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Drilling methods classification

By the nature of rock breaking the applied drilling methods are divided into: mechanical, when drilling tool directly has an effect on rock formation and breaks it and non-mechanical when at breaking there is no direct contact between rock and source of effect (thermal, blasting and others).

Mechanical drilling methods are subdivided into rotary and impact methods (as well as rotary-percussive and percussion-rotary methods). During rotary drilling rock is broken by means of pressed to the bottom tool rotation. Depending on the rock resistance for rotary drilling it is used drilling rock-breaking tool of cutting type (see Drill bit and Bore bit); diamond drilling tool; drag bits breaking rock with shot (see Shot drilling). Impact drilling methods are divided into: cable or percussive drilling (perforating drilling, including in-the-hole, bob-tail, pole-tool etc., when the tool is rotated at the moment between tool bottom strokes); percussion-rotary (in-the-hole pneumatic or hydraulic submersible impact tools, as well as drilling with perforating drills with unrelated rotation etc.), when strokes are made by continuously rotating tool; rotary-percussive, whereby rock breaking drilling tool is under heavy axial pressure and constant contact with rock and breaks rock using rotation along the bottom and repetitive bottom strokes. Downhole rock breaking is done throughout the downhole (full hole drilling) or annular space drilling with core extraction (core drilling). Alteration product extraction could be periodic made with bailer and continuous made with screw conveyor, twisted spear or with gas, liquid or sludge supply to the bottom (see Mud fluid). Sometimes drilling is divided by drilling tool type (auger drilling, pole-tool, diamond, roller drilling etc.); by drilling machine type (perforating, pneumatic rock drills, turbine units etc.), by methods of well construction (directional, pad drilling etc.). Drilling equipment consists mainly of drilling machines (drilling rigs) and drilling rock-breaking tools.

Among non-mechanical methods jet drilling is widely used for quartz-flooded rock shothole drilling, blast hole drilling implementation works are in process.

Drilling was developing and specializing as applied to three main arts: the longest holes (several km) are drilled for oil and gas, less long holes (hundreds of meters) are drilled for solid mineral exploration and prospecting, wells and holes from several meters up to tens of meters are drilled for explosive blasts placing (mainly in mining and construction).