A Pore‐Scale Investigation of Mineral Precipitation Driven Diffusivity Change at the Column‐Scale

Journal Article · 02 May 2021 · Water Resources Research

DOI: https://doi.org/10.1029/2020WR028483 · OSTI ID:1784817

Deng, H.  ^[1]; Tournassat, C.  ^[2]; Molins, S.  ^[1]; Claret, F.  ^[3]; Steefel, C. I.  ^[1]

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1. Energy Geosciences Division Lawrence Berkeley National Laboratory Berkeley CA USA
2. Energy Geosciences Division Lawrence Berkeley National Laboratory Berkeley CA USA, BRGM Orléans France, Institut des Sciences de la Terre d’Orléans, Université d’Orléans—CNRS/INSU—BRGM Orléans France
3. BRGM Orléans France

Abstract Mineral precipitation affects the pore structure and thus transport properties of porous media. In this study, we investigated the pore‐scale dynamics of precipitation in diffusion controlled systems and the resulting impacts on the effective diffusivity, using a micro‐continuum reactive transport model. Forty two‐dimensional pore structures representing both idealized and realistic geometries were simulated with consideration of different precipitation scenarios and rates. A homogeneous nucleation scenario reproduced patterns observed in previous experimental study showing mixing‐induced precipitation, and a surface growth scenario captured the pattern for mineral precipitation on a substrate with the same or similar mineral structures. In all cases, local precipitation resulted in the reduction in the average porosity of the domain ( Φ ) until the cessation of diffusive transport and the termination of precipitation. The minimum porosity reached was referred to as the critical porosity ( Φ _c ). The effective diffusivity ( D _eff ) decreased with Φ and dropped sharply to effectively zero, that is, the critical effective diffusivity ( D _{eff c} ), as Φ _c was reached. These pore‐scale dynamics can be captured by a revised relationship that explicitly considers the critical porosity and the corresponding effective diffusivity, and the pre‐exponential coefficient and the exponent of the relationship varied with initial pore structure and the precipitation kinetics. Overall, the homogeneous nucleation scenario results in systematically larger Φ _c and coefficients that give rise to a sharper decrease in diffusivity as Φ _c is approached, compared to the surface growth scenario. The revised relationship was also implemented at continuum scale and used to examine column scale diffusivity change and reactions.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: Agence Nationale de la Recherche (ANR); European Union; USDOE; USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1784817
• Journal Information: Water Resources Research, Journal Name: Water Resources Research Journal Issue: 5 Vol. 57; ISSN 0043-1397
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English