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| Titel |
Joint numerical microscale simulations of multi-phase flow and NMR relaxation behaviour in porous media |
| VerfasserIn |
Oliver Mohnke, Benjamin Ahrenholz, Norbert Klitzsch |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054693
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| Zusammenfassung |
| In addition to the classical experimental approaches to derive flow and transport properties of
rocks and soils - in particular for the vadose zone - Computational Fluid Dynamics (CFD) has
proven to be a viable complementary tool for analyzing and predicting complex transport
systems. In nuclear magnetic resonance (NMR), the measured relaxation signals originate
from the pore spaces filled with NMR-active fluid (e.g., water, oil) and gas (e.g. methane)
phases. The rate of NMR relaxation - of the wetting phase - is sensitive to the pore
size and physicochemical properties of the rock-fluid/-gas interfaces (i.e., surface
relaxivity), as well as the concentration of paramagnetic ions in the bulk phases (bulk
relaxivity). Thus, the method can be applied to derive hydraulic parameters such
as pore size distributions or (relative) permeability. To improve the fundamental
understanding of the pore scale processes necessary to translate measured NMR
relaxometry signals into soil structural and state properties, numerical simulations of
the NMR relaxation (i.e., Bloch equation) and multi-phase flow on a pore scale
dimension have been implemented using Lattice Boltzmann methods. To jointly
study the transport and NMR behavior of partially saturated soils we carry out
sequential CFD simulations using a modified Rothmann-Keller (RK) model for multi
phase flow modeling (i.e., de-saturation) and due to its improved efficiency, high
accuracy and stability an advection/diffusion model developed by Ginzburg is used to
subsequently calculate the NMR relaxation signals at different saturation states.
Simulations have been compiled for synthetic as well pore systems derived from
micro-CT images of porous ceramics (reference samples) and natural unconsolidated
sediments. The simulations have been validated by (1) using analytical and finite
element models for simple geometries and (2) corresponding joint pressure-curve and
NMR measurements on fully and partially saturated reference and soil samples.
In a next step we aim to further advance the model by implementing simulations
of Induced Polarization (IP) responses in the time and frequency domain that are
complementary to NMR data. Based on these simulations we aim to develop a
joint interpretation scheme for combined NMR and (Spectral) IP measurements
in order to assess structure, state and thus flow properties of partially saturated
soils. |
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