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

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

doi:10.1190/geo2011-0145.1

Cited by 9 publications

(6 citation statements)

References 13 publications

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“…(a) Layered model, (b) voltage decay, and (c) anomalous effects of the thin resistive layer. L = 1000 m, R = 1414 m, total current I CED = I VEL = 1000 A, and offset is 2000 m. Evaluation of the external noise in electric field components is given in (Constable ; Flekkøy, Haland and Maløy ). The vertical arrow indicates the time at which the responses reach the CED/VEL moment‐normalised threshold noise 1E‐15 V/A/m/m.…”

Section: Circular Electric Dipole and Vertical Electric Dipolementioning

confidence: 99%

Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

Mogilatov

Zlobinskiy

Balashov

2016

Geophysical Prospecting

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The theory behind transient electromagnetic surveys can be well described in terms of transverse magnetic and transverse electric modes. Soundings using transverse magnetic and transverse electric modes require different source configurations. In this study, we consider an alternating transverse magnetic field excitation by a circular electric dipole. The circular electric dipole transmitter is a horizontal analogue of the vertical electric dipole. Offshore surveys using circular electric dipole might represent an alternative to the conventional marine controlled‐source electromagnetic method at shallow sea and/or for exploring relatively small targets. Field acquisition is carried out by recording either electric or magnetic responses. Electric responses bear information on the 1D structure of a layered earth and successfully resolve high‐resistivity targets in marine surveys. Land‐based circular electric dipole soundings are affected by induced polarisation. On the contrary, magnetic responses are absent on the surface of a 1D earth, and as a result, they are very sensitive to any and even very small 3D conductivity perturbations. In addition, they are sensitive to induced polarisation or some other polarisation effects in the subsurface. At present, circular electric dipole transmitters and magnetic receivers are successfully used in on‐land mineral and petroleum exploration.

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Section: Circular Electric Dipole and Vertical Electric Dipolementioning

confidence: 99%

Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

Mogilatov

Zlobinskiy

Balashov

2016

Geophysical Prospecting

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“…Evaluation of the external noise in vertical and horizontal electric field components is given by Flekkøy et al (2012). The results obtained after processing experimental data measured at a sea depth of 120 m -300 m with a maximum deviation of the receiving dipoles from vertical of ϕ < 0.1°indicate that the energy spectrum of the field component E z in the range of periods 2-20 s is less than 10 −19 V 2 /m 2 s (i.e., at period of 10 s, the noise amplitude does not exceed ß10 −9 V/m).…”

Section: E V a L U A T I O N O F N O I S Ementioning

confidence: 99%

“…The vertical dotted lines indicate the time at which the responses reach the VEB moment-normalized threshold noise 10 −15 V/Am 2(Constable 2010;Flekkøy et al 2012). Sea depth H w = 1 km, ρ = 0.33 Ωm, and offset R = 1 km.…”

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confidence: 99%

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Marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs: principles, methodologies and limitations

Barsukov

Fainberg

2016

Geophysical Prospecting

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The possibility of a time‐domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated. The method operates on source–receiver offsets, which are several times less than the depth of the reservoir. Geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field. The basics of the method, as well as its sensitivity, resolution, and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths, are analyzed. For the analysis, 1D and 3D geoelectric models of hydrocarbon reservoirs are used. It is shown that under existing technologies of excitation and measurement of vertical electric fields, the highest accessible depth of soundings can be up to 4 km. Technology for the inversion and interpretation of transient responses is demonstrated on experimental data.

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“…In order to break through the limitation that the CSAMT method can only be observed in the far-field zone, He et al ( 2014He et al ( , 2015 proposed to observe only the Ex field instead of Cagniard apparent resistivity, which can reduces the offset and enhance sensitivity verified by the results of numerical simulation and field observation, and is successfully applied in shale gas exploration ( Yuan et al, 2017). Some scholars are employing vertical electric source to obtain the response of deep resistive targets (Holten et al, 2009;Flekkøy et al, 2012;Um, 2012;Tietze et al, 2019 ). The above studies mostly obtained conclusions by directly studying electromagnetic fields.…”

Section: Introductionmentioning

confidence: 99%

A More Efficient Observation Way With Electric Dipole Sources

wang

Chang

Deng

2020

Preprint

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The Ex and Hz amplitude are monotonic functions of the resistivity, and numerical algorithm can be utilized to obtain the high-precision apparent resistivity for all frequencies. On this basis, we focus on the comparative analysis of the resolution for Ex field, Hz field, and Cagniard apparent resistivity to conductive and resistance targets, which proves that the Ex field may have a better resolution for the resistance bodies, and the Hz field can better identify the conductive target. Besides, the electromagnetic data is often distorted by the static effect, which seriously affects the application effect of the electromagnetic method. The influence of the static effect on the Ex field, Hz field, is also analyzed. The apparent resistivity based on the Ex field and Cagniard apparent resistivity are severely affected by the static effect which can cover deep anomalous bodies, but the apparent resistivity based on the Hz field is almost unaffected by the static effect. At last, a more efficient observation way is provided for the resistance and conductive targets, respectively.

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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

Cited by 9 publications

References 13 publications

Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

Marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs: principles, methodologies and limitations

A More Efficient Observation Way With Electric Dipole Sources

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