124-7 Temporal Variability in Methane Emissions from Non-Producing Oil and Gas Wells

Session: Fixing the Silent Leak: Identifying, Quantifying, Prioritizing, and Mitigating the Environmental and Health Impacts of Legacy Oil and Gas Drilling in North America

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Abstract:

Non-producing oil and gas wells (OGWs) are increasingly relevant in methane mitigation policy, yet most greenhouse gas inventories depend on snapshot measurements without considering how emissions may be varying over time. We combine short (two-day, n=9) and long-term (three-to-five-year, n=26) repeat measurements of methane emissions from non-producing OGWs in Canada and the United States. We measured surface casing vents (SCVs) and wellheads separately, as well as performed geochemical analysis of hydrocarbon gas composition (C₁/(C₂+C₃) and stable carbon isotope signature of methane (δ¹³C-CH₄). In the short term, high-emitting wells (>1,000 mg/h) showed far greater stability over time: their relative variability was three to four times lower than that of medium (100–1,000 mg/h) and low (<100 mg/h) emitters, and SCVs fluctuated less than wellheads. Geochemical parameters (δ¹³C-CH₄ and C₁/(C₂+C₃)) were respectively 1.4 and 1.8 times more consistent at high-emitting (>1,000 mg/h) SCVs compared to wellheads at the two-day timescale.  The variability in geochemical parameters was generally reflected in variable source attribution categories of emissions.  Over three to five years, emission rates did not exhibit consistent upward or downward trends in emission rates, regardless of emission rates, and even at plugged wells. However, at the only well measured before and after plugging, we saw two and six orders of magnitude decrease in SCV and wellhead emissions, respectively. Overall, both the magnitudes and geochemical parameters of methane emissions can change over time at both multi-day and multi-year time scales. However, additional studies are needed to understand the drivers of these changes.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8425

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