A spatially resolved fuel-based inventory of Utah and Colorado oil and natural gas emissions

Abstract:

A fuel-based approach is presented for estimating emissions from US oil and natural gas production that utilizes state-level fuel surveys of oil and gas engine activity, well-level production data, and emission factors for oil and gas equipment. Emissions of carbon dioxide (CO₂) and nitrogen oxides (NO_x) are mapped on a 4 km x 4 km horizontal grid for 2013-14 in Utah and Colorado. Emission sources include combustion from exploration (e.g., drilling), production (e.g., heaters, dehydrators, and compressor engines), and natural gas processing plants, which comprise a large fraction of the local combustion activity in oil and gas basins. Fuel-based emission factors of NO_x are from the U.S. Environmental Protection Agency, and applied to spatially-resolved maps of CO₂ emissions. Preliminary NO_x emissions from this study are estimated for the Uintah Basin, Utah, to be ~5300 metric tons of NO₂-equivalent in 2013. Our result compares well with an observations-based top-down emissions estimate of NO_x derived from a previous study, ~4200 metric tons of NO₂-equivalent. By contrast, the 2011 National Emissions Inventory estimates oil and gas emissions of NO_x to be ~3 times higher than our study in the Uintah Basin. We intend to expand our fuel-based approach to map combustion-related emissions in other U.S. oil and natural gas basins and compare with additional observational datasets.