Column drilling of wells in engineering-geological surveys

Column drilling is the drilling of wells,at which a column (core) of unbroken rock is drilled, since 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,that they can drill almost all the rocks with the selection of core. The core is provided with the opportunity to obtain the most reliable information about the geological 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 onremoval from the face of destroyed rock particles, to such methods of drilling wells: dry, with blowing with compressed air, with the use of washing liquid (water or clay).

Column drilling is used in dry drillingdense clayey and rustle rocks. With intensive pacing of the drilling tool, the rate of penetration will be most effective, but the core column is significantly deformed, which leads to distorted information and is unacceptable if engineering wells are being drilled. 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, and a large error (up to 0.5 m) in the delineation of the layers is also possible, therefore, individual rock layers with a thickness of 0.25 and more (up to 0.5 m ) can be omitted (not fixed) during documentation, which is also unacceptable for engineering and geological studies.

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

Column drilling of weathered rocks forThe best preservation of the core is carried out by double core tubes or ejector core projectiles 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 washing method takes into account the volume (l / min) of the liquid supply.