Modeling of VOCs and criteria pollutants from multiple natural gas well pads in close proximity, for different terrain conditions: A Barnett Shale case study

Abstract

Despite potential advantages in spatial/temporal coverage compared to measurement studies, few modeling studies have been conducted of non-methane air pollutants associated with natural gas. The objective of this study was to model volatile organic compound (VOC) and criteria pollutants from natural gas production, considering multiple well pads under different terrain conditions, using the Texas Barnett Shale as a case study.Primary criteria pollutants from compressor engines (carbon monoxide, CO; nitrogen oxides, NOx; particulate matter, PM10; sulfur dioxide, SO2) were modeled using AERMOD, along with benzene as a VOC with potential worst health impacts, from condensate tanks, fugitive sources, and compressor engines. Modeling was conducted for level, moderate, and strong sloping terrain, with well pad densities of 1.4–1.9 well pads/km2, exemplifying common maximum densities in the Barnett Shale.In most cases, well pads were far enough away from each other that maxima at individual well pads were not influenced by other pads. When the same well pad arrangement and emission rates were modeled in different terrain types, strong sloping terrain gave the highest maximum concentrations.For the well pad arrangements and emission scenarios modeled, CO, NOx, PM10, and SO2 maximum concentrations were less than the 1-h National Ambient Air Quality Standards (NAAQS). Benzene concentrations, however, exceeded the 1-h effect screening level (ESL) for level and strong sloped terrain, and the annual ESL for all terrain types. The maximum benzene emissions modeled likely represent a reasonable worst-case for the Barnett Shale but underestimate emissions for areas with wetter gas.