A Physically Based Model for the Streaming Potential Coupling Coefficient in Partially Saturated Porous Media

The electrokinetics methods have great potential to characterize hydrogeological processes in porous media, especially in complex partially saturated hydrosystems (e.g., the vadose zone). The dependence of the streaming coupling coefficient on water saturation remains highly debated in both theoretical and experimental works. In this work, we propose a physically based model for the streaming potential coupling coefficient in porous media during the flow of water and air under partially saturated conditions. The proposed model is linked to fluid electrical conductivity, water saturation, irreducible water saturation, and microstructural parameters of porous materials. In particular, the surface conductivity of porous media has been taken into account in the model. In addition, we also obtain an expression for the characteristic length scale at full saturation in this work. The proposed model is successfully validated using experimental data from literature. A relationship between the streaming potential coupling coefficient and the effective excess charge density is also obtained in this work and the result is the same as those proposed in literature using different approaches. The model proposes a simple and efficient way to model the streaming potential generation for partially saturated porous media and can be useful for hydrogeophysical studies in the critical zone.

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A physically based model for the electrical conductivity of partially saturated porous media

Geophysical Journal International ◽

10.1093/gji/ggaa307 ◽

2020 ◽

Vol 223 (2) ◽

pp. 993-1006

Author(s):

Luong Duy Thanh ◽

Damien Jougnot ◽

Phan Van Do ◽

Nguyen Van Nghia A ◽

Vu Phi Tuyen ◽

...

Keyword(s):

Electrical Conductivity ◽

Porous Media ◽

Fractal Dimension ◽

Water Saturation ◽

Theoretical Models ◽

Fluid Composition ◽

Physically Based Model ◽

Partially Saturated ◽

Proposed Model ◽

Physically Based

SUMMARY In reservoir and environmental studies, the geological material characterization is often done by measuring its electrical conductivity. Its main interest is due to its sensitivity to physical properties of porous media (i.e. structure, water content, or fluid composition). Its quantitative use therefore depends on the efficiency of the theoretical models to link them. In this study, we develop a new physically based model that takes into account the surface conductivity for estimating electrical conductivity of porous media under partially saturated conditions. The proposed model is expressed in terms of electrical conductivity of the pore fluid, water saturation, critical water saturation and microstructural parameters such as the minimum and maximum pore/capillary radii, the pore fractal dimension, the tortuosity fractal dimension and the porosity. Factors influencing the electrical conductivity in porous media are also analysed. From the proposed model, we obtain an expression for the relative electrical conductivity that is consistent with other models in literature. The model predictions are successfully compared with published experimental data for different types of porous media. The new physically based model for electrical conductivity opens up new possibilities to characterize porous media under partially saturated conditions with geoelectrical and electromagnetic techniques.

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Experimental study on retardation of a heavy NAPL vapor in partially saturated porous media

Hydrology and Earth System Sciences ◽

10.5194/hess-21-1381-2017 ◽

2017 ◽

Vol 21 (3) ◽

pp. 1381-1396 ◽

Cited By ~ 1

Author(s):

Simon Matthias Kleinknecht ◽

Holger Class ◽

Jürgen Braun

Keyword(s):

Porous Media ◽

Aqueous Phase ◽

Unsaturated Zone ◽

Large Scale ◽

Water Saturation ◽

Solid Matrix ◽

Saturated Porous Media ◽

Gaseous State ◽

Partially Saturated ◽

Partially Saturated Porous Media

Abstract. Non-aqueous-phase liquid (NAPL) contaminants introduced into the unsaturated zone spread as a liquid phase; however, they can also vaporize and migrate in a gaseous state. Vapor plumes migrate easily and thus pose a potential threat to underlying aquifers. Large-scale column experiments were performed to quantify partitioning processes responsible for the retardation of carbon disulfide (CS2) vapor in partially saturated porous media. The results were compared with a theoretical approach taking into account the partitioning into the aqueous phase as well as adsorption to the solid matrix and to the air–water interface. The experiments were conducted in large, vertical columns (i.d. of 0.109 m) of 2 m length packed with different porous media. A slug of CS2 vapor and the conservative tracer argon was injected at the bottom of the column followed by a nitrogen chase. Different seepage velocities were applied to characterize the transport and to evaluate their impact on retardation. Concentrations of CS2 and argon were measured at the top outlet of the column using two gas chromatographs. The temporal-moment analysis for step input was employed to evaluate concentration breakthrough curves and to quantify dispersion and retardation. The experiments conducted showed a pronounced retardation of CS2 in moist porous media which increased with water saturation. The comparison with an analytical solution helped to identify the relative contributions of partitioning processes to retardation. Thus, the experiments demonstrated that migrating CS2 vapor is retarded as a result of partitioning processes. Moreover, CS2 dissolved in the bulk water is amenable to biodegradation. The first evidence of CS2 decay by biodegradation was found in the experiments. The findings contribute to the understanding of vapor-plume transport in the unsaturated zone and provide valuable experimental data for the transfer to field-like conditions.

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Experimental study on retardation of a heavy NAPL vapor in partially saturated porous media

10.5194/hess-2016-440 ◽

2016 ◽

Author(s):

Simon M. Kleinknecht ◽

Holger Class ◽

Jürgen Braun

Keyword(s):

Porous Media ◽

Aqueous Phase ◽

Unsaturated Zone ◽

Large Scale ◽

Water Saturation ◽

Saturated Porous Media ◽

Gaseous State ◽

Partially Saturated ◽

Retardation Coefficient ◽

Partially Saturated Porous Media

Abstract. NAPL contaminants introduced into the unsaturated zone spread as a liquid phase; however, they can also vaporize and migrate in a gaseous state. Heavy vapors preferentially migrate downward due to their greater density and, thus, pose a potential threat to underlying aquifers. Large-scale column experiments were performed to quantify partitioning processes responsible for the retardation of carbon disulfide (CS2) vapor in partially saturated porous media. The results were compared with a theoretical approach taking into account the partitioning into the aqueous phase. The experiments were conducted in large, vertical columns (i.d. = 0.109 m) of 2 m length packed with different porous media. A slug of CS2 vapor and the conservative tracer argon was injected at the bottom of the column followed by a nitrogen chase. Different seepage velocities were applied to characterize the transport and to evaluate their impact on retardation. Concentrations of CS2 and argon were measured at the top outlet of the column using two gas chromatographs. The temporal-moment analysis for step input was employed to evaluate concentration breakthrough curves and to quantify diffusion/dispersion and retardation. The experiments conducted showed a pronounced retardation of CS2 in moist porous media as a function of porous medium and water saturation. An increase in the retardation coefficient with increasing water saturation was observed. Thus, the novel vapor-retardation experiments demonstrated that migrating CS2 vapor is retarded as a result of partitioning into the aqueous phase. Moreover, CS2 which is dissolved in the pore water is amenable to biodegradation. First evidence of CS2 decay by biodegradation was found in the experiments. The findings contribute to the understanding of vapor plume transport in the unsaturated zone and provides valuable experimental data for the transfer to field like conditions.

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