Roller-Bit Drilling

a drilling method that uses a roller bit (seeDRILL BIT). The method was first used in the USA in the 1920’s and in the USSR in the 1930’s to drill oil and gas wells.

In roller-bit drilling, rock is cut by steel or hard-alloy teeth projecting from rolling cutters, which rotate on the drill-bit bearings. In turn, the drill bit rotates at a rate of 60–600 rpm and presses against the bottom hole with a high axial force of 500–2,000 kg per cm of the bit diameter. The teeth of the rolling cutters roll over the bottom hole and, owing to the large stresses that develop in the area of contact between the teeth and the rock, cut the rock by crushing and chipping. As the hardness of the rock increases, the rotation rate decreases and the axial force increases. The rock that is cut at the bottom of a well is removed to the surface by washing, blowing, or a combination of washing and blowing.

Roller-bit drilling is carried out by stationary, self-propelled, or mobile drilling rigs using the rotary method (seeROTARY DRILLING) or the turbine method (seeTURBODRILLING) of transmitting torque to the roller bit. Less often, electrodrills are used.

Roller-bit drilling is used to drill deep (up to several kilometers in depth) exploratory, oil, and gas wells. It is also used to drill blastholes in underground and open-pit mining, to bore raises in underground mines, and to sink mine shafts.

The efficiency of roller-bit drilling is evaluated on the basis of the shift or monthly drilling rate per rig and the volume of drilling with a roller bit before the bit is replaced. Depending on the hardness of the rock and on the field of application, the cited indicators vary over a wide range. As of 1978, roller-bit drilling was superior to other drilling methods in performance.