3.1.3 Viscous fingering

Supercritical CO2 is much less viscous than water and oil (by an order of magnitude or more) and this induces a considerable mobility difference between CO2 and in-situ formation fluids. Due to this difference, only some of the oil and water can be displaced and viscous fingering can cause CO2 to bypass much of the pore space, depending on the heterogeneity and anisotropy of rock permeability. Viscous fingering leads to an average saturation of CO2 in the range of 30-60% left behind in the reservoir. On the other hand, viscous fingering is limited in the natural gas reservoirs since CO2 is more viscous than natural gas. Lengler et al., 2010 recommends the use of 3D simulations when processes are active in two main planes, that is, gravity effects in the vertical plane and viscous fingering and channelling in the horizontal plane. Silin et al., 2009 and Lengler et al., 2010 stated that the dispersion of the front of the plume is caused by the heterogeneity, rather than a consequence of intrinsic instabilities such as viscous fingering.