Based on theoretical and experimental investigations, the following results have been obtained:
– the possibility of increasing pellet impact drilling efficiency in tough rocks by accurate technological process coordination and adequate construction of tool string elements has been proved;
– for the first time high-speed photography (3600 shots per second) has been carried out to explore rapid processes and to develop a physical model of drilling;
– functional correlation between drilling mode efficiency and the pellet diameter, the height of operating windows, the mass of pellet portion, the nozzle diameter, the distance between the nozzle outlet and the top slice of operating windows, the distance between tool string and hole bottom, the length of the mixing chamber, the cone angle of arrestor, mud flow rate, the opening angle of a diffuser have been assessed.
Pellet impact drilling method being considered prospective, the following theoretical and experimental researches are further required:
– research on methods to maintain optimal distance between pellet impact tool string and bottom hole;
– development of runout decrease methods;
– design of detector to determine hydrodynamic parameters of two-phase flow;
– design of catching-charging device which can replace worn out pellets, run in and pull out pellets to reduce round-trip time.
