Controlled-Source Electromagnetic sounding (CSEM)

Calibration, analysis, and visualization of CSEM data

Shell


Calibrating a single receiver.



Map view.



Calibrating a whole towline.



V-plot.



Challenge

Controlled-Source Electromagnetic sounding (CSEM) is a new tool for marine oil exploration. Sensitive electric and magnetic field detectors are deployed to the seafloor over a prospect. A ship then tows a low-frequency electric source over the detectors. Variations in the electromagnetic properties of the rock below the detectors, specifically those due to the presence of oil, cause detectable changes in the magnitude and phase of the signal received by the detectors. Because ship time is such a precious resource, extensive data cleaning and post-processing is required to make the most of the available data. Since CSEM is a new technique, geophysicists are still working out the best practices for analyzing the data. CSEM software must be lightweight and flexible to evolve with the field.

Solution

We wrote a calibration tool for CSEM frequency-domain data. There are several artifacts in the CSEM data that appear as bulk shifts in the magnitude and phase of the received signal. Algorithms for doing the calibration automatically from a putative earth model do exist; however, they are not robust and require significant handholding and human intervention in order to work well. Shell used to do this process through the manual manipulation of Excel spreadsheets and some Matlab scripts. The process was tedious, prone to error and data loss, and time-wasting. Our tool lets the user explore their datasets through tables, maps, and graphs and apply different calibrations to different subsets of the data. Once calibrated, the data can be inverted to get an earth model. The tool can then be used to compare the actual data with the synthetic data from the fitted earth model.

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