scholarly journals New insights into tracer propagation in partially saturated porous media

2020 ◽  
Vol 75 ◽  
pp. 29
Author(s):  
Vlasios Leontidis ◽  
Souhail Youssef ◽  
Daniela Bauer
Keyword(s):  
Transport Process ◽  
Dispersion Coefficient ◽  
Water Saturation ◽  
Saturated Porous Medium ◽  
Local Concentration ◽  
Concentration Profiles ◽  
Background Solution ◽  
Partial Saturation ◽  
Tracer Transport ◽  
Partially Saturated

This work deals with the influence of partial saturation on the transport process of a passive tracer. Transport experiments were done in a water-wet glass micromodel combined with specific optical techniques. Full water saturation was achieved by injecting initially the background solution and then the tracer, whereas for the partial saturation conditions, the micromodel was initially saturated with oil, and then sequential the background solution and the tracer were injected at the same flow rate. We have shown that in the investigated range of water saturations it exists a transition in the oil ganglia structure and size. For high water saturations oil ganglia have one or two pores in size, however for lower water saturations they comprise an important number of pores. Transport strongly depends on the size distribution of the oil ganglia as they create large percolating paths and stagnant zones. We also showed the existence of two different types of stagnant zones: zones accessible by diffusion into pores and zones only accessible by spatially limited diffusion in films. The major advantage of using glass micromodels lies in the fact that dispersion coefficients can be computed from concentrations averaged over the pore space or from concentrations at the outlet and simultaneously from spatial concentration profiles. Curves were fitted using the Advection–Dispersion Equation (ADE) with adequate boundary conditions. The fitting quality of the temporal evolution of the average and outlet concentration was very good. However, fitting of the concentration profiles could only be done for the higher water saturations. This is due to the fact that the Representative Elementary Volume (REV) of lower water saturations is larger than the micromodel. The results show that fitting the breakthrough curve in order to determine the dispersion coefficient in a partially saturated porous medium might be misleading. Indeed, when fitting the breakthrough curves we were able to compute a dispersion coefficient even in the case where the REV of the water saturation is larger than the micromodel. Consequently, the knowledge of the local concentration profiles as a function of time is necessary as it provides an additional information on the spatio-temporal behavior of the transport process and therefor a supplementary constraint of the fitting procedure. Finally, we observed a time dependent dispersion coefficient in the regime where oil ganglia comprise several pores. This fact might be attributed to the non-Gaussian nature of the transport.

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

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.

BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium

2012 ◽  
Vol 9 (2) ◽  
pp. 213-222 ◽  
Author(s):  
Jian-Xin Nie ◽  
Jing Ba ◽  
Ding-Hui Yang ◽  
Xin-Fei Yan ◽  
Zhen-Yu Yuan ◽  
...  
Keyword(s):  
Porous Medium ◽  
Saturated Porous Medium ◽  
Partially Saturated ◽  
Model Based ◽  
Bisq Model

Fluid distribution effect on sonic attenuation in partially saturated limestones

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 154-160 ◽  
Author(s):  
Thierry Cadoret ◽  
Gary Mavko ◽  
Bernard Zinszner
Keyword(s):  
Wave Attenuation ◽  
Water Saturation ◽  
High Water ◽  
Fluid Distribution ◽  
Computer Assisted ◽  
Fluid Content ◽  
Partially Saturated ◽  
Fluid Saturation ◽  
Distribution Effect ◽  
Saturation Method

Extensional and torsional wave‐attenuation measurements are obtained at a sonic frequency around 1 kHz on partially saturated limestones using large resonant bars, 1 m long. To study the influence of the fluid distribution, we use two different saturation methods: drying and depressurization. When water saturation (Sw) is higher than 70%, the extensional wave attenuation is found to depend on whether the resonant bar is jacketed. This can be interpreted as the Biot‐Gardner‐White effect. The experimental results obtained on jacketed samples show that, during a drying experiment, extensional wave attenuation is influenced strongly by the fluid content when Sw is between approximately 60% and 100%. This sensitivity to fluid saturation vanishes when saturation is obtained through depressurization. Using a computer‐assisted tomographic (CT) scan, we found that, during depressurization, the fluid distribution is homogeneous at the millimetric scale at all saturations. In contrast, during drying, heterogeneous saturation was observed at high water‐saturation levels. Thus, we interpret the dependence of the extensional wave attenuation upon the saturation method as principally caused by a fluid distribution effect. Torsional attenuation shows no sensitivity to fluid saturation for Sw between 5% and 100%.

Pore-scale fluid distributions determined by nuclear magnetic resonance spectra of partially saturated sandstones

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. MR107-MR114 ◽  
Author(s):  
Chunhui Fang ◽  
Baozhi Pan ◽  
Yanghua Wang ◽  
Ying Rao ◽  
Yuhang Guo ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Water Saturation ◽  
Acoustic Property ◽  
P Wave ◽  
Distribution Model ◽  
Fluid Distribution ◽  
Pore Scale ◽  
Saturation Model ◽  
Partially Saturated ◽  
P Wave Velocity

The acoustic property and the P-wave velocity of partially saturated rocks depend not only on the water saturation but also on the pore-scale fluid distribution. Here, we analyzed the pore-scale fluid distribution using nuclear magnetic resonance (NMR) [Formula: see text] spectra, which present the variation of porosity components associated with NMR transverse relaxation time [Formula: see text]. Based on the [Formula: see text] spectra, we classified the pore-scale fluid distribution during water imbibition and drainage into three models: a low-saturation model, a patchy distribution model, and a uniform distribution model. We specifically assigned the low-saturation model to deal with the acoustic property of the rocks at the imbibition starting stage and the drainage final stage because cement softening has a nonnegligible effect. We studied the acoustic properties of sandstone rocks with various pore-scale fluid distributions, at the imbibition process and the drainage process. We confirmed that, once the variations in water saturation and pore-scale fluid distribution are taken into account, the P-wave velocity prediction matches well with the laboratory measurement of samples, representing nearly tight sandstone rocks that are partially saturated with distilled water.

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

2017 ◽  
Vol 21 (3) ◽  
pp. 1381-1396 ◽  
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.

Centrifugal modelling of nonsorbing, nonequilibrium solute transport in a locally inhomogeneous soil

1994 ◽  
Vol 31 (4) ◽  
pp. 471-477 ◽  
Author(s):  
L. Li ◽  
D.A. Barry ◽  
K.J.L. Stone
Keyword(s):  
Mathematical Modelling ◽  
Key Words ◽  
Transport Process ◽  
Physical Modelling ◽  
Model Parameters ◽  
Tracer Transport ◽  
Nonequilibrium Transport ◽  
Geotechnical Centrifuge ◽  
Heterogeneous Soil ◽  
Region Model

This paper presents results of centrifugal modelling of physical nonequilibrium transport of nonsorbing solute in a locally inhomogeneous soil. Mathematical modelling of this class of transport process is restricted by the difficulties in determining the model parameters. The modelling results suggest that physical modelling on a geotechnical centrifuge may offer another approach to tackle this problem under certain conditions. Key words : tracer transport, centrifuge, physical modelling, heterogeneous soil, two-region model, scaling.

Evaluating 3-D and 1-D mathematical models for mass transport in heterogeneous biofilms

2000 ◽  
Vol 41 (4-5) ◽  
pp. 347-356 ◽  
Author(s):  
E. Morgenroth ◽  
H. Eberl ◽  
M.C. van Loosdrecht
Keyword(s):  
Three Dimensional ◽  
Average Concentration ◽  
Local Concentration ◽  
Concentration Profiles ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
One Dimensional ◽  
Bacterial Competition ◽  
Variable Diffusion ◽  
Three Dimensional Simulations

Results from a three dimensional model for heterogeneous biofilms including the numerical solution of hydrodynamics were compared to simplified one dimensional models. A one dimensional model with a variable diffusion coefficient over the thickness of the biofilm was well suited to approximate average concentration profiles of three dimensional simulations of rough biofilms. A new compartmentalized one dimensional model is presented that is then used to evaluate effects of pores and channels on microbial competition in heterogeneous biofilms. Surface and pore regions of the biofilm are modeled using separate compartments coupled by a convective link. Local concentration profiles from the three dimensional simulations could be adequately reproduced using the compartmentalized one dimensional model. The compartmentalized one dimensional model was then used to evaluate bacterial competition in a growing biofilm and in a mushroom type biofilm assuming different modes of detachment.

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