Use of Dispersion Relationships To Model Adverse-Mobility-Ratio Miscible Displacements

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Abstract
Summary: Improved predictions of petroleum reservoir performance are needed to reduce the risks associated with field-scale miscible flooding. A major shortcoming of established prediction techniques is their failure to model accurately the effects of mobility ratio and viscous fingering on volumetric sweep and displacement efficiency. This paper establishes the feasibility of using physical dispersion relationships to account for fluid mixing associated with viscous fingering. The dispersion relationships use an additional parameter to incorporate a dependence on the local viscosity gradient. Adverse viscosity gradients increase mixing, while favorable viscosity gradients decrease mixing. The dispersion relationships reduce to the normal form when no viscosity gradients are present. The dispersion parameter needed is determined with published data for flow in a long, sandstone core system. Once established, the dispersion relationships are used to predict the performance of a much more complex displacement of reservoir oil by CO2. The simulations reproduce all the salient features observed experimentally and establish the validity of the approach. In particular, the effect of system length is modeled correctly.

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