KazDuCoDrilling

Water well drilling is a complex technological process that could be divided into stages with the most important stage being drilling a shaft itself. In general, well drilling can be performed by a large number of methods that can be classified based on three attributes: according to a manner in which rock is crashed, by a character of rock disintegration and by a type of used bit.

1. By method of rock crushing, drilling may be subdivided into:
- mechanical (percussion or rotary methods);
- non-mechanical (hydraulic, explosive, thermal, electro physical);

2. by the type of disintegration:
- noncore drilling
- core drilling

3. by the type of used bit:
- cutting-shearing action;
- chipping crushing action;
- cutting-grinding action;

Rotary drilling in its turn, may be divided into rotary drilling or down hole drilling. Downhole drilling is carried out using electric motor drill or turbo drill. This classification is true for all types of drilling including water well drilling, oil and gas drilling and exploration drilling.
Hydraulic rotary drilling is a method most often used for water drilling. Chipping crushing action bit is used while the teeth of a bit are constantly flushed with drilling fluid.
There are two types of water wells distinguished by well design and by drilling method: filter (sand) wells and artesian wells depending upon depth and mode of occurrence of the aquifer.

Water supply from sand horizon have two significant disadvantages - short life time (up to 10 years) and relatively small flow rate (up to 500 liters per hour). Water supply of such type is usually feasible for small country sites with modest water demands. Capacity and life time of such water well depend upon sand fraction of sand horizon and thickness of this horizon, which is unfortunately impossible to determine in advance. Therefore successful water drilling on the neighboring site does guarantee the same result on your site.

Water well drilling in limestone horizon (artesian) greatly varies by depth depending on the area of drilling. However, the undoubtable advantage is lack of the risk of drilling of so called "dry well". This advantage and two others - high flow rate (from 2 cubic meters per hour) and long life time (25 years and more depending upon well design) set artesian well upon from the sand ones. Although due to the depth of limestone occurrence, drilling of such wells cost much more than drilling of sand wells. There are many peculiarities related to drilling of such deep wells and ignoring them may lead to wellbore collapse, significant decrease in well life time and deterioration of water quality.

Core drilling. Internal core of rock mass is preserved. This type of drilling is one of technical methods for exploration of mineral deposits. It is applied for drilling of hard rock. Rocks of high hardness are drilled by drag and diamond bits, tungsten-carbide and wolframite bits are used for medium hard rocks, and steel drill bits are used for softer rocks. Boreholes are flushed during drilling (using water or clay solution).
Core drilling has a number of advantages as compared to other types of drilling producing core of drilled rock - undistracted integral cylinders of rock. For that purposes the core is periodically keyed on, recovered from the borehole and lifted to the surface.

Core drilling features:
- core is extracted from borehole;
- opportunity to drill under various angles to horizon and drill rock of any hardness and stability;
- small diameter of borehole at its big depth;
- application of relatively light equipment.

Main drilling methods

Rotary drilling (mechanical drilling where crashing force is created by rotation of rock destruction tool with application of axial stress);
Rotor drilling (rotary drilling where drill instrument is rotated by the tool with rotation type rotary);
Diamond drilling (rotary drilling, where rock is crashed by rock destruction tool, enforced by diamonds);
Hard-alloy drilling (rotary drilling, where rock is crashed by rock destruction tool, enforced by hard alloys);
Cable drilling (percussion drilling where spudding action of the rig is transferred to the rock crashing tool through cable);
Percussive-rotary drilling (mechanical drilling, where destructive force is created as the result of joint impact of kicks and rotation of rock destruction tool);
Vibration drilling (mechanical drilling, where a drill tool is inserted by oscillations of a drilling tool are induced by a vibrator);
Fluid circulation drilling (drilling with rock cuttings are flushed by stream of washing fluid);
Air drilling (drilling with rock cuttings are lifted out of the wellbore by the stream of gas).