Percussion Drilling

Percussion drilling is similar to the early cable drilling done before the 1920s. A hammer unit is driven by compressed air giving a series of short, rapid blows to the drill rods or bit, and at the same time applies a rotating motion. These drills may vary in size from small hand held units to large truck mounted rigs capable of drilling large diameter holes. Drill cuttings are flushed to the surface by a stream of compressed air. There are two types of this kind of drilling: down the hole or top hammer percussion drilling rigs. The down the hole hammer unit is lowered into a hole that is attached to the lower end of the drill rods to operate a non coring drill bit, which is sometimes known as a “button bit.” It can drill depths of around 100 to 150 metres. Drill cuttings are pushed to the surface by a stream of compressed air. Track mounted drilling rigs, like little tanks, can negotiate slopes of up to thirty degrees and can drill on slopes in excess of twenty-five degrees, making the access to the exploration site easier than taking larger vehicles up these inclines.

The hammer unit for top drilling is also powered by compressed air and uses non coring drill bits. This type of system is usually smaller than down-the-hole drills and they are used for holes up to ten centimetres in diameter and drill up to depths of 100 metres. This type of drilling rig is only used to drill a maximum of twenty metres. Most use light portable air compressors, which restricts the drilling depth to a few metres above the water table. This is due to the compressed air being too light to blow back the heavy, wet, sludge-coated rock chips to the surface. Mounted on either light trucks or tractors, this type of drill is easy to air lift into an exploration drilling site.

Evidence suggests that percussion drilling can increase penetration in hard-rock formations, create better and larger cuttings of the rock for analysis, and lower drilling costs. However, the oil and gas industry have not fully embraced this type of drilling. It is because rock fragmentations increase safety risks. In addition, further research needs to be conducted on the actual benefits of using percussion drilling versus other methods.