Natural gas and crude oil are often connected and extracted simultaneously in the same field or in the same production area. Liquid hydrocarbons come from crude oil at an average rate of about 80%. The other 20%, the lightest part, propane and butane are almost always liquefied to facilitate transportation.
Exploration (deposit exploration) and natural gas extraction use much the same technology as the oil industry. A significant portion of the gas deposits known worldwide were also discovered during exploration campaigns for oil.
During pressurized gas extraction, cooling and expansion at the wellhead results in condensation of hydrocarbons (which may contain C5 to C8) and water26. The recovered light liquid hydrocarbons are called “natural gas condensates” or “natural gas well liquids” and correspond to very high-value superlight (gasoline and naphtha yields). Everything else (C1-C4 hydrocarbons, carbon dioxide, hydrogen sulfide and helium) is gaseous at room temperature and is piped to a gas processing plant. Therefore, two collection networks are required. One for gas and one for condensate.
In this plant (which may be close to the sediment or close to the point of consumption) the gas is dehydrated by the dew point and the other components are separated. C2-C4 hydrocarbons are sold under the name Liquefied Petroleum Gas (LPG, not LNG). Most of the carbon dioxide is simply emitted into the atmosphere unless there are users nearby. It is sometimes reinjected into underground formations (CO2 sequestration) to reduce greenhouse gas emissions. Sour gas is sold to the chemical industry or sequestered. Helium is sold separately if present in sufficient quantities. In some cases, it represents a very significant addition to the revenue generated by the field.
Condensate and LPG have a market value, so certain fields are developed just for them, and the “poor gas” (methane) is reinjected when there are no local outlets. Even when most of the lean gas is sold, some is often injected back to the site to slow the pressure drop and ultimately recover a significant portion of the condensate and LPG.
The other part (the largest part) is transported via gas pipelines or LNG tankers to the point of consumption.
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