An experimental investigation of the balance between capillary, viscous, and gravitational forces during CO2 injection into saline aquifers

Abstract

Abstract Understanding of the processes which take place within a reservoir during and after CO2 injection is essential for successful selection of a storage site for carbon capture and storage. Flow regimes that occur when CO2 is injected into a geological formation control how much CO2 can be effectively injected and stored in the formation. This paper presents an experimental investigation of the scaling laws which describe CO2 injection into saline aquifers. Quasi two-dimensional experiments were performed in initially water-filled glass-bead packs to demonstrate the influence of gravitational, viscous and capillary effects on the vertical flow of CO2. The properties of fluids used in the experiments are analogous to the properties of CO2 and brine at possible reservoir conditions. Experiments are performed for a range of dimensionless capillary and CGR numbers which may describe conditions at existing storage sites. The use of dimensionless numbers links the laboratory experiments with the field scale observations and hence these numbers can be applied for the screening of potential storage sites. The experiments represent gravity and viscous unstable floods with fractal-like fronts. The gravity effects were more pronounced in cases with a low injection rate and high permeability, causing less brine displacement. Higher injection rates caused more fingering and increased total displacement.