FUGITIVE HYDROCARBON EMISSIONS FROM INDIANA OIL/GAS WELLS INTO THE ATMOSPHERE

Regional studies in the USA indicate that hydrocarbon gas emissions from improperly sealed and abandoned oil/gas wells contribute significantly to anthropogenically emitted greenhouse gases, predominantly in the form of methane. There are more than 80,000 active, inactive, plugged and abandoned oil/gas wells in Indiana and their fugitive emissions so far have not been quantitatively studied. This study is a first attempt to (i) explore the extent of hydrocarbon gas emissions from oil/gas wells in Indiana and (ii) to evaluate strategies to mitigate hydrocarbon emissions into the atmosphere. We investigated 25 active, temporarily deactivated or plugged-abandoned oil/gas wells across Monroe, Daviess and Sullivan counties in Indiana. Fugitive emissions on the order of liters per hour qualified one of those wells in the north of Bloomington to serve as a research site. Methane emissions were measured repeatedly using a static flux chamber. We found that the methane concentration in the flux chamber increased linearly with time at an average methane leakage rate of ca. 2 L/hour. Methanotrophs are widely known to oxidize methane in soils, especially strongly in areas with natural seepage of methane. Soils adjacent to the leaking well and control soils 20 m away from the well were deployed in mesocosm experiments to evaluate comparative methanotrophic activities. During mesocosm experiments at room temperature over 138 hours, 4 g of soil from close to the well consumed 96.9 % of the 0.5 mL methane that had been added to the headspace of a 70-mL glass culture bottle, while the same amount of soil from 20 m away consumed only 14.4 % of added methane. Soil adjacent to the well exhibits higher methanotrophic activity than control soils. Ongoing experiments are evaluating whether prolonged exposure of soil methanotrophs to elevated concentrations of methane will enhance the methanotrophic activity. We further experimentally test the feasibility of a “methanotrophic mound” over geologic point sources of methane to sustainably mitigate hydrocarbon emissions.

Key words: gas well; hydrocarbon emission; Indiana; methane; methanotroph