The Processing of Natural Gas

The natural gas used by consumers is much different from the natural gas that is brought up to the wellhead from underground. The processing of natural gas is in many respects less complicated than the processing and refining of crude oil, but it is equally as necessary before the end users receive it. The natural gas used by consumers is composed almost entirely of methane. Although still composed primarily of methane, the natural gas found at the wellhead is by no means as pure.

Raw natural gas comes from three types of wells: oil wells, gas wells, and condensate wells. Natural gas termed ‘associated gas’ is that which comes from oil wells. This gas can exist separate from oil in the formation (free gas), or dissolved in the crude oil (dissolved gas). Natural gas from gas and condensate wells, in which there is little or no crude oil, is termed ‘nonassociated gas’. Gas wells typically produce raw natural gas by itself. Condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate. Once separated from crude oil (if present), whatever the source of the natural gas, it commonly exists in mixtures with other hydrocarbons. The other hydrocarbons are principally ethane, propane, butane, and pentanes. Raw natural gas also contains water vapor, hydrogen sulfide (H2S), carbon dioxide, helium, nitrogen, and other compounds.

Pipeline-quality dry natural gas is the result of processing consisting of separating all of the various hydrocarbons and fluids from the natural gas. Before the natural gas can be transported in the pipelines, it must be purified. The ethane, propane, butane, and pentanes must be removed from natural gas. The actual practice of processing natural gas to pipeline dry gas quality levels usually involves four main processes to remove the various impurities: oil and condensate removal, water removal, separation of natural gas liquids, and lastly, sulfur and carbon dioxide removal. In addition to these, heaters and scrubbers installed near wellheads remove sand and other large-particle impurities such as the formation of hydrates resembling ice like crystals.

The associated hydrocarbons that are removed, known as Natural Gas Liquids (NGLs) can be very valuable by-products of natural gas processing. Ethane, propane, butane, iso-butane, and natural gasoline are among these.

The complete processing of natural gas takes place at a processing plant, usually located in a natural gas producing region. Some of the needed processing can be accomplished at or near the wellhead.
In addition to processing done at the wellhead and at centralized processing plants, some final processing is also sometimes accomplished at straddle extraction plants which are located on major pipeline systems.

The processing system ensures that the natural gas intended for consumer use is as clean and pure as possible. Companies like Triple Diamond Energy Corporation make sure that processing removes all impurities and separates out the associated hydrocarbons before the natural gas goes through the pipelines to reach the consumer.