Borehole Drilling methods variety from simple digging with hand tools to high-speed drilling using sophisticated equipment. The most commonly used Borehole Drilling Methods are briefly described below for the general information of readers who do not have a drilling background.
BOREHOLE DRILLING METHODS AND THEIR APPLICATIONS
- Cable tool drilling
Cable tool drilling also known as percussion drilling, is the oldest drilling method. This involves lifting and reducing a string of solid steel drilling tools suspended from a wire rope to hit the bottom of the hole. This process drives the cutting bit, fracturing or pulverising the formation.
In cable tool or percussion drilling there are three major operations:
- Drilling the hole by crushing the rock or clay by the impact of the drill bit.
- Removing the cuttings with a bailer as cuttings accumulate in the hole.
- Forcing the bore casing down into the hole as the drilling proceeds.
Because of the relatively low initial cost and simplicity of equipment used, the cost per unit drilled is relatively low. However, the technique is slow, and when the increased cost of labour is considered, there is usually little advantage over faster rotary Borehole Drilling Methods when drilling new bores.
- Rotary air drilling
The rotary air is one of the Borehole Drilling Methods used to drill holes in joined formations such as sandstone or shales that are self-supporting.
The cuttings that this process produces are cleared by circulating air, which is resulting from a compressor and fed down the drill pipe to emerge through a bit.
- Down-hole hammer method
Down-hole hammer drilling is the fastest method of penetrating hard rock. This method is mostly used for hard rock drilling and to enable water bores to be established from fractured hard rock aquifers.
However, it is not operative for drilling loose, unconsolidated materials.
- Rotary mud drilling
Rotary mud drilling uses drilling mud (mixes of water, bentonite clays, polymers, and additives) as the circulation medium. In the rotary mud system, drilling mud is pumped down through the drill pipe and out through nozzles in the bit.
Such Borehole Drilling Methods are useful for drilling operations in soft, deep bores, and pressure bores.
- Sonic drilling
Sonic drilling is a one of the newest techniques of Borehole Drilling Methods. This technique is relatively continuous and uninterrupted geological samples are obtained without the use of drilling fluids or other potential contaminants.
The technique is best suited to drilling unconsolidated formations, but its depth capability is limited by current technology.