Methane and Bonding Supplementary Information

Mitchell Chandler The Wilderness Society Western Energy Project (WEP) and Conservatives for Responsible Stewardship (CRS) estimate that 3.8 million oil and/or gas wells could potentially be drilled on all of the lands open to leasing as a result of the Trump administration’s leasing regime. Eventually, these wells become abandoned or orphaned. Abandoned wells are unplugged oil and gas wells that are no longer economically viable but have a responsible party who is liable for plugging and site restoration, while orphaned wells are unplugged and non-producing oil and gas wells with no responsible party (DOI Orphaned Wells Program Office 2024). These categories are typically considered together for the purposes of discussing methane emissions from oil and gas wells (DOI Orphaned Wells Program Office 2024;Williams et al. 2020;Riddick et al. 2024), though it is plausible that orphaned wells emit more methane than abandoned wells due to a lack of maintenance and therefore greater deterioration of infrastructure (Riddick et al. 2024). Nevertheless, the distinction between methane emissions from orphaned wells and from abandoned wells is not considered here, and I use the term abandoned wells to refer to both abandoned and orphaned wells. Unplugged abandoned wells are a substantial source of anthropogenic methane emissions. As part of the Bipartisan Infrastructure Law, the Orphaned Wells Program Office has supported orphaned well plugging and site remediation (DOI Orphaned Wells Program Office 2024). Under this program, methane tests have been conducted at 1446 orphaned wells and these wells subsequently plugged as of June 2024. The average methane emission rate across these 1446 unplugged orphaned wells was approximately 70 grams/hour (g/h; 1 ounce ≈ 28.3 grams; DOI Orphaned Wells Program Office 2024). Applying this emission rate to the 3.8 million potential wells gives a methane emission rate of: 70 g/h/well ·3.8×106wells = 266 ×106g/h = 266 t/h, where t is metric tons. Therefore, over the course of a year, these abandoned wells would emit: 266 t/h·8760 h = 2 330 160 t ≈2.3 million metric tons, equivalent to the greenhouse gas emissions from more than 15 million gasoline-powered passenger vehicles driven for one year (EPA). Plugging abandoned wells significantly decreases their methane emissions. For example, as of June 2024, the BLM reported that all eight methane-emitting orphaned wells they plugged through the Orphaned Wells Program were no longer emitting detectable levels of methane (DOI Orphaned Wells Program Office 2024). Riddick et al. (2024) estimate the average methane emission rate for plugged abandoned wells in the US to be 1.2 g/h. Applying this emission rate to the 3.8 million potential wells gives a methane emission rate of: 1.2 g/h/well ·3.8×106wells = 4.56 ×106g/h = 4.56 t/h or 4.56 t/h·8760 h = 39 945.6 t of methane emitted each year, the equivalent to the greenhouse gas emissions from almost 261 thousand gasoline-powered passenger vehicles driven for one year (EPA). It is clear that plugging abandoned wells is essential for reducing anthropogenic methane emissions. 1 Mitchell Chandler The Wilderness Society Furthermore, a recent study in Colorado identified an abandoned well emitting an unprecedented 76 000 g/h of methane (Riddick et al. 2024) – a super-emitter – which therefore indicates that earlier studies (e.g. Williams et al. 2020) likely underestimate average methane emissions from abandoned wells. Riddick et al. (2024) estimated an average methane emission rate of 1.2 g/h for plugged wells and 198 g/h for unplugged wells across the US, for an average rate of approximately 88 g/h (they assumed 1.9 million unplugged abandoned wells and 1.5 million plugged abandoned wells in the US based on EPA reporting). Using the Riddick et al. (2024) average methane emission rate for unplugged wells would obviously give a larger methane emissions total than using the DOI Orphaned Wells Program Office (2024) value. Such large uncertainty and variability in methane emissions between studies arises because the number of abandoned wells that have actually had their methane emissions measured is minuscule compared to the total number of abandoned wells, and variability in methane emission rates between abandoned wells can be large. 2