Managing a Mature Miscible Flood in Rainbow Field, Alberta, Canada

Paul Frydl, Diane Bilozir

Rainbow is the third largest light-oil field in western Canada. Devonian organic buildups in Rainbow contain approximately 1.6 billion bbl of original oil in place. The AA pool is a dolomitized buildup in a mature stage of a miscible flood. The long history of enhanced recovery in the pool and the recently expanded data base formed an ideal framework for an interdisciplinary reevaluation of the pool and its miscible flood.

Newly acquired three-dimensional (3-D) seismic data changed the concept of the shape and size of the buildup and led to the drilling of step-out wells. The 3-D seismic data, information from new wells, and reinterpretation of old wells resulted in a reassessment of pool volumetrics. In combination with a reevaluated material balance and review of miscibility, the new reservoir interpretation explained past performance, demonstrated the success of the miscible flood, and helped define future production strategy.

Core and log data were used to develop a geologic model of the pool and to reconstruct its depositional history. The growth of the buildup was interrupted by several stages of lowered sea level resulting in the development of exposure surfaces, which form horizons of low permeability. These vertical permeability baffles influence fluid movement in the reservoir and result in local bypassing of oil by the solvent front.

Nearly 14 million bbl of oil still remain between the original oil-water contact and the present solvent front. Maximizing recovery from this thin zone requires innovative production engineering solutions based on intimate knowledge of the reservoir in the "sandwich" zone. Relating reservoir characteristics to depositional facies has permitted the construction of a reservoir model with the required degree of detail.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.