Derisking a Heavy-Oil Development: A Case Study of the Bentley Field

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 172858, “Derisking a Heavy-Oil Development—A Case Study of the Bentley Field, UKCS Block 9/3b,” by B.H. Brennan, SPE, C. Lucas-Clements, S. Kew, SPE, and P.F. Dempsey, SPE, Xcite Energy Resources, prepared for the 2014 SPE International Heavy Oil Conference and Exhibition, Kuwait City, Kuwait, 8–10 December. The paper has not been peer reviewed.

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. In addition, it is estimated that 48 million STB of 2C contingent resources could be extracted commercially beyond the end of the currently planned facility life.

Derisking the Field

When the operator acquired the license, it was already known, on the basis of recovered samples, that the crude was heavy and viscous, but the full nature of the crude and its flow properties were poorly understood. The Bentley structure is a giant field, approaching 1 billion bbl in place. All wells had demonstrated excellent reservoir quality with high net/ gross, and there was therefore reasonable confidence in reservoir connectivity and volume. It had been demonstrated that the field had a large underlying aquifer with thickness greater than 400 ft. In summary, although there was reasonable confidence in the geological description of the field, it was clear that, before development sanction, a number of uncertainties remained.