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Berlin Brandenburg

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  • Porous Materials
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  • 1
    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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  • 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: Advances in Water Resources, January 2013, Vol.51, pp.217-246
    Description: ► We provide a review of recent developments and advances in pore-scale X-ray tomographic imaging of subsurface porous media. ► The particular focus is on immiscible multi-phase fluid flow and quantitative analyses. ► Advances in both imaging techniques and image processing are discussed and future trends are addressed. We report here on recent developments and advances in pore-scale X-ray tomographic imaging of subsurface porous media. Our particular focus is on immiscible multi-phase fluid flow, i.e., the displacement of one immiscible fluid by another inside a porous material, which is of central importance to many natural and engineered processes. Multiphase flow and displacement can pose a rather difficult problem, both because the underlying physics is complex, and also because standard laboratory investigation reveals little about the mechanisms that control micro-scale processes. X-ray microtomographic imaging is a non-destructive technique for quantifying these processes in three dimensions within individual pores, and as we report here, with rapidly increasing spatial and temporal resolution.
    Keywords: X-Ray Tomography ; Porous Media Characterization ; Multi-Phase Flow ; Image Analysis and Quantification ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 4
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Advancements in noninvasive imaging methods such as X-ray computed tomography (CT) have led to a recent surge of applications in porous media research with objectives ranging from theoretical aspects of pore-scale fluid and interfacial dynamics to practical applications such as enhanced oil recovery and advanced contaminant remediation. While substantial efforts and resources have been devoted to advance CT technology, microscale analysis, and fluid dynamics simulations, the development of efficient and stable three-dimensional multiphase image segmentation methods applicable to large data sets is lacking. To eliminate the need for wet-dry or dual-energy scans, image alignment, and subtraction analysis, commonly applied in X-ray micro-CT, a segmentation method based on a Bayesian Markov random field (MRF) framework amenable to true three-dimensional multiphase processing was developed and evaluated. Furthermore, several heuristic and deterministic combinatorial optimization schemes required to solve the labeling problem of the MRF image model were implemented and tested for computational efficiency and their impact on segmentation results. Test results for three grayscale data sets consisting of dry glass beads, partially saturated glass beads, and partially saturated crushed tuff obtained with synchrotron X-ray micro-CT demonstrate great potential of the MRF image model for three-dimensional multiphase segmentation. While our results are promising and the developed algorithm is stable and computationally more efficient than other commonly applied porous media segmentation models, further potential improvements exist for fully automated operation. Journal Article.
    Keywords: Engineeringalgorithms ; Computerized Tomography ; Efficiency ; Fluids ; Glass ; Image Processing ; Optimization ; Three-Dimensional Calculations;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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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, December 2018, Vol.122, pp.251-262
    Description: We introduce a new method for defining a pore-body to pore-throat aspect ratio from segmented 3D image data, based on a connectivity metric applicable to porous media with widely varying pore-space connectivity and pore-space morphology. The ‘Morphological Aspect Ratio’ (MAR) is identified from the pore-space connectivity, using the Euler number (χ) as a function of a pore-space size defined by a morphological opening (erosion and dilation) of the pore space. We show that residual non-wetting phase trapping in porous media resulting from secondary imbibition scales with the MAR. Trapping was investigated in a Bentheimer sandstone core and five columns of partially sintered glass-particle packs with different combinations of glass beads and crushed glass ranging in size from 0.3 to 1.2 mm, resulting in porosity levels of 22–36%. Residual non-wetting phase trapping scales with the MAR, in contrast to the aspect ratio calculated with the traditional Maximum Inscribed Sphere (MIS) algorithm applied after partitioning the pore space into pore bodies and pore throats with a watershed transform followed by a region merging algorithm. This novel aspect ratio is a robust method that is less affected by segmentation errors compared to other methods for calculating aspect ratio and is applicable to residual non-wetting phase trapping resulting from capillary-driven flow of a wetting fluid through water-wet porous media.
    Keywords: Connectivity ; Capillary-Dominated Flow ; Morphological Opening ; Nonwetting Phase Trapping ; X-Ray Micro-Tomography ; Porous Media ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 7
    Language: English
    In: Advances in Water Resources, September 2016, Vol.95, pp.288-301
    Description: Biofilm growth changes many physical properties of porous media such as porosity, permeability and mass transport parameters. The growth depends on various environmental conditions, and in particular, on flow rates. Modeling the evolution of such properties is difficult both at the porescale where the phase morphology can be distinguished, as well as during upscaling to the corescale effective properties. Experimental data on biofilm growth is also limited because its collection can interfere with the growth, while imaging itself presents challenges. In this paper we combine insight from imaging, experiments, and numerical simulations and visualization. The experimental dataset is based on glass beads domain inoculated by biomass which is subjected to various flow conditions promoting the growth of biomass and the appearance of a biofilm phase. The domain is imaged and the imaging data is used directly by a computational model for flow and transport. The results of the computational flow model are upscaled to produce conductivities which compare well with the experimentally obtained hydraulic properties of the medium. The flow model is also coupled to a newly developed biomass–nutrient growth model, and the model reproduces morphologies qualitatively similar to those observed in the experiment.
    Keywords: Porescale Modeling ; Imaging Porous Media ; Microtomography ; Biomass and Biofilm Growth ; Parabolic Variational Inequality ; Multicomponent Multiphase Flow and Transport in Porous Media ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 8
    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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  • 9
    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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  • 10
    Language: English
    In: Vadose Zone Journal, 01 November 2011, Vol.10(4)
    Description: Engineered capillary barriers typically consist of two layers of granular materials designed so that the contrast in material hydraulic properties and sloping interface retains infiltrating water in the upper layer. We report here on the results of two bench-top capillary barrier experiments, interpretation, and numerical modeling. We measured hydraulic parameters for two coarse materials using standard methods and found that the materials had similar hydraulic properties despite being morphologically different (round vs. angular). The round sand provided a better functioning capillary barrier than the angular sand, but neither experiment could be characterized as a perfectly working capillary barrier. In both cases, more than 93% of the infiltrating water was successfully diverted from the lower layer, however, infiltration into the underlying layer was observed in both systems. Based on this work, we believe that non-continuum processes such as vapor diffusion and film flow contribute to the observed phenomena and are important aspects to consider with respect to capillary barrier design, as well as dry vadose zone processes in general. Using a theoretical film flow equation that incorporates the surface geometry of the porous material we found that infiltration into the coarse underlying sand layer appeared to be dominated by water film flow. The NUFT (Non-isothermal Unsaturated-saturated Flow and Transport) model was used for qualitative comparison simulations. We were able to reproduce the barrier breach observed in the experiments using targeted parameter adjustment, by which pseudo-film flow was successfully simulated.
    Keywords: Materials Science ; Engineering ; Design ; Diffusion ; Film Flow ; Geometry ; Granular Materials ; Hydraulics ; Performance ; Porous Materials ; Sand ; Simulation ; Transport ; Water ; Water Film, Vadose Zone, Capillary Barrier ; Agriculture ; Engineering
    ISSN: 1539-1663
    E-ISSN: 1539-1663
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