Depth of Investigation and Vertical Resolution of Surface Geoelectric Arrays

Szalai, S.; Novák, Attila; Szarka, László

doi:10.2113/jeeg14.1.15

Cited by 85 publications

(41 citation statements)

References 17 publications

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“…they are not independent and are usually excluded from the data, CARPENTER and HABBERJAM, 1956). The data is collected within the same borehole (inhole) and between the two boreholes (crosshole) in vertical (v), horizontal (h) and circulating (c) modes (SZALAI et al, 2009;. HAGREY (2011) introduced two non-standard complex datasets of bhtp (sum of bh and tp-p or tripole-pole of GOES and MEEKES, 2004) and abvcs (sum of avcs and bvcs, s = symmetrical around the midpoint).…”

Section: Introductionmentioning

confidence: 99%

2D Optimized Electrode Arrays for Borehole Resistivity Tomography and CO2 Sequestration Modelling

Hagrey

2011

Pure Appl. Geophys.

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Modern optimization approaches for electrode configurations can significantly improve the resolution of 2.5D resistivity imaging surveys. This study presents a brief review of the 2.5D optimization approach, particularly for borehole-borehole surveys with applications for mapping virtual CO 2 plumes sequestrated in deep saline reservoir formations. The applied algorithm searches for arrays that maximize the spatial resolution of the survey among the comprehensive dataset of best possible spatial resolution (i.e. least temporal resolution). A main goal of this study is to increase the temporal resolution of ERT boreholeborehole surveys by selecting optimized electrode configurations in order to minimise the required data acquisition time while sustaining a high spatial resolution. The optimized dataset starts with a base set and is iteratively increased based on the model resolution matrix (R) until the required number of data points is achieved. Among four different optimization methods, the compare R (CR) method of the best resolution is applied to directly calculate R for each new array added to the optimized dataset. Small optimized datasets generated by this technique are only \5% of their comprehensive sets but of an average resolution ratio (R r ) of[0.95 (i.e. almost the same resolution). With increasing the size of the optimized dataset (during its generation), the algorithm progressively enhances R r values in the central interwell region (of low sensitivities and low resolution) far higher than in the near borehole region (of high sensitivities). Also the inverted tomogram reliability increases by increasing the optimized data size. Briefly, the optimized arrays improve the resolution in the interwell region which is commonly low in borehole-borehole ERT studies. The inverted output model is evaluated quantitatively using the model difference relative to the input model. The results reflect the common smearing effects and artefacts of varying degrees that overpredict volumes, underpredict magnitudes and blur boundaries of the target anomalies. This input model is a synthetic resistivity model that was used to generate synthetic (forward solution) data used during the inversion. Applications on synthetic CO 2 models show that the mapping resolution for optimized datasets is better than that for other highly resolving arrays of the same number of data points. Problems of smeared boundaries and thin layers are less visible in the optimized array than in the other highly resolving arrays.

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Section: Introductionmentioning

confidence: 99%

2D Optimized Electrode Arrays for Borehole Resistivity Tomography and CO2 Sequestration Modelling

Hagrey

2011

Pure Appl. Geophys.

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“…Edwards (1977) found that this was in better agreement with his field experience. Szalai et al, (2009) have computed the parameter by means of both the Roy and Apparao (1971) and the Edwards' (1977) approach for all 30 arrays it was reliable. As they have found that the median depth can be determined from the Roy-Apparao depth values by a multiplication with 1.59 ± 0.31.…”

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confidence: 88%

Multiplication of the depth of detectability using γ11n arrays

Szalai¹,

Lemperger²,

Metwaly³

et al. 2014

Journal of Applied Geophysics

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The depth from which one can get information has always been a crucial parameter in the geophysical exploration. This paper deals with the depth of detectability (DD) of 2D electric resistivity tomography configurations. DD is the maximal depth from which a given model body is detectable in the presence of a given noise level. Based on previous DD calculations for conventional electrode arrays it is shown in this paper that there is a nearly linear relation between the maximum value of their parameter-sensitivity (PS) maps and their DD values. Studying the PS maps of other arrays, as well, we found that many of them have higher PS max values than those of the conventional arrays. These so-called γ 11n arrays are therefore expected to have larger DD values, too. The performed DD-calculations have confirmed this expectation. γ 11n arrays are linear geoelectric arrays where γ refers to the CPCP order of the current (C) and potential (P) electrodes whilst the subscript numbers refer to the distance of the neighbouring electrodes. In case of the studied prism and dyke models the γ 11n arrays -if n is larger or equal to 2 -consistently produced higher DD-values than the best conventional arrays. The DD value of these arrays can be even 2-3 times larger than that of the best conventional array value. Such an increase in the DD value is especially useful if the available place for measurements is limited, e.g. due to infrastructural conditions. Anomalies in large depth, for example, which are not seen by traditionally used arrays, may become detectable using γ 11n arrays as it was verified also by numerical studies. These arrays require moreover less measurement than most conventional arrays resulting in shorter measuring time.

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“…Some suggest the depth of penetration of < 30% of the array length (Roy and Apparao 1971;Szalai et al 2009). Edwards (1977) suggests that the effective median depth of investigation of a dipole-dipole array is between 14 and 22% of total line length.…”

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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Depth of Investigation and Vertical Resolution of Surface Geoelectric Arrays

Cited by 85 publications

References 17 publications

2D Optimized Electrode Arrays for Borehole Resistivity Tomography and CO2 Sequestration Modelling

2D Optimized Electrode Arrays for Borehole Resistivity Tomography and CO2 Sequestration Modelling

Multiplication of the depth of detectability using γ11n arrays

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

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