Text “Types of raw natural gas wells. Natural gas processing”.

Raw natural gas comes primarily from any one of three types of wells: crude oil wells, gas wells, and condensate wells. Natural gas that comes from crude oil wells is typically termed associated gas. This gas can have existed as a gas cap above the crude oil in the underground formation, or could have been dissolved in the crude oil. Natural gas from gas wells and from condensate wells, in which there is little or no crude oil, is termed non-associated gas. Gas wells typically produce only raw natural gas, while condensate wells produce raw natural gas along with other low molecular weight hydrocarbons. Those that are liquid at ambient conditions (i.e., pentane and heavier) are called natural gas condensate (sometimes also called natural gasoline or simply condensate).Natural gas is termed sweet gas when relatively free of hydrogen sulfide; however, some produced gas does contain this substance and thus is called sour gas. Raw natural gas can also come from methane deposits in the pores of coal seams, and especially in a more concentrated state of adsorption onto the surface of the coal itself. Such gas is referred to as coalbed gas or coalbed methane. Coalbed gas is a form of natural gas that is has being extracted from coalbed. This coalbed gas has become an important source of energy in recent decades.

Natural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas. Natural-gas processing begins at the well head. The composition of the raw natural gas extracted from producing wells depends on the type, depth, and location of the underground deposit and the geology of the area. Oil and natural gas are often found together in the same reservoir. The natural gas produced from oil wells is generally classified as associated-dissolved, meaning that the natural gas is associated with or dissolved in crude oil. Natural gas production absent any association with crude oil is classified as “non-associated.”

Most natural-gas production contains, to varying degrees, small (two to eight carbons) hydrocarbon(any class of compound containing only hydrogen and carbon; examples are methane gas, benzene) molecules in addition to methane. Although they exist in a liquid state at underground pressures, these molecules will become gaseous at normal atmospheric pressure. Collectively, they are called condensates or natural gas liquids (NGLs). The natural gas extracted from coal reservoirs and mines (coalbed methane) is the primary exception, being essentially a mix of mostly methane and carbon dioxide (about 10 percent).

Natural-gas processing plants, (or whatever apparatus capable of separating liquid substance into component parts) are used to purify the raw natural gas produced from underground gas fields or extracted at the surface from the fluids produced from oil wells. A fully operational plant will deliver pipeline-quality natural gas that can be used as fuel by residential, commercial and industrial consumers. Contaminants have been removed and heavier hydrocarbons have been captured for other commercial uses. For economic reasons, however, some plants may be designed to yield an intermediate product typically containing over 90% pure methane and smaller amounts of nitrogen, carbon dioxide, and sometimes ethane. This can be further processed in downstream plants or used as feedstock for chemicals manufacturing.