GREENHOUSE GAS EMISSIONS ESTIMATES FOR PLUGGED OIL AND GAS WELLS ON FEDERAL LEASES (Invited Presentation)

The U.S. Geological Survey (USGS) is estimating fugitive (non-combustion) greenhouse gas (GHG) emissions from non-active oil and gas wells on Federal subsurface mineral lands (here after "Federal leases", which are distinct from and not always co-located with Federal surface lands). This emissions estimate is a new addition to the USGS Federal Lands Greenhouse Gas Emissions and Sequestration in the United States report. The study presented here is limited to estimates of the GHG emissions from plugged wells on Federal leases. Obtaining well counts for unplugged non-active wells will be a future effort.

Plugged well counts were provided by the Bureau of Land Management for 2005-2022, and this study estimated emission across that timeframe. For example, in 2022, the plugged Federal lease counts were 19,157 oil wells and 10,763 gas wells. Using the U.S. Environmental Protection Agency (EPA) GHG Inventory methodology, we estimated 2022 plugged well Federal lease emissions for methane to be just 28.5 metric tons in CO₂ equivalent units. This value is a very small proportion (<< 0.1%) of the total estimated Federal fugitive methane emissions (energy infrastructure, production, and transport). The future inclusion of unplugged non-active wells, with emissions factors two orders of magnitude larger, should result in a more complete inventory of non-active wells.

The current EPA GHG Inventory methodology uses four emissions factors for non-active wells, essentially whether they are in Appalachia or not, or the wells are plugged or not. These emissions factors are based on studies by Kang et al. and Townsend-Small et al., both in 2016. A review of average emissions rates from recent studies indicates that the existing emissions factors are still appropriate within the uncertainty of the method, however they might be enhanced by utilizing additional, underlying data. More fugitive methane measurements for plugged and unplugged wells, particularly from continuous measurement studies, could increase estimate accuracy by revealing the parameters that drive emissions observations in the field (well age, geology, depth, water table, etc.). Combining more accurate emissions factors with more precise well count information could result in both improved methods and more accurate estimates of GHG emissions.