An appraisal program involving the Bentley field located on the UK continental shelf has addressed the key technical concerns associated with developing viscous crude in an offshore environment. The program demonstrates how sustainable commercial flow rates can be achieved through the selection of a suitable completion design—including a downhole electrical submersible pump (ESP) and a downhole diluent-injection strategy—and through keeping within an appropriate operating-pressure and -temperature envelope.
The Bentley Field
The Bentley field, located in Block 9/3b in 110 m of water, contains approximately 900 million STB in place of heavy (10 to 12 °API) viscous (1,500-cp) crude. The field exhibits four-way dip closed at the uppermost Palaeocene, lowermost Eocene, and Dornoch sandstone level and covers an area of approximately 16×5 km at a depth of approximately 1.1‑km true vertical depth subsea. The reservoir is high porosity (33%), with net-/gross-pay ratio of 90%, and with ultrahigh apparent horizontal permeabilities approaching 50 darcies on the basis of flow-test measurements, but consistent with unconsolidated sand.
Following an extensive appraisal program, a development was planned of which 257 million STB of 2P reserves is estimated to be recovered over a 35-year production period.
