rotary drilling[′rōd·ə·rē ′dril·iŋ]
a drilling method in which the drill bit is rotated in the well by a drilling column driven from a rotary table on the surface. Rotary drilling is used for drilling blast holes and test and producing wells.
The rotary table is rotated by a horizontal shaft driven by an engine, such as an electric motor, gas turbine, or internal-combustion engine. Weighted drill pipes, designed to put added weight on the bit during drilling, are installed between the drill pipes and the bit. A kelly (the square pipe at the top of the drilling column) passes through the rotary table and is connected to a swivel, through which drilling fluid is supplied from a mud pump to the drilling column by means of a pressure hose. Rotary drilling is sometimes accompanied by blowing gas or air through the bottom of the well.
After the initial portion of the well is drilled from the surface, the first casing column (string) is lowered; this casing covers the weak, unstable rock and seals off the upper water-bearing horizons. For this purpose, casing cement is pumped into the annular space between the casing and the wall of the well. The drilling is continued with a smaller-diameter bit (one that can pass within the casing) to the designated depth; another casing string—the intermediate string or, if it is the last string, the producing string—is lowered into the well.
Rotary drilling was first used in Louisiana (USA) in the late 1880’s; it was first used in Russia in Groznyï in 1902. The deepest well drilled by the rotary method is a 9,583-m well in Oklahoma (USA; 1974).
R. A. IOANNESIAN