Methane inventories: system-level vs site-level

Canada’s second most abundant greenhouse gas methane (CH4) makes up 13% of Canada’s total GHG emissions, and the energy sector is the largest contributor of CH4. In response to the climate crisis, Canada’s federal government committed to reducing CH4 emissions 40-45% below 2012 levels by 2025 and these targets are based on current component or system level inventories, which are disputed.

Canada’s current methane inventory (system-level) is based on a “bottom-up” approach whereby unintentional methane leaks from equipment are estimated by multiplying equipment components by corresponding average emission factors. There are several problems with this method which is prone to under-estimations of total methane emissions.

  • It relies on the OGI survey method and several studies have flagged discrepancies between industry reported inventories and measurements.
  • There is uncertainty surrounding equipment component counts due to field technician variability and bias, and given the high number of equipment components at production sites only a portion of equipment are measured.
  • The number of Canadian production sites is also high (22,000 facilities plus 165,000 wells) and due a very high number of components, the percentage of samples is low
  • Furthermore, individual emission reports come from more than 50 subtypes of facilities and wells, which don’t provide complete explanations of equipment and disregard geolocations of infrastructure, which might matter.

FluxLab’s inventory (site-level) begins with calculating emission factors (generated from the mobile-based measurements) for physical sites, which we define as any infrastructure that falls within a 90 m area. The size was determined using our field experience and 90 m was judged as the size of a “typical” well pad. We then group and identify every cluster (90-m wide) of infrastructure. We next allocate a site type (e.g., single oil well) and an emission factor to each site. The emission factor is based on the site type, and region when possible. Finally, we sum these values to get a total inventory estimate.

Using a site-level method, we calculated a Canadian methane inventory of ~5,337,000 m3 CH4 day-1 for 2018, which is consistent with results from studies. Our inventory is almost twice that of the government’s system-level method (~2,880,000 m3 CH4 day-1, in 2018), and we continue to work in partnership with federal and provincial governments and organizations to improve inventory calculations and knowledge. Fluxlab’s alternate methane emission inventory method for Canada’s oil and gas industry combines existing and new gas measurement data in quality methane maps. Via an interactive app this inventory is available for tech developers, operators, regulators and others working on methane reduction strategies.

In order to understand the effectiveness of our greenhouse gas reduction efforts, we must first have accurate inventories that can be used to benchmark policies, measurement technologies, emission reporting, and, hopefully, our national successes.

Martin Lavoie