Computational fluid dynamics-based modeling of methane flows around oil and gas equipment

Abstract

Recent studies estimate that emissions from oil and gas (O&G) production facilities contribute between 20 to 50% of the total methane emitted in the US; therefore, quantifying and reducing these emissions is crucial for achieving climate goals. Some methane quantification depends on both measuring methane concentrations and converting these to emissions through a modeling framework. Currently, simple atmospheric dispersion models are primarily used to quantify emissions and concentrations, but these estimates are highly uncertain when quantifying emissions from complex aerodynamic sources, such as oil and gas facilities. This investigation uses a CFD modeling approach, which can account for aerodynamic complexity but has hitherto not been used to model methane concentrations downwind of a methane release of known rate and compared against in-situ measurements. High-time resolution (1 Hz) methane concentration and meteorological data were measured during experiments conducted at Methane Emissions Technology Evaluation Center (METEC) on 21st March and 11th July 2024. The METEC site configuration, measured wind data, and controlled emission rates were used as input for CONVERGE CFD to model downwind methane concentration. The downwind modeling was done between 20-70 meters, each from two different points of release in two separate controlled release experiments— one from a separator and another from a wellhead. In these experiments, we found that the CFD model can predict methane concentrations downwind of the release to a good degree. The fractional bias in maximum modeled concentration was under 32%, and the fractional bias in time-averaged mean methane concentration was under 41%. The model evaluated on multiple metrics to assess its performance in estimating methane concentrations at typical fence-line distances (∼30 m). These results help to understand external flows and the ability of CFD models to predict downwind concentrations in aerodynamically complex environments.