Changes in Pore Structure and Connectivity Induced by CO2 Injection in Carbonates: A Combined Pore-Scale Approach

Abstract

We investigate at the pore scale fluid-rock interactions that occur in the context of carbon dioxide (CO2) storage in saline carbonate aquifers. Brine saturated with super critical CO2 is injected into two carbonate samples (Estaillades limestone and an aquifer sample) at typical storage conditions (9MPa and 50oC). Dry high resolution micro-computed tomography scans are obtained prior to and after the experiments and thepore structure, connectivity and computed flow fields are compared using image analysis and pore-scale modeling techniques. We perform direct simulations of transport properties and velocity fields on the 3Dscans and we extract representative pore-throat networks to compute average coordination number and assess changes in pore and throat size distributions. In this study, we experimentally mimic near wellbore region conditions by injecting fluids at relatively high flow rates. For high Péclet and Damkö hler numbers, experimental observations confirm the formation of highly conductive channels i.e wormholes.A significant increase in porosity and permeability is found with fewer pore and throats after dissolutionwhile the average coordination number does not change significantly. Flow becomes concentrated in the wormhole regions after reactions although a very wide range of velocities is still observed.