Highly Complex Nigerian Offshore Field Development – A Successful Case History

Porrera, Federico¹; Bernard, Vincent; Jefford, Leigh; Otevwemerhuere, Joseph E.; Oke, Mujeeb; Ghilardini, Laurent; Malherbe, Mathieu; Abraham, Rohan; and Olewczynska, Marzena
¹[email protected]

During the last decade ever smaller sized and increasingly complex offshore oil fields are being developed and successfully brought on production. The main challenges in developing these fields are to minimize geological risk, reduce Capital and Operating expenditure and finally optimize both production and recovery. Better management of the geological risk, together with improved drilling strategy coupled to intelligent completions and appropriate facilities all play a key role in achieving such objectives. The Development we describe here represents such a successful case history.

The field is located offshore Nigeria in water depth of 450ft. The field is a heavily faulted collapsed anticline located in the hanging-wall of a major growth fault. The intense faulting created a multitude of small fault blocks, 300m to 500m in width. Vertically the reservoirs are stacked into ten separate units with oil columns ranging from 10ft to 350ft. The trapping mechanism is structural, vertical sealing provided by shales and lateral sealing by fault closures through sand/shale juxtapositions. No less than 120 proven and un-appraised accumulations have been identified in the field. The reservoirs are shallow marine sands of Upper Miocene to Pliocene age with excellent poroperm properties (up to 5 Darcies). The oil is of excellent quality, up to 40° API.

The initial Field Development Plan was based on a low reserves base, and called on six production wells, each with dedicated flowline tiebacks and direct hydraulic controls to a FPSO. Produced gas is re-injected in a neighbouring field for pressure maintenance and flares down.

The development strategy changed when the field was found to be performing better than expected. Development wells were re-designed to test a maximum of un-appraised objectives on their way to the production targets. Wells were also designed to complete a maximum number of proven targets through highly deviated or horizontal drains, each completed separately with intelligent completions and sand control.

Production started in 2005, and to date a total of 19 wells have been successfully brought on production with a further 12 wells planned.

The revised development strategy has allowed production to be maintained at higher levels and for far longer than initially anticipated. In parallel, ultimate recovery has increased significantly from 30 MMstb at the onset of production to more than 100 MMstb today, with 64 MMstb produced to date.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013