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Natural gas is a type of homogeneous fluid of low viscosity and density. It can also be classified as an amalgam of ignitable hydrocarbon gases and contaminants. As gas is a fluid, it contains both gases and liquids. Gases, however, differ from liquids in that they have no definable volume or shape. Consequently, gases are able to expand in order to fill a container.
Natural gas is a mixture of hydrocarbon gases that occur naturally. As a result, each natural gas stream produced is comprised of its own distinctive composition. Even natural gas wells stemming from the same reservoir may possess various compositions. Furthermore, those compositions may change in nature as that formation is depleted.
Natural Gas Process / Treating Natural Gas
In a reservoir, natural gas is always present along with oil. When gas is under pressure, it provides the primary force needed for oil recovery. Gas may be dissolved in the oil, known as associated gas, or it may be separate from the oil, referred to as free unassociated gas. Gas may be found as a natural combination of liquid hydrocarbons and gas in some formations. This is referred to as condensate. The precise relationship that exists between gas and oil will typically depend on the amount of liquid that is saturated with dissolved gas.
Oil and gas will remain in solution provided the pressure is high and the temperature is low. When oil is pumped to the surface and the pressure is consequently lowered in the separator, the gas will then be expelled from the solution. In the event there is less gas present in the reservoir than the oil is able to absorb, the oil will be under-saturated. In the reverse, the oil will be super-saturated.
If free gas is present within the formation, it will then rise to the top. A gas cap will then form. When there is a gas cap present, the oil located below will then be steeped with dissolved gas in solution. Due to the fact that saturated oil has less of an ability to flow or a lower viscosity level, the oil present in the reservoir will be able to move more easily through the formation to the well casing.
Equal parts of produced water, crude oil, and natural gas will naturally separate into three different layers if they are deposited into a sealed glass container. The gas will rise to the top, while the produced water will remain in the bottom of the container and the oil will hover in the middle. This same type of separation will occur in reservoir: gas will remain at the top, water will remain at the bottom, and the oil will remain in the middle. It should be noted, however, that not all of the water would eventually settle to the bottom. Some water will stay with the oil and gas.
When treating natural gas, it is not uncommon for the pressure on the oil to be so significant that gas bubbles are not able to form. Once the pressure is relieved when the well is drilled, the gas will then escape the solution and bubbles will begin to form. As the bubbles begin to expand, that pressure will naturally force the oil through the well casing and eventually up to the surface.
Natural gas is just one form of energy that is essentially comprised of a blend of hydrocarbons along with some impurities, water and sand, which are typically removed near the wellhead. Other contaminants such as hydrogen sulfide, nitrogen, carbon dioxide, mercury, water vapor, and arsenic will also be removed at the wellhead, gathering station, or at a gas processing plan, based on pipeline specifications. This is referred to as natural gas processing.