Calculation of Ball Jet Drilling Processes in the Optimal Mode of Rock Destruction

This article is devoted to the study of ball jet drilling method, which in the future may increase the mechanical speed and driving of the bit during drilling of solid rocks for various purposes. Ball jet method of drilling wells is to destroy rocks by strikes of metal balls continuously circulating in the near wellbore area by means of a jet system, laid to the basis of ball jet – ejector drilling unit. The main advantages of ball jet drilling include simplicity of drill construction, absence of necessity in the bit rotation and creation of axial load on it. Destruction of rocks by ball strikes can occur in a variety of modes, the most effective of which is the optimal (volumetric), accompanied by the formation of a large chipping funnel. The aim of this work is to develop methods for calculating ball jet drilling processes in the optimal mode of rock destruction. Method of calculation is based on the results obtained by the authors of theoretical and experimental studies, as well as some provisions of the predecessors. It allows us to determine the optimal geometric parameters of the drilling units, rational technological parameters of drilling mode, and also to make the choice of pumping equipment for specific geological and technical conditions. In the proposed calculation method the values of the washing liquid flow are limited in the presence of intervals intent to erosion of the borehole walls, the ejection rate of the jet device and the pressure drop on the nozzle to prevent its intense wear at the expiration of the drilling fluid.