Question

There are two primary methods of drilling cable tool and ________

(a) Rotary

(b) Rotatory

(c) Penetrating

(d) Insertion

This question was posed to me at a job interview.

My question comes from Wells topic in section Irrigation Works, Culverts, Bridges and Wells of Civil Engineering Drawing

Answer 1

The correct choice is (a) Rotary

The explanation: Rotary drilled wells are constructed using a drill bit on the end of a rotating drillstem. Drilling fluid or air is circulated down through the drillstem in the hole and back to the surface to remove cuttings. Rotary drilling rigs operate quickly and can reach depths of over 300 m (1000 ft.), with casing diameters of 10-45 cm (4-18 in.).

Cable tool drilled wells are constructed by lifting and dropping a heavy drill bit in the bore hole. The resulting loose material, mixed with water, is removed using a bailer or sand pump. This method, also called percussion drilling, reaches depths up to 300 m (1000 ft.). Well diameters can range from 10-45 cm (4-18 in.). The drilling rate is typically much slower than for a rotary rig, but when aquifers are low yielding, they may be more easily identified using this method.