Gaussian Plume Inversions of Methane Fluxes from a Super-Emitting Orphan Well using Ambient Observations to Prioritize Plugging & Carbon Credits
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Citation: "Gaussian Plume Inversions of Methane Fluxes from a Super-Emitting Orphan Well using Ambient Observations to Prioritize Plugging & Carbon Credits" (in prep) Corresponding Author: Emily Follansbee (efollansbee@lanl.gov) Abstract The U.S. has ~3.6 million abandoned wells that emit 0.05-0.55 Tg methane (CH4) y-1. Of these ~2.3% are orphan wells that contribute ~3% to CH4 emissions are funded for plugging with $4.7B in the US Bipartisan Infrastructure Law. Super-emitting orphan wells (>10 kg CH4 h-1) that can increase average emissions by over an order of magnitude are under-sampled. Furthermore, these emissions are at or below the detection threshold of current airborne and satellite remote sensing surveys. Therefore, more sensitive, reliable, affordable, and scalable CH4 flux quantification methods are needed to prioritize orphan well plugging. We evaluate a simple method to estimate emissions using in situ ground measurements of CH4 concentrations and winds downwind of an orphan well in the Permian basin. A gaussian plume model constrained by empirical estimates of plume dispersion was used to derive fluxes of 10.53 ± 1.16 Kg CH4 h-1 during a venting procedure that agrees with directly measured volumetric flow rate of 9.0 ± 0.25 Kg CH4 h-1. This leak rate is 71% greater than that measured 7-months earlier and attributed to the reservoir pressure buildup from closing the vent that will bias reporting. We discovered a leak through the surface-casing that is inferred to be 0.43-0.67 Kg CH4 h-1 by both our gaussian analysis and by transecting the plume with an uncrewed aerial system. We demonstrate that gaussian inversions can accurately quantify fugitive leaks from orphan wells, and reduce uncertainties associated with super-emitters, a small fraction that contribute the most to total CH4 emissions. Version 1 created: 2024-04-18