Saturday, September 22, 2007

"Bore"hole Surveying

For those uninitiated, who are wondering about the exciting, thrill-a-minute, action-packed life of a geophysicist working in the subarctic, I offer this photo. I suggest that the image portrays the drudgery of the hurry-up-and-wait life that accompanies borehole surveys. The large spool in the center is the kevlar-sheathed, three conductor, 1.2km long cable that we use to lower the probes down the 3 inch diameter hole (you can see the cable heading off diagonally up to the hole casing. The poor sap sitting in the chair is waiting for the receiver to finish collecting the data before lowering the probe 10 meters to the next station. It takes a couple of minutes to read the Z-component, and about 5 minutes or more for the XY. The average depth of holes in Raglan is probably 800 to 850 meters, and we usually survey half the length of the. Meaning that surveying a hole can take anywhere from 6 to 24 hours or more, depending on what happens to go wrong on a particular survey, and if the whole has to be read in more than one section because of risk of collapse. This type of survey has been aptly nicknamed "snorehole".
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