Methane Emissions from Abandoned Oil and Gas Wells: Lessons Learned from the Current Status of Empirical Data

Abstract:

Methane emissions from abandoned oil and gas wells have recently been included in national greenhouse gas inventories in the United States and Canada. However, they are yet to be included in national inventories of any other oil-and-gas-producing country. Studies show that abandoned wells are sources of methane emissions, but the rates of these emissions remain uncertain. Most measurements from abandoned wells have been made in the United States. Outside of the United States, measurements have been made in Canada, the United Kingdom, and the Netherlands but differ from the U.S-based studies as they focused on soil gas emission rates.

Here, we analyze direct methane flowrate measurements from the United States, including new measurements from British Columbia (Canada) and Oklahoma (United States). Methane emission factors range from 0.10 g/hour per well to 37 g/hour per well depending on the plugging status and well type, with the overall average at 6.4 g/hour, which is higher than the 1.7 g/hour recorded from soil gas emissions in the United Kingdom and lower than the average of 15 g/hour recorded in the Netherlands.

We scale these emission factors up to the national level for the United States and Canada. We geospatially and statistically analyze 455 direct methane flowrate measurements from abandoned oil and gas wells and apply these emission factors to well counts across both countries. We find that annual methane emissions from abandoned wells are underestimated by 330% in Canada and by 40% in the United States on average. The degree of underestimation in Canadian inventories, where published empirical measurements are still lacking, highlights the importance of acquiring country-specific emission factor data. Overall, we find that abandoned wells remain the most uncertain methane source in the U.S. and Canada, and likely elsewhere, which emphasizes the need for further research into this new and uncertain source category.