Determining times to detection for large methane release events using continuously operating methane sensing systems at simulated oil and gas production sites

Methane release events with large instantaneous emission rates are significant sources of emissions in multiple oil and gas production regions. Large release events detections are generally based on short duration observations, such as observations from aircraft or satellites. To be included in annual emissions reporting, instantaneous emission rate observations must be coupled with an estimate of event duration. Continuously operating, fixed point methane monitoring systems provide a mechanism for narrowly constraining event durations, however even continuously operating monitoring systems do not detect releases from all emission sources at all times. A method for using continuous monitoring system data to evaluate time to event detection was developed and demonstrated using data from a monitoring network operating in the Permian Basin of west Texas. Time to detection for events depends on meteorological conditions, the number and precision of the sensors, the criteria used in defining a detection and the positioning of the sensors relative to emission sources. For the case study in the Permian Basin, the presence of a single monitoring system per site enabled a time to detection of large release events that averaged less than half a day, and the methodology for determining bounds on event duration is applicable to a wide range of locations and types of sites.