Processing Natural Gas: Processing natural gas means separating all the hydrocarbons, fluids, and gases from pure methane. Field processing, completed at or near the wellhead, produces ‘pipeline quality’, dry natural gas ("NaturalGas.org"). Major pipelines usually have restrictions that require natural gas to be purified before it can be transported across the country. The byproducts that are removed are then sold to a variety of different companies for many uses, including, but not limited to, enhanced oil recovery, providing raw materials, or other sources of energy.
After field processing, natural gas is fed into a regional network of gathering pipelines, which are smaller in diameter and are at a lower pressure, and transported to a central processing plant. These networks can sometimes contain thousands of miles of pipes that can connect the processing plant to over hundreds of wells in one area.
The processing of natural gas involves four main processes:
After these processes have been completed, the natural gas that is left is almost ready for consumers. The last step, one of the most important, is to remove sulfur, in the form of hydrogen sulfide, and carbon dioxide. With a high sulfur content, there is a distinctive sour or foul odor. Sulfur must be removed, as it can be anywhere from extremely harmful to lethal to inhale, it is extremely corrosive, and it can be extracted and sold separately. According to the United States Geological Survey, United States sulfur production from gas processing plants accounts for about 15 percent of the total U.S. production of sulfur. The process of removing sulfur from natural gas is often referred to as ‘sweetening’ the gas. Pure sulfur, a bright yellow powder, can then be sold, if it is in its elemental form.
In order to further remove elemental sulfur at the processing plant, it must be further treated in a process known as the Claus process, where thermal and catalytic reactions extract the sulfur from the hydrogen sulfide solution ("NaturalGas.org"). This process removes around ninety seven percent of sulfur, but because sulfur is a harmful and polluting substance, it must undergo further refinement.
Post Production: Post production begins after all the natural gas or oil has been economically recovered from the specific reservoir. During this time, the land where the well is located is restored to pre-drilling conditions through removal of equipment, replanting of trees, filling in the area where the drill pad was located with dirt, closing off the well with cement, and cutting the pipes below ground level. If everything is done properly, there will be virtually no sign of the drilling pad or any equipment, and the landowner will be able to use the land for any other activity.
After field processing, natural gas is fed into a regional network of gathering pipelines, which are smaller in diameter and are at a lower pressure, and transported to a central processing plant. These networks can sometimes contain thousands of miles of pipes that can connect the processing plant to over hundreds of wells in one area.
The processing of natural gas involves four main processes:
- Oil and condensate removal is often done at or near the wellhead. Natural gas from different regions of the country have different amounts of byproducts, and thus, the process varies from region to region. In many cases, natural gas is only mixed with oil due to high pressures underground, so when it reaches lower pressures at the surface, it will separate without any equipment needed. In these simple cases, each type of hydrocarbon is sent its own way for separate processing. When the natural gas does not separate by itself, special equipment is used to separate the hydrocarbons based on the conditions the natural gas is under
- The removal of water is also an extremely important step. Most of the liquid water is removed at the wellhead, while the water vapor removal process can be more complex. The natural gas must be dehydrated through either absorption, where the vapor is removed using a dehydrating agent, or through adsorption, where the water vapor condenses and is collected at the surface.
- After the water has been removed, separation of natural gas liquids from methane is used to separate valuable byproducts. Natural Gas Liquids (NGLs) can be separated by many methods. According to the Gas Processors Association, the two methods that account for around ninety percent of total natural gas liquid production are the absorption method, similar to the absorption method used in water removal, and the cryogenic expander process, where the temperature is reduced to around -120 °F. Cryogenic expansion is required for high recovery rates of lighter hydrocarbons.
- Natural gas liquid fractionation separates the different natural gas liquids based on the unique boiling points of each hydrocarbons in the stream of NGLs. This process occurs in stages, where each hydrocarbon is boiled off one by one as the temperature increases. Each hydrocarbon is separated by unique fractionators, usually named for the hydrocarbon it boils off. The following fractionators are used in order:
- Deethanizer separates ethane from the other natural gas liquids; ethane is the lightest hydrocarbon, and boils at - 128.2 °F.
- Depropanizer is the next step separates the propane, which is heavier than ethane, and has a boiling point of - 43.6
- Debutanizer boils off butanes, with a boiling point of 30.2 °F, and leaves pentanes and heavier hydrocarbons.
- Butane Splitter or Deisobutanizer is the final step, and is where the isobutane, a butane molecule with a lower boiling point of 10.94 °F due to it having the same chemical formula as butane, but a different molecular structure than normal butanes.
After these processes have been completed, the natural gas that is left is almost ready for consumers. The last step, one of the most important, is to remove sulfur, in the form of hydrogen sulfide, and carbon dioxide. With a high sulfur content, there is a distinctive sour or foul odor. Sulfur must be removed, as it can be anywhere from extremely harmful to lethal to inhale, it is extremely corrosive, and it can be extracted and sold separately. According to the United States Geological Survey, United States sulfur production from gas processing plants accounts for about 15 percent of the total U.S. production of sulfur. The process of removing sulfur from natural gas is often referred to as ‘sweetening’ the gas. Pure sulfur, a bright yellow powder, can then be sold, if it is in its elemental form.
In order to further remove elemental sulfur at the processing plant, it must be further treated in a process known as the Claus process, where thermal and catalytic reactions extract the sulfur from the hydrogen sulfide solution ("NaturalGas.org"). This process removes around ninety seven percent of sulfur, but because sulfur is a harmful and polluting substance, it must undergo further refinement.
Post Production: Post production begins after all the natural gas or oil has been economically recovered from the specific reservoir. During this time, the land where the well is located is restored to pre-drilling conditions through removal of equipment, replanting of trees, filling in the area where the drill pad was located with dirt, closing off the well with cement, and cutting the pipes below ground level. If everything is done properly, there will be virtually no sign of the drilling pad or any equipment, and the landowner will be able to use the land for any other activity.
Sources: "Chemical Use In Hydraulic Fracturing." Chemical Use In Hydraulic Fracturing. Ground Water Protection Council and Interstate Oil and Gas Compact Commission. Web. 10 May 2015. http://fracfocus.org/water-protection/drilling-usage.
"Delivery and Storage of Natural Gas." Energy Explained, Your Guide To Understanding Energy. United States Department of Energy, 6 June 2014. Web. 10 May 2015. http://www.eia.gov/energyexplained/index.cfm?page=natural_gas_delivery.
"DOE - Fossil Energy: How Fossil Fuels Were Formed." DOE - Fossil Energy: How Fossil Fuels Were Formed. Fossil Energy Office of Communications, 12 Jan. 2013. Web. 10 May 2015. http://www.fe.doe.gov/education/energylessons/coal/gen_howformed.html.
Estefani, Guillermo. "Natural Gas." Artinaid. 12 Apr. 2013. Web. 10 May 2015. http://www.artinaid.com/2013/04/natural-gas/.
"How Is Gas Extracted from the Ground?" How Is Gas Extracted from the Ground? United Kingdom Onshore Oil and Gas, 2013. Web. 10 May 2015. http://www.ukoog.org.uk/knowledge-base/drilling-process-kb/how-is-gas-extracted-from-the-ground.
"NaturalGas.org." NaturalGas.org. 20 Sept. 2013. Web. 10 May 2015. http://naturalgas.org/naturalgas/.
"Delivery and Storage of Natural Gas." Energy Explained, Your Guide To Understanding Energy. United States Department of Energy, 6 June 2014. Web. 10 May 2015. http://www.eia.gov/energyexplained/index.cfm?page=natural_gas_delivery.
"DOE - Fossil Energy: How Fossil Fuels Were Formed." DOE - Fossil Energy: How Fossil Fuels Were Formed. Fossil Energy Office of Communications, 12 Jan. 2013. Web. 10 May 2015. http://www.fe.doe.gov/education/energylessons/coal/gen_howformed.html.
Estefani, Guillermo. "Natural Gas." Artinaid. 12 Apr. 2013. Web. 10 May 2015. http://www.artinaid.com/2013/04/natural-gas/.
"How Is Gas Extracted from the Ground?" How Is Gas Extracted from the Ground? United Kingdom Onshore Oil and Gas, 2013. Web. 10 May 2015. http://www.ukoog.org.uk/knowledge-base/drilling-process-kb/how-is-gas-extracted-from-the-ground.
"NaturalGas.org." NaturalGas.org. 20 Sept. 2013. Web. 10 May 2015. http://naturalgas.org/naturalgas/.