Advective Displacement Method for the Characterisation of Pore Water Chemistry and Transport Properties in Claystone

Abstract

The advective displacement method applies large hydraulic gradients to a confined rock core sample to yield small aliquots of the preserved in situ pore water, applicable to aquitard rocks with hydraulic conductivities as low as 10 −14 m/s. Examples from argillaceous rocks indicate that only minor artefacts are induced and that analytical methods optimized for small aliquots provide a comprehensive chemical and isotopic characterisation. Multicomponent transport properties are derived from extending experimental time and using a traced artificial pore water for injection. Examples include quantification of the anion exclusion effect that can even resolve a small difference between transport properties for chloride and bromide in claystone. Controls by mineral saturation and cation exchange processes are also constrained by data from this approach. Technical details are provided for construction, material selection, components, sensors, and analytical issues.

4. Reactive Transport Modeling of Coupled Processes in Nanoporous Media

“…In addition, injection of tracers and the record of their breakthrough, or the elution of elements present initially in the sample, make it possible to derive a range of parameters for transport, adsorption/desorption, and dissolution/precipitation reactions using a reactive transport approach (Grambow et al, 2014;Montavon et al, 2014;Mäder and Waber, 2017;Mäder, 2018). Reactive transport modeling of advective displacement experiments have been carried out in a handful of studies with the consideration of the presence of a diffuse layer and the dual continuum model described in a previous section (Grambow et al, 2014;Alt-Epping et al, 2015, 2018. In all of these studies, a simplifying approximation was made: the porosity affected by the advective flow was set to the same exact value as the initial bulk porosity defined with the dual continuum model (Fig.…”

“…In the presence of a more complicated electrolyte composition (seawater dilution), the mean electrostatic potential model overestimates the contribution of the monovalent counter-ions in the diffuse layer, and underestimates the contribution of the divalent counter-ions. The mean electrostatic potential model is often referred as a Donnan model in the literature (Revil and Leroy, 2004;Appelo and Wersin, 2007;Birgersson and Karnland, 2009;Appelo et al, 2010;Tournassat and Appelo, 2011;Alt-Epping et al, 2015, 2018Gimmi and Alt-Epping, 2018). The Donnan equilibrium model, however, relies on two fundamental assumptions (Babcock, 1960): (1) that chemical equilibrium exists between two distinct aqueous phases, a hydrated clay phase and a bulk aqueous solution phase, and (2) that Henry's Law applies at infinite dilution to all of the ions in both phases.…”

“…a scale with resolution intermediate between true pore scale models and macro-continuum models, and in which parameters and properties such as permeability or reactive surface area need to be averaged or upscaled in some fashion. This corresponds to the matrix domains in the hybrid microcontinuum scale description defined by Soulaine et al (2016;2018), in which flow in true pore scale domains are described with the Navier-Stokes equation, whereas flow in matrix is described with Darcy's Law. Clayey materials are, by far, the most studied nanoporous media using reactive transport modeling.…”

A novel mechanistic anion exclusion model to investigate partially water‐saturated transport in soils and shales: A case study of nitrate solution flow

“…Since the bromide is considered as a conservative tracer (i.e. due to its neutrality it is conserved in the porous media) and its breakthrough curves have been smooth, it was chosen among other available data for chloride (the breakthrough curve of which is non-smooth) and sulphate (which is considered reactive in the porous media; Mäder, 2018). The test duration was 420 days.…”

Reactive Transport Modeling of Coupled Processes in Nanoporous Media

“…In addition, injection of tracers and the record of their breakthrough, or the elution of elements present initially in the sample, make it possible to derive a range of parameters for transport, adsorption/desorption, and dissolution/precipitation reactions using a reactive transport approach (Grambow et al 2014;Montavon et al 2014;Mäder and Waber 2017;Mäder 2018). Reactive transport modeling of advective displacement experiments have been carried out in a handful of studies with the consideration of the presence of a diffuse layer and the dual continuum model described in a previous section (Grambow et al 2014;Alt-Epping et al 2015, 2018. In all of these studies, a simplifying approximation was made: the porosity affected by the advective fl ow was set to the same exact value as the initial bulk porosity defi ned with the dual continuum model (Fig.…”