| |
U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
  
A Sample-Freezing Drive Shoe for a Wireline-Piston Core Sampler
by
Fred Murphy (U.S. Geological Survey, Menlo Park, Calif.) and W.N.
Herkelrath (U.S. Geological Survey, Menlo Park, Calif.)
Abstract
The loss of fluids and sample during retrieval of cores of noncohesive
sediments results in incorrect measures of fluid distributions and a less-than-ideal
measure of the stratigraphic position of the sample. In order to reduce
these errors, a hollow drive shoe was developed that allows freezing in
place the lowest 75 millimeters of a 48-millimeter-diameter, 1.5-meter-long
sediment sample taken using a commercial wireline piston-core sampler. The
end of the core is frozen by piping liquid carbon dioxide at ambient temperature
through a steel tube from a bottle at the land surface to the drive shoe
where it evaporates and expands, cooling the interior surface of the shoe
to about -70 C°. The freezing process takes about 10 minutes. This device
was used to collect samples for a study of oil-water-air distributions in
unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota.
Before freezing was employed, samples of sandy sediments from near the water
table sometimes flowed out of the core barrel as the sampler was withdrawn.
Freezing the bottom of the core ensured the retention of all material that
entered the core barrel and lessened the redistribution of fluids within
the core.
|
