Storage of anthropogenic CO2 in geological formations relies on a caprock as the primary seal preventing buoyant super-critical CO2 escaping. Although natural CO2 reservoirs demonstrate that CO2 may be stored safely for millions of years, uncertainty remains in predicting how caprocks will react with CO2-bearing brines. This uncertainty poses a significant challenge to the risk assessment of geological carbon storage. Here we describe mineral reaction fronts in a CO2 reservoir-caprock system exposed to CO2 over a timescale comparable with that needed for geological carbon storage. The propagation of the reaction front is retarded by redox-sensitive mineral dissolution reactions and carbonate precipitation, which reduces its penetration into the caprock to ∼7 cm in ∼105 years. This distance is an order-of-magnitude smaller than previous predictions. The results attest to the significance of transport-limited reactions to the long-term integrity of sealing behaviour in caprocks exposed to CO2.

Lattice artefacts are used, through modified lattice actions, as a tool to find the largest instantons in a toroidal geometry [0,L]^3X[0,T] for T to infinity. It is conjectured that the largest instanton is associated with tunnelling through a sphaleron. Existence of instantons with at least 8 parameters can be proven with the help of twisted boundary conditions in the time direction. Numerical results for SU(2) gauge theory obtained by cooling are presented to demonstrate the viability of the method.Comment: 15p, 3 figs appended in PostScript (uudecoded), preprint INLO-PUB-11/93, FTUAM-93/31. Correction of eq.(16) and the discussion on pg.

We compute the one-loop coefficients for an alternative Symanzik improved pure gauge SU{N} lattice action (N=2 and N=3). For the standard Symanzik improved action we confirm previous results by L\"{u}scher and Weisz.Comment: 45 pages, LaTeX, includes library.ps for generating Feynman diagram

(2014), Microscale solute transport and precipitation in complex rock during drying, Geophys. Res. Lett., 41, 8369-8376, doi:10.1002 Abstract Formation drying and salt precipitation due to gas injection or production can have serious consequences for upstream operations in terms of injectivity and productivity. Recently, evidence has been found that the complexity of the pore space and microscopic capillary-driven solute transport plays a key role in the relationship between permeability and porosity. In this study, we investigate drying and salt precipitation due to supercritical CO 2 injection in single-porosity and multiporosity systems under near well-bore conditions. We image fluid saturation states and salt deposition by means of microcomputerized tomography scanning during desaturation. We observe capillary-driven transport of brine and the respective solutes on the pore scale. Solute transport between porosity classes determines the distribution of the deposits in the pore space and the permeability porosity relationships-K( )-for flow-through drying.

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