Auger drilling is a method that uses a helical screw-shaped drill bit, known as an auger, to bore holes into the ground. As the auger rotates, its spiral blades (called “flights”) cut into the soil and mechanically transport the excavated material to the surface, keeping the borehole open and minimizing the risk of collapse. Let’s explore the various types of Auger drilling.
Continuous light augers are driven by a top-drive rotary machine with adequate torque rating. In deep, small diameter holes, continuous light augers are supported by the hole. Cuttings are carried to the surface on the helical lights.
Hollow augers are continuous light augers that have a hollow center tube. They are normally used with a plug bit held in place by a secondary internal rod string, or simply by friction.
More recently, wireline (or cable recovery) hollow auger systems have been developed, allowing recovery of the plug bit and insertion of sampling tools, via a wireline and overshot system identical to the wireline diamond coring system.
Hollow augers are operated as for conventional continuous light augers to the depth of interest. At that point the central plug bit is withdrawn (or the plug driven out).
Sampling methods are then used to suit the geological conditions. This may be either an SPT drive sampler, or a core barrel may be run inside the hollow auger using a conventional internal rod string or a wireline system.
A further advantage of the hollow auger system is that when hard rock (which could not be drilled with conventional auger) is encountered, it is relatively simple to convert to diamond coring down through the hollow rod auger. Water sampling can also be conducted in the auger string, or using small-diameter wells set through the inside of the string.
Short light and plate augers: Short light and plate augers are loaded with cuttings and then pulled out of the hole. At the surface, the cuttings are spun of the auger. Short light and bucket augers are used for large diameter holes.
Bucket augers: The cuttings are picked up in the bucket, hoisted to the surface and dumped through the hinged bottom of the bucket. Extensions are added as the hole gets deeper.
