Laboratory-Based Injectivity Decline Prediction During Supercritical CO2 Injection into Weakly Consolidated Sandstones

Abstract

The aim of this work is to characterize the impacts of formation damage resulting from fines migration on CO2 storage in weakly consolidated sandstone rocks. A mathematical formulation and upscaling procedure presented in this work aims to quantify the injectivity decline and sweep efficiency during CO2 injection. For CO2 storage in aquifers, formation damage can be present during two stages: during the two-phase displacement of water by supercritical CO2, and during the evaporation of irreducible water. By quantifying the effects of fines migration in a saturation-dependent critical retention function and integrating fines migration into the gas relative permeabilities, its impacts on flow can be characterized directly. The specific case of weakly consolidated reservoirs is targeted through a sensitivity study on the impacts of the total detachable fines concentration, which is expected to be much larger for these reservoirs. The full 3D equations are upscaled into a 1D Buckley-Leverett equation using the assumptions of uniaxial flow and vertical equilibrium, where capillary and gravitational forces determine the vertical distribution of the gas and water. A new averaged flux function accounts for evaporation, two-phase flow, and formation damage. An explicit expression for the condition of vertical equilibrium and the large-scale approximation is presented. Under these assumptions, the mass balance equation reduces to a form that allows for an exact solution. The exact solution allows calculating injectivity, sweep efficiency, and the distribution of CO2 across the reservoir at different points during injection. The results show substantially lower injectivity and higher sweep efficiency when the concentration of detached fines is increased. The new mathematical model provides a fast and simple way to predict the decline in injectivity during CO2 injection resulting from fines migration. The analysis clearly highlights the higher risk that weakly consolidated reservoirs may experience due to higher detachment of natural fine particles.