Hydraulic Rotary Boring Method:
This method is generally called rotary boring method. This method can be successfully used for rock as well as unconsolidated formation. The method is therefore used for water well as well as oil well drilling. Oil wells are generally very deep and this method is well suited for them because unlike other methods the drilling rate is not dependent on the depth of the hole.
In this method drilling is done by means of rotating bits attached to lower end of hallow steel pipe. The steel pipe is attached to a square section of a steel rod at the top which is called kelly. Kelly fits in a rotating table at the surface. The rotating table is rotated by power. The powdered rock and cuttings are removed by continuous circulation of drilling fluid.
The hydraulic rotary drilling rig consists of a derrick or mast, a rotating table, a pump for injecting drilling mud, a hoist and an engine. The drill pipes are seamless steel tubings generally available in 6 m lengths. The external diameter of the pipes ranges from 6 to 12 cm.
Generally adequate size of pipe is used because well drilling requires large quantity of drilling fluid in circulation. The drilling bits attached to the lower end of the drill pipe is provided with short nozzles to direct the jets of drilling fluid down the faces of the blades ofg drilling bit. Figure 18.8 shows schematic diagram of rotary boring method.