Characterization of Early Stage Marcellus Shale Development Atmospheric Emissions and Regional Air Quality Impacts using Fast Mobile Measurements

Abstract:

The Marcellus shale is the largest shale gas resource in the United States and is found in the Appalachian region. Rapid large-scale development, and the scarcity of direct air measurements make the impact of Marcellus shale development on local and regional air quality and the global climate highly uncertain. Air pollutant and greenhouse gas emission sources include transitory emission from well pad development as well as persistent sources including the processing and distribution of natural gas. In 2012, the Aerodyne Inc. Mobile Laboratory was equipped with a suite of real-time (~ 1 Hz) instrumentation to measure source emissions associated with Marcellus shale development and to characterize regional air quality in the Marcellus basin. The Aerodyne Inc. Mobile Laboratory was equipped to measure methane, ethane, N₂O (tracer gas), C₂H₂ (tracer gas), CO₂, CO, NO_x, aerosols (number, mass, and composition), and VOC including light aromatic compounds and constituents of natural gas. Site-specific emissions from Marcellus shale development were quantified using tracer release ratio methods. Emissions of sub-micron aerosol mass and VOC were generally not observed at any tracer release site, although particle number concentrations were often enhanced. Compressor stations were found to have the largest emission rates of combustion products with NO_x emissions ranging from 0.01 to 1.6 tons per day (tpd) and CO emissions ranging from 0.03 to 0.42 tpd. Transient sources, including a well site in the drill phase, were observed to be large emitters of natural gas. The largest methane emissions observed in the study were at a flowback well completion with a value of 7.7 tpd. Production well pads were observed to have the lowest emissions of natural gas and the emission of combustion products was only observed at one of three well pads investigated. Regional background measurements of all measured species were made while driving between tracer release sites and while stationary at night. Median background mixing ratios of methane in Pennsylvania were observed to be 19.7 ppmv in the Southwestern part of the state and 20.5 ppmv in Northeast. The atmospheric background measurements provide information about the temporal and spatial characteristics of the Marcellus basin during the early stages of shale gas development.