Analytical Vertical Equilibrium Model Accounting for Fines Migration and CO2-Water Partial Miscibility

Abstract

The injection of humid (or wet) CO2 into geological aquifers offers a practical means of mitigating near-wellbore impairment caused by connate-water evaporation and the consequent formation damage induced by salt-precipitation in the dry zone. This study aims to develop a novel analytical model for this process. We extend the traditional Vertical Equilibrium (VE) formulation for immiscible displacement of brine by CO2 in layer-cake reservoirs to incorporate partial brine-CO2 miscibility, and formation damage due to fines migration and salt precipitation in the dry zone. The depth-averaging of the quasi-2D VE model yields explicit expressions for upscaled phase permeabilities and effective capillary pressure. The resulting 1D model allows for an exact self-similar solution, which provides explicit expressions for determining sweep efficiency and injectivity decline. The analysis of the model reveals the emergence of two distinct displacement fronts—a CO2 dissolution-displacement front (advanced front) and a full-evaporation front (receded front)—which delineate the two-phase flow region. The explicit analytical expressions derived enable rapid multivariate sensitivity studies on how CO2 humidity, reservoir heterogeneity, viscosity ratio and formation damage parameters influence overall sweep efficiency and well injectivity.