Uncertainty Management in a Major CO2 EOR Project

Occidental is the operator of a large turbidite sandstone reservoir in California that has progressed through primary depletion, limited gasflooding, and extensive waterflooding. A fraction of the reservoir is shut-in at this time due to uneconomic water cut. Oxy is currently evaluating a miscible CO2 injection project in this light oil reservoir. Although a CO2 injection project has the potential to significantly increase oil reserves and extend productive field life, the project includes significant technical and economic challenges. This paper describes the evaluation of subsurface uncertainties, including the use of a two stage design of experiments approach to choose optimal operator choices, regardless of subsurface uncertainties, and preparation of probabilistic production forecasts for project valuation. The steps in generating a robust model, discretization study, tornado analysis, uncertainty analysis, and generating forecast type curves are described. Operator choices and subsurface uncertainties each have significant impact on oil recovery, CO2 utilization, and project valuation. Though fundamentally different, both must be included in any uncertainty analysis. The authors believe the two step approach is a novel technique to evaluate operational trade-offs and find optimal solutions.