Effect of Heterogeneity on Residual Trapping of CO2 *

Effect of Heterogeneity on Residual Trapping of CO2

We analyze the buoyancy driven spreading of a plume of CO₂ through a subsurface permeable aquifer initially saturated with aqueous saline solution. We show that if the permeable rock includes two regions of different permeability, k₁ and k₂ say, then the volume of CO₂ in the plume spreads through the two layers in the ratio  (k₂/k₁)^{( 1/2 )} . Furthermore, in the case that there is some residual trapping of CO₂, we show that the volume of CO₂ partitions between the two layers in the ratio (k₂/k₁)^{( 1+2*gamma(s) )/( 2 + gamma(s) )} where the total volume of fluid decays with time as a power of time with exponent gamma(s) , here s is the fraction of CO₂ which is trapped in the pore-space. These results have implications for the efficiency of trapping during CO₂ sequestration.