Methane Dispersion from Leaky Petroleum Wells Into Groundwater: Can Point-Source Well Leaks Cause Large Plumes?

Leakage of fugitive gas, mostly methane, from some oil and gas industry wells is a long-standing, unresolved engineering problem causing concern for groundwater resources and the atmosphere. This played a central role in the banning or placing moratoria on shale development in four Canadian provinces and most European countries. Gas leakage measurement at the wellheads is now common but determination of leaky gas in the subsurface away from wells is rare. Sampling domestic/farm wells in areas of shale development is standard but generates controversy because these wells have many complications. Isotope signatures in Pennsylvania provide evidence of methane from recently drilled gas wells showing up in domestic/farm wells within one kilometer of gas wells. This implies that somehow gas manages to find pathways for buoyancy-driven gas movement with advection of dissolved methane from leakage points along gas wells outward and upward to eventually cause detectable presence in the shallow freshwater zone supplying the household wells. For there to be reasonable likelihood of fugitive methane being detected in these wells, point-source methane from well leaks must undergo strong spreading for the methane to expand into a large plume and the methane must be recalcitrant enough to endure during plume migration. This presentation uses the literature for plumes from NAPL, air sparging and CO2 field injection experiments along with a recent methane injection experiment in the shallow sand aquifer at the Borden field experiment site in Ontario. Here, methane injected at two well points resulted in strong effective dispersion due to process combinations acting on the gaseous and dissolved methane. This experiment sets the stage for the design of methane injection experiments planned for a new field experiment station focused on sedimentary bedrock established by the Containment and Monitoring Institute (CaMI) and the University of Calgary near Brooks, Alberta.