Turbodrill

a hydraulic bottom-hole motor for drilling deep oil or gas wells.

In the USSR the turbodrill invented in 1922 by M. A. Kape-liushnikov, N. A. Kornev, and S. M. Volokh was used in the first phase of turbodrilling, which lasted from 1924 to 1934. In this turbodrill a high-speed single-stage turbine imparts rotation to the bit by means of oil-filled planetary reduction gears. From 1935 to 1950 a turbodrill without reduction gears and with a multistage turbiné was used. In this multistage turbodrill, which was invented by P. P. Shumilov, R. A. Ioannesian, E. I. Tagiev, and M. T. Gusman, the shaft directly rotates the bit. The total pressure drop in the drill is divided among turbine stages, but the torque on the shaft is determined by the sum of the torques developed by each stage.

The multistage turbodrill is an open-type machine with rubber-metal radial and axial bearings, which are cooled and lubricated by a drilling fluid called drilling mud. To obtain maximum efficiency, the turbine blades are contoured, so that the shock-free flow past the blades corresponds to the turbine’s maximum power. The turbines are unit cast and have a total of up to 120 turbine stages. Turbodrills for deep wells have a diameter of 164, 172, 195, 215, 240, or 280 mm; the rotation rate of the turbine shaft ranges from 150 to 800–1,000 rpm. The working torque on the turbine shaft depends on the drill’s diameter and ranges from 1 to 5–6 kilonewton meters (1 newton meter = 0.1 kilogram-force meter).

Since 1950, tandem turbodrills, in which 2–3 turbine sections with a total of 300–450 stages are connected in series, have been used in order to increase the torque on the shaft. The use of tandem turbodrills has made it possible both to increase the torque and to reduce the rotation rate of the turbine shaft to 300–450 rpm; such a reduction in the rotation rate provides for more efficient operation of the chopping bits. In tandem turbodrills an axial ball bearing is dropped down a special spindle that is attached to the lower section of the turbodrill. The spindle also has radial bearings and a stuffing box, which permits the use of jet bits. Hy-dromatic braking stages, which make possible drilling at 150–250 rpm, were introduced in 1970 in order to effect a further reduction in the rotation rate of the turbine shaft.

Turbodrills with independent tandem suspension and damping devices were introduced in the early 1970’s. These drills need not be repaired as often as ordinary tandem turbodrills and subject the chopping bits to less wear, owing to decreased vibration of the drill string. Turbodrills with a split flow in the lower section have been employed in order to use jet bits without additional charging of the mud pumps. In these turbodrills the pressure drop in the lower section is equal to the pressure drop in the jet-bit fittings. In this case, the lower section of the turbodrill is driven by the mud supplied to the well.

In exploratory drilling, a removable core barrel is placed in the hollow shaft of a turbodrill for core sampling. A turbodrill with a rotating drill pipe is used to prevent curvature of the borehole.

As of 1975, research was being conducted on the development of a combined turbodrill-chopping bit tool that would considerably increase the drilling speed.