Project Design of a CO₂ Miscible Flood in a Waterflooded Sandstone Reservoir

The Port Neches CO₂ miscible flood project began CO₂ injection in September, 1993 into a waterflooded sandstone reservoir along the Texas Gulf Coast. Sponsored by the U.S. Department of Energy (DOE) in their Class I Oil Program, this project will determine the recovery efficiency of CO₂ flooding a sandstone reservoir which has been extensively waterflooded down to a residual oil saturation of 30%. The design of this project utilized the various tools available for predicting the recovery performance of such projects, with DOE's CO₂ Predictive Model CO₂PM¹  and a compositional model being used. In addition a streamtube model^2,3  has been developed to predict the recoveries associated with the waterflood and CO₂ recovery processes. The validity of this streamtube model, the CO₂PM program, and previous compositional reservoir simulation work, has been evaluated by the use of a compositional five-spot model where an equation-of-state for the current reservoir oil is incorporated. This work points out the streamtube model's ability as an effective screening device for CO₂ flood prediction. Furthermore, the importance of properly characterizing the permeability within each layer of the reservoir is demonstrated by the improved recoveries seen in fining-upward sequence reservoirs.