Predicting controlled-source electromagnetic responses from seismic velocities

Werthmüller, Dieter; Ziolkowski, Anton; Wright, David

doi:10.1190/int-2013-0153.1

Cited by 4 publications

(2 citation statements)

References 30 publications

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“…FFTLog, introduced by Hamilton (2000), is another transform algorithm which proved to be powerful for the frequency-to-time domain transformation of EM responses (e.g. Werthmüller et al 2014). In our tests they are both about equal in speed and accuracy.…”

Section: Frequency Selectionmentioning

confidence: 77%

Fast Fourier transform of electromagnetic data for computationally expensive kernels

Werthmüller

Mulder

Slob

2021

Geophysical Journal International

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SUMMARY 3-D controlled-source electromagnetic data are often computed directly in the domain of interest, either in the frequency domain or in the time domain. Computing it in one domain and transforming it via a Fourier transform to the other domain is a viable alternative. It requires the evaluation of many responses in the computational domain if standard Fourier transforms are used. This can make it prohibitively expensive if the kernel is time-consuming as is the case in 3-D electromagnetic modelling. The speed of modelling obtained through such a transform is defined by three key points: solver, method and implementation of the Fourier transform, and gridding. The faster the solver, the faster modelling will be. It is important that the solver is robust over a wide range of values (frequencies or times). The method should require as few kernel evaluations as possible while remaining robust. As the frequency and time ranges span many orders of magnitude, the required values are ideally equally spaced on a logarithmic scale. The proposed fast method uses either the digital linear filter method or the logarithmic fast Fourier transform together with a careful selection of evaluation points and interpolation. In frequency-to-time domain tests this methodology requires typically 15–20 frequencies to cover a wide range of offsets. The gridding should be frequency- or time-dependent, which is accomplished by making it a function of skin depth. Optimizing for the least number of required cells should be combined with optimizing for computational speed. Looking carefully at these points resulted in much smaller computation times with speedup factors of ten or more over previous methods. A computation in one domain followed by transformation can therefore be an alternative to computation in the other domain domain if the required evaluation points and the corresponding grids are carefully chosen.

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Section: Frequency Selectionmentioning

confidence: 77%

Fast Fourier transform of electromagnetic data for computationally expensive kernels

Werthmüller

Mulder

Slob

2021

Geophysical Journal International

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“…The geological setting and the presence of upwardly migrating free gas via vertical structures, both increase the probability for anisotropy at CNE03. Electrical anisotropy is commonly defined as the ratio between the vertical resistivity and the horizontal resistivity and a ratio above 1.5 indicates the existence of significant anisotropy (Werthmüller et al 2014). Analyzing anisotropic structure by applying isotropic CSEM inversion may provide biased results that are inconsistent with other datasets such as seismic and well logging (Ramananjaona & MacGregor 2010).…”

Section: Anisotropy At Cne03mentioning

confidence: 99%

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

et al. 2016

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SUMMARYDeep sea pockmarks underlain by chimney-like or pipe structures that contain methane hydrate are abundant along the Norwegian continental margin. In such hydrate provinces the interaction between hydrate formation and fluid flow has significance for benthic ecosystems and possibly climate change. The Nyegga region, situated on the western Norwegian continental slope, is characterized by an extensive pockmark field known to accommodate substantial methane gas hydrate deposits. The aim of this study is to detect and delineate both the gas hydrate and free gas reservoirs at one of Nyegga's pockmarks.In 2012, a marine controlled-source electromagnetic (CSEM) survey was performed at a pockmark in this region, where high-resolution three-dimensional seismic data were previously collected in 2006. Two-dimensional CSEM inversions were computed using the data acquired by ocean bottom electrical field receivers. Our results, derived from un- constrained and seismically constrained CSEM inversions, suggest the presence of two distinctive resistivity anomalies beneath the pockmark: a shallow vertical anomaly at the underlying pipe structure, likely due to gas hydrate accumulation, and a laterally extensive anomaly attributed to a free gas zone below the base of the gas hydrate stability zone. This work contributes to a robust characterization of gas hydrate deposits within sub-seafloor fluid flow pipe structures.

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Principles and Methods

Sainson¹

2017

Electromagnetic Seabed Logging

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Predicting controlled-source electromagnetic responses from seismic velocities

Cited by 4 publications

References 30 publications

Fast Fourier transform of electromagnetic data for computationally expensive kernels

Fast Fourier transform of electromagnetic data for computationally expensive kernels

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

Principles and Methods

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