Column drilling of wells in engineering-geological surveys

Column drilling is the drilling of wells, in which a column (core) of unbroken rock is drilled, as the destruction of rocks occurs only along the face ring. The technological drilling tool is made up of a crown, a core pipe, pipe adapters, drill rods, a guide pipe and a drilling gland. Column drilling was proposed in 1862 by the Swiss J. Leschot.

The advantage of the column method is that it can drill almost all the rocks with core sampling. According to the core, it is possible to obtain the most reliable information about the geologic section. Column drilling is used in oil and gas drilling, geological survey and mapping. It is indispensable for prospecting and exploration of mineral deposits, and is also often used for hydrogeological wells, for geochemical exploration and for engineering and geological surveys.

This type of drilling is classified, depending on the removal from the face of the destroyed rock particles, on such methods of drilling wells: dry, with blowing with compressed air, using a washing liquid (water or a clay solution).

Column dry drilling is used for the penetration of dense clayey and rustle rocks. With intensive pacing of the drilling tool, the rate of penetration will be most effective, but the core column will be significantly deformed, which leads to distorted information and is unacceptable if drilling of engineering wells is conducted. When driving through clayey rocks, their natural structure and humidity are disturbed due to core heating and its deformation (twisting or stretching). Drilling on dry weathered rocks will also give a distorted information on the degree of weathering of these rocks, it is also possible a large error (within 0.5 m) in determining the boundaries of the layers, therefore, separate rock layers with a thickness of 0.25 and more (up to 0.5 m ) Can be omitted (not fixed) when documenting, which is also unacceptable for engineering-geological studies.

Column drilling with air blowing is used for the penetration of weathered rocky, stable sandy-clay and frozen rocks. Rational application will be with washing water in strong rocky and in stable semi-rocky rocks. This method provides good quality of engineering-geological information.

The columnar drilling of weathered rocks for the best preservation of the core is carried out by double core tubes or ejector-type shells are used. Soft breeds (up to category III), medium hardness (categories IV-V) and hard (V -VIII) buryat with hard-alloy crowns. For hard rocks (IX - XII) and partially solid, use diamond and shot crowns. In core drilling, it is important to comply with the drilling mode - the axial load on the breaking tool, the speed of the projectile (rpm), and the flushing method takes into account the volume (l / min) of the liquid supply.