Structural drilling is used to obtain cores of lithological strata. The main goal of coring is to obtain a quality sample. One of the methods of coring is the high frequency rotary or the sonic coring method, which proved to be highly efficient and versatile in obtaining continuous and intact samples of rock formations and soil formations. These are obtained with the method’s hydraulic powered drill head fitted with two counter-oriented and balanced eccenters that produce high frequencies. These frequencies are transferred through the drill rods and core barrel to the drill bit in the form of adaptive high frequency waves as well as with the rotation of the drilling tools. When the material is in contact with the drill bit, it pulses; if the material is rock strata, it breaks up and if the material is soil strata, it is pushed out. Because of the use of high frequency waves, the drill rig and tools are appropriately adjusted. The drill tools are made out of high quality steel with special temperature treatment. Depending on the coring of various lithological layers, we distinguish several types of different core barrels: the Aqualock piston sampler, the single wall core barrel sampler, the dual wall core barrel sampler and the sonic wireline system, which is still in the development phase.
The sonic coring method has proved to be able to obtain cores with faster progression, averaging from two to three times faster in comparison to conventional rotary coring methods. Because the method only uses water as mud, it is ideal for structural drilling purposes in environment protected areas.
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