Interpretation of controlled-source electromagnetic data from iron ores under rough topography

Concepts such as reflections, refractions, diffractions, and transmissions are very useful for the interpretation of seismic data. Moreover, these concepts play a key role in the design of processing algorithms for seismic data. Currently, however, the same concepts are not widely used for the analysis and interpretation of marine controlled-source electromagnetic (CSEM) data. Connections between seismic and marine CSEM data are established by analytically transforming the diffusive Maxwell equations to wave-domain Maxwell equations. Seismic data and wave-domain electromagnetic data are simulated with 3D finite-difference schemes. The two data types are similar; however, the wave-domain electromagnetic data must be transformed back to the diffusive domain to properly describe realistic field propagation in the earth. We analyzed the inverse transform from the wave domain to the diffusive domain. Concepts like reflections, refractions, diffractions and transmissions were found to be valid also for marine CSEM data but the properties of the inverse transform favored refracted and guided events over reflected and diffracted events. In this sense, marine CSEM data were found to be similar to refraction seismic data.

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A modeling study of augmenting coarse-grid 3D controlled-source electromagnetics with data from a towed receiver array

Geophysics ◽

10.1190/geo2014-0583.1 ◽

2016 ◽

Vol 81 (1) ◽

pp. E33-E42 ◽

Cited By ~ 1

Author(s):

Jan Petter Morten ◽

Jean-Michael Poudroux ◽

Rune Mittet

Keyword(s):

Coarse Grid ◽

The Other ◽

Burial Depth ◽

3D Inversion ◽

Simultaneous Inversion ◽

Controlled Source ◽

Hydrocarbon Reservoir ◽

Electromagnetic Data ◽

Receiver Array ◽

3D Geometry

We have considered the simultaneous 3D inversion of controlled-source electromagnetic data from a towed receiver array and a coarse grid of stationary seabed receivers. Our 3D synthetic model demonstrated the sensitivity and effect on imaging of towed and seabed receiver data. The short-offset data from the towed receivers at 1–3 km offset are effective at resolving a shallow resistor at a 400-m burial depth. On the other hand, the data from the stationary seabed receivers have less noise and will resolve the 3D geometry of resistive structures buried at the 1–2 km depths typical of a hydrocarbon reservoir. We have determined how the complementary sensitivity of data from the two receiver types can be used in simultaneous inversion to recover the shallow and deep resistors.

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Target signal enhancement in near-surface controlled-source electromagnetic data

Geophysics ◽

10.1190/1.1926573 ◽

2005 ◽

Vol 70 (3) ◽

pp. G59-G67 ◽

Cited By ~ 6

Author(s):

Alfonso Benavides I. ◽

Mark E. Everett

Keyword(s):

Power Law ◽

Wavelet Transforms ◽

Discrete Wavelet ◽

Discrete Wavelet Transforms ◽

Near Surface ◽

Controlled Source ◽

Electromagnetic Data ◽

Apparent Conductivity ◽

Fractal Statistics ◽

Detection And Localization

Controlled-source electromagnetic-conductivity profiles and maps were obtained on the Brazos Valley, Texas, floodplain to study the fractal statistics of geologic noise and the effects of man-made conductive metal targets. Fourier transform, discrete wavelet transforms, and variogram analyses were used. Targets tend to flatten the power-law power spectrum at small wavenumbers and shift power to higher wavenumbers. Detection and localization of targets can be achieved using wavelet spectrogram techniques. Additionally, variograms from pure background conductivity maps show a power-law trend for all lags, whereas, in the presence of targets, a short power-law trend is followed by a sill corresponding to a loss in spatial correlation. A simple preprocessing step that combines responses from two perpendicular transmitter-receiver orientations enhances the localization of targets and rejects background signals in profiles and 2D apparent-conductivity maps. Finally, a field example shows how the use of wavelet filtering is able to separate target responses from the geologic background.

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