Measuring, imaging and modelling solute transport in a microporous limestone

Kurotori, Takeshi; Zahasky, Christopher; Hejazi, Sayed Alireza Hosseinzadeh; Shah, Saurabh; Benson, Sally M.; Pini, Ronny

doi:10.1016/j.ces.2018.11.001

Cited by 36 publications

(42 citation statements)

References 59 publications

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“…The full set of radio-tracer experiments carried out in this study are presented in Figure 6, again in the form of RTD functions. By means of comparison, previously reported observations on a random BP (using a brine tracer) (Kurotori et al, 2019) are also shown in the figure. The width of the measured effluent concentration profiles increases in the order BP < BS < EB < KL, indicating an increase of the nonequilibrium effects anticipated above.…”

Section: Characteristic Rtd Functionsmentioning

confidence: 79%

“…In other words, in carbonates heterogeneities can increase the overall strength of mixing, thereby effectively homogenizing the transport process. We anticipate that more quantitative insight into this mixing process could be obtained from the simultaneous application of noninvasive methods to the study of transport in rocks (Kurotori et al, 2019; Zahasky et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…Pulse‐tracer tests were carried out on the three water‐saturated rock cores over a range of flow rates (

q = 2 - 19

ml/min) and at ambient pressure and temperature conditions (Tables S1–S3). For the experiments, a custom‐built core‐flooding apparatus was used that is described in detail in a previous publication (Kurotori et al, 2019). Briefly, the main components of the experimental system are (i) the high‐pressure aluminum core‐holder (Figure S3); (ii) a differential pressure transducer (Keller UK, model PRD‐33X, accuracy: 0.05%FS) connected to the inlet and outlet faces of the sample; (iii) radioactivity detectors mounted upstream and downstream of the core holder (Carroll and Ramsey Associates, USA) to measure inlet and effluent concentration of the radio tracer (or conductivity microflow cells, Model 829 by Amber Scientific, USA, when a brine‐tracer is used); (iv) three high‐pressure syringe pumps (Teledyne ISCO, Model 1000D) for continuous delivery of carrier fluid, for maintaining constant confining pressure and for maintaining a back‐pressure, respectively); and one two‐way valve for tracer injection (Cheminert, HPLC 6 port injection valve, VICI, Thames Restek UK Ltd).…”

Section: Methodsmentioning

confidence: 99%

“…(a) Three‐dimensional concentration map of a tracer plume in Ketton Limestone (Kurotori et al, 2019) and (b) conceptualization of the porous medium with subcore‐scale heterogeneities in the form of low permeability zones and microporous grains.…”

Section: Modelingmentioning

confidence: 99%

“…For the range of Péclet numbers considered in this work (

P e = v D_{normale} false/ 𝒟 > 10

), advection dominates over diffusion everywhere and (i) is therefore satisfied. Assessing the validity of (ii) is more complex: While the imposed linearity holds for uniform media at sufficiently large Peclet number (see, e.g., data on beadpacks [BPs] reported in Kurotori et al, 2019), it is likely to be invalid for highly heterogeneous media, such as those characterized by strong spatial variation in permeability in the direction of flow or by pronounced mobile and immobile zones. It is one of the aims of this study to verify the applicability of this parameterization for the three rock samples considered.…”

Section: Modelingmentioning

confidence: 99%

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Description of Chemical Transport in Laboratory Rock Cores Using the Continuous Random Walk Formalism

Kurotori

Zahasky

Benson

et al. 2020

Water Resources Research

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We investigate chemical transport in laboratory rock cores using unidirectional pulse tracer experiments. Breakthrough curves (BTCs) measured at various flow rates in one sandstone and two carbonate samples are interpreted using the one-dimensional Continuous Time Random Walk (CTRW) formulation with a truncated power law (TPL) model. Within the same framework, we evaluate additional memory functions to consider the Advection-Dispersion Equation (ADE) and its extension to describe mass exchange between mobile and immobile solute phases (Single-Rate Mass Transfer model, SRMT). To provide physical constraints to the models, parameters are identified that do not depend on the flow rate. While the ADE fails systematically at describing the effluent profiles for the carbonates, the SRMT and TPL formulations provide excellent fits to the measurements. They both yield a linear correlation between the dispersion coefficient and the Péclet number (D L ∝ Pe for 10 < (Pe) < 100), and the longitudinal dispersivity is found to be significantly larger than the equivalent grain diameter, D e. The BTCs of the carbonate rocks show clear signs of nonequilibrium effects. While the SRMT model explicitly accounts for the presence of microporous regions (up to 30% of the total pore space), in the TPL formulation the time scales of both advective and diffusive processes (t 1 (Pe) and t 2) are associated with two characteristic heterogeneity length scales (d and l, respectively). We observed that l ≈ 2.5 × D e and that anomalous transport arises when l∕d ≤ (1). In this context, the SRMT and TPL formulations provide consistent, yet complementary, insight into the nature of anomalous transport in laboratory rock cores.

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Section: Characteristic Rtd Functionsmentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

“…Pulse‐tracer tests were carried out on the three water‐saturated rock cores over a range of flow rates (

q = 2 - 19

Section: Methodsmentioning

confidence: 99%

Section: Modelingmentioning

confidence: 99%

“…For the range of Péclet numbers considered in this work (

P e = v D_{normale} false/ 𝒟 > 10

Section: Modelingmentioning

confidence: 99%

See 3 more Smart Citations

Description of Chemical Transport in Laboratory Rock Cores Using the Continuous Random Walk Formalism

Kurotori

Zahasky

Benson

et al. 2020

Water Resources Research

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Relevance of charge interactions for contaminant transport in heterogeneous formations: a stochastic analysis

Muniruzzaman

Rolle

2023

Stoch Environ Res Risk Assess

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The electrostatic properties of clay (or other charged) mineral surfaces play a significant role in the fate, transport, persistence, and remediation of subsurface contaminant plumes. This study presents a stochastic assessment of the impact and relevance of microscale electrostatic effects on macroscopic, field-scale contaminant transport in heterogeneous groundwater systems involving spatially distributed clay zones. We present Monte Carlo simulations in two-dimensional heterogeneous fields, comprising heterogeneous distributions of physical (i.e., hydraulic conductivity, porosity, tortuosity) and electrostatic (i.e., surface charge) properties, and compare scenarios with different combination and extent of physical and electrostatic processes. The simulations were performed with the multi-continua based reactive transport code, MMIT-Clay, and considering an explicit treatment of the diffuse layer processes. The results reveal that the microscopic electrostatic mechanisms within clay’s diffuse layer can significantly accelerate or retard a particular contaminant depending on its charge, leading to considerably different solute breakthroughs and mass loading/release behaviors in low permeability inclusions. Furthermore, we show that such variations in the macroscale transport behavior, solely driven by charge interactions, are statistically significant over the ensembles of Monte Carlo realizations. The simulations also demonstrate that the omission of electrostatic processes, which is still a common practice in subsurface hydrology, can lead to substantial over- or underestimation of contaminant migration.

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Flow Path Resistance in Heterogeneous Porous Media Recast into a Graph-Theory Problem

et al. 2021

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This work aims to describe the spatial distribution of flow from characteristics of the underlying pore structure in heterogeneous porous media. Thousands of two-dimensional samples of polydispersed granular media are used to (1) obtain the velocity field via direct numerical simulations, and (2) conceptualize the pore network as a graph in each sample. Analysis of the flow field allows us to distinguish preferential from stagnant flow regions and to quantify how channelized the flow is. Then, the graph’s edges are weighted by geometric attributes of their corresponding pores to find the path of minimum resistance of each sample. Overlap between the preferential flow paths and the predicted minimum resistance path determines the accuracy in individual samples. An evolutionary algorithm is employed to determine the “fittest” weighting scheme (here, the channel’s arc length to pore throat ratio) that maximizes accuracy across the entire dataset while minimizing over-parameterization. Finally, the structural similarity of neighboring edges is analyzed to explain the spatial arrangement of preferential flow within the pore network. We find that connected edges within the preferential flow subnetwork are highly similar, while those within the stagnant flow subnetwork are dissimilar. The contrast in similarity between these regions increases with flow channelization, explaining the structural constraints to local flow. The proposed framework may be used for fast characterization of porous media heterogeneity relative to computationally expensive direct numerical simulations. Article Highlights A quantitative assessment of flow channeling is proposed that distinguishes pore-scale flow fields into preferential and stagnant flow regions. Geometry and topology of the pore network are used to predict the spatial distribution of fast flow paths from structural data alone. Local disorder of pore networks provides structural constraints for flow separation into preferential v stagnant regions and informs on their velocity contrast.

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Measuring, imaging and modelling solute transport in a microporous limestone

Cited by 36 publications

References 59 publications

Description of Chemical Transport in Laboratory Rock Cores Using the Continuous Random Walk Formalism

Description of Chemical Transport in Laboratory Rock Cores Using the Continuous Random Walk Formalism

Relevance of charge interactions for contaminant transport in heterogeneous formations: a stochastic analysis

Flow Path Resistance in Heterogeneous Porous Media Recast into a Graph-Theory Problem

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