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24/08/16
12:31
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Originally posted by joebop
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Just a quick word on the deviation.
After the hole is drilled a tool is run down the hole to give to record a number of measurements, including one to measure the deviation. After drilling so many holes now, they would have a fair idea of how straight they are going. I would imagine that MOD would have a certain tolerance for deviation in the holes, so maybe there might be grounds to haggle on the price of the redrill if they go ahead with one.
To check for deviation as you drill would require all the drill string to be pulled and, run the verticality tool, pull that out and then reinsert the drill string. The deeper you go, this takes considerably longer as the drill string gets heavier and slower to pull. This could easily add up to 24 hours to a hole over this depth.
Hindsight is useful, but the costs would add up if you were to check it on each hole.
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Downhole survey single shot ( the cheapest ) takes about 20mins in a 500m hole and is usually (should be) performed every 30 or 50m - it can be mag affected but will give an honest dip reading.