Petroleum was formed long ago from the remains of animals and plants. When the remains of once-living things are buried for millions of years under layers and layers of sediment, they begin to change. They are converted into oil and natural gas which then is trapped in porous rock or fractured rock formations. Despite the long history of petroleum exploration, these are still the formations that we drill for today.
We can use seismic testing to explore the underground rock layers to determine where the petroleum may be locked deep underground. A small explosion may be used to create the sound waves which travel down through the rock layers and reflect back to the recording equipment. The recorded data is interpreted by a computer and translated into a map for further study.
Once the underground layers of rock and soil are mapped and a likely location for the oil is determined, a drilling rig or derrick is brought in and drilling can begin.
Drilling is the process of making a hole with the use of mechanical action. Using a rotary rig, a well can be drilled into the surface of the earth for the extraction of a natural resource such as ground water, natural gas, or petroleum.
A drill bit is what actually cuts into the rock when drilling an oil or gas well. Located at the tip of the drill-string, below the drill collar and the drill pipe, the drill bit is a rotating apparatus that usually consists of two or three cones made up of the hardest of materials (usually steel, tungsten carbide, and/or synthetic or natural diamonds) and sharp teeth that cut into the rock and sediment below.
The rotary drilling rig has three main parts;
1) The draw-works is a system of cables and pulleys that lowers drill pipe and casing into the hole and hoists the string of drill pipe out of the hole.
2) The rotary table and related equipment rotates the drill string to turn the bit at the bottom of the hole.
3) The mud system circulates drilling fluid to the bottom of the hole and back to the surface to flush cuttings from the bottom of the hole, to cool and lubricate the bit, and to control pressures in the drill hole.
There are two main forces at work which the driller can control to effectively drill through the earth. The rotational speed of the drill bit, how fast the drill spins, and the down-hole pressure, the amount of force pushing down on the drill string. These forces need to be properly matched to the rock, the drill bit being used, and the mud flow to avoid damage to the drill bit and to successfully drill through the various layers of rock.