Coring Procedures in Rock

Basic techniques of air-rotary coring are almost identical to techniques of hydraulic-rotary coring: air, rather than a drilling mud, is circulated to lift and carry the drill cuttings out of the hole, and, at the same time, cool the bit. All working components are the same, except the mud pump is replaced with an air compressor. In air-rotary coring, the same hydraulic-rotary problems of loss of circulation can occur, and, if the additives described in the following section are not adequate to stop lost circulation, more positive measures of cementing and casing out those zones may be needed.

The Water Resources Division of the U.S. Geological Survey sometimes contracts for air-rotary coring in possibly contaminated or known contaminated lithologic environments. Special coring procedures are used, such as grouted insurface casing; using drive-core or other samplers for obtaining cores of unconsolidated interbedded sediments; and using only wire-line-coring methods, to prevent smearing or downward contamination of the hole that could occur if conventional coring (tripping in and out of the hole) methods were used. For discussions of these precautionary methods, see "Hydrology of the Solid-Waste Burial Ground, as Related to the Potential Migration of Radionuclides," (Burgus and Maestas, 1975).

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