Reverse Circulation Drilling-RC

RC drilling is similar to air core drilling, in that the drill cuttings are returned to surface inside the rods. The drilling mechanism is a pneumatic reciprocating piston known as a hammer driving a tungsten-steel drill bit. RC drilling utilizes much larger rigs and machinery and depths of up to 500 meters are routinely achieved. RC drilling ideally produces dry rock chips, as large air compressors are used to dry the rock out ahead of the advancing drill bit. RC drilling is slower and costlier but achieves a better sample than RAB or air core drilling; it is also faster and cheaper than diamond coring and is thus preferred for most initial mineral exploration programs.

Reverse circulation is achieved by blowing air down the rods, the differential pressure at the bit face creating air lift of the water and cuttings up the outside of the rods while the sample is blown up the inner tube which is inside each rod. It reaches a deflector at the top of the hole, then moves through a sample hose which is attached to the top of a hopper called the cyclone. The drill cuttings travel around the inside of the cyclone until they fall through an opening at the bottom and are collected in a sample bag (generally at one meter intervals).

Although RC drilling utilises air for drilling, water is also used, mainly to reduce dust but also when collaring a new hole. A drilling mud or foam is mixed with water and pumped into the rod string, down the hole. This helps to aerate any water in the hole making it easier for the compressed air to dry out the sample at the bit face.

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Last modified: 11/21/07