ATMOSPHERIC MIXING MODELS OF FUGITIVE METHANE EMISSIONS FROM SHALE GAS DEPOSITS

Natural gas emits less CO₂ during combustion than traditional petroleum fuel sources. However since its primary component is methane – which has ~25 times the “greenhouse potential” as CO₂ – it is actually worse for the environment prior to combustion. Even relatively small leaks of pre-combusted natural gas (from infrastructure such as drill sites and pipelines) therefore have significant environmental implications. Quantifying these “fugitive” gas emissions is critical for assessing the holistic environmental impact of natural gas. It is possible that methane inadvertently added to the atmosphere from fugitive emissions actually nullifies any benefit from lowering direct CO₂ emissions. Thus, locating and quantifying fugitive emissions is crucial to preventing leaks on a reasonable timescale.

To further understand these highly variable emissions this project investigates the design and implementation of various fugitive gas models from laboratory to field scale. A MatLab™ mixing model simulates the expected concentration of fugitive gases after mixing with the atmosphere under various conditions and across a broad area. This is used to determine lower limits to which analytical (compositional and isotopic) approaches can detect leaks, optimize spatial and statistical sampling strategies, and estimate the volume/flux of fugitive emissions. To strengthen the model it will be tested with a physical “sandbox” experiment and compared to previous studies. Eventually this model will be applied to samples from the Antrim Shale, Michigan Basin, where carbon dioxide that is extremely enriched in ¹³C (+20‰ compared to atmospheric values of -9‰) produced alongside methane may serve as a “marker” for detecting leaks.