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Berlin Brandenburg

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  • 1
    In: Geophysical Research Letters, 28 September 2016, Vol.43(18), pp.9677-9685
    Description: We utilize synchrotron X‐ray tomographic imaging to investigate the pore‐scale characteristics and residual trapping of supercritical CO (scCO) over the course of multiple drainage‐imbibition (D‐I) cycles in Bentheimer sandstone cores. Capillary pressure measurements are paired with X‐ray image‐derived saturation and connectivity metrics which describe the extent of drainage and subsequent residual (end of imbibition) scCO trapping. For the first D‐I cycle, residual scCO trapping is suppressed due to high imbibition capillary number (Ca ≈ 10); however, residual scCO trapping dramatically increases for subsequent D‐I cycles carried out at the same Ca value. This behavior is not predicted by conventional multiphase trapping theory. The magnitude of scCO trapping increase is hysteretic and depends on the relative extent of the sequential drainage processes. The hysteretic pore‐scale behavior of the scCO‐brine‐sandstone system observed in this study suggests that cyclic multiphase flow could potentially be used to increase scCO trapping for sequestration applications. We observe cyclic pore‐scale behavior of supercritical CO2 (scCO2) via synchrotron X‐ray microtomography Residual scCO2 saturation increases over multiple drainage‐imbibition (D‐I) cycles reaching a value of 50% after three cycles The ultimate driver for this behavior may be a combination of cycling and associated surface chemistry reactions
    Keywords: Co 2 Sequestration ; Residual Trapping ; Capillary Trapping ; Cyclic Injections ; X‐Ray Microtomography ; Multiphase Flow
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 2
    In: Water Resources Research, June 2017, Vol.53(6), pp.4709-4724
    Description: The relaxation dynamics toward a hydrostatic equilibrium after a change in phase saturation in porous media is governed by fluid reconfiguration at the pore scale. Little is known whether a hydrostatic equilibrium in which all interfaces come to rest is ever reached and which microscopic processes govern the time scales of relaxation. Here we apply fast synchrotron‐based X‐ray tomography (X‐ray CT) to measure the slow relaxation dynamics of fluid interfaces in a glass bead pack after fast drainage of the sample. The relaxation of interfaces triggers internal redistribution of fluids, reduces the surface energy stored in the fluid interfaces, and relaxes the contact angle toward the equilibrium value while the fluid topology remains unchanged. The equilibration of capillary pressures occurs in two stages: (i) a quick relaxation within seconds in which most of the pressure drop that built up during drainage is dissipated, a process that is to fast to be captured with fast X‐ray CT, and (ii) a slow relaxation with characteristic time scales of 1–4 h which manifests itself as a spontaneous imbibition process that is well described by the Washburn equation for capillary rise in porous media. The slow relaxation implies that a hydrostatic equilibrium is hardly ever attained in practice when conducting two‐phase experiments in which a flux boundary condition is changed from flow to no‐flow. Implications for experiments with pressure boundary conditions are discussed. What happens to fluids in a porous medium after pumping is stopped? Fast X‐ray tomography shows that even in a sample smaller than a sugar cube fluid interfaces continue to move for hours until an optimal fluid configuration is reached. The pace is limited by slow relaxation of dynamic contact angles. Therefore hydrostatic equilibrium, which is the state at which all fluid interfaces come to rest, is hardly ever attained in practice when conducting two‐phase flow experiments where the flow is stopped in much larger soil or rock samples. Relaxation dynamics through internal redistribution of fluids after fast drainage occurs in two stages A quick dissipation within seconds is followed by slow relaxation within several hours due to relaxation of dynamic contact angles Fluid configurations during relaxation are very different from those during quasi‐static drainage and imbibition
    Keywords: Two‐Phase Flow ; Dynamic Effects ; Hydraulic Nonequilibrium ; Dynamic Contact Angle ; Fluid Configuration ; Fluid Topology
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 3
    In: Water Resources Research, February 2011, Vol.47(2), pp.n/a-n/a
    Description: A new method to resolve biofilms in three dimensions in porous media using high‐resolution synchrotron‐based X‐ray computed microtomography (CMT) has been developed. Imaging biofilms in porous media without disturbing the natural spatial arrangement of the porous medium and associated biofilm has been a challenging task, primarily because porous media generally preclude conventional imaging via optical microscopy; X‐ray tomography offers a potential alternative. Using silver‐coated microspheres for contrast, we were able to differentiate between the biomass and fluid‐filled pore spaces. The method was validated using a two‐dimensional micromodel flow cell where both light microscopy and CMT imaging were used to image the biofilm.
    Keywords: Biofilm ; X‐Ray Computed Microtomograph ; Porous Media
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 4
    In: Water Resources Research, August 2010, Vol.46(8), pp.n/a-n/a
    Description: In this work, the constitutive relationship between capillary pressure (), saturation (), and fluid‐fluid interfacial area per volume (IFA) is characterized using computed microtomography for drainage and imbibition experiments consisting of a nonaqueous phase liquid and water. The experimentally measured relationship was compared to a thermodynamic model that relates the area under the − curve to the total IFA, , and the capillary‐associated IFA, . Surfaces were fit to the experimental and modeled − − and − − data in order to characterize the relationship in three dimensions (3D). For the experimental system, it was shown that the − − relationship does not exhibit hysteresis. The model is found to provide a reasonable approximation of the magnitude of the 3D surfaces for and , with a mean absolute percent error of 26% and 15%, respectively. The relatively high mean absolute percent errors are primarily the result of discrepancies observed at the wetting‐ and nonwetting‐phase residual saturation values. Differences in the shapes of the surfaces are noted, particularly in the curvature (arising from the addition of scanning curves and presence of − hysteresis in the predicted results) and endpoints (particularly the inherent nature of thermodynamic models to predict significant associated with residual nonwetting‐phase saturation). Overall, the thermodynamic model is shown to be a practical, inexpensive tool for predicting the − − and − − surfaces from − data.
    Keywords: Multiphase Flow ; Capillary Pressure ; Saturation ; Interfacial Area ; Microtomography ; Thermodynamic
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 5
    In: Geophysical Research Letters, 01 October 2000, Vol.27(19), pp.3085-3088
    Description: A series of laboratory experiments, including measurements of electrical properties, permeability, and porosity, were performed on saturated sand‐clay mixtures. Different mixtures and packing geometries of quartz sand and 0 to 10% Na‐montmorillonite clay were investigated using solutions of CaCl and deionized water. Two main regions of electrical conduction exist: a region dominated by surface conduction and a region where the ionic strength of the saturating fluid controlled conduction. For low fluid conductivities, the sample geometry was found to greatly affect the magnitude of the surface conductance. The influence of the microstructural properties on the electrical properties was quantified by estimating formation factors, Λ‐parameters, and surface conductances. The surface conductances estimated using the theory of [1986] agreed well with measured values. We suggest that high and low bounds on the expected surface and bulk conductances in a natural system can be derived from the measurements on these artificial geometries.
    Keywords: Hydrogeology ; Clastic Sediments ; Clay ; Conductance ; Conductivity ; Cracks ; Electrical Properties ; Experimental Studies ; Hydrodynamics ; Laboratory Studies ; Microstructure ; Permeability ; Porosity ; Porous Materials ; Sand ; Sediments ; Textures;
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 6
    In: Water Resources Research, December 2007, Vol.43(12), pp.n/a-n/a
    Description: A Shan‐Chen–type multiphase lattice Boltzmann (LB) model was applied to observed computed microtomography data from water‐air and water‐Soltrol displacement experiments in a glass bead porous medium. Analysis of the Bond, Reynolds, and Capillary numbers for these systems showed that capillary forces were dominant removing the need to model viscous, gravitational, and density effects. A numerical parameterization of the LB model yielded lattice surface tension and contact angle, and appropriate pressure boundary conditions. Two scaling relations provided a link between lattice pressure and physical pressure and lattice time and physical time. Results showed that there was a good match between measured and simulated pressure‐saturation data for the water‐air system, but that there were large differences between the simulations and observations for the water‐Soltrol system. The discrepancies for the water‐Soltrol system were probably due to inconsistencies between experimental conditions and simulated conditions such as nonzero contact angle in the experiments. Analysis of saturation profiles indicated increasing saturation near the wetting boundary and decreasing saturations near the nonwetting boundary. We attribute these saturation transitions to pore‐neck and percolation effects. While computationally intensive, results of this study were very encouraging for the application of LB simulations to microscale interfacial phenomena. Future studies will carry out a further validation in terms of interfacial areas, contact lines, and fluid distributions.
    Keywords: Lattice Boltzmann ; Pressure Saturation ; Comparison
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    In: Water Resources Research, December 2004, Vol.40(12), pp.n/a-n/a
    Description: Multiphase flow and contaminant transport in porous media are strongly influenced by the presence of fluid‐fluid interfaces. Recent theoretical work based on conservation laws and the second law of thermodynamics has demonstrated the need for quantitative interfacial area information to be incorporated into multiphase flow models. We have used synchrotron based X‐ray microtomography to investigate unsaturated flow through a glass bead column. Fully three‐dimensional images were collected at points on the primary drainage curve and on the secondary imbibition and drainage loops. Analysis of the high‐resolution images (17 micron voxels) allows for computation of interfacial areas and saturation. Corresponding pressure measurements are made during the course of the experiments. Results show the fluid‐fluid interfacial area increasing as saturation decreases, reaching a maximum at saturations ranging from 20 to 35% and then decreasing as the saturation continues to zero. The findings support results of numerical studies reported in the literature.
    Keywords: Interfacial Area ; Porous Media ; Unsaturated Flow
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    In: Water Resources Research, April 2014, Vol.50(4), pp.3615-3639
    Description: Easier access to X‐ray microtomography (μCT) facilities has provided much new insight from high‐resolution imaging for various problems in porous media research. Pore space analysis with respect to functional properties usually requires segmentation of the intensity data into different classes. Image segmentation is a nontrivial problem that may have a profound impact on all subsequent image analyses. This review deals with two issues that are neglected in most of the recent studies on image segmentation: (i) focus on multiclass segmentation and (ii) detailed descriptions as to why a specific method may fail together with strategies for preventing the failure by applying suitable image enhancement prior to segmentation. In this way, the presented algorithms become very robust and are less prone to operator bias. Three different test images are examined: a synthetic image with ground‐truth information, a synchrotron image of precision beads with three different fluids residing in the pore space, and a μCT image of a soil sample containing macropores, rocks, organic matter, and the soil matrix. Image blur is identified as the major cause for poor segmentation results. Other impairments of the raw data like noise, ring artifacts, and intensity variation can be removed with current image enhancement methods. Bayesian Markov random field segmentation, watershed segmentation, and converging active contours are well suited for multiclass segmentation, yet with different success to correct for partial volume effects and conserve small image features simultaneously. First survey of image processing methods for multiphase fluid images A novel protocol is suitable for various types of porous media Many routines come with a freely available open‐source library
    Keywords: Image Processing ; Multiphase Flow ; X‐Ray Tomography ; Structure Analysis ; Segmentation ; Soil Structure
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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