MIGRATION AND FATE OF FUGITIVE METHANE: LESSONS LEARNED THROUGH A MULTI-DISCIPLINARY CONTROLLED METHANE RELEASE EXPERIMENT

Fugitive methane associated with shale gas development became a controversial issue of significant public and scientific concern following a decade of intensive and widespread development. Subsequent research activity has significantly advanced our understanding of both natural and anthropogenic methane in the subsurface. In particular a suite of advanced geochemical and isotopic tracer tools have been developed able to characterize baseline conditions in areas of potential development and delineate sources of CH₄ in areas of contested impact. However, very little research has been conducted aiming to characterize migration and fate of fugitive CH₄ during and after leakage events, despite such events considered to be likely to continue to occur. Consequently a multi-disciplinary controlled methane release experiment was designed and conducted in order to characterize migration, impacts and fate of fugitive methane in a shallow aquifer system. During the experiment ~50 m³ of methane were injected into a shallow, unconsolidated, phreatic beach-sand aquifer over 72 days. Migration of injected gas was monitored at high resolution spatio-temporally via a combination of aqueous chemistry, microbial characterization, soil gas and surface efflux measurements and geophysical methods over 300 days. Our multi-disciplinary observations give unprecedented insight into the migration, impact and fate of fugitive CH₄ during and after a leakage event. Here, key results will be presented and conclusions made which have profound implications for monitoring methodologies and understanding of impacts of fugitive methane.