Strong temporal variability in methane fluxes from natural gas well pad soils

Özet

We measured methane and carbon dioxide fluxes at natural gas well pad soils and undisturbed soils in the RockyMountain and Gulf Coast regions of the United States, including producing and gas storage wells. We collectedboth short-term (15 min) and multi-day (between 3 and 8), continuous measurements at 47 well pads and twoundisturbed locations. Methane fluxes varied by more than an order of magnitude over periods as short as30 min (e.g., 19–593 mg m−2 h−1 in one instance), and diurnal and seasonal variability was also significant(e.g., spring-to-fall change from 509 to 14174 mg m−2 h−1). We hypothesize that short-term flux variability wascaused by pulsed flow of methane during its migration through the subsurface. Barometric pressure and wellconditions likely impacted fluxes, but we found only weak evidence for this. Bacterial methanotrophy appearedto impact methane flux magnitude and variability. We injected methane into the subsurface at one well, and wefound that, while fluxes of methane and carbon dioxide, and combustible soil gas concentrations, increased inresponse to the injection, the response was not uniform, and fluxes exhibited high hourly-scale variability, inspite of a constant injection rate. Methane fluxes tended to be higher at well pad soils compared to backgroundsoils (often much higher), and fluxes tended to be higher at well pad locations closer to the well head.