Simulation of chemical reaction localization using a multi-porosity reactive transport approach

Abstract

Results of reactive transport laboratory experiments often suggest that pore scale heterogeneity induces localization of reactions (the generation of local micro environments favoring reactions that would not occur in a well-mixed Representative Elementary Volume, REV). Multi-Rate Mass Transfer (MRMT), which has been employed to reproduce hydrodynamic heterogeneity, may also be used to simulate geochemical localization. We extended the Water Mixing Approach (WMA) designed for single porosity media, to simulate chemical reactions caused by the mixing of mobile and immobile zones. The method is termed Multi-Rate Water Mixing (MRWM). The MRWM approach was employed to simulate laboratory experiments of CO2-rich brine transport through carbonate rich samples (Luquot et al., 2016, in this issue). Chemical heterogeneity in space was reproduced by varying the mineral assemblages in immobile regions. This enabled us to reproduce the generally low pH environment while allowing for high pH local zones required for the localized precipitation of kaolinite, which has been observed in reality, but cannot be modeled with conventional reactive transport formulations. The resulting model is very rich, in that it can reproduce a broad range of pore scale processes in a Darcy scale model, and complex, in that the interaction between chemical kinetics and immobile zones physical parameters is non-trivial.Peer ReviewedPostprint (author's final draft

Heletz experimental site overview, characterization and data analysis for CO 2 injection and geological storage

“…This behavior can be explained by diffusive mass transfer and dissolution/precipitation localization into immobile zones where local chemical micro-environments develop. These mechanisms are also studied in detail emphasizing the role of the local hydrodynamic properties and mineralogical heterogeneities in Soler-Sagarra et al (2016).…”

“…The second objective is to provide a coherent data-base and conceptual model that can be used by different groups in their further analyses, modeling studies and other studies related to the Heletz site in particular and even for more generic CO 2 injection related studies. While this paper provides an overview of the field work and laboratory analyses carried out in terms of characterizing the site, in particular in the vicinity of the proposed injection area, several of the other papers in this same special edition address the related laboratory findings in detail (Edlmann et al, 2016;Elhami et al, 2016;Hingerl et al, 2016;Luquot et al, 2016;Soler-Sagarra et al, 2016;Tatomir et al, 2016).…”

Convective‐Reactive CO2 Dissolution in Aquifers With Mass Transfer With Immobile Water

“…Having a pure calcium carbonate system with no chemical heterogeneity, the partitioning of the porous medium is only due to the physical heterogeneity at pore scale (fracture/matrix), and therefore, no localization of reactions is assumed. We consider one immobile zone only, to align the formulation with the time‐dependent single‐rate mass transfer model as opposed to multiple rate mass transfer model where multiple mass transfer processes occur simultaneously in a porous medium (see, e.g., Fernandez‐Garcia & Sanchez‐Vila, ; Geiger et al, ; Maier et al, ; Soler‐Sagarra et al, ; Tecklenburg et al, ). As such equation (3) can be rewritten as …”

“…We have collected data for α in Figure . Furthermore, Soler‐Sagarra et al () estimated α to be ~2 × 10 −5 s −1 for CO 2 ‐rich brine transport through carbonate rich samples. Using the values for dimensional variables, we attribute the dimensionless variables of equations (9) and .…”

Computational Efficiency of Decoupling Approach in Solving Reactive Transport Model: A Case Study of Pyrite Oxidative Dissolution

“…In laboratory experiments and its simulation, the approach is applied in a laboratory experiment where a sand column saturated with a MgSO 4 solution is subject to evaporation [24]. And some programs and models are built up based on the decoupling approach for hydrogeochemical calculations, such as CHEPROO++ [25] and MRWM [26].…”