Linear Response Concept Combining Advection and Limited Rock Matrix Diffusion in a Fracture Network Transport Model

1996 ◽  
Vol 32 (11) ◽  
pp. 3285-3296 ◽  
Author(s):  
W. Barten
Keyword(s):  
Linear Response ◽  
Transport Model ◽  
Fracture Network ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Network Transport

scholarly journals Field, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes

Soil Systems ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 18
Author(s):  
Steven Chapman ◽  
Beth Parker ◽  
Tom Al ◽  
Richard Wilkin ◽  
Diana Cutt ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Fracture Network ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Laboratory Methods ◽  
Field Laboratory ◽  
Bedrock Aquifer ◽  
Reaction Processes ◽  
Low Solubility

This study uses a combination of conventional and high resolution field and laboratory methods to investigate processes causing attenuation of a hexavalent chromium (Cr(VI)) plume in sedimentary bedrock at a former industrial facility. Groundwater plume Cr(VI) concentrations decline by more than three orders of magnitude over a 900 m distance down gradient from the site. Internal plume concentrations generally exhibit stable to declining trends due to diffusive and reactive transport in the low permeability matrix as fluxes from the contamination source dissipate due to natural depletion processes and active remediation efforts. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix, and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates, confirmed by high spatial resolution rock matrix contaminant concentrations and comparisons with groundwater concentrations from multi-level sampling within the plume. Field characterization data for the fracture network and matrix properties were used to inform 2-D discrete-fracture matrix (DFM) numerical model simulations that quantify attenuation due to diffusion and reaction processes, which show consistency with field datasets, and provide insights regarding future plume conditions. The combination of field, laboratory and modeling evidence demonstrates effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer. This approach has important implications for characterization of sites with Cr(VI) contamination for improved site conceptual models and remediation decision-making.

Diffusion Measurements on Crystalline Rock Matrix

1994 ◽  
Vol 353 ◽  
Author(s):  
Kari Hartikainen ◽  
A. HautojÄrvi ◽  
H. Pietarila ◽  
J. Timonen
Keyword(s):  
Power Law ◽  
Gas Flow ◽  
Crystalline Rock ◽  
New Technique ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Model Calculations ◽  
Short Time ◽  
Drill Cores

AbstractA new gas flow technique is introduced such that experiments on very long samples are possible. This new technique together with increased accuracy of the measurements, allows the observation of power law tails in the break-through curves. Dispersion in these experiments can be controlled in great detail, and therefore the power law tails can be used to determine very accurately the parameters relevant in matrix diffusion. Results for rock and metal samples are shown, and they are fitted with model calculations which include both dispersion and matrix diffusion. The introduced technique, which is designed for ordinary drill cores, is suitable for scanning a large number of samples in a very short time.

Study of the Uranium Heterogeneous Diffusion through Crystalline Rocks and Effects of the “Clay-Mediated” Transport

2003 ◽  
Vol 807 ◽  
Author(s):  
U. Alonso ◽  
T. Missana ◽  
M. García-Gutiérrez ◽  
A. Patelli ◽  
J. Ravagnan ◽  
...  
Keyword(s):  
Surface Area ◽  
Bentonite Clay ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Mineral Surface ◽  
Transport Models ◽  
Actual Surface ◽  
Disturbed Areas ◽  
High Level ◽  
Preferential Pathways

ABSTRACTRock matrix diffusion is one of the possible mechanisms for radionuclide retardation in a deep geological high-level radioactive waste repository, and it is usually considered that radionuclides diffuse as solutes through the rock. Nonetheless, the potential effects that clay, from the bentonite barrier, may induce on the radionuclides migration should be taken into account. Furthermore, transport models generally assume that the whole mineral surface is accessible to transport, whereas transport is highly conditioned by the heterogeneous mineral distribution, since different minerals may act as preferential pathways, while others may present higher sorption capability. It is therefore necessary to determine the actual surface area accessible to transport.The aim of the present work is the identification of the uranium preferential pathways to the granite, both in presence or absence of bentonite clay. Results showed that uranium as solute diffused in specific mineral areas, indicating that the actual surface area accessible to matrix diffusion, and/or sorption on the surface, is significantly lower than the whole mineral surface. By the other hand, the uranium in presence of the clay was randomly distributed on the surface, and penetrated into the granite mainly through “defects” (as fractures or grain boundaries); its migration being enhanced on specially fractured or disturbed areas.

scholarly journals Analytical and Numerical Methods for a Preliminary Assessment of the Remediation Time of Pump and Treat Systems

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2850
Author(s):  
Matteo Antelmi ◽  
Francesca Renoldi ◽  
Luca Alberti
Keyword(s):  
Groundwater Remediation ◽  
Transport Model ◽  
Cost Benefit Analysis ◽  
Cost Benefit ◽  
Matrix Diffusion ◽  
Preliminary Evaluation ◽  
Pump And Treat ◽  
Advection Dispersion ◽  
The Matrix ◽  
Analytical Approaches

Several remediation technologies are currently used to address groundwater pollution. “Pump and treat” (P&T) is probably one of the most widely applied, being a process where contaminated groundwater is extracted from the subsurface by pumping and then treated before it is discharged or reinjected into the aquifer. Despite being a very adaptable technology, groundwater remediation is often achieved in long and unsustainable times because of limitations due to the hydrogeological setting and contaminant properties. Therefore, the cost–benefit analysis over time results in an inefficient system and a preliminary evaluation of the clean-up time is crucial. The aim of the paper is to compare, in an integrated manner, the application of some models to estimate the time to compliance of a P&T system in relation to the specific hydrogeological condition. Analytical solutions are analyzed and applied to an industrial site and to a synthetic case. For both cases, batch flushing and the advection-dispersion-retardation (ADR) model underestimate remediation times comparing the results to real or simulated monitoring data, whereas the Square Root model provided more reliable remediation times. Finally, for the synthetic case, the reliability of analytical approaches and the effects of matrix diffusion are tested on the basis of a numerical groundwater transport model specifically implemented, which confirm the results of the analytical methods and the strong influence of the matrix diffusion on the results.

scholarly journals A dual fracture model to simulate large-scale flow through fractured rocks

2002 ◽  
Vol 39 (6) ◽  
pp. 1302-1312 ◽  
Author(s):  
E Z Wang ◽  
Z Q Yue ◽  
L G Tham ◽  
Y Tsui ◽  
H T Wang
Keyword(s):  
Groundwater Flow ◽  
Large Scale ◽  
Fractured Rock ◽  
Network Models ◽  
Total Porosity ◽  
Seepage Flow ◽  
Fracture Network ◽  
Fracture Model ◽  
Rock Masses ◽  
Rock Matrix

Discrete fracture network models can be used to study groundwater flow in fractured rock masses. However, one may find that it is not easy to apply such models to practical projects as it is difficult to investigate every fracture and measure its hydraulic parameters. To overcome such difficulties, a dual fracture model is proposed. Taking into account the hydraulic characteristics of the various elements of the fracture system, a hydrogeological medium is assumed to consist of two components: the dominant fracture network and the fractured rock matrix. As the dominant fracture network consists of large fractures and faults, it controls the groundwater flow in rock masses. Depending on the permeabilities of the in-fill materials, these fractures and faults may serve as channels or barriers of the flow. The fractured rock matrix, which includes rock blocks and numerous small fractures, plays a secondary role in groundwater flow in such medium. Although the small fractures and rock blocks possess low permeability, their numbers and their total porosity are relatively large. Therefore, they provide large volume for groundwater storage. In this paper, the application of the proposed model to simulate the groundwater flow for a hydropower station before and after reservoir storage is reported. The implications of the results on the design of the station are also highlighted.Key words: seepage flow, dual fracture model, dominant fracture, fractured rock matrix, case studies, rock-filled dam.

Brownian Simulation of Matrix Diffusion

2000 ◽  
Vol 663 ◽  
Author(s):  
Sofie Andersson ◽  
Allan T. Emrén
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Boltzmann Distribution ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Dissolved Species ◽  
Apparent Diffusion ◽  
Wide Variability ◽  
Far From Equilibrium ◽  
Solid Piece

ABSTRACTThe commonly used approach in dealing with matrix diffusion is to assign an effective diffusion constant for the radionuclide in the rock matrix. The idea behind this approach is that, on a scale much larger than the pore size, the irregularities tend to cancel out. Although it might look plausible at first sight, this approach has been questioned both for theoretical and experimental reasons.Here, Brownian simulation has been used to investigate the transport of dissolved material in a rock matrix modeled as a system of pores with a wide variability in size and shape. The Boltzmann distribution is used locally, although the system globally is far from equilibrium.The simulation consists of two main parts. First, the model rock is formed by precipitation of irregular mineral grains from a liquid phase. As the grains grow, they tend to form a mostly solid piece of rock.In the second part of the simulation, a dissolved species is introduced at one side of the rock and allowed to diffuse through its pore system. It is found that no apparent diffusion constant, D, can explain the properties of the system. Rather, D is found to be a function of both distance and time.

scholarly journals Modelling the variation in the behaviour of pre-fractured rocks subjected to hydraulic fracturing with permeability of the rock matrix using finite-discrete element method

2020 ◽  
Vol 205 ◽  
pp. 08001
Author(s):  
Shahrzad Roshankhah ◽  
Arman K. Nejad ◽  
Orlando Teran ◽  
Kami Mohammadi
Keyword(s):  
Rock Mass ◽  
Finite Elements ◽  
Hydraulic Fracturing ◽  
Discrete Element Method ◽  
Fractured Rocks ◽  
Discrete Element ◽  
Fracture Network ◽  
Rock Matrix ◽  
Flow Through ◽  
Element Method

In this study, we present the results of two-dimensional numerical simulations for the effects of rock matrix permeability on the behaviour of hydraulic fractures in intact and pre-fractured rocks. The simulations are performed using the Finite-Discrete Element Method (FDEM). In this method, the deformation and fluid pressure fields within the porous rock blocks, pre-existing fracture network, and hydraulically induced fractures are calculated through a fully coupled hydromechanical scheme. Furthermore, new fractures can initiate in crack elements located between each pair of finite elements and can propagate in any path that the boundary and loading conditions require according to non-linear fracture mechanics criteria. Fluid channels are also defined between pairs of finite elements simulating the inter-connected flow paths through porous media. Four models of the rock mass are created in this study: (i) homogeneous-impermeable, (ii) homogeneous-permeable, (iii) heterogeneous-impermeable matrix, and (iv) heterogeneous-permeable matrix. Heterogeneous rock masses contain a discrete fracture network (natural fractures) in the rock mass structure. Hydraulic fracturing is modelled in domains of 40×40 m2 with the four different structures and mass transport capacities, and the results are compared to each other. The results highlight the significant effect of diffusive fluid flow through rock blocks, in addition to the flow through fracture network, on the global hydromechanical behaviour of the rock mass. These results help to understand the governing hydromechanical processes taking place in fractured rocks with matrix of different permeability, such as granites, shales, carbonate rocks, and sandstones and the extent of complexities required to model their behaviour to achieve reasonable accuracy.

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