What is reverse circulation drilling?
10 Nov 2014
Reverse circulation (RC) drilling is used to collect rock samples quickly and efficiently using a large rotary drill and air compressor. The high speed and lower cost per metre of RC drilling makes it ideal for obtaining mineral samples in the early phases of an exploration project.
The RC drilling process comprises rods with inner and outer tubes that bring rock samples to the surface using a pneumatic reciprocating piston known as a hammer driving a tungsten-steel drill bit.
Reverse circulation is achieved by blowing air down the rod with differential pressure creating airlift that brings water and drill cuttings up the inner tube inside the rod. Once the drill cuttings reach the deflector box at the top of the drill string, they move through a sample hose that is attached to the top of 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. Each sample bag is marked with the drilling depth. Samples are commonly collected at one metre intervals.
RC drill rigs are capable of drilling to depths of greater than 800 metres below the surface, however commonly only required to reach depths of 300m to 400m. The drill rigs come in wheel or track-mounted options with the ability to climb hilly regions of the countryside.
Once samples are logged by a geologist, they are collected and sent to a laboratory to determine mineral composition.
Figure 1. Reverse circulation drill rig
RC Drilling – www.rcdrilling.com
Boart Longyear – www.boartlongyear.com
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