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There are two parts in natural gas production. They are
In extraction, the natural gas is extracted from various wells and other sources where the natural gas is present.
In purification, the extracted natural gas is purified. That is, various other impurities present in the natural gas are removed and a clean natural gas is delivered to the customer.
Mostly, the natural gas is drilled out of the earth where the deposits are found. For finding the various deposits the geologists use various technologies. They normally check the surface geology of the area by the seismic energy and the magnetic properties of the underground rock formations. It is very difficult to drill the gas out the well. Various measures must be considered so that it does not affect the groundwater supply. The holes that are drilled to get the gas out of the underground rocks, must be covered tightly such that the gas does not escaped when it is being drilled out. The depth of the rocks that contain the gas varies from 1000 meters to several kilometers. Natural gas can be extracted from wells. These are specially built wells. They are called as producing or operating wells.
Natural gas reserves can be divided into three types they are:
Proved: they are the reserves from which we can economically extract the natural gas. They are present in an area of 164 thousand billion cubic meters and they will last until 2060 at the current rate of extraction.
Probable: they are the reserves that are found to have natural gas but no technology is available to extract the natural gas. They can be very economical and useful like the proved reserves if the technology to extract them is identified.
Potential: they are the unconventional sources. They are mostly found under the ocean. They are mostly methane hydrates which contains 20% of methane and 80% of water. Their extraction is very difficult. Currently, extraction is done using the thermal breakup and depressurization.
Before the natural gas reaches the customer, we must ensure that it contains certain quality for the use of the customer. To ensure that, natural gas processing must be done. The processing is based on the composition of the natural gas.
Normally, the natural gas is present along with the crude oil before extraction. So it obviously contain some amount of higher hydrocarbons. The natural gas may also contain water and other sulfurous substances. Water and methane together form solid hydrates which clogs the pipelines. So care must be taken so as to remove water from the natural gas. In addition to this, the natural gas may also contain some dust particles, which cause many problems.
So after extraction,
Natural gas is dried (water is removed).
Solid particles are removed (dust particles are removed).
At last, higher hydrocarbons and any sulfurous substances that are present may be removed from the natural gas, if necessary.
Although there are several ways that methane, and thus natural gas, may be formed, it is usually found underneath the surface of the earth. As natural gas has a low density, once formed it will rise toward the surface of the earth through loose, shale type rock and other material. Some of this methane will simply rise to the surface and dissipate into the air. However, a great deal of this methane will rise up into geological formations that ‘trap’ the gas under the ground. These formations are made up of layers of porous, sedimentary rock (kind of like a sponge that soaks up and contains the gas), with a denser, impermeable layer of rock on top.
This impermeable rock traps the natural gas under the ground. If these formations are large enough, they can trap a great deal of natural gas underground, in what is known as a reservoir. There are a number of different types of these formations, but the most common is created when the impermeable sedimentary rock forms a ‘dome’ shape, like an umbrella that catches all of the natural gas that is floating to the surface.
There are a number of ways that this sort of ‘dome’ may be formed. For instance, faults are a common location for oil and natural gas deposits to exist. A fault occurs when the normal sedimentary layers ‘split’ vertically, so that impermeable rock shifts down to trap natural gas in the more permeable limestone or sandstone layers. Essentially, the geological formation, which layers impermeable rock over more porous, oil and gas rich sediment, has the potential to form a reservoir. The picture below shows how natural gas and oil can be trapped under impermeable sedimentary rock, in what is known as an anticlinal formation. To successfully bring these fossil fuels to the surface, a hole must be drilled through the impermeable rock to release the fossil fuels under pressure. Note that in reservoirs that contain oil and gas, the gas, being the least dense, is found closest to the surface, with the oil beneath it, typicall followed by a certain amount of water. With natural gas trapped under the earth in this fashion, it can be recovered by drilling a hole through the impermeable rock. Gas in these reservoirs is typically under pressure, allowing it to escape from the reservoir on its own.