For suppliers of natural gas liquids, the CO₂ associated with natural gas liquids (NGLs) supplied to the U.S. economy (i.e., ethane, propane, butane, isobutane and pentanes plus) has gradually increased from 211.6 million metric tons (MMT) in 2011 to 403.0 MMT in 2019. Except for a small decrease in 2012, the supply of NGLs has increased steadily every year with ethane and propane making up about 70 percent by volume of the NGLs supplied each year by U.S. fractionators. [1]

The increase in NGL supply is due to increased production of natural gas in areas that are high in natural gas liquids; increased U.S. demand for NGL products; increased production capacity due to construction of new fractionation plants; and increased exports due to the construction of new pipelines and export terminals. In the last two years, the year-over-year increases in the CO₂ emissions from NGLs have been approximately 12 percent. This increase is partly due to new export capacity that came online in late 2017 and allowed fractionators to export more NGL products. [2] Ethane supply increased in 2019 in response to increased demand from new petrochemical facilities that use ethane as a feedstock. [3]

The reported CO₂ for 2011 and 2012 are also affected by changes in the default emission factors. For suppliers of natural gas liquids, the default emission factors used for calculating the CO₂ for ethane, propane, butane and isobutene were revised in 2013. The default emission factors for propane, butane and isobutane were increased by a few percent over those used prior to 2013, while the default emission factor for ethane was decreased by over 30 percent. The impact these changes had on the total CO₂ reported by an NGL fractionator depends on the mixture of products the plant supplies and whether the fractionator used the default value or a measured value. Since most NGL fractionators supply ethane, the reported CO₂ across the industry was lower beginning in 2013 than would have been reported if the factors had not been updated.

[1]     U.S. Department of Energy, Energy Information Administration, U. S. Energy Information Administration/Petroleum Supply Annual 2019, Volume 1, Table 15. Natural Gas Plant Net Production and Stocks of Petroleum Products by PAD and Refining Districts, 2019, August 31, 2020. Available at: https://www.eia.gov/petroleum/supply/annual/volume1/pdf/table15.pdf.

[2]     U.S. Department of Energy, Energy Information Administration, This Week in Petroleum, In 2020, Increased Propane, Other HGL Exports Contribute to Continued Strong Product Exports Despite Reductions in Major Transport Fuels, September 23, 2020. Available at: https://www.eia.gov/petroleum/weekly/archive/2020/200923/includes/analysis_print.php.

[3]     U.S. Department of Energy, Energy Information Administration, Hydrocarbon Gas Liquids Explained. October 31, 2019. Available at: https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/prices-for-hydrocarbon-gas-liquids.php.