June 2024
Executive Summary
Methane (CH4) is a colourless, odourless, and flammable Greenhouse Gas (GHG) that can be released into the atmosphere during exploration, extraction, production, and distribution of natural gas. The International Panel on Climate Change (IPCC) indicated in 2021 that approximately 60% of global CH4 emissions originate from anthropogenic sources, and approximately 82.5 megatonnes (Mt) can be attributed to oil and gas activity. Fugitive CH4 accounted for 8.2% of total emissions in Canada in 2021 (Environment and Climate Change Canada (ECCC), 2023a). Despite having a shorter atmospheric lifespan than carbon dioxide (CO2), CH4 absorbs more energy making it 28-36x more potent than CO2 as a GHG over a 100-year period.The IPCC estimated that in 2021, 180 billion cubic meters of gas have leaked globally during oil and gas operations. Leaks can be unplanned events as well as intentional due to specific required maintenance procedures associated with equipment design, such as pneumatic valve controllers. In Canada, 13% of the nation’s total GHG emissions are due to CH4, and of this, approximately 40% is sourced from the oil and gas sector (ECCC, 2021).
To reduce contributions to GHG emissions, the Leak Detection and Repair (LDAR) initiative has become a regulated (ECCC with provincial equivalency agreements) industry standard in Canada. Emissions associated with leaks must be reported in addition to regular annual disclosure of GHG emissions from typical oil and gas industrial operations that are not associated with leaks. Emission rates are reported on a tonnes/year basis, which is a mass flow rate metric. Requiring emissions to be reported using this metric creates challenges for LDAR programs based on a part per million volume-based metric (a concentration metric).
The LDAR compliance threshold is defined by ECCC as 500 ppmv – leaks detected at higher concentrations are flagged for mitigative action. Methods have been developed to measure fugitive volatile organic compounds (VOCs) as well as CH4 concentrations. The United States Environmental Protection Agency (US EPA) developed Method 21 (US EPA, 2017) for measuring VOC and CH4 concentrations. Various measurement instruments are available for assessing compliance, as laid out in Method 21. ECCC (2018a) similarly lists eligible leak detection instruments, primarily referencing the Method 21 document.
GHG emission inventories can be determined based on equipment component counts, fluid throughput, and estimates of component-specific leakage rates and probability (Jamin, 2018). Average emission factor (EF) values can be applied (such as those summarized by US EPA, 1995) to derive mass emission leak rates for GHG reporting, albeit with considerable uncertainty and lack of accuracy.
While ppmv measurements are of considerable value for an LDAR program as compliance is measured against a ppmv threshold, they have limited value for reporting GHG mass emissions under section 46 of the Canadian Environmental Protection Act (CEPA) (ECCC, 1999), which requires a tonnes/yr metric. Correlations are available, such as those provided by US EPA (1995), for estimating mass emission rates from ppmv data for GHG reporting. These correlations can be infrastructure component (e.g., valve, flange) and VOC type specific, leading to greater refinement, and were primarily focused on VOCs rather than CH4.
While correlations that are component and VOC type specific may have improved accuracy over the use of EFs and equipment counts for estimating mass emission rates, they do not reflect variability in mass emission rates due to differences in equipment status, meteorological conditions, operating environment, and numerous other factors. As a result, the use of correlations is associated with uncertainty when LDAR data on a ppmv basis are used to quantify leak-related GHG emission rates. For example, the California Air Resources Board (Sage, 2019) citing regression work summarized by the US EPA (1995), indicated r2 values for regressions specific to equipment types such as valves and flanges of 0.609 and 0.753, respectively. While a r2 > 0.7 can be considered a good correlation, it is associated with considerable variability in quantifying emissions on a mass emission rate basis extrapolated from a ppmv measurement.
More recently, technological advances have improved detection limits and accuracy of equipment that measures mass emission rates of CH4, which has the potential to improve the quality of GHG emission inventories as well as the implementation of LDAR programs. This in part requires a LDAR threshold expressed on a mass emission (or flow rate) basis, which can be considered comparable to the federal threshold of 500 ppmv or provincial threshold of 10,000 ppmv.
20-ARPC-06