Some implications of cold CO2 injection into deep saline aquifers

When CO2 is injected down a well, the temperature at the bottom of the well depends on surface conditions, heat exchange with the wall of the well and pressure work within the well. Typically, the temperature of the CO2 at the bottom of the well is lower than the local geothermal temperature. As this relatively cold CO2 flows into the porous matrix, local thermal equilibrium manifests a thermal front, behind which the porous matrix and CO2 adjust to the cold injection temperature. As the temperature of the injected CO2 increases across the thermal front, the CO2 becomes less viscous and less dense. In relatively high permeability rock, as the flow spreads from the well, it becomes buoyancy-driven, and so at the thermal front, the flow adjusts from a deep, slow flow to a relatively shallow, fast flow. The increased depth in the near source cold region has two significant implications. First, it increases the near source storage potential as more rock is flooded with CO2, but it may also enhance the leakage into the seal rock which occurs in regions where the current is sufficiently deep for the pressure to exceed the capillary entry pressure. Citation: Rayward-Smith, W. J., and A. W. Woods (2011), Some implications of cold CO2 injection into deep saline aquifers, Geophys. Res. Lett., 38, L06407, doi: 10.1029/2010GL046412.