A One-Dimensional Framework for Three-Phase Flow in Immiscible and Near-Miscible CO2 Injection: Application to Enhanced Oil Recovery and CO2 Storage

Oranan Ariyarit , Martin J Blunt 

We develop an integrated analytical framework for one-dimensional three-phase flow - involving rarefaction waves, shocks generated through the elliptic region and shock locus, as well as water and oil banks - for the analysis of oil recovery and CO2 storage. The solutions are compared with numerical approximations from a commercial reservoir simulator and an explicit finite difference code, showing good agreement between the approaches. Fractional flow solutions for three-phase immiscible and near-miscible injections were constructed semi-analytically. Relative-permeability inputs were carefully selected by fitting Corey-type curves to high-quality relative-permeability experimental data from the literature. The study was conducted under two wettability conditions: water-wet and non-water-wet. The results show that the displacement process, governed by relative permeability and viscosity, has a significant impact on oil recovery and CO2 storage design. The model used to represent the gas relative permeability has a significant impact on the results. In non-water-wet reservoirs, gas is no necessarily the most non-wetting phase in the presence of mobile water, leading to a much lower gas relative permeability than would be assumed using gas-oil data or oil-water analogues. Using a low gas relative permeability, consistent with recent measurements in the literature, leads to the formation of water or oil banks, which improve oil recovery. In addition, near-miscible injection results in a slower gas front and greater CO2 retention within the pore space. The findings of this study can be incorporated into reservoir management, field-development planning, and measurement, monitoring, and verification strategies for CO2 storage.