent Resources could be commercially extracted beyond the end of the currently planned facilities life. Investigations are underway to accelerate this tail-end production, with initial studies indicating that a polymer flood, enhanced oil recovery scheme, could be attractive.

This paper describes the appraisal programme, the lessons learnt and how these have been applied in designing the field development plan.

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