Some implications of cold CO 2 injection into deep saline aquifers

When CO 2 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 CO 2 at the bottom of the well is lower than the local geothermal temperature. As this relatively cold CO 2 flows into the porous matrix, local thermal equilibrium manifests a thermal front, behind which the porous matrix and CO 2 adjust to the cold injection temperature. As the temperature of the injected CO 2 increases across the thermal front, the CO 2 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 CO 2 , 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.