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Hello everyone,
First, it is important to understand that there are several mechanisms that can lead to seismoelectric signals. The ones that are pursued
by these companies are likely of electrokinetic origin. Thompson was the first to experiment with the modulation of electrical signals by a seismic wave in 1936. Three years later, Ivanov (1939) reported experimental results that showed that this effect existed
without any external electrical source. These methods were largely developed by the researchers of the former USSR and they were applied to a number of different environments such as mining and groundwater. Don Russell’s group at UBC (Anton Kepic and Karl
Butler) studied this phenomenon in the early 1990s. I am a direct descendant of that group ;). The experiments performed by Professor Russell’s lab and a group at MIT confirmed that it is possible to measure seismoelectric signals in the lab and in the field.
Since then a number of other western researchers have continued to develop the science related to this phenomenon. For readers that are interested
in this field I would suggest to look at my doctoral thesis titled : Field measurements and analyses of electrokinetic seismoelectric
signals generated in sedimentary environments: https://www.ece.unb.ca/petersen/pubs/theses/students/Du08/Du08.pdf.
The first chapter provides a good overview of what was the state of the art up to 2008. Since then I’ve done a few experiments with Schlumberger to see if we could get better penetration with large vibe trucks.
The unfortunate reality is that these signals are small… very small. With typical weight-drops (e.g. PEG45) the signals we have measured are on the order of hundreds of nV/m. Our paper on the seismoelectric imaging of the vadose zone of a sandy
aquifer (https://library.seg.org/doi/10.1190/1.2773780) is still often cited as one of the best example of seismoelectric measurements. Given the strength of a hammer source and the efficiency
of the seismoelectric conversion there is no chance of getting an image down to 2000 or 4000 m depth. Having performed a number of these experiments, I see the most promise in the borehole experiments. There are a number of variables that affect the signal
measured and they make the quantitative interpretation of seismoelectric signals very complex. Since this electromagnetic signal is generated from a disturbance in a poroelastic medium we end up with all of the variables from each side. With borehole experiments,
wireline logs can provide a few additional controls and help the interpretation. We have seen a good relationship between co-seismic signals and free-fluid porosity.
I have recently co-authored a chapter in a new book titled : Seismoelectric Exploration : Theory, Experiments and Applications. This chapter looks at field acquisition and the design of appropriate signal buffering to perform seismoelectric experiments.
Most of the researchers that have been active in this field during the last decade have contributed to this work : https://www.bookdepository.com/Seismoelectric-Exploration-Theory-Experiments-Applications-Andr%C3%A9-Revil/9781119127376?ref=grid-view&qid=1567524897768&sr=1-1.
I recently spoke with a few hydrogeologists in Alberta and Saskatchewan who were approached by farmers who wanted to use seismoelectric methods to characterize groundwater. It seems like commercial operators are aggressively
promoting these services. One of the oiginal system was from the UK and was called Ground Flow but I think that there are now multiple new systems on the market (http://groundwaterlocators.com/home/ProductBrochure2.pdf).
These commercial systems often use only one or two pairs of electrodes. This means that the signals that are recorded are a mixture of near-source effects, ground-roll and other seismic modes. I am not convinced by the results that are obtained using this
configuration. It is, however, how they can provide a service at a reasonable cost. A multi-channel seismoelectric survey should cost the same as a seismic survey in terms of logistics (source, receiver + crew). It would be beyond the financial resources of
most farmers looking to drill a well.
If you have specific questions or would like to discuss this subject further I would be happy to help ;)
Best regards,
Christian
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A. Prof. J. Christian Dupuis (Ph. D.)
Chaire de leadership en enseignement en géophysique d’exploration - Osisko Geology and geological engineering Université Laval ------------ |
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