Saturation Dependence of Non‐Fickian Transport in Porous Media

Hasan, Sharul; Niasar, Vahid; Karadimitriou, Nikolaos; Sahimi, Muhammad

doi:10.1029/2018wr023554

Cited by 51 publications

(61 citation statements)

References 50 publications

(81 reference statements)

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“…There are alternative methods such as using the MIM ( 22 ) and MRMT ( 23 ) models to estimate the dispersion coefficients. However, they may lead to an incorrect estimation of the fitted parameters due to the inherent assumptions in those models ( 25 ). As an alternative approach, spatial moments ( 51 ) and time moments ( 52 ) can be used to estimate the dispersion coefficient.…”

Section: Resultsmentioning

confidence: 99%

“…None of the commonly used theories, including the mobile–immobile model (MIM) ( 22 ), the multirate mass transfer (MRMT) ( 23 ), and continuous time random walk ( 24 ) models include two-phase flow formulations in their theoretical developments. To date, the capability of such models to match the experimental data using inverse modeling has been tested, but the physical consistency of such models is still open to be evaluated ( 25 , 26 ).…”

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confidence: 99%

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Direct characterization of solute transport in unsaturated porous media using fast X-ray synchrotron microtomography

Hasan

Niasar

Karadimitriou

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Solute transport in unsaturated porous materials is a complex process, which exhibits some distinct features differentiating it from transport under saturated conditions. These features emerge mostly due to the different transport time scales at different regions of the flow network, which can be classified into flowing and stagnant regions, predominantly controlled by advection and diffusion, respectively. Under unsaturated conditions, the solute breakthrough curves show early arrivals and very long tails, and this type of transport is usually referred to as non-Fickian. This study directly characterizes transport through an unsaturated porous medium in three spatial dimensions at the resolution of 3.25 μm and the time resolution of 6 s. Using advanced high-speed, high-spatial resolution, synchrotron-based X-ray computed microtomography (sCT) we obtained detailed information on solute transport through a glass bead packing at different saturations. A large experimental dataset (>50 TB) was produced, while imaging the evolution of the solute concentration with time at any given point within the field of view. We show that the fluids’ topology has a critical signature on the non-Fickian transport, which yet needs to be included in the Darcy-scale solute transport models. The three-dimensional (3D) results show that the fully mixing assumption at the pore scale is not valid, and even after injection of several pore volumes the concentration field at the pore scale is not uniform. Additionally, results demonstrate that dispersivity is changing with saturation, being twofold larger at the saturation of 0.52 compared to that at the fully saturated domain.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Direct characterization of solute transport in unsaturated porous media using fast X-ray synchrotron microtomography

Hasan

Niasar

Karadimitriou

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Multiphase flow through porous media has a crucial importance in applications as diverse as groundwater resources [1][2][3], geothermal fields [4], chemical transport [5][6][7], gas diffusion in fuel cells [8], oil recovery [9], environmental remediation [10], and CO 2 sequestration [11]. The most important macroscopic parameters that describe multiphase flow through porous media are capillary pressure (P c ) and relative permeability (k r ) [9,12].…”

Section: Introductionmentioning

confidence: 99%

Pore-by-pore modeling, analysis, and prediction of two-phase flow in mixed-wet rocks

et al. 2020

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A pore-network model is an upscaled representation of the pore space and fluid displacement, which is used to simulate two-phase flow through porous media. We use the results of pore-scale imaging experiments to calibrate and validate our simulations, and specifically to find the pore-scale distribution of wettability. We employ energy balance to estimate an average, thermodynamic, contact angle in the model, which is used as the initial estimate of contact angle. We then adjust the contact angle of each pore to match the observed fluid configurations in the experiment as a nonlinear inverse problem. The proposed algorithm is implemented on two sets of steady state micro-computed-tomography experiments for water-wet and mixed-wet Bentheimer sandstone. As a result of the optimization, the pore-by-pore error between the model and experiment is decreased to less than that observed between repeat experiments on the same rock sample. After calibration and matching, the model predictions for capillary pressure and relative permeability are in good agreement with the experiments. The proposed algorithm leads to a distribution of contact angle around the thermodynamic contact angle. We show that the contact angle is spatially correlated over around 4 pore lengths, while larger pores tend to be more oil-wet. Using randomly assigned distributions of contact angle in the model results in poor predictions of relative permeability and capillary pressure, particularly for the mixed-wet case.

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“…Recently, several research groups started using 2D micromodels in combination with specific optical methods to study tracer propagation in porous media at full [13] and partial saturation [14][15][16][17][18]. All research groups observed non-Gaussian transport and related them to the presence of stagnant zones in the partially saturated porous medium.…”

Section: Introductionmentioning

confidence: 99%

New insights into tracer propagation in partially saturated porous media

Leontidis

Youssef

Bauer

2020

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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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.

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Saturation Dependence of Non‐Fickian Transport in Porous Media

Cited by 51 publications

References 50 publications

Direct characterization of solute transport in unsaturated porous media using fast X-ray synchrotron microtomography

Direct characterization of solute transport in unsaturated porous media using fast X-ray synchrotron microtomography

Pore-by-pore modeling, analysis, and prediction of two-phase flow in mixed-wet rocks

New insights into tracer propagation in partially saturated porous media

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