Optimized arrays for 2D cross‐borehole electrical tomography surveys

Loke, M.H.; Wilkinson, Paul; Chambers, Jonathan; Strutt, M.H.

doi:10.1111/1365-2478.12072

Cited by 57 publications

(39 citation statements)

References 33 publications

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“…Figure 1 shows that the PSF and the radius of resolution independently mark out a circular area of approximately the same size around the cell of investigation and thereby emphasizes the validity of the common approach to only use the diagonal entries as a quantitative measure of resolution. This is in agreement with the recent finding of Loke et al (2014), who demonstrated that optimizations of individual four-point configurations based on PSF measures do not notably improve the information content of the resulting arrays compared to optimizations based exclusively on the diagonal entries, while the former is computationally considerably more cumbersome. Yet it should be emphasized that the comparable performances of the diagonal entries and PSF measures during array optimizations are by no means evidence of their equality.…”

Section: Image Appraisal and Experimental Designsupporting

confidence: 92%

“…Friedel, 2003). Despite the drawback of being computationally expensive, the model resolution is the preferred choice in ERT experimental design studies and has proven to be a good forecaster of the eventual inversion performance (Stummer et al, 2004;Coscia et al, 2008;Wilkinson et al, 2006Wilkinson et al, , 2010Wilkinson et al, , 2012Loke et al, 2014). Individual columns of R m , so called point spread functions (PSF), show how a resistivity perturbation in the subsurface is mapped into the final inversion image (Oldenborger and Routh, 2009).…”

Section: Image Appraisal and Experimental Designmentioning

confidence: 99%

“…In electrical resistivity imaging, most experimental design studies have concentrated on the identification of individual four-point configurations that optimally exploit the information content offered by modern multi-electrode arrays (e.g. Stummer et al, 2004;Wilkinson et al, 2006;Furman et al, 2007;Coscia et al, 2008;Loke et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Constructive optimization of electrode locations for target-focused resistivity monitoring

et al. 2015

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Crosshole resistivity tomography has received consideration as a tool for quantitative imaging of carbon dioxide stored in deep saline aquifers. With regard to the monitoring responsibility of site operators and the substantial expenses associated with permanent downhole installations, optimized experimental design gains particular importance. Based on an iterative appraisal of the formal model resolution matrix, we present a method to estimate optimum electrode locations along the borehole trajectories with the objective to maximize the imaging capability within a prescribed target horizon. For the presented crosshole case, these layouts are found to be symmetric, exhibiting refined electrode spacings within the target horizon. Our results demonstrate that a sparse, but well conceived set of electrodes can provide a large part of the information content offered by comparably dense electrode distributions. In addition, the optimized layout outperforms equidistant setups with the same number of electrodes since its resolution is focused on the monitoring target. The optimized electrode layouts presented provide a powerful and cost-efficient opportunity to complement permanent installations, particularly at, but not limited to, future CO 2 storage sites. Although preliminarily developed to support the design of crosshole resistivity layouts, our approach is directly applicable to other survey geometries including surface and surface-to-hole acquisitions.

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Section: Image Appraisal and Experimental Designsupporting

confidence: 92%

Section: Image Appraisal and Experimental Designmentioning

confidence: 99%

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Constructive optimization of electrode locations for target-focused resistivity monitoring

et al. 2015

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“…However, acquiring all of these electrode arrangements is prohibitively time-consuming and does not guarantee a superior outcome. Optimized arrays, with trade-offs between acquisition efficiency and optimum ERI resolution, is an active field of research for ERI imaging (e.g., Loke et al 2014aLoke et al , b, 2015bStummer et al 2002;Szalai et al 2013;Wilkinson et al 2012Wilkinson et al , 2006. Several methods of optimization exist; however, the analysis of resolution matrices has proven popular.…”

Section: Background: Electrical Resistivity Imagingmentioning

confidence: 99%

Electrical Resistivity Imaging and the Saline Water Interface in High-Quality Coastal Aquifers

2018

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Population growth and changing climate continue to impact on the availability of natural resources. Urbanization of vulnerable coastal margins can place serious demands on shallow groundwater. Here, groundwater management requires definition of coastal hydrogeology, particularly the seawater interface. Electrical resistivity imaging (ERI) appears to be ideally suited for this purpose. We investigate challenges and drivers for successful electrical resistivity imaging with field and synthetic experiments. Two decades of seawater intrusion monitoring provide a basis for creating a geo-electrical model suitable for demonstrating the significance of acquisition and inversion parameters on resistivity imaging outcomes. A key observation is that resistivity imaging with combinations of electrode arrays that include dipole-dipole quadrupoles can be configured to illuminate consequential elements of coastal hydrogeology. We extend our analysis of ERI to include a diverse set of hydrogeological settings along more than 100 km of the coastal margin passing the city of Perth, Western Australia. Of particular importance are settings with: (1) a classic seawater wedge in an unconfined aquifer, (2) a shallow unconfined aquifer over an impermeable substrate, and (3) a shallow multi-tiered aquifer system over a conductive impermeable substrate. We also demonstrate a systematic increase in the landward extent of the seawater wedge at sites located progressively closer to the highly urbanized center of Perth. Based on field and synthetic ERI experiments from a broad range of hydrogeological settings, we tabulate current challenges and future directions for this technology. Our research contributes to resolving the globally significant challenge of managing seawater intrusion at vulnerable coastal margins.

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“…The sides of the model used to calculate the resolution values are extended 4 m in both the x and y directions beyond the edges of the survey grid. This is to ensure that all the regions of the subsurface that have significant resolution values are included (Loke et al 2014a). The subsurface is subdivided into model cells with widths of 1 m in both the x and y directions.…”

Section: Model Resolution Sectionsmentioning

confidence: 99%

Computation of Optimized Arrays for 3-D Electrical Imaging Surveys

Wilkinson¹,

Loke²,

Chambers³

2013

Proceedings

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S U M M A R Y3-D electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artefacts. Many 3-D surveys use a grid where the number of electrodes along one direction (x) is much greater than in the perpendicular direction (y). Frequently, due to limitations in the number of independent electrodes in the multi-electrode system, the surveys use a roll-along system with a small number of parallel survey lines aligned along the x-direction. The 'Compare R' array optimization method previously used for 2-D surveys is adapted for such 3-D surveys. Offset versions of the inline arrays used in 2-D surveys are included in the number of possible arrays (the comprehensive data set) to improve the sensitivity to structures in between the lines. The array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set. Comparisons of the conventional (consisting of dipole-dipole and Wenner-Schlumberger arrays) and optimized arrays are made using a synthetic model and experimental measurements in a tank. The tests show that structures located between the lines are better resolved with the optimized arrays. The optimized arrays also have significantly better depth resolution compared to the conventional arrays.

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Optimized arrays for 2D cross‐borehole electrical tomography surveys

Cited by 57 publications

References 33 publications

Constructive optimization of electrode locations for target-focused resistivity monitoring

Constructive optimization of electrode locations for target-focused resistivity monitoring

Electrical Resistivity Imaging and the Saline Water Interface in High-Quality Coastal Aquifers

Computation of Optimized Arrays for 3-D Electrical Imaging Surveys

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