Other instruments such as gravimeters and magnetometers are also used in the search for petroleum. Extracting crude oil normally starts with drilling wells into an underground reservoir. When an oil well has been tapped, a geologist (known on the rig as the "mudlogger") will note its presence.
Oil is not exactly mined, it is extracted from the earth. Oil fields are located with the help of seismological experiments. Oil fields or wells are usually sections of shale rocks that have accumulated oil. These shale rocks are porous in nature and hold the oil that is extracted.
After the oil well is located a drill, known as an oil rig, digs a deep hole into the well. Once this hole is dug, a steel pipe is put into it to provide structural integrity to the newly dug hole. There are mainly three stages of oil extraction.
The first stage is called primary recovery. On digging of an oil well, the natural gas in it expands and searches for an outlet. A series of valves are created and the gas provides the necessary pressure and the oil rises on its own. This procedure extracts around 10% to 15% of the oil in the well.
After some time, the primary recovery method fails due to decreasing pressure of the gas and the secondary recovery method is put into effect. In the secondary recovery method, a material is forcibly injected into the well to provide the energy for the oil to rise. This material is decided based on the properties of the rock and quality of the oil. These materials include water, the natural gas that was previously extracted, carbon dioxide etc. Around 50% of the oil is extracted by this process.
Once the secondary methods fail, there is an enhanced recovery method. This method is applied by decreasing the viscosity of the oil that is being extracted. The usual method for this is by increasing the temperature of the oil well.
Once the oil is extracted, it is sent to the purification plants through pipelines.
Oil is normally extracted from shale. Movements in the Earth have trapped oil in the reservoir rocks between layers of impermeable rock. First of all, a geologist finds the right conditions for an oil trap -- the right source rock, then determines whether the first sample brought to the surface evidences that oil is present. He marks the location. Extracting crude oil normally starts with drilling wells into an underground reservoir.
VArious holes are dug, a smaller drill, then the main one using a power system such as an electrical generator, a hoist system, a turntable and more, as well as the drills themselves. Mud and rock fragments go up a cement pipe as the deepest drilling extracts the oil, which is set to flow through sandstone and into a prepared well. This is only a very brief and crude description of a lengthy and intricate process.