Associated petroleum gas (APG), or associated gas, is a form of natural gas which is found with deposits of petroleum, either dissolved in the oil or as a free "gas cap" above the oil in the reservoir.[1][2] The gas can be utilized in a number of ways after processing: sold and included in the natural-gas distribution networks, used for on-site electricity generation with engines[3] or turbines, reinjected for secondary recovery and used in enhanced oil recovery, converted from gas to liquids producing synthetic fuels, or used as feedstock for the petrochemical industry,[4] but much of it worldwide is flared.


See also: Natural-gas processing

APG is primarily a mixture of hydrocarbon molecules that are classified as alkanes. The following table lists typical percentages of the major alkanes in APG, and includes the typical levels of nitrogen and carbon dioxide. Water (wet gas) and hydrogen sulfide (sour gas) contaminate APG at more varied levels. Helium is present in significant amounts in some cases, and is a relatively valuable by-product. APG is processed to separate out most other components before the methane-rich gas is sold into natural-gas distribution networks.

Component Chemical formula Volume fraction (%) Weight fraction (%)[5]
Methane CH
81 60
Ethane C
5.5 7.7
Propane C
6.6 13.5
Butane C
4.0 10.8
Pentane C
1.4 4.8
Nitrogen N
1.0 1.3
Carbon dioxide CO2 0.17 0.33


Main article: Natural gas § Uses

Like crude oil, APG is both a primary energy resource and a primary commodity that enables much of the modern world economy. Statistics from the International Energy Agency show that the natural-gas supplies steadily increased during 1990-2017 to meet the demands of expanding global population and consumerism.[6] APG is nevertheless a finite fossil fuel, and the crossing of planetary boundaries could impose earlier limits on its value and usefulness.[7]

Following extraction, petroleum companies prefer to transport both crude oil and APG to their respective refiners for processing and distribution to consumers. Most modern wells are planned to include gas pipeline transport, but some oil wells are drilled only to get the more lucrative oil, in which case the options are to locally use, process, or dispose of the APG. A traditional local use is to re-inject the gas for storage, and to re-pressurize the well to extend the oil production lifetime. On-site processing with various mobile systems also exist for producing natural gas liquids (NGL), compressed natural gas (CNG), liquified natural gas (LNG), and gas to liquids (GTL) fuels that can be transported by truck or ship. Electricity generation from on-site microturbines and engines is also compatible with minimally processed APG.[8]: 50–54 


Main article: Routine flaring

Historically APG was, and still may be, a waste product from the petroleum extraction industry. It may be a stranded gas reserve due to the remote location of the oil field, either at sea or on land. The gas is then simply vented or, preferably, burnt off in gas flares. When this occurs it is referred to as flare gas.[9]

APG flaring is controversial since it is a pollutant, a source of global warming[10] and a waste of a finite fuel source. APG is flared in many countries where there are significant power shortages.[11] In the United Kingdom, gas may not be flared without written consent from the UK government to prevent unnecessary waste and protect the environment.[12] Russia is the world leader and contributed 30 percent of total global APG flared in 2009.[13]

The World Bank estimates that over 150 billion cubic metres of natural gas are flared or vented annually. Flared natural gas is worth approximately 30.6 billion dollars and equivalent to 25 percent of the United States' yearly gas consumption or 30 percent of the European Union's annual gas consumption.[14]

See also


  1. ^ Røland, Tonje Hulbak (2010). Associated Petroleum Gas in Russia: Reasons for Non-utilization (PDF). FNI Report 13/2010 (Report). Lysaker: Fridtjof Nansen Institute. p. 53. Archived from the original (PDF) on 2011-07-20. Retrieved 2018-10-26.
  2. ^ "Glossary of terms used in Petroleum Reserves/Resources Definitions" (PDF). The Society of Petroleum Engineers. 2005. Retrieved 24 December 2013.
  3. ^ "Associated Petroleum Gas in Gas Engines". Clarke Energy. Retrieved 25 November 2011.
  4. ^ (Roland 2010 cites Knizhnikov, A. and N Poussenkova (2009) ‘Russian Associated Gas Utilization: Problems and Prospects’, Annual Project Report Environment and Energy: International Context Issue 1. Moscow: World Wildlife Fund and Institute of World Economy and International Relations of the Russian Academy of Sciences
  5. ^ Попутный нефтяной газ: основные способы переработки – утилизации ПНГ [Associated Petroleum Gas (APG): Basic Methods of Processing and Utilization] (in Russian). New Generation. 2013-05-05.
  6. ^ "Global Data and Statistics". International Energy Agency. Retrieved 10 January 2020.
  7. ^ Linnenluecke, Martina K.; Birt, Jac; Lyon John; Sidhu, Baljit K. (2015), "Planetary boundaries: implications for asset impairment", Accounting & Finance, 55 (4): 911–929, doi:10.1111/acfi.12173
  8. ^ "Natural Gas Flaring and Venting: State and Federal Regulatory Overview, Trends, and Impacts" (PDF). U.S. Department of Energy. 2019-06-01. Retrieved 2019-12-29.
  9. ^ "Flare gas - Oilfield Glossary". Schlumberger Limited. Archived from the original on 6 January 2011. Retrieved 20 May 2011.
  10. ^ "Gas flaring in Nigeria" (PDF) (Press release). London. Friends of the Earth. October 2004. Retrieved 20 May 2011.
  11. ^ Walker, Andrew (13 January 2009). "Nigeria's gas profits go up in smoke". Nigeria. BBC News. Retrieved 20 May 2011.
  12. ^ "Atmospheric Emission - Flaring". Oil & Gas UK. Retrieved 24 December 2013.
  13. ^ "Flaring Up - Companies Pay High Costs to be Green". Oil&Gas Eurasia. 26 April 2009. Archived from the original on 24 July 2011. Retrieved 20 May 2011.
  14. ^ "World Bank, GGFR Partners Unlock Value of Wasted Gas". World Bank Group. 14 December 2009. Retrieved 17 March 2010.