Abstract
Reactive transport processes in a porous medium will often both cause changes to the pore structure, via precipitation and dissolution of biomass or minerals, and be affected by these changes, via changes to the material’s porosity and permeability. An understanding of the pore structure morphology and the changes to flow parameters during these processes is critical when modeling reactive transport. Commonly applied porosity–permeability relations in simulation models on the REV scale use a power-law relation, often with slight modifications, to describe such features; they are often used for modeling the effects of mineral precipitation and/or dissolution on permeability. To predict the reduction in permeability due to biomass growth, many different and often rather complex relations have been developed and published by a variety of authors. Some authors use exponential or simplified Kozeny–Carman relations. However, many of these relations do not lead to fundamentally different predictions of permeability alteration when compared to a simple power-law relation with a suitable exponent. Exceptions to this general trend are only few of the porosity–permeability relations developed for biomass clogging; these consider a residual permeability even when the pore space is completely filled with biomass. Other exceptions are relations that consider a critical porosity at which the porous medium becomes impermeable; this is often used when modeling the effect of mineral precipitation. This review first defines the scale on which porosity–permeability relations are typically used and aims at explaining why these relations are not unique. It shows the variety of existing approaches and concludes with their essential features.
Highlights
Flow through porous media can be described and analyzed on different spatial scales
The objective of this paper is to review the existing porosity– permeability relation concepts, to summarize their typical features, and to conclude with some recommendations focusing on systems withgeochemical pore space alterations
As pore morphology depends on the availability of flow components, which are in turn controlled by permeability, accurate relations for defining the changes to the permeability are imperative in understanding the flow processes
Summary
Flow through porous media can be described and analyzed on different spatial scales. Usually, this flow occurs in the fluid-filled void space bounded by an impermeable solid matrix. Alterations in the pore surface structure or the pore morphology can occur through a whole variety of processes coupled to and interacting with the flow of fluids. While changes in the pore surface properties, and the pore’s void space geometry, occur on the pore scale or even on the molecular scale, the scales of the application or of the engineering problem are typically much larger It is often appropriate, and required for the sake of computational feasibility, that the impacts of such morphology changes to the flow field be described by effective hydraulic properties. The objective of this paper is to review the existing porosity– permeability relation concepts, to summarize their typical features, and to conclude with some recommendations focusing on systems with (bio-)geochemical pore space alterations.
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