Drilling the earth in order to reach the water, gas, or oilfield. Oil well drilling is more complicated than water wells because its exploration and extraction are mainly located on the bottom of the sea floor.
The drilling operations should be carried out at a high speed, 24 hours a day, because the operation is expensive because of the cost of the mast and drilling rig. The location of excavation is very specialized and carried out by geological engineers. Geological studies predict only the possibility of reservoirs to ensure that oil is the only way to dig a well.
This location should be located at a distance from residential areas, adjacent wells, high voltage electricity and…. After locating the road engineer, the engineer begins to install the necessary equipment, rooms, roads, and so on. Afterwards, the mast is brought to the area separately from each other, then it is assembled and the drilling operation is carried out. The following figure shows the general design of the drilling:
Well drilling was initially hand-crafted, which is still common in many places, with the advent of different mechanical means, these excavations are now done with mechanical methods, which are generally two-way, Tapping Drilling and Rotary Drilling .
Now, most of the oil wells are drilled in a rotational way because it has more advantages. The drill rotates from a sharp and rotating drill to penetrate the earth’s crust. It consists of four main components, whereby rotary drilling is performed.
Rotary drilling has several types:
The well drilling method is mainly vertical, except in special situations where drilling of oil wells is required deviant, including the presence of surface barriers such as the sea, the river, residential areas, or mountainous region or the enormous cost of creating a road and the location of the road and expenditures Very high on drilling rigs.
Some of the reservoirs are such that if the drill is done vertically, the well will sit in the brine and will not work.
Sometimes in the sea areas, the cost of the oil platform is expensive, so they can harvest a number of different reservoirs with an oil platform This is possible only by Diverting drilling.
Recently, the oil industry has provided equipment that makes it possible to drill wells, narrow well drilling can dramatically reduce drilling costs.
Spiral drilling is also a special type of narrow well drilling that has recently been used.
In this method, integrated gratings of high grade steel are used. This method has environmental effects as well as lower costs.
There are also two special types of drilling:
Under balanced drilling, termed UBD, is a negative pressure drilling method, in which the pressure of the fluid in the reservoir is greater than the pressure of drilling fluid at the bottom of the well.
In the drilling of oil and gas wells by under balanced drilling, the fluid reservoirs easily penetrate the well due to higher pressure. This operation improves the efficiency of well drilling and does not cause any damage to the reservoir. Also, due to the pressure in the basement, the drilling speed rises.
In Over balanced drilling, the pressure of the column of drilling fluids is greater than the pressure of the reservoir. This method is more commonly and used for shallow wells and unstable soils.
The drilling equipment are divided into, Well head and Down Hole Equipment.
Components of drilling rig like;
Block Crown, Derrick, Sub base, Draw works , Rotary table, Mud Pumps, Power Traveling Block ،Commy Unit , Blow Out Prevention(BOP) ، Power Generator ,Kelly , Top Drive.
Base Flange, Side Valve, Bottom Main Valve, Top Main Valve, Surface Safety Valve
Drill Bits, Pup joint, Drill pipe, Heavy weight Drill pipe, Drill Collar, Jar Pipe ، Stabilizer, casing، Liner, Tubing, PDM(In-well engines).