The term diamond core drilling originally comes from the ‘diamond bit’ drill that is used in this specific process. This type of drill is made from a group of small, industrial grade diamonds, which are set into a metallic, soft matrix. As you drill into the ground, the matrix wears away and exposes more diamonds.
The diamond bit is the attached to a drill rod, this rod measures to more or less 10 feet in length.
You can also attach more sections of pipe to the top of the drill rod, which will allow for greater depths to be drilled if need be. Within a drill rod, a core tube is attached to a cable by a latch.
The core tube is lifted up to the surface using the cable to allow for the removal of the solid core.
Rotary and Wire Line diamond Drilling
When it comes to diamond drilling, there are two primary types, Wire line and rotary drilling.
Wire line drilling is used for more solid core sampling whereas rotary drilling is used primarily for bore hole drilling.
Five standard tube sizes that are associated with wire line drilling:
AQ, BQ, NQ, HQ and PQ.
The drill size that you would use for wireline drilling will depend on the desired core diameter and the depth of drilling.
For example, if you need a wider tube diameter, it will require much more power to drive the drilling.
The core extraction
In order to extract core, the drill rod will rotate the diamond bit and spin in into the ground.
As you bore into the rock with the drill bit, there is solid rock that is taken into the round opening at the end of the bit, into the core tube and can only then be recovered at the surface as it all piles up.
Once you recover the core at the surface, it is broken along the natural fractures and stored in core trays to be analyzed. Your standard core tray is able to hold up to 10 feet of core.
In order to keep the drill going through the rock as smoothly as possible, the drill needs to be well lubricated with water, which will prevent sticking or overheating.
For the best core extraction, the driller should listen carefully to the drill to evaluate subsurface conditions. To ensure that drilling remains efficient, the pressure, rotation and water circulation needs to be strictly monitored at all times.
Often, when drilling in highly fractured zones, overheating may occur because of a stuck bit. This problem can usually be counteracted by the injection of sawdust or mud to plug fractures in the rock.
Buenti Drilling is a South African registered drilling service company that provides specialized drilling solutions. Visit our website on www.buentidrilling.co.za for more information.