[1] The capillary trapping of supercritical CO 2 (s-CO 2 ) is postulated to comprise up to 90% of permanently trapped CO 2 injected during geologic sequestration. Successive s-CO 2 / brine flooding experiments under reservoir conditions showed that water-wet rounded beads trapped 15% of injected s-CO 2 both as clusters and as individual ganglia, whereas CO 2 -wet beads trapped only 2% of the injected s-CO 2 as minute pockets in pore constrictions. Angular water-wet grains trapped 20% of the CO 2 but flow was affected by preferential flow. Thus, capillary trapping is a viable mechanism for the permanent CO 2 storage, but its success is constrained by the media wettability. Citation: Chaudhary, K., M. Bayani Cardenas, W. W. Wolfe, J. A. Maisano, R. A. Ketcham, and P. C. Bennett (2013), Pore-scale trapping of supercritical CO 2 and the role of grain wettability and shape, Geophys. Res. Lett., 40,[3878][3879][3880][3881][3882]

We studied the role of intra‐pore eddies, from viscous to inertial flows, in modifying continuum‐scale flow inside pores. Flow regimes spanning Reynolds NumberRe∼ 0 to 1350 are divided into three zones – one zone follows Darcy flow, and the other two zones describe non‐Darcy or Forchheimer flow. During viscous flows, i.e.,Re < 1, stationary eddies occupy about 1/5 of the pore volume. Eddies grow when Re > 1, and their growth leads to the deviation from Darcy's law and the emergence of Forchheimer flow manifested as a characteristic reduction in the apparent hydraulic conductivity Ka. The reduction in Ka is due to the narrowing of the flow channel which is a consequence of the growth in eddies. The two zones of Forchheimer flow correspond to the changes in rate of reduction in Ka, which in turn are due to the changes in eddy growth rate. Since the characteristics of Forchheimer flow are specific to pore geometry, our results partly explain why a variety of Forchheimer models are expected and needed for different porous media.

Pore-level foam generation, propagation, and sweep efficiency were visualized using a two-dimensional sandstone pore structure etched in a silicon wafer with accurate representation of grain shape, grain size and aspect ratios. In situ foam generation occurred by snap-off in the interior of the porous network (rectilinear snap-off) and at permeability discontinuities. Lamella creation by the two snap-off mechanisms identified here resulted in different foam textures. During foam injection for enhanced oil recovery, microvisual data revealed that the aqueous phase advanced as film flow along water-wet grains whereas discontinuous gas bubbles were located in the center of pores. Individual gas bubbles were mobilized by lamella displacement. Experimental results showed enhanced sweep efficiency in terms of greater pore occupancy by gas and larger contact area with displaced fluid for foam injection compared to continuous gas injection.

No abstract

Anomalously high (up to +8°C) and low (-2°C) groundwater temperatures, as compared to undisturbed geothermal profiles, have been observed in unconsolidated siliciclastic aquifers off-set by normal-faults in the Lower Rhine Embayment, Germany. High hydraulic head gradients, induced by pumping, over the same faults suggest that they form effective barriers to lateral groundwater flow. Numerical analysis of the geothermal data presented here shows that the observed thermal anomalies can be explained under the assumption that the faults form a sub-vertical pathway that is connecting deep and shallow aquifers that are elsewhere separated by confining units. The hydraulic head and temperature observations taken together are consistent with the hypothesis that these faults behave as a conduit-barrier systems. Such behavior would arise from clay-smearing and drag of sand along the fault plane. Most current models of fault hydrology in unconsolidated sedimentary sequences assume faults to be effective barriers to fluid flow. Therefore our findings can have important consequences for the assessment of contaminant flow or hydrocarbon migration in sedimentary aquifer systems cut by faults