Waterflood-WAG Project Design in Compartmentalized West-End Reservoirs at Prudhoe Bay, Alaska

D. M. Neuhart, J. A. Spatz, K. D. Hagedorn, S. L. Reynolds, J. Flynn, B. W. Brice

The Ivishak sandstone reservoir at Prudhoe Bay, Alaska contains approximately 22 billion barrels of OOIP. In the western area, known as the West End, 600 million of those barrels are isolated from the main field by a plunging syncline. While the syncline effectively compartmentalizes hydrocarbons in the West End from those in the main field, pressure communication exists between the two via a common aquifer. Primary development of the West End includes pressure maintenance through gas cap injection. Pressure surveillance and material balance calculations during this primary depletion phase provide valuable indications as to the continuity within the West End reservoir.

In the geologic model, additional West End compartmentalization is postulated due to stratigraphic layering and normal faulting. Stacked cycles of correlative fluvial sand complexes overlain by laterally persistent floodplain shales separate similar reservoir rock types by impermeable barriers. Further reservoir segregation is identified from 3D seismic interpretation and well log analysis in which the Ivishak section is subdivided vertically into three separate fault blocks with slightly varying fluid contacts.

Combined geologic and surveillance data describe a complex, partitioned reservoir consisting of five separate regions: A-E. These data are incorporated into computer simulation models to investigate flow streams and design the waterflood-WAG well patterns. In region B, injector and producer well placement is planned to take advantage of lateral barriers where sealing faults juxtapose pay and non-pay in separate fault blocks. In regions A, C and E, vertical barriers of floodplain shales may be used to prevent migration of MI into a gas cap. While region D appears not to be suitable for EOR.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995