Shot Drilling

a type of rotary drilling using shot as an abrasive material. Shot drilling was proposed in the USA in 1899 for driving wells in hard rock. In the USSR it was introduced by V. M. Kreiter (1927) in Transbaikalia. Shot drilling techniques were improved by B. I. Vozdvizhenskii, F. A. Shamshev, and others. The modern technology of core shot drilling was developed between 1945 and 1951 by S. A. Volkov, and later a technique with steel shot was devised by I. A . Ostroushko.

In shot drilling, iron and steel shot 2.5-3.0 mm in size is dropped into the borehole. Under the impact of a flushing liquid jet the shot enters the tip of the drill bit through a slot. As a result of rotation of the drill and of axial pressure, the shot disintegrates the rock on the face of the borehole, drilling out the core. The disintegrated rock, used shot, and metal particles are removed from the bit by a flushing liquid or compressed air. The pressure exerted on the face of a well by cast-iron shot is 2-3 meganewtons per sq m (MN/m²), or 20-30 kilograms-force per sq cm (kgf/cm²), in the working area at the face of the bit; with steel shot, the pressure is up to 4 MN/cm². Annular shot bits with a diameter of 75-150 mm and wall thickness of 10-12 mm are used in shot drilling. Shot drilling is replaced by diamond and hydraulic-percussion drilling only in extremely hard, abrasive rock.