Abstract: Integrated Reservoir Management, Ubit Field, Offshore Nigeria

Clayton, C. A.; M. Anis; T. W Cooley; W. H. Troyer; J. P. Wallace; M. F. Cohen; M. M. Honarpour; K. A. Miner; M. R. Chambers; J. Gormly - Mobil Technology Co.; A. O. Fadase; F. N. Pebdani; E. G. Odior; E. O. Ekworomadu; E. U. Nwaeri; and A. H. Membere - Mobil Producing Nigeria

Ubit field is an example of a highly successful application of integrated reservoir management to an old field. For 25 years, Ubit had produced only 30 thousand barrels per day (TBD) with a high gas-oil ratio. Rejuvenation through reservoir management has quadrupled production. High drawdowns from the conventional directional wells had been problematic, and gas breakthrough plagued the field resulting in very low recoveries. Previous interpretations characterized the western portion of the field as "bedded" with good associated production. The eastern two-thirds of the field were described as a chaotic mixture of eroded, re-deposited, poor quality "Rubble Beds" sands. Poor production seemed to confirm this. Combining fundamentals with appropriate technology application and new data yielded a vastly improved interpretation. Key was placement of Ubit in the regional stratigraphic context of a shelf-edge delta that had collapsed into a complex series of rotated, tilted slump blocks. Identifying the mechanics of deformation was necessary to define the block geometries. Seventy blocks were identified from new 3-D seismic. Sixty-five of these were in the east, interpreted as younger sequences affected by down-slope translation and slumping. Ubit's depositional system is composed of prograding strandplain-lower delta plain unconsolidated sands. Lithologic, stratigraphic and deformational information from 6 new cores was integrated into the evolving model. Seven major hydraulic-focused reservoir facies were identified and defined. Properties were distributed defining the fluid flow relationships between blocks. Interpretations utilizing new techniques and methodologies allowed us to unravel the geologic complexities and build a cell-efficient, horizontally layered simulation model. The model captures the reservoir hydraulics in the thin 160' oil column spanning the 15,000-acre field. Gas column thickness ranges from 0-550'. Key reservoir management strategies were applied to maximize performance and ultimate recovery in this gas expansion, gravity drainage reservoir. Reservoir simulation results are utilized to guide Ubit's reservoir management. A total of 57 horizontal wells are planned. To date, 37 have been drilled, with low drawdown pressures and high sustainable rates. The development and operating strategy provide for optimal well placing and timing, balancing the non-uniform areal gas cap, maintaining stable gas cap movement and pressure throughout, establishment of a field rate plateau, and minimizing free gas production. Surface facilities were "de-bottlenecked" resulting in a 100% increase in throughput capacity.

Through integration of three key technology areas, the new reservoir model, horizontal drilling and surface facilities, this old field is now producing 140 TBD, with ultimate oil recoveries expected to exceed 1 billion barrels. The project has been a joint effort of affiliate, technology center and Nigerian government technologists. Multi-disciplinary teamwork, integration, new data, appropriate technology applications, and new techniques were key elements for ultimately delivering the business impact.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil