3,377 research outputs found
Fractal model and Lattice Boltzmann Method for Characterization of Non-Darcy Flow in Rough Fractures.
The irregular morphology of single rock fracture significantly influences subsurface fluid flow and gives rise to a complex and unsteady flow state that typically cannot be appropriately described using simple laws. Yet the fluid flow in rough fractures of underground rock is poorly understood. Here we present a numerical method and experimental measurements to probe the effect of fracture roughness on the properties of fluid flow in fractured rock. We develop a series of fracture models with various degrees of roughness characterized by fractal dimensions that are based on the Weierstrass-Mandelbrot fractal function. The Lattice Boltzmann Method (LBM), a discrete numerical algorithm, is employed for characterizing the complex unsteady non-Darcy flow through the single rough fractures and validated by experimental observations under the same conditions. Comparison indicates that the LBM effectively characterizes the unsteady non-Darcy flow in single rough fractures. Our LBM model predicts experimental measurements of unsteady fluid flow through single rough fractures with great satisfactory, but significant deviation is obtained from the conventional cubic law, showing the superiority of LBM models of single rough fractures
Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects.
Accurate understanding and predicting the flow paths of immiscible two-phase flow in rocky porous structures are of critical importance for the evaluation of oil or gas recovery and prediction of rock slides caused by gas-liquid flow. A 2D phase field model was established for compressible air-water two-phase flow in heterogenous porous structures. The dynamic characteristics of air-water two-phase interface and preferential paths in porous structures were simulated. The factors affecting the path selection of two-phase flow in porous structures were analyzed. Transparent physical models of complex porous structures were prepared using 3D printing technology. Tracer dye was used to visually observe the flow characteristics and path selection in air-water two-phase displacement experiments. The experimental observations agree with the numerical results used to validate the accuracy of phase field model. The effects of channel thickness on the air-water two-phase flow behavior and paths in porous structures were also analyzed. The results indicate that thick channels can induce secondary air flow paths due to the increase in flow resistance; consequently, the flow distribution is different from that in narrow channels. This study provides a new reference for quantitatively analyzing multi-phase flow and predicting the preferential paths of immiscible fluids in porous structures
Use of groundwater lifetime expectancy for the performance assessment of a deep geologic waste repository: 1. Theory, illustrations, and implications
Long-term solutions for the disposal of toxic wastes usually involve
isolation of the wastes in a deep subsurface geologic environment. In the case
of spent nuclear fuel, if radionuclide leakage occurs from the engineered
barrier, the geological medium represents the ultimate barrier that is relied
upon to ensure safety. Consequently, an evaluation of radionuclide travel times
from a repository to the biosphere is critically important in a performance
assessment analysis. In this study, we develop a travel time framework based on
the concept of groundwater lifetime expectancy as a safety indicator. Lifetime
expectancy characterizes the time that radionuclides will spend in the
subsurface after their release from the repository and prior to discharging
into the biosphere. The probability density function of lifetime expectancy is
computed throughout the host rock by solving the backward-in-time solute
transport adjoint equation subject to a properly posed set of boundary
conditions. It can then be used to define optimal repository locations. The
risk associated with selected sites can be evaluated by simulating an
appropriate contaminant release history. The utility of the method is
illustrated by means of analytical and numerical examples, which focus on the
effect of fracture networks on the uncertainty of evaluated lifetime
expectancy.Comment: 11 pages, 8 figures; Water Resources Research, Vol. 44, 200
Regional Flow Simulation in Fractured Aquifers Using Stress-Dependent Parameters
A model function relating effective stress to fracture permeability is
developed from Hooke's law, implemented in the tensorial form of Darcy's law,
and used to evaluate discharge rates and pressure distributions at regional
scales. The model takes into account elastic and statistical fracture
parameters, and is able to simulate real stress-dependent permeabilities from
laboratory to field studies. This modeling approach gains in phenomenology in
comparison to the classical ones because the permeability tensors may vary in
both strength and principal directions according to effective stresses.
Moreover this method allows evaluation of the fracture porosity changes, which
are then translated into consolidation of the medium.Comment: 10 pages, 7 figures, submitted to Ground Water 201
A double scale methodology to investigate flow in karst fractured media via numerical analysis. The Cassino plain case study (Central Apennine, Italy)
A methodology to evaluate the hydraulic conductivity of the karstmedia at a regional scale has been proposed, combining pumping
tests and the hydrostructural approach, evaluating the hydraulic conductivity of fractured rocks at the block scale. Obtaining
hydraulic conductivity values, calibrated at a regional scale, a numerical flow model of the Cassino area has been developed, to
validate the methodology and investigate the ambiguity, related to a nonunique hydrogeological conceptual model. The Cassino
plain is an intermontane basin with outstanding groundwater resources.The plain is surrounded by karst hydrostructures that feed
the Gari Springs and Peccia Springs. Since the 1970s, the study area was the object of detailed investigations with an exceptional
density of water-wells and piezometers, representing one of the most important karst study-sites in central-southern Italy.
Application of the proposed methodology investigates the hydraulic conductivity tensor at local and regional scales, reawakening
geological and hydrogeological issues of a crucial area and tackling the limits of the continuum modelling in karst medi
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