I may as well learn something whilst we have the great man Esh in our presence.... RAB (Rotary Air Blast)
Rotary air blast (RAB) drilling is one of the fastest, cheapest and easiest ways for miners to obtain a sample from their resource. In RAB operation, a spinning tungsten drill bit forces its way down through the ore, blowing fragments back up to the surface for examination. RAB drilling is generally used for relatively shallow depths up to 25m, or to remove soft rock on top of the deposit. RAB drilling is used primarily for mineral exploration, water bore drilling and blast-hole drilling in mines, as well as for other applications such as engineering. The use of multiple high-powered air compressors, ensures drilling of a deeper hole up to ~1250m due to higher air pressure which pushes all rock cuttings and any water to the surface.
Percussion Drilling
Air percussive drilling is used when the layers of rock are quite hard. Instead of a rotating drill bit, in air percussion, a hammer bit strikes the rock, forcing its way through to cut samples from the ore which are then blown back up the drill hole in the same way as in an air rotary operation.
Mud Rotary
Mud rotary is similar to the rotary air drilling method in many respects. The only major difference is that water, not air, is the medium by which fragments travel back to the surface. Mixing water with the cuttings yields a "slurry", upon which geologists perform analysis after removal.
Diamond Core Drilling
A hollow, cylindrical diamond encrusted drill bit rotates at high speed, cutting through the ore and extracting a solid sample that travels up through the drill pipe. This gives an unbiased estimate of the deposit, because no other particles have a chance to contaminate the ore on its journey up the drill hole.
Diamond core drilling (Exploration diamond drilling) utilises an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock.
The diamonds used are fine to microfine industrial grade diamonds. They are set within a matrix of varying hardness, from brass to high-grade steel. Matrix hardness, diamond size and dosing can be varied according to the rock which must be cut. Holes within the bit allow water to be delivered to the cutting face. This provides three essential functions; lubrication, cooling, and removal of drill cuttings from the hole.
Reverse Circulation
Reverse Circulation (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 utilises much larger rigs and machinery and depths of up to 500 metres are routinely achieved. RC drilling ideally produces dry rock chips, as large air compressors dry the rock out ahead of the advancing drill bit. RC drilling is slower but achieves better penetration than RAB or air core drilling.
Geotechnical Drilling
The drilling of holes for gathering and evaluating earth materials in order to design and monitor construction projects. Geotechnical data are required for the accurate, safe and efficient design and construction of buildings, bridges, highways, dams, and mining sites. The data is derived from analysis of soil and rock samples obtained by drilling.
Air Core Drilling
Air core drilling and related methods use hardened steel or tungsten blades to bore a hole into unconsolidated ground. Air core drilling can occasionally produce small chunks of cored rock spaa. This method of drilling is used to drill the weathered regolith, as the drill rig and steel or tungsten blades cannot penetrate fresh rock. Where possible, air core drilling is preferred over RAB drilling as it provides a more representative sample. Air core drilling can achieve depths approaching 300 meters in good conditions. As the cuttings are removed inside the rods and are less prone to contamination compared to conventional drilling where the cuttings pass to the surface via outside return between the outside of the drill rob and the walls of the hole.
Cable Tool Rig
Cable tool rigs are a traditional way of drilling water wells internationally and in the United States. The majority of large diameter water supply wells, especially deep wells completed in bedrock aquifers, were completed using this drilling method. Although this drilling method has largely been supplanted in recent years by other, faster drilling techniques, it is still the most practicable drilling method for large diameter, deep bedrock wells, and is widespread use for small rural water supply wells. The impact of the drill bit fractures the rock and in many shale rock situations increases the water flow into a well over rotary.
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