Experimental and Modeling Study of Multicontact Miscible Displacements

In order to estimate the potential incremental hydrocarbon recovery by CO₂ injection, compositional reservoir simulators are commonly used in the industry. Successful design and implementation of CO₂ injection processes rely in part on the accuracy by which the available simulation tools can represent the physics that govern the displacement behavior in a reservoir. In this paper, we investigate the accuracy of some physical models that are frequently used to describe dispersive mixing and mass transfer in compositional reservoir simulation.

We have designed a quaternary analog fluid system (alcohol-water-hydrocarbon) that mimics the phase behavior of CO₂- hydrocarbon mixtures at high pressure and temperature. A porous medium was designed using PolyTetraFlouroEthylene (PTFE) materials to ensure that the analog oil acts as the wetting phase, and the properties of the porous medium were characterized in terms of porosity, permeability and dispersivity. Relative permeability and interfacial tension (IFT) measurements were also performed to delineate interactions between the fluid system and the porous medium.

The effluent concentrations from 2-component first-contact miscible displacement experiments exhibit a tailing behavior that is attributed to imperfect sweep of the porous medium: a feature that is not captured by normal dispersion models. To represent this behavior in displacement calculations, we use a dual-porosity model including mass transfer between flowing and stagnant porosities. Two 4-component two-phase displacement experiments were performed at multicontact miscible conditions and the effluent concentrations were interpreted by numerical calculations.

We demonstrate that the accuracy of our displacement calculations relative to the experimental observations is sensitive to the selected models for dispersive mixing, mass transfer between flowing and stagnant porosities, and IFT scaling of relative permeability functions. We also demonstrate that numerical calculations substantially agree with the experimental observations for some physical models with limited need for model parameter adjustment.

The work presented in this paper is directly applicable to the study and design of EOR/sequestration processes through an improved understanding of dispersive mixing and mass transfer in these processes.