Electrodrill

a bottom-hole drilling machine that has a downhole electric motor and that is used to drill deep oil or gas wells. In 1899, the Russian engineer V. I. Delov proposed the idea of a percussion electrodrill. In the USSR, A. P. Ostrovskii and N. V. Aleksandrov built and used the world’s first rotary electrodrill between 1938 and 1940; the drill was lowered into a borehole on drill pipes.

An electrodrill consists of an oil-filled electric motor and a drive rod. The power rating of the three-phase motor depends on the drill diameter and ranges from 75 to 240 kilowatts. Reduction gears, which are installed between the motor and the drive rod, are used to increase the drill torque. The reduction gears reduce the drilling speed to 350, 220, 150, or 70 rpm. The drilling speed of an electrodrill without reduction gears is 455–685 rpm. The length of electrodrills ranges from 12 to 16 m; the outside diameter, from 164 to 290 mm.

In drilling, an electrodrill is attached to the lower end of a drilling column. The drill imparts rotation to a bit. Electric power is supplied to the drill through a cable that is installed in sections in drill pipes. When the drill pipes are screwed together, the cable sections are joined by means of special contacts. Electric power is supplied to the cable through a current collector whose sliding contacts make it possible to rotate the drilling column. When an angle hole or a horizontal branch hole is drilled, special down-hole equipment, including telemetric equipment, is used for the continuous monitoring of the borehole’s spatial position and of the drilling parameters. When an electrodrill is used, cuttings are removed from the bottom of a borehole by means of drilling mud, air, or gas.

In the USSR, electrodrills have been used to drill more than 300,000 m of wells, that is, more than 2 percent of the drilling in terms of total depth. Owing to the presence of communications lines extending to the bottom of a borehole, the use of electrodrills is especially valuable for the study of drilling operations.