Emissions of reactive organics from oil and gas-related combustion sources

Abstract:

While methane emissions from oil and gas operations have been the focus of many recent studies, less work has been carried out to understand oil and gas-related emissions of non-methane organics. Much of the available information on this topic is decades old, contains few samples, and does not include the full speciation needed to understand the air quality and human health impacts of these important emission sources. We have engaged in several recent projects to better understand the magnitude and speciation of non-methane organic compound emissions from oil and gas sources. This presentation focuses on findings from deployments of 17 portable sample collection stations around Utah’s Uinta Basin. We used these stations to collect hundreds of atmospheric samples in several deployment configurations over two years and analyzed the samples for a suite of 72 volatile organics, including hydrocarbons, alcohols, and carbonyls.

We found that concentrations of reactive organics, including alkenes and aldehydes, were higher in areas dominated by oil development compared to areas dominated by gas development. Ethylene and propylene stood out in particular, with a few samples exhibiting ethylene+propylene concentrations higher than the sum of all alkanes. Overall, alkenes were more than 10% of total organics in oil-dominated areas, compared with just 2% in gas-dominated areas, and aldehydes were significantly higher in oil-dominated areas as well. What is more, light alkenes were responsible for about 40% of the total ozone reactivity of atmospheric organics in the oil-producing Uinta Basin, and carbonyls accounted for 10%.

Most oil wells in the Uinta Basin utilize two-stroke, rich-burning artificial lift engines to bring oil to the surface, while gas wells do not. Combustion processes like those from engines are known to emit alkenes and aldehydes, and rich-burn conditions are associated with incomplete combustion and increased emissions of reactive organics. Recent direct emissions measurements also point to artificial lift engines as the probable source of elevated alkenes and aldehydes in the oil-producing Uinta Basin. These lines of evidence together show that emissions of reactive organics from oilfield engines are likely higher than has previously been assumed.