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PostPosted: Mon Apr 02, 2012 7:44 am 
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Joined: Mon Mar 26, 2012 5:37 pm
Posts: 1
I am a geophysicist more experienced in Electromagnetic surveys than GPR surveys. I have the following problem and I am wondering if GPR will work. I am working on a oil storage site that has been active since 1950. The site is located at the coast and is located 5m above mean sea level. We have a high rainfall in the area (>1000mm a year), thus all the salt has been leached from the area. The geology is well sorted sand down to about 15 meters. At 15 meters we encounter a clay layer about 6m thick. My area of interest is only the top 2 meters. The water table is located at ± 1.75m below ground level. I have been using the Geonics EM31 system to measure the ground conductivity/resistivity. I know from the work that the resistivity of the sand is approximately 100 ohm-m. The ground water is badly contaminated and acidic (thus conductive).

We are trying to detect fresh hydrocarbon spills along the buried pipelines. (The pipes have reached the end of their design life) A fresh hydrocarbon spill has nearly an infinite resistivity and floats on top of the water. (Once hydrocarbons bio-degrade they become as conductive as sea-water)

I suspect that if we use GPR that we will get a reflection from the pipe and nothing near the pipe (the pipes are buried to 1.5m depth) if there is no hydrocarbon spill, and a pipe reflection and a flat reflector if we do have a spill, as the hydrocarbons would be floating on top of the water. Am I correct with my assumptions, or am I showing my ignorance again.

Would we be able to use the GPR to track the movement of these fresh hydrocarbons when we start dewatering the area as well.

I have access to a Mala GPR with a 50, 100 and 250 mHz antennas

Regards

Leon Engelbrecht


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PostPosted: Tue Apr 03, 2012 5:09 am 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
10mS/m sounds pretty tough to me, but if you already got the equipment why don't you give it a try?
Regards,

_________________
Reinaldo Alvarez Cabrera
Geoscanners AB
Sweden
http://www.geoscanners.com


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PostPosted: Sun Apr 22, 2012 8:49 pm 
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Joined: Sun Oct 30, 2011 7:17 pm
Posts: 6
Hi Leon,
I think that with GPR can be established a leakage of hydrocarbons.
You can make measurements with 250 MHz antenna.
I recommend resolution dx<2.5 cm and DT <0.4 nanoseconds, number of samples> 400.
You can share a single record of the measurements here in the forum or send me data an e-mail
info@gpr-geosolutions.eu
We can check whether it is registered representation of leaked hydrocarbons.
Here I show an example from my practice by chemical plant.
Other examples you can see of the link here in the forum:
viewtopic.php?f=29&t=1955
Regards,
V.V.


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