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Berlin Brandenburg

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  • 1
    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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  • 2
    Language: English
    In: International Journal of Greenhouse Gas Control, March 2016, Vol.46, pp.175-186
    Description: We investigate capillary trapping and fluid migration via x-ray computed microtomography (x-ray CMT) of nonwetting phase (air) and wetting phase (brine) in Bentheimer sandstone cores which have been treated to exhibit different degrees of uniform wettability. x-Ray CMT scans were acquired at multiple steps during drainage and imbibition processes, as well as at the endpoints; allowing for assessment of the impact of wettability on nonwetting phase saturation and cluster size distribution, connectivity, topology and efficiency of trapping. Compared with untreated (water-wet) Bentheimer sandstone, cores treated with tetramethoxylsilane (TMS) were rendered weakly water-wet, and cores treated with octadecyltrichlorosilane (OTS) demonstrate intermediate-wet characteristics. As apparent contact angle increases, drainage flow patterns deviate from those derived for water-wet systems, total residual trapping and trapping efficiency decrease, and buoyancy plays a larger role during nonwetting phase mobilization; this has significant implications for CO migration and trapping during CO sequestration operations.
    Keywords: Wettability ; Drainage Flow Pattern ; Capillary Trapping ; Residual Trapping ; Pore Scale ; Geologic Co2 Sequestration ; Engineering
    ISSN: 1750-5836
    E-ISSN: 1878-0148
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  • 3
    Language: English
    In: Advances in Water Resources, Dec, 2013, Vol.62, p.47(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.advwatres.2013.09.015 Byline: Anna L. Herring, Elizabeth J. Harper, Linnea Andersson, Adrian Sheppard, Brian K. Bay, Dorthe Wildenschild Abstract: acents We examine the effect of NW phase connectivity on capillary trapping in porous media. acents We establish relationships of NW connectivity as a function of NW saturation. acents High initial NW connectivity results in reduced trapping for Bentheimer sandstone. acents Multiple drainage-imbibition cycles do not change the NW connectivity of the media. acents A WAG injection scheme reduces connectivity and promotes capillary trapping of CO.sub.2. Article History: Received 15 May 2013; Revised 25 September 2013; Accepted 27 September 2013
    ISSN: 0309-1708
    Source: Cengage Learning, Inc.
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  • 4
    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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  • 5
    Language: English
    In: Advances in Water Resources, 2015, Vol.79, p.91(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.advwatres.2015.02.005 Byline: Anna L. Herring, Linnea Andersson, Steffen Schluter, Adrian Sheppard, Dorthe Wildenschild Abstract: * We investigate residual trapping of nonwetting (NW) phase (air) in sandstone cores. * We describe initial air configurations with connectivity metrics. * Factors influencing trapping are a function of dominant pore-scale forces. * Trapping efficiency decreases as initial air connectivity increases. * Pore-scale forces and NW connectivity are important for engineering applications. Article History: Received 23 August 2014; Revised 6 February 2015; Accepted 9 February 2015
    ISSN: 0309-1708
    Source: Cengage Learning, Inc.
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  • 6
    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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  • 7
    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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