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Berlin Brandenburg

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  • 1
    Language: English
    In: SEG Technical Program Expanded Abstracts, 1999, Vol.18(1), p.461
    Description: We have performed a series of laboratory experiments on saturated sand-clay mixtures. Measurements include frequency-dependent electrical properties using the four-electrode technique (10 mHz to 1 MHz), permeability, porosity, and acoustic velocities. We mixed clean quartz sand with Na-montmorillonite in a number of different configurations containing 0 to 10% clay: as a dispersed mixture, as discrete clay clusters, and arranged in distinct layers. Solutions of CaCl2 ranging from 0.0005 N to 0.75 N (0.05 to 64 mS/cm) and deionized water were used as saturating fluids. We found the electrical properties to be dependent on clay content, fluid conductivity, and microstructure in a complex fashion. Increasing fluid conductivity and increasing clay content generally resulted in higher electrical conductivity. For an individual sample, two main regions of conduction exist: a region dominated by surface conduction and a region where the ionic strength of the saturating fluid controlled conduction. The sample geometry (dispersed, non-dispersed, or layered clay configuration) was found to greatly affect the magnitude of the surface conductance in the range of low fluid conductivity.
    Keywords: Applied Geophysics ; Bentonite ; Clastic Rocks ; Clastic Sediments ; Clay ; Clay Minerals ; Electrical Conductivity ; Electrical Methods ; Electrical Properties ; Experimental Studies ; Fluid Phase ; Geometry ; Geophysical Methods ; Laboratory Studies ; Mathematical Methods ; Measurement ; Montmorillonite ; Permeability ; Physical Properties ; Properties ; Sample Preparation ; Sand ; Saturation ; Sedimentary Rocks ; Sediments ; Sheet Silicates ; Silicates ; United States ; Wyoming;
    ISSN: 10523812
    Source: Society of Exploration Geophysicists (SEG, includes EEGS) (via CrossRef)
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  • 2
    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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  • 3
    Language: English
    In: Transport in Porous Media, 2012, Vol.92(3), pp.819-835
    Description: Microbial enhanced oil recovery (MEOR) is a technology that could potentially increase the tertiary recovery of oil from mature oil formations. However, the efficacy of this technology in fractional-wet systems is unknown, and the mechanisms involved in oil mobilization therefore need further investigation. Our MEOR strategy consists of the injection of ex situ produced metabolic byproducts produced by Bacillus mojavensis JF-2 (which lower interfacial tension (IFT) via biosurfactant production) into fractional-wet cores containing residual oil. Two different MEOR flooding solutions were tested; one solution contained both microbes and metabolic byproducts while the other contained only the metabolic byproducts. The columns were imaged with X-ray computed microtomography (CMT) after water flooding, and after MEOR, which allowed for the evaluation of the pore-scale processes taking place during MEOR. Results indicate that the larger residual oil blobs and residual oil held under relatively low capillary pressures were the main fractions recovered during MEOR. Residual oil saturation, interfacial curvatures, and oil blob sizes were measured from the CMT images and used to develop a conceptual model for MEOR in fractional-wet systems. Overall, results indicate that MEOR was effective at recovering oil from fractional-wet systems with reported additional oil recovered (AOR) values between 44 and 80%; the highest AOR values were observed in the most oil-wet system.
    Keywords: Microbial enhanced oil recovery ; X-ray microtomography ; Multiphase flow ; Interfacial curvature
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 4
    Language: English
    In: Computational Geosciences, 2010, Vol.14(1), pp.15-30
    Description: Image analysis of three-dimensional microtomographic image data has become an integral component of pore scale investigations of multiphase flow through porous media. This study focuses on the validation of image analysis algorithms for identifying phases and estimating porosity, saturation, solid surface area, and interfacial area between fluid phases from gray-scale X-ray microtomographic image data. The data used in this study consisted of (1) a two-phase high precision bead pack from which porosity and solid surface area estimates were obtained and (2) three-phase cylindrical capillary tubes of three different radii, each containing an air–water interface, from which interfacial area was estimated. The image analysis algorithm employed here combines an anisotropic diffusion filter to remove noise from the original gray-scale image data, a k-means cluster analysis to obtain segmented data, and the construction of isosurfaces to estimate solid surface area and interfacial area. Our method was compared with laboratory measurements, as well as estimates obtained from a number of other image analysis algorithms presented in the literature. Porosity estimates for the two-phase bead pack were within 1.5% error of laboratory measurements and agreed well with estimates obtained using an indicator kriging segmentation algorithm. Additionally, our method estimated the solid surface area of the high precision beads within 10% of the laboratory measurements, whereas solid surface area estimates obtained from voxel counting and two-point correlation functions overestimated the surface area by 20–40%. Interfacial area estimates for the air–water menisci contained within the capillary tubes were obtained using our image analysis algorithm, and using other image analysis algorithms, including voxel counting, two-point correlation functions, and the porous media marching cubes. Our image analysis algorithm, and other algorithms based on marching cubes, resulted in errors ranging from 1% to 20% of the analytical interfacial area estimates, whereas voxel counting and two-point correlation functions overestimated the analytical interfacial area by 20–40%. In addition, the sensitivity of the image analysis algorithms on the resolution of the microtomographic image data was investigated, and the results indicated that there was little or no improvement in the comparison with laboratory estimates for the resolutions and conditions tested.
    Keywords: Multiphase flow ; Porous media ; Computed microtomography ; Image analysis ; Marching cubes
    ISSN: 1420-0597
    E-ISSN: 1573-1499
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  • 5
    Language: English
    In: Advances in Water Resources, September 2012, Vol.46, pp.55-62
    Description: ► Computed tomography datasets were analyzed for interfacial curvature. ► Curvature and transducer-based measurements compare well. ► Disconnected and connected phase interfaces have significantly different curvatures. ► Connected phase interfacial curvature relaxes as the system equilibrates. Synchrotron-based tomographic datasets of oil–water drainage and imbibition cycles have been analyzed to quantify phase saturations and interfacial curvature as well as connected and disconnected fluid configurations. This allows for close observation of the drainage and imbibition processes, assessment of equilibrium states, and studying the effects of fluid phase disconnection and reconnection on the resulting capillary pressures and interfacial curvatures. Based on this analysis estimates of capillary pressure calculated from interfacial curvature can be compared to capillary pressure measured externally with a transducer. Results show good agreement between curvature-based and transducer-based measurements when connected phase interfaces are considered. Curvature measurements show a strong dependence on whether an interface is formed by connected or disconnected fluid and the time allowed for equilibration. The favorable agreement between curvature-based and transducer-based capillary pressure measurements shows promise for the use of image-based estimates of capillary pressure for interfaces that cannot be probed with external transducers as well as opportunities for a detailed assessment of interfacial curvature during drainage and imbibition.
    Keywords: Capillary Pressure ; Interfacial Curvature ; Young–Laplace ; Drainage ; Imbibition ; Computed Microtomography ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 6
    Language: English
    In: Advances in Water Resources, May 2015, Vol.79, pp.91-102
    Description: We investigate trapping of a nonwetting (NW) phase, air, within Bentheimer sandstone cores during drainage–imbibition flow experiments, as quantified on a three dimensional (3D) pore-scale basis via x-ray computed microtomography (X-ray CMT). The wetting (W) fluid in these experiments was deionized water doped with potassium iodide (1:6 by weight). We interpret these experiments based on the capillary–viscosity–gravity force dominance exhibited by the Bentheimer–air–brine system and compare to a wide range of previous drainage–imbibition experiments in different media and with different fluids. From this analysis, we conclude that viscous and capillary forces dominate in the Bentheimer–air–brine system as well as in the Bentheimer–supercritical CO –brine system. In addition, we further develop the relationship between initial (post-drainage) NW phase connectivity and residual (post-imbibition) trapped NW phase saturation, while also taking into account initial NW phase saturation and imbibition capillary number. We quantify NW phase connectivity via a topological measure as well as by a statistical percolation metric. These metrics are evaluated for their utility and appropriateness in quantifying NW phase connectivity within porous media. Here, we find that there is a linear relationship between initial NW phase connectivity (as quantified by the normalized Euler number, ) and capillary trapping efficiency; for a given imbibition capillary number, capillary trapping efficiency (residual NW phase saturation normalized by initial NW phase saturation) can decrease by up to 60% as initial NW phase connectivity increases from low connectivity ( ≈ 0) to very high connectivity ( ≈ 1). We propose that multiphase fluid-porous medium systems can be engineered to achieve a desired residual state (optimal NW phase saturation) by considering the dominant forces at play in the system along with the impacts of NW phase topology within the porous media, and we illustrate these concepts by considering supercritical CO sequestration scenarios.
    Keywords: Co2 Sequestration ; Topology ; Pore-Scale ; Force Balance ; Nonwetting Phase Trapping ; X-Ray Microtomography ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 7
    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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  • 8
    Language: English
    In: Advances in Water Resources, December 2013, Vol.62, pp.47-58
    Description: This work examines the influence of (i.e. post drainage) nonwetting (NW) fluid topology on total (i.e. after imbibition) NW phase saturation. Brine and air (used as a proxy for supercritical CO ) flow experiments were performed on Bentheimer sandstone; results were quantified via imaging with X-ray computed microtomography (X-ray CMT), which allows for three dimensional, non-destructive, pore-scale analysis of the amount, distribution, and connectivity of NW phase fluid within the sandstone cores. In order to investigate the phenomenon of fluid connectivity and how it changes throughout flow processes, the Bentheimer sandstone results are compared to previously collected X-ray CMT data from similar experiments performed in a sintered glass bead column, a loose packed glass bead column, and a column packed with crushed tuff. This allows us to interpret the results in a broader sense from the work, and draw conclusions of a more general nature because they are not based on a single pore geometry. Connectivity is quantified via the of the NW fluid phase; the Euler number of a particular sample is normalized by the maximum connectivity of the media, i.e. the Euler number of the system at 100% NW phase saturation. General connectivity-saturation relationships were identified for the various media. In terms of trapping, it was found that residual NW phase trapping is dependent on initial (i.e. post-drainage) NW phase connectivity as well as imbibition capillary number for the Bentheimer sandstone. Conversely, the sintered glass bead column exhibited no significant relationship between trapping and NW topology. These findings imply that for a CO sequestration scenario, capillary trapping is controlled by both the imbibition capillary number and the initial NW phase connectivity: as capillary number increases, and the normalized initial Euler number approaches a value of 1.0, capillary trapping is suppressed. This finding is significant to CO sequestration, because both the drainage (CO injection) and imbibition (subsequent water injection or infiltration) processes can be engineered in order to maximize residual trapping within the porous medium. Based on the findings presented here, we suggest that both the Euler number-saturation and the capillary number-saturation relationships for a given medium should be considered when designing a CO sequestration scenario.
    Keywords: Connectivity ; Topology ; Co2 Sequestration ; Capillary Trapping ; Porous Media ; X-Ray Tomography ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 9
    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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  • 10
    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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