Comparison of pseudo-random binary sequence and square-wave transient controlled-source electromagnetic data over the Peon gas discovery, Norway

The square wave is frequently used as the transmitter waveform in marine controlled-source electromagnetics (CSEM) surveys. This waveform has the advantage of transferring maximum energy to the subsurface because the transmitter current is running at its peak amplitude at all times. However, a limitation of the square wave is that most of the transmitted energy is in the first harmonic. Processing methods such as depth migration and inversion have shown improved results if a transmitter waveform with substantial amounts of energy at multiple frequencies is used. We propose a method for designing transmitter waveforms where current amplitudes as a function of frequency can have an approximate predefined or desired distribution. At the same time, we require that the transmitter operate at its peak current at all times to maximize the energy transferred to the subsurface. To obtain the desired current spectra, the number of switching times in a period is allowed to be larger than two, which is the number of switching times per period for a standard square wave. The method is based on matching the desired frequency spectra with the spectra obtained from these generalized square waves. This optimization problem is solved by a Monte Carlo method. The resultant waveforms can be used for an electric-dipole transmitter.

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The importance of using geometrical constraints in marine controlled source electromagnetic data inversion

10.1190/1.2144394 ◽

2005 ◽

Author(s):

Paolo Dell'Aversana

Keyword(s):

Controlled Source ◽

Electromagnetic Data ◽

Data Inversion ◽

Geometrical Constraints

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Seismic wave propagation concepts applied to the interpretation of marine controlled-source electromagnetics

Geophysics ◽

10.1190/geo2014-0215.1 ◽

2015 ◽

Vol 80 (2) ◽

pp. E63-E81 ◽

Cited By ~ 9

Author(s):

Rune Mittet

Keyword(s):

Seismic Data ◽

Maxwell Equations ◽

Seismic Wave Propagation ◽

Finite Difference Schemes ◽

Data Types ◽

Controlled Source ◽

Electromagnetic Data ◽

Inverse Transform ◽

Refraction Seismic ◽

Marine Csem

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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