Rotary drilling is any form of drilling that creates a hole by rotating a bit at the bottom of the hole while using a fluid to remove the cuttings. This method employs either:
- rods under tension — to maintain the hole reasonably straight, with minimal bending or wear on the joints. Heavy drill collars are positioned just above the bit to generate the necessary force for cutting the hole. The weight of these drill collars should be equivalent to the maximum weight required on the bit, ensuring that the drill rods always remain under tension.
- rods in compression – can be used on all sizes of drill rigs and can be used at any angle. This method uses drill head pull-down to create the force on the bit until the depth of the hole is suicient for the weight of the rods to supply this force. At all times some part of the drill rods will be in compression.
Rotary mud drilling
This method is used to drill water bores and monitoring bores in the environmental, mineral exploration, and water well sectors. Drilling mud is used as a drilling luid to stabilise the
hole and remove the cutings.
Rotary mud single-tube reverse circulation drilling
This method is used in the water well sector to drill large-diameter holes. It utilizes:
• reverse circulation of the drilling mud
• an auger, blade, or roller-type bit with no waterways or jets, but a large center hole
• large single-tube drill pipe (can be flanged)
• a water swivel with a large internal diameter
• an open impeller, high solids capacity, centrifugal pump to create sufficient suction to remove the fluid and drilled cuttings from inside the drill string
• a large settling pit for discharged drilling fluid.