Characterizing Methane Emissions from Orphaned Coalbed Methane Wells in the Powder River Basin

The latest US EPA Greenhouse Gas Inventory (GHGI) includes methane emissions from abandoned oil and gas (AOG) wells and estimates that they may constitute up to 4% of total methane emissions from the oil and gas sector. Several studies have shown that these emissions vary by location which introduces regionally dependent uncertainty into inventory estimates. In Wyoming, there are over 1000 wells classified as "orphaned" indicating that they are both abandoned and unplugged, 80% of which are coalbed methane wells. In this study, ten orphaned coalbed methane wells were sampled to characterize AOG well emission rates in the Powder River Basin in Wyoming. The mean methane emission rate measured at these wells was 651 mg CH4/hr with the majority of these wells emitting in the 100-1000 mg CH4/hr range. The highest emitting well in the study was measured at 4.53 g CH4/hr. Compared to the GHGI AOG wells emission factor of 10.04 g CH4/hr, these findings suggest that AOG wells emission rate in the PRB are overestimated in the national inventory. Finally, these findings also suggest that abandoned coalbed methane wells may emit less methane than abandoned conventional oil and gas wells.