Evaluation of an Atmospheric Tracer Method at an Airfield for Use in Quantifying Natural Gas Well Development and Completion Emissions

Oil and natural gas production throughout the United States has been dramatically increasing in recent years, due in large part to hydraulic fracturing processes that allow for extraction of these fuels from unconventional wells. With this rise in well drilling sites comes the concern of air quality impacts on nearby communities. The various steps involved in well development processes may be possible sources of ambient emissions of methane and other VOCs. One way to quantify these emissions is through the tracer ratio method. Straightforward in principle, a tracer gas is released at a known rate near the source of emissions and its concentration, along with the concentrations of the compounds released from the source, are measured at points downwind. The ratio of these concentrations along with the flow rate of the tracer will be used to predict the emission rates of the gases from the well source.

In order to evaluate the effectiveness of this method before using it at an emission source, a series of experiments were conducted at an airfield in Fort Collins, Colorado. These experiments involved releasing both acetylene, as a tracer gas, and methane (to simulate an emission source) at known flow rates. The measured concentrations were used to compare the predicted emission rate of methane via the tracer ratio method to its actual emission rate. To obtain real-time measurements downwind of the methane and acetylene sources, an SUV equipped with a PICARRO A0941 mobile measurement kit and a PICARRO G2203 analyzer traversed the emission plume to locate peak concentrations. Additionally, a 3-D sonic anemometer was used on site to provide information on local meteorological conditions. Further analysis involved the deployment of silonite-coated canisters along the plume trajectory for the measurement of acetylene at a later date using a GC-FID instrument. These two methods of measuring acetylene concentrations will aid in validating the tracer ratio method, and the results from these field experiments are presented and discussed here.