core drilling called drilling in which the drill out a column (core) intact rock, since the destruction of the species occurs only in the ring face.Technological drilling tool made up of bits, coring tube, pipe adapters, drill rods, drill guide tube and gland.Core drilling proposed in 1862 Swiss J. Lesho.
core advantage of the method is that it can be drilled almost all rocks cored.As cores are given the opportunity to obtain the most accurate information about the geological section.Core drilling is used in oil and gas drilling in geological surveying and mapping works.It is indispensable for the exploration of mineral deposits, and is often used for water wells, in geochemical studies and geological engineering surveys.
This type of drilling is classified, depending on the distance from the bottom of destroyed rock particles such drilling methods: dry, with a purge with compressed air, using a washing liquid (water or mud).
Core drilling is used in dry sinking of dense clay and rocks ruhlyakovyh.With vigorous drilling tool reciprocation dry ROP will be most effective, but the column core is deformed significantly, resulting in distorted information and unacceptable in the case of engineering wells being drilled.When the sinking of clay rocks disrupted their natural structure and moisture content due to heating of the core and deformation (twisting or stretching).Drilling dry on weathered rocks also give misleading information about the degree of weathering of rocks is also possible large error (within 0.5 m) in the definition of the boundaries of the layers, so the individual layers of rocks with a capacity of 0.25 or more (up to 0.5 m) can be skipped (not fixed) with documentation, which is also unacceptable in geotechnical studies.
Core drilling with the air purge is used when driving weathered rock, sand-resistant clay and permafrost.The rationale is to use water washing in hard rock and sustainable poluskalnyh rocks.This method provides high quality engineering and geological information.
Core drilling weathered rocks for the best preservation of the core is carried out double column pipes or used ejector Core barrels.Breed soft (up to Category III), the average hardness (category IV -V) and solid (V -VIII) drilled carbide bits.For hard rock (IX - XII) and partially used solid diamond and the shot of the crown.With core drilling, it is important to respect the drilling - razruschayuschy axial load on the tool, the speed of the projectile (turnover / min), and in the process to take into account the amount of washing (L / min) liquid feed.
