There are a variety of drill mechanisms which can be used to sink a borehole into the ground. Each has its advantages and disadvantages, in terms of the depth to which it can drill, the type of sample returned, the costs involved and penetration rates achieved. There are two basic types of drills: drills which produce rock chips, and drills which produce core samples.
Auger drilling is done with a helical screw which is driven into the ground with rotation; the earth is lifted up the borehole by the blade of the screw. Auger drilling is restricted to generally soft unconsolidated material or weak weathered rock. It is cheap and fast.
Percussion rotary air blast drilling (RAB)
RAB drilling is used most frequently in the mineral exploration industry. (This tool is also known as a Down-the-hole drill.),water bore drilling and blast-hole drilling in mines, as well as for other applications such as engineering, etc.
Air core drilling
Air core drilling and related methods use hardened steel or tungsten blades to bore a hole into unconsolidated ground.
Cable tool drilling
Cable tool rigs are a traditional way of drilling water wells. The majority of large diameter water supply wells, especially deep wells completed in bedrock aquifers, were completed using this drilling method.
Cable tool rigs are simpler and cheaper than similarly sized rotary rigs, although loud and very slow to operate.
Reverse circulation (RC) drilling
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.
Diamond core drilling
Diamond core drilling (exploration diamond drilling) utilizes an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock.
Diamond rigs can also be part of a multi-combination rig. Multi-combination rigs are a dual setup rig capable of operating in either a reverse circulation (RC) and diamond drilling role (though not at the same time).
Direct push rigs
Direct push technology includes several types of drilling rigs and drilling equipment which advances a drill string by pushing or hammering without rotating the drill string.
Hydraulic rotary drilling
Oil well drilling utilises tri-cone roller, carbide embedded, fixed-cutter diamond, or diamond-impregnated drill bits to wear away at the cutting face.
Sonic (vibratory) drilling
A sonic drill head works by sending high frequency resonant vibrations down the drill string to the drill bit, while the operator controls these frequencies to suit the specific conditions of the soil/rock geology.