Vertical and horizontal components of the electric background field at the sea bottom

Håland, Endre; Flekkøy, Eirik Grude; Måløy, Knut Jørgen

doi:10.1190/geo2011-0039.1

Cited by 6 publications

(6 citation statements)

References 19 publications

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“…The 3-and 10-m tripods are very close, and the interesting observation in the figure is that the low-frequency oscillations appear to be in phase, indicating that the oscillations are not linked to the tripods themselves but the external fields. The frequency is consistent with that of surface sea waves with a wavelength of roughly 500 m (Håland et al, 2012). The binning and the P8 averaging are carried out as so-called running averages.…”

Section: Measurements and Noise Removalmentioning

confidence: 86%

“…The data sampling rate is a 1000 Hz. The noise has a wide range of frequencies because there is the rapid electronic noise, some oscillations with a period of order 18 s, most likely caused by ocean waves (see Håland et al, 2012), and an overall drift in the data of roughly 100 nV, which is usually associated with electrode drift. The noise causes the field values to drift over more than 100 nV∕m in three minutes, but we require accuracies around 1 nV∕m.…”

Section: Measurements and Noise Removalmentioning

confidence: 99%

“…A theory for the electromagnetic effect of microseismics was put forward by Longuett-Higgins (1950) 60 years ago, and the effect of Rayleigh-Stoneley waves has been studied by Webb and Cox (1982). Recently, Håland et al (2012) demonstrated that ocean surface waves give rise to noise mainly in the E z -component on the sea floor, whereas other sources appear to dominate in the horizontal field components.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of the low-frequency variations of the vertical and horizontal components of the electric background field at the sea bottom

2012

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Natural electric field variations are measured at the sea bottom over long periods of time by means of stationary, vertical, and horizontal galvanic antennas. We compare the power spectra of the vertical and horizontal field components and the extent to which they may be reduced by standard averaging techniques. Although the raw spectra of the vertical and horizontal components do not differ greatly, the difference in the spectra after averaging is significantly greater. Most significantly, in the frequency range between 0.0005 and 0.03 Hz, this averaging scheme suppresses the vertical electric field component more strongly than the horizontal component.

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Section: Measurements and Noise Removalmentioning

confidence: 86%

Section: Measurements and Noise Removalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of the low-frequency variations of the vertical and horizontal components of the electric background field at the sea bottom

2012

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“…E z data have been recorded as part of marine CSEM (e.g. Chave & Filloux 1985;Bindoff et al 1986;Holten et al 2009;Håland et al 2012), cross-well EM and a few landbased magnetotelluric (MT) measurements (e.g. Jones & Geldart 1967a,b;Bahr 1983).…”

Section: Measurements Of the Vertical Electric Field On Landmentioning

confidence: 99%

Repeatability of land-based controlled-source electromagnetic measurements in industrialized areas and including vertical electric fields

Tietze

Ritter²,

Patzer³

et al. 2019

Geophysical Journal International

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Over the last decade, an increasing number of numerical studies have proposed controlledsource electromagnetic (CSEM) techniques for monitoring of fluid flow in reservoirs, for example, in the framework of hydrocarbon production or CO 2 storage scenarios. A fundamental prerequisite for any monitoring application in practice is repeatability of the measurements, particularly in areas with high noise levels.Here, we report on CSEM data acquired across a producing oil field on land in three consecutive surveys between 2014 and 2016. As major conductivity changes in the reservoir structure are not expected for this time frame, the data sets provide an excellent basis to study accuracy and repeatability of such measurements over a time span of 2.5 yr.Our results show that uncertainties of single CSEM measurements lie between 0.1 and 10 per cent with a focus around 1 per cent in all surveys. For source-receiver offsets <2 km uncertainties are in the range of ∼0.1-0.3 per cent, proportional to the transfer function amplitudes, and are dominated by intrinsic noise of the measuring system. At source-receiver distances >4 km external noise resulting from natural electromagnetic field variations and powered installations dominates uncertainties that assume minimum absolute values of 10 −9 -10 −10 V A −1 m −1 with lowest values at frequencies between 0.1 and 10 Hz.Overall, repeatability of CSEM measurements depends on a range of factors, including source-receiver distances, component of the transfer function, source-polarization and relocation errors, in particular at sites close to the source, where the geometry and characteristics of the source fields vary rapidly in space. Best repeatability was observed for receiver stations at 2-4 km distance from the source and frequencies <20 Hz. At these stations, phases and amplitudes of transfer functions usually agreed within ±1 • and ±5 per cent between measurements. Such values are in a range as expected from time-lapse signals due to resistivity changes in target (reservoir) formations. Hence, precise surveying procedures are essential.We also measured the vertical electric field (E z ) with a newly developed receiver chain in a 200 m deep observation borehole. The vertical electric field component shows generally higher sensitivity to resistivity changes in reservoir structures than the horizontal electric fields measured at surface. Although amplitudes of E z are about one to two orders of magnitude smaller than amplitudes of horizontal electric fields, recordings of E z are stable. More importantly, E z transfer functions of three measurements between 2015 and 2016 show excellent quality and repeatability within <±2 • and <±5 per cent, similar as horizontal electric fields indicating that noise conditions at depth improve when compared with sensors at surface.

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“…As for the marine electric field measuring devices, bottom metering systems are usually used both for deep sea and shallow sea. For example, Filloux [7], Håland [8], Flekkøy [9] and Wang Meng [10] used a 3-axis electric field sensor to measure the electric field signal on the seafloor. There are also a small number of other measurement devices, such as Qualls [11], who used an AUV (Autonomous underwater vehicle) equipped with the electric field sensor to measure the electric field near the hull.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the natural electric field at different sea depths

Zhang

Jin-fang

et al. 2021

J. Inst.

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The natural electric field at the depth of 0 ∼ 1500 m in high seas of South China Sea is obtained by using a new type of measuring device. The electric field data in the 0.01 ∼ 0.5 Hz and 0.5 ∼ 30 Hz frequency range are analyzed respectively. The results show that the induced electric field generated by the surface wave (about 0.14 Hz in the experiment) is obvious at the depth of 50 m but can be ignored at the depth greater than 100 m. When the depth increases from 50 m to 1500 m, the peak-to-peak value of the natural electric field gradually decreases. At the depth of 1000 m, the peak-to-peak values are 0.04 ∼ 0.08 μV/m in the 0.01 ∼ 0.5 Hz range, and 0.07 ∼ 0.1 μV/m in the 0.5 ∼ 30 Hz range. At last, the natural electric field in coastal water near Sanya City, where the water depth is 15 m, is measured by means of a sinking device. The results show that the peak-to-peak values are about 2 ∼ 4 μV/m in the 0.01 ∼ 0.5 Hz range and 2 μV/m in the 0.5 ∼ 30 Hz range. By comparing the natural electric field in high seas with that of coastal water, we find the latter has a larger peak-to-peak value at nearly the same water depth. In addition, line spectrum noise often occurs in coastal water, while it is rarely observed in high seas when the water depth is more than 50 m.

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Vertical and horizontal components of the electric background field at the sea bottom

Cited by 6 publications

References 19 publications

Comparison of the low-frequency variations of the vertical and horizontal components of the electric background field at the sea bottom

Comparison of the low-frequency variations of the vertical and horizontal components of the electric background field at the sea bottom

Repeatability of land-based controlled-source electromagnetic measurements in industrialized areas and including vertical electric fields

Analysis of the natural electric field at different sea depths

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