Mathematical modeling of hot carbonated waterflooding as an enhanced oil recovery technique

Abstract

Due to environmental concerns, carbon dioxide has been increasingly used in Enhanced Oil Recovery (EOR) projects. Among other options, it can be dissolved in injected water and due to phase equilibrium conditions, part of the injected carbon dioxide is exchanged with the oil phase, creating a miscible EOR process. Thermal EOR methods are the most suitable, and sometimes the only option to produce viscous reservoir fluids. Recently, combined EOR methods have called the attention of oil companies and researchers. In this work we present the analytical solution for the problem of oil displacement by hot carbonated waterflooding, a combined thermal-miscible EOR technique. We consider one-dimensional, two-phase, three-component (oil, carbon dioxide, and water) flow in a homogeneous and isotropic porous medium. Other hypotheses of the model are incompressible system with no diffusion and no chemical reactions; gravitational, dispersive and capillary effects are neglected. Following Amagat’s law, we do not consider volume of mixing, and Henry’s law is used to model the solvent (carbon dioxide) distribution between phases. The heat capacities of the components and the rock were considered constant. The dependent variables of the problem are oil saturation, carbon dioxide concentration in the oil phase, and temperature. The solution of this 3 × 3 quasi-linear hyperbolic system is composed of shock and rarefaction waves and constant states, and it was obtained using the method of characteristics. Solutions for different relations between Henry’s constants were developed, and a sensitivity analysis for the CO2 concentration was performed. It is shown that there is an optimum parameter (relation between Henry’s constants) for obtaining the highest recovery factor. The efficiency of this technique is compared to hot waterflooding.