Geochemical self-organization II; the reactive-infiltration instability

Ortoleva, P.; Chadam, John; Merino, Enrique; Sen, Asok K.

doi:10.2475/ajs.287.10.1008

Cited by 316 publications

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“…Such a channel network could be produced as a result of the reactive infiltration instability [Chadam et al, 1986;Ortoleva et al, 1987]. According to this theory, diffuse flow of a solvent through a soluble porous matrix is unstable.…”

Section: Discussionmentioning

confidence: 99%

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Kelemen

Braun

Hirth

2000

Geochem Geophys Geosyst

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[1] Ophiolites are on-land exposures of igneous crust and residual upper mantle formed beneath submarine spreading ridges. Upper mantle outcrops in ophiolites provide insight into focusing of melt transport from a $100 km wide region of partial melting into an $5 km wide zone of igneous crustal accretion beneath the ridges. Dunite veins, composed of the minerals olivine and spinel, mark conduits for melt transport through at least the uppermost 30 km of the mantle. New data in this paper, on dunite veins in the Ingalls ophiolite, central Washington Cascades, show a power law relationship between frequency and width, in which frequency/m %0.02 width À3 over a size interval from $0.1 to 2 m. There may be several ways to generate this relationship, but we favor the hypothesis that the dunites represent a coalescing melt transport network. This conclusion is broadly consistent with the related hypothesis that mantle melt extraction occurs in a fractal, branching network, and with recent results on formation of a coalescing network of dissolution channels via flow of a solvent through a partially soluble, compacting porous medium.

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Section: Discussionmentioning

confidence: 99%

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Kelemen

Braun

Hirth

2000

Geochem Geophys Geosyst

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“…Within the domain of reactive flow in unsaturated soils three main types of interfering instabilities occur: (i) reaction instabilities due to initial heterogeneities in the hydraulic properties with dissolution of wormholes and karst phenomena [1,[96][97][98][99][100][101][102][103][104][105], (ii) flow instabilities with moisture content fingering during the infiltration of a moisture front [106][107][108][109][110][111][112][113][114][115][116] and (iii) density instabilities due to local differences of solution densities [117][118][119][120][121][122][123][124]. However, the scope of this paper is not to investigate instability phenomena, but to propose a new approach that relates changes in mineral volumes and hydraulic properties.…”

Section: General Model Discussionmentioning

confidence: 99%

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Wissmeier

Barry

2009

Advances in Water Resources

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT AbsThe selective radius shift model was used to relate changes in mineral volume due to precipitation/dissolution reactions to changes in hydraulic properties affecting flow in porous media. The model accounts for (i) precipitation/dissolution taking place only in the water-filled part of the pore space and further that (ii) the amount of mineral precipitation/dissolution within a pore depends on the local pore volume. The pore bundle concept was used to connect pore-scale changes to macroscopic soil hydraulic properties. Precipitation/dissolution induces changes in the pore radii of water-filled pores and, consequently, in the effective porosity. In a time step of the numerical model, mineral reactions lead to a discontinuous pore-size distribution because only the water-filled pores are affected. The pore-size distribution is converted back to a soil moisture characteristic function to which a new water retention curve is fitted under physically plausible constraints. The model equations were derived for the commonly used van Genuchten/Mualem hydraulic properties. Together with a mixed-form solution of Richards' equation for aqueous phase flow, the model was implemented into the geochemical modelling framework PHREEQC, thereby making available PHREEQC's comprehensive geochemical reactions. Example applications include kinetic halite dissolution and calcite precipitation as a consequence of cation exchange. These applications showed marked changes in the soil's hydraulic properties due to mineral precipitation/dissolution and the dependency of these changes on water contents. The simulations also revealed the strong influence of the degree of saturation on the development of the saturated hydraulic conductivity through its quadratic dependency on the van Genuchten parameter . Furthermore, it was shown that the unsaturated hydraulic conductivity at fixed reduced water content can even r tract increase du ing precipitation due to changes in the pore-size distribution.

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“…The quasi-steady state approximation [Lichtner, 1988;Ortoleva et al, 1987] permits the application of much larger time intervals when solving discretized transient differential equations relative to other schemes. In the case of solute mass conservation equations for solute precipitation and dissolution involving fracture geometry and permeability changes, the approximation is valid when the time required to change the fracture geometry is long relative to the time required to achieve steady state with respect to solute concentrations, that is, when geometrical changes are very slow relative to flow and transport-induced changes.…”

Section: Numerical Solutionmentioning

confidence: 99%

Precipitation and dissolution of reactive solutes in fractures

Dijk¹,

Berkowitz²

1998

Water Resources Research

107

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Abstract. The precipitation and dissolution of reactive solutes, transported under the action of fully developed laminar flow in saturated fractures, is analyzed assuming an irreversible first-order kinetic surface reaction for one component. Equations describing solute transport, precipitation and dissolution, and the evolution of fracture aperture were approximated and solved using combined analytical and numerical techniques; dimensionless transport parameters incorporated into the solutions were estimated from data available in the literature. Fractures with initially flat, linearly constricted, and sinusoidal apertures were investigated. The initial fracture geometry and the solute saturation content of the inflowing fluid have a profound effect on the reaction processes. The results show that the evolution of the solute transport and fracture geometry can be adequately described by the Damk6hler and P6clet numbers. Two extreme transport regimes were identified: relatively uniform evolution of fracture apertures and nonuniform evolution of fracture apertures restricted to the inlet region of fractures. In the case of precipitation with half-life times of the order of seconds to years and with fluid residence times of the order of minutes to days, the time for a fracture to close completely is of the order of days to millions of years. This is consistent with the order of magnitude of hydrogeological timescales. In the model the process of dissolution is the inverse of precipitation, although the combined solute transport and reaction processes are irreversible. These results and the applied dimensionless analysis can be used as a basis for the development of more complex models of reactive solute transport, precipitation, and dissolution in saturated fractured media. IntroductionThe transport of contaminants through fractured geological media has received considerable attention in recent years. While many studies have analyzed the transport of conservative solutes in discrete fracture networks, relatively little attention has been devoted to the analysis of the transport of reactive solutes. Even less work has been devoted to the influence of reactive solutes on the physical and chemical properties of the fracture networks and the surrounding porous matrix. This is in part due to the highly complex interaction between the mass transport mechanisms and the changing properties of a fractured porous medium.Precipitation and dissolution can significantly modify the physical and chemical properties of fractured media. Physical changes of fracture aperture, tortuosity, and thus effective mass diffusivities and permeabilities are coupled to the subsequent fluid flow and solute transport and the precipitation and dissolution reactions. Chemical changes of the fractures, such as sorption and reaction capacities, also have a significant effect on solute transport. As such, a variety of closure patterns can be observed in the field, which range from fully filled (mineralized) fractures to those with pockets or irregul...

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Geochemical self-organization II; the reactive-infiltration instability

Cited by 316 publications

References 0 publications

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Precipitation and dissolution of reactive solutes in fractures

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