EXPERIMENTAL RESEARCHES REGARDING THE DRILLING PROCESS OF THE MINE SHAFTS BY MEANS OF SURFACE INSTALLATIONS

ABSTRACT. In order to realize in economic conditions aerating and exploitation mine shafts of coal, iron ore, bituminous schist and petroleum from depleted reservoirs, were built in Romania drilling rigs for large diameters ranging between 72 inches (1.83 m) and 245 inches (6.223 m). All these are using the technology of rotary drilling with hydrostatic transmission, drill column and with reverse circulation of drilling fluid and airlift. In the paper the determinant factors of the drilling process of large diameter and the accompanying phenomena, which characterize its specific dynamics are presented. The technological and technical problems (the last ones concerning the hydrostatic driving system, durability and implicitly construction of bit and drill pipe), which appeared in practice of the exploitation of these drilling rigs, imposed an experimental approach of drilling process in field conditions. In this way, in the paper are shown the experiment conditions in case of drilling a mine shaft having a diameter of 142.5 inches (3.62 m) and the methodological aspects of experimental electrical strain-gauges investigation by using some stress captors designed with this end in view, a collector with sliding contacts having unusual sizes adjusted to type-size of the drill pipe of 10 inches and a recording appliance in real-time. Also, some recordings are presented and pointed out by means of some diagrams and empirical formulas, a series of dependences among the physical sizes which define the drilling process: the weight on bit, the drilling torque, the rotational speed and the power and moment of friction between the drilling column and the drilling fluid. The obtained results have been already used in the practice of big holes drilling, for improving the drill pipe construction, in design o