Anion exclusion effects in compacted bentonites: Towards a better understanding of anion diffusion

Multicomponent diffusion of a suite of tracers (HTO, Cl, Br, I, Na, Sr, Cs) in a single sample of Opalinus Clay

Natural tracer profiles across argillaceous formations

[1] We consider the case of a cylindrical cored specimen of a saturated argillaceous sediment located between two reservoirs filled with an electrolyte. One of the boundaries of the sample is submitted to a sharp pressure (or salinity change). The migration of the resulting pressure (or saline) front through the core specimen is responsible for the apparition of an electrical field, which is called the streaming potential (the diffusion potential for a salinity gradient, respectively). The temporal variation of this electrical field is recorded with Ag/AgCl nonpolarizable electrodes and used to monitor the evolution of the pressure (or saline) front between the two reservoirs. There is a finite interval of time before which the steady state condition holds through the core. In both cases, the electrical potentials exhibit a relaxation with a relaxation time constant depending on the square of the length of the cylindrical core specimen and on its hydraulic (or ionic) diffusivity. The experiments described here provide new methodologies to determine the hydraulic and ionic diffusivities of clay-rich materials. These experiments confirm also the predictions of a transport model developed recently for such materials and illustrate a powerful geophysical method to obtain transport properties, not only in the laboratory, but also in the field using a network of nonpolarizable electrodes to remotely monitor dissipation processes occurring inside the investigated system.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004JB003442

Characterization of transport properties of argillaceous sediments: Application to the Callovo‐Oxfordian argillite

Carbon capture and storage (CCS) is likely to be a critical technology to achieve large reductions in global carbon emissions over the next century. Research on the subsurface storage of CO2 is aimed at reducing uncertainties in the efficacy of CO2 storage in sedimentary rock formations. Three key parameters that have a nanoscale basis and that contribute uncertainty to predictions of CO2 trapping are the vertical permeability kv of seals, the residual CO2 saturation Sg,r in reservoir rocks, and the reactive surface area ar of silicate minerals. This review summarizes recent progress and identifies outstanding research needs in these areas. Available data suggest that the permeability of shale and mudstone seals is heavily dependent on clay fraction and can be extremely low even in the presence of fractures. Investigations of residual CO2 trapping indicate that CO2-induced alteration in the wettability of mineral surfaces may significantly influence Sg,r. Ultimately, the rate and extent of CO2 conversion ...

J.-Y. Boisson

Papers

Long-term diffusion experiment at Mont Terri: first results from field and laboratory data