Shelby Tube Samples

Sometimes, undisturbed, Shelby-tube samples may be required from a hydraulic-rotary drilled hole. The use of the Shelby-tube sampler is restricted, however, because the sampler cannot be washed in due to the ball-check valve in the sampler. The ball-check valve is needed in the head assembly of the sampler to retain the sample in the tube upon withdrawal of the sampler from the hole. To sample using the Shelby-tube sampler first spot the bottom several feet of the hole with the high-gel strength drilling mud. If any caving or bridging is anticipated when the string of drill pipe is to be removed from the hole, follow the procedure of circulating out of the hole as described on page 24. Otherwise, caved material will feed up into the sampler, resulting in bad or total contamination of the sample. After the Shelby-tube sampler has been returned to the surface, the upper few inches of contaminated material (filter cake, etc.) can be removed from the tube before sealing and waxing the ends of the Shelby tube.

Procedures of Sampling in Cable-Tool Percussion Drilling

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