Shaping optimal transmitter waveforms for marine CSEM surveys

Mittet, Rune; Schaug-Pettersen, T.

doi:10.1190/1.2792479

Cited by 17 publications

(12 citation statements)

References 7 publications

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“…Multiple simultaneous frequencies can be obtained with these switching TXs by using pseudo-random square-wave signals (Duncan et al, 1980;Luo and Li, 2010;Mittet and Schaug-Pettersen, 2008;Constable and Cox, 1996). These high-power TXs can be used with the multi-frequency tuning circuit described in Sternberg and Dvorak (2013) for high efficiency or with an untuned coil and high-voltage output to overcome the high impedance of an untuned coil.…”

Section: The Vertical Array-dtac Measuring Systemmentioning

confidence: 98%

Experimental Studies and Verification of the Vertical Array-Differential Target Antenna Coupling (DTAC) Method for Rapid Sensing and Imaging of Subsurface Targets

Sternberg

Feng

Dvorak

et al. 2015

JEEG

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We have developed a new electromagnetic geophysical system that has significantly improved target sensing and imaging capabilities compared to conventional measurements. In a previous series of papers, we described a new measurement technology called the Differential Target Antenna Coupling (DTAC) method, which used a magnetic-field transmitter (TX) and a magneticfield receiver (RX), oriented in a horizontal array, with separation distances of the order of tens of meters, and up to tens of kilometers. In the present paper, we use the DTAC method in a verticalarray configuration, with the TX coil directly above two null-coupled RX coils. This vertical array provides a number of important advantages over the large-offset horizontal array for some applications. For example, the vertical array-DTAC method can be adapted to rapidly moving measurements, such as from a helicopter. In addition, the vertical array-DTAC method also suppresses surface clutter, such as fences, steel buildings, and parked vehicles.The DTAC method uses at least two frequencies. One frequency is used as a reference signal to establish the null direction at that frequency, and then a different frequency is used to measure the change in the null at the new frequency. We can also use an arbitrary number of frequencies with just one reference frequency for wide-bandwidth spectral measurements. We first describe the vertical array-DTAC measurement system and discuss the calibration procedure for the instrumentation. Next, we discuss the methods employed for scale-model testing of the system. We validate the vertical array-DTAC method using small-scale controlled tests and demonstrate the enhanced resolution and sensitivity of the vertical array-DTAC method. Suitable TX moments and frequency ranges can be selected for effective study of nearsurface targets (civil engineering, water resource, and environmental characterization) as well as deep targets (mining and other natural-resource exploration).

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Section: The Vertical Array-dtac Measuring Systemmentioning

confidence: 98%

Experimental Studies and Verification of the Vertical Array-Differential Target Antenna Coupling (DTAC) Method for Rapid Sensing and Imaging of Subsurface Targets

Sternberg

Feng

Dvorak

et al. 2015

JEEG

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show abstract

“…The source emitted a composite waveform [4] optimized for the frequencies of 0.25, 0.5 and 0.75 Hz. Using such composite waveform, the transmitter operates at its peak current of 1250 A at all times and focuses the available source power on those frequencies that the prospects proved most sensitive to during the survey feasibility modeling.…”

Section: Fig 1-examples Of Resistivity Logs From the Survey Area Exhmentioning

confidence: 99%

Application of Electromagnetic Scanning to an Australian Frontier Basin with Complex Bathymetry

David¹,

Ross²,

Roth³

et al. 2008

Proceedings of Offshore Technology Conference

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“…More recently, customized source waveforms have become standard, in which a frequency spectrum can be tuned to accommodate a specific depth of investigation or resolution [19]. More recently, customized source waveforms have become standard, in which a frequency spectrum can be tuned to accommodate a specific depth of investigation or resolution [19].…”

Section: Source Waveform and Spectrummentioning

confidence: 99%

3D Inversion-Based Interpretation of Seabed Logging Data

Zach

Frenkel

2009

All Days

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The Marine Controlled-Source Electromagnetic (CSEM) method has been evolving into a geophysical imaging tool for increasingly complex geological settings, in which multiple resistive bodies can be resolved. An advanced subsurface imaging workflow for 3D CSEM surveys is presented, which reproduces the subsurface to within a spatial resolution determined frequencies included. The performance of our advanced processing workflow is demonstrated using a case study from the Gulf of Mexico, where a dense 3D grid was acquired over an area where high-quality seismic data, as well as well log control was given.At the heart of our 3D workflow is an inversion methodology with approximate Hessian-based optimization and a fast finitedifference time-domain forward operator. The optimization matches the synthetic to the measured field within 100-200 iterations and is sufficiently robust in 3D to avoid expensive regularization schemes. The sensitivity of the gradient-based inversion to the starting model is addressed by investing considerable effort in building 1D inversion-based starting model. At the same time, 3D inversion algorithms for survey layouts including azimuthal data demand high quality data conditioning, for which we present a processing sequence from time-domain electromagnetic data acquired by seabed receivers to frequency domain data and weights for inversion.Detection and delineation of reservoirs in the presence of salt is recognized as a major challenge to CSEM methods. In order to accurately interpret 3D data in such a complex environment, the true resistivity cube is built from a sequence of constrained inversion-based interpretation steps. Using a dataset acquired in 2008 in the Gulf of Mexico, we demonstrate the ability of our 3D-technology to resolve small (2km x 2km), low resistivity pay (Δρ<5Ωm) targets with in the vicinity (< 1km) of large salt bodies. In this case study, the 3D method converged within 1 week running on 150 parallel nodes.

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Shaping optimal transmitter waveforms for marine CSEM surveys

Cited by 17 publications

References 7 publications

Experimental Studies and Verification of the Vertical Array-Differential Target Antenna Coupling (DTAC) Method for Rapid Sensing and Imaging of Subsurface Targets

Experimental Studies and Verification of the Vertical Array-Differential Target Antenna Coupling (DTAC) Method for Rapid Sensing and Imaging of Subsurface Targets

Application of Electromagnetic Scanning to an Australian Frontier Basin with Complex Bathymetry

3D Inversion-Based Interpretation of Seabed Logging Data

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