Greenhouse Gas Footprint of Oilfield Flares Accounting for Realistic
Flare Gas Composition and Distribution of Flare Efficiencies
Abstract
The greenhouse gas footprint of oilfield flares comprises carbon dioxide
and uncombusted hydrocarbons. It has been broadly assumed that oilfield
flares are 98% efficient, and that the unburned fraction is
predominantly methane. Recent studies have shown that neither assumption
is necessarily true. Gas associated with tight oil production, now the
largest source of flared gas in the United States, is a mixture of
hydrocarbons in which methane is not necessarily more than half the
total. Aerial surveys have found that while many flares function
efficiently, a substantial fraction are very inefficient. This work
builds on those studies to show how greenhouse gas footprints can be
computed when flared gas is a mixture of hydrocarbons, and when flare
efficiencies are best represented as statistical distributions. This
work finds that the best estimate of GHG footprint of current Bakken
oilfield flares is 56,400 tonnes carbon dioxide equivalent per day,
compared to an estimate of 31,400 tonnes carbon dioxide equivalent per
day under the assumption of 100% methane flares operating at 98%
efficiency. Both these estimates considerably exceed the expected GHG
footprint for flares based on data from the Environmental Protection
Agency Greenhouse Gas Reporting Program.