The leakage of natural gas from compromised well casings can lead to the upward migration of methane through saturated and unsaturated zones, and in some cases to the atmosphere. A primary goal of this research was to evaluate the fate and transport of methane at seven natural gas venting pilot sites. At each of the seven pilot sites, natural gas wells were vented two meters below surface into the unsaturated zone above the shallow water table. At each site, seventeen soil gas sampling probes installed 0.3 meters below surface were sampled on several occasions for oxygen, methane, and carbon dioxide concentrations. Surface methane readings were taken at each location. This primary data set was supplemented with methane and carbon dioxide flux measurements and carbon stable isotope analyses at selected locations. The highest concentrations of methane were in general detected near the vents. Spatial and temporal patterns in methane, carbon dioxide, and oxygen concentrations in the soil gas probes and flux meters indicate significant microbial methane oxidation (methanotrophy) that decreased methane migration. The implications of these findings on the natural and enhanced attenuation of methane at leaking wells will be discussed.
Primary Author / Conference Presenter:
Dr. Glenn Ulrich
Rolla, Missouri, USA
Tara Coulombe, Parsons, Calgary, Alberta, Canada
Branko Marjanovic, Parsons, Calgary, Alberta, Canada