Case Study – A Towed EM Test at the Peon Discovery in the North Sea

Mattsson, Johan; Lund, Linnea; Lima, Jostein; Engelmark, Folke; Mckay, Allen

doi:10.3997/2214-4609.201400675

Cited by 7 publications

(6 citation statements)

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“…It is not reported how long the measurements took but a single time-domain waveform at long offsets was 13.5 minutes long. Mattsson et al (2010) reported the use of a near-surface towed version of this equipment with source-receiver offsets of up to 2.5 km. Both time-domain and frequency-domain transmissions were made but analysis seems to be in the frequency domain.…”

Section: T O W E D S O U R C E -R E C E I V E R S Y S T E M Smentioning

confidence: 99%

Review paper: Instrumentation for marine magnetotelluric and controlled source electromagnetic sounding

Constable

2013

Geophysical Prospecting

125

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We review and describe the electromagnetic transmitters and receivers used to carry out magnetotelluric and controlled source soundings in the marine environment. Academic studies using marine electromagnetic methods started in the 1970s but during the last decade these methods have been used extensively by the offshore hydrocarbon exploration industry. The principal sensors (magnetometers and non‐polarizing electrodes) are similar to those used on land but magnetotelluric field strengths are not only much smaller on the deep sea‐floor but also fall off more rapidly with increasing frequency. As a result, magnetotelluric signals approach the noise floor of electric field and induction coil sensors (0.1 nV/m and 0.1 pT) at around 1 Hz in typical continental shelf environments. Fluxgate magnetometers have higher noise than induction coils at periods shorter than 500 s but can still be used to collect sea‐floor magnetotelluric data down to 40–100 s. Controlled source transmitters using electric dipoles can be towed continuously through the seawater or on the sea‐bed, achieving output currents of 1000 A or more, limited by the conductivity of seawater and the power that can be transmitted down the cables used to tow the devices behind a ship. The maximum source‐receiver separation achieved in controlled source soundings depends on both the transmitter dipole moment and on the receiver noise floor and is typically around 10 km in continental shelf exploration environments. The position of both receivers and transmitters needs to be navigated using either long baseline or short baseline acoustic ranging, while sea‐floor receivers need additional measurements of orientations from compasses and tiltmeters. All equipment has to be packaged to accommodate the high pressure (up to 40 MPa) and corrosive properties of seawater. Usually receiver instruments are self‐contained, battery powered and have highly accurate clocks for timekeeping, even when towed on the sea‐floor or in the water column behind a transmitter.

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Section: T O W E D S O U R C E -R E C E I V E R S Y S T E M Smentioning

confidence: 99%

Review paper: Instrumentation for marine magnetotelluric and controlled source electromagnetic sounding

Constable

2013

Geophysical Prospecting

125

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“…The attenuation and phase shift of the transmitted signal is recorded by an array of seafloor EM receivers containing electric field sensing dipoles (of order 10 m length) and inductioncoil magnetometers. For the magnetotelluric method, the seafloor receivers measure naturally occurring lowfrequency electromagnetic plane waves that diffuse into Earth to a more economical single ship operation for shallow water use, with successful application to imaging a gas reservoir reported by Mattsson et al (2010). A trade-off with the streamer configuration is that it only records inline horizontal electric fields at relatively short offsets, whereas traditional nodal receivers record the full vector electric and magnetic fields, and can be located inline and offline to great distances in order to better constrain 3D structure, although this could be partially mitigated with the streamer system by collecting additional tows on crossing lines.…”

Section: Introductionmentioning

confidence: 99%

Marine Electromagnetic Studies of Seafloor Resources and Tectonics

Key

2011

Surv Geophys

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The past decade has been a period of rapid growth for marine electromagnetic (EM) methods, predominantly due to the industrial adoption and promotion of EM as a valuable tool for characterizing offshore hydrocarbon reservoirs. This growth is illustrated by a database of marine EM publications spanning from the early developments in the 1960's to the present day; while over 300 peer-reviewed papers on marine EM have been published to date, more than half of these papers have been published within the last decade. This review provides an overview of these recent developments, covering industrial and academic use of marine EM for resource exploration and tectonic investigations, ranging from acquisition technology and modeling approaches to new physical and geological insights learned from recent data sets.

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“…As an illustration, we consider a simple marine CSEM survey consisting of a horizontal electric bipole transmitter towed behind a boat and a set of towed horizontal electric dipole receivers (Figure 1). This marine data acquisition system has recently been developed [11]. The moving platform geometry enables the TSEM survey to be acquired over very large areas in both frontier and mature basins for higher production rates and relatively lower cost compared to conventional MCSEM surveys, characterized by arrays of fixed oceanbottom receivers and towed transmitters [12].…”

Section: Issn: Jgg An Open Access Journal J Geol Geoscimentioning

confidence: 99%

Focusing Controlled Sensitivity of Geophysical Data

Zhdanov¹

2013

J Geol Geosci

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Different geophysical surveys have a specific sensitivity to geological targets, determined by the physical nature of the observed geophysical field, the design of the data acquisition system, and the configuration and type of the source of the recorded data. The sensitivity is usually limited to some part of the examined geological formation, located relatively close to the sensors. This paper introduces a concept of controlled sensitivity, which enables the sensitivity of a geophysical data to be increased within a specific target area of a geological formation. In particular, this method can be used to increase the sensitivity of the data with the depth. The developed approach is demonstrated with a numerical study of the sensitivity of marine Towed Streamer Electro-Magnetic (TSEM) surveys. However, a general mathematical formulation of the method, presented in this paper, makes it possible to apply the developed technique to a wide variety of geophysical data.

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Case Study – A Towed EM Test at the Peon Discovery in the North Sea

Cited by 7 publications

References 0 publications

Review paper: Instrumentation for marine magnetotelluric and controlled source electromagnetic sounding

Review paper: Instrumentation for marine magnetotelluric and controlled source electromagnetic sounding

Marine Electromagnetic Studies of Seafloor Resources and Tectonics

Focusing Controlled Sensitivity of Geophysical Data

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