--> Spatial and Temporal Variability of Methane Emissions Near Coal Seam Gas Fields Associated With Base Level and Anthropogenic Sources

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Spatial and Temporal Variability of Methane Emissions Near Coal Seam Gas Fields Associated With Base Level and Anthropogenic Sources

Martin J. Kennedy, Murray Hamilton, Michael Hatch and Vincent Robert

Earth and Planetary Sciences, Macquarie University, Sydney, New South Wales, Australia
Department of Physics, University of Adelaide, Adelaide, South Australia, Australia

June 20, 2016 Monday 9:05 A.M. AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada

Abstract

We address the issue of source attribution for anthropogenic emissions of methane. Mobile survey measurements of methane concentration from a cavity ring down spectrometer (CRDS) are reported from a range of areas in eastern and southern Australia associated with anthropogenic methane relase. We confirm reports of increased concentration of CH4 downwind in some parts of coal seam gas fields (less than 5 ppm) but note that elevated concentration was not endemic throughout this gas field. The greatest CH4 concentrations (>16ppm) in the region was associated with geological (natural) gas seeps. While CSG serves as a focal point for the debate surrounding fugitive emission regulation, in general, higher CH4 concentration values were associated with other anthropogenic sources including urban landfills (>350ppm) and pipelines (17 ppm), agricultural activities (>20 ppm), and open pit coal mines(> 10ppm). Mobile CRDS methods provide the capability of tracing sources of CH4 emissions in the landscape through concentration gradients. Repeat measurements, however, demonstrate the extreme temporal and spatial variability of CH4 concentration that is influenced not only by the release rate of a particular source but by the meterological conditions controlling the stability of the local air column. Our data show that turbulence and mixing during daytime in summer lead to rapid mixing and transport and insensitivity to all but the most active sources while inversions forming at nighttime in winter trap CH4 close to the ground increasing its concentration. While CRDS offers a quantum step forward in moving from inference of methane sources in a study region to direct determination of the number and locations of different sources, quantifying the flux of CH4 from each type of source requires integration of concentration with the dimensions and exchange rate of the air mass containing the plume. Additional methods of flux determination are necessary to improve GHG management plans.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016