Kirk Osadetz, CMC Research Institutes Inc.
December 15, 2016
Abstract
Natural and anthropogenic methane emissions are ubiquitous in sedimentary basins. Some human activities like the petroleum and coal based energy systems, agriculture and municipal solid waste disposal are human sources of these emissions. There are multiple potential sources that generate methane, but the impacts are similar regardless of their source. Unsaturated soils provide the major methane sink due to microbial methane oxidation, which reduces the net atmospheric methane flux from subsurface sources that migrate through the soil.
Most methane sources are not explicitly measured or monitored, but inferred using rational methods that are based on limited sampling and monitoring datasets. The 2010 Environment Canada national inventory, inferred Alberta upstream petroleum activities contributed emissions of 987.8 kt methane/yr, including “Accidental and Equipment Failure” methane emissions of 192.5 kt methane/year (19.5%) of which 78% (150.2 kt methane) is inferred attributed to surface casing vent lows and gas migration (SCVF/GM) from wells.
SCVF/GM is also measured annually and centrally compiled by some Provincial regulatory agencies such as the AER and BCOGC. Many leaking wells have been remediated, especially wells >300 m3/day. Currently, (2016/06/02) the Alberta annual SCVF/GM emission rate is about 84.4 × 106 m3, (~56.5 kt methane). The 2010 Alberta SCVF/GM methane emissions data was 63.5 kt methane or only about 42% of the 2010 National Inventory value. Measured and monitored SCVF/GM emissions have decreased progressively since 2008 and they are currently 11% less than the 2010 measured value, but 62% lower than the 2010 Alberta National Inventory estimates, an unexplained difference. Existing literature and reports do not portray wellbore SCVF/GM leakage accurately, primarily due to the reduction of these emissions with time, but also because some previous studies contain errors in fact.
The Upstream petroleum industry methane emission situation in in Canada is inferred different from that in the United States, where atmospheric methane emission increases are attributed to increased upstream petroleum activities. Canadian air quality studies find methane concentrations like the global atmospheric average and associated anomalies in heavier volatile organic carbon compounds are attributed to transportation emissions primarily.
Methane emissions effect: Public Safety and Human and Plant Health – although typically indirectly, as well as the climate. Impacts are similar regardless of the source of the methane and whether it is an emission of natural or anthropogenic origin. Rarely are significant specific impacts associated with Canadian upstream petroleum activities including SCVF/GM wellbore issues. Impacts from wellbores occur in the immediate vicinity of some wells, but similar effects at a distance may have other natural or anthropogenic sources, most which are not well characterized or documented. Cases of demonstrated or inferred contamination by leaking petroleum wellbores is commonly based on isotopic hydrocarbon composition and the assumption, probably incorrect, that light hydrocarbon compositional components are stratigraphically immobile generally.
There is also an unsubstantiated perception that other potential sources of methane emissions such as water wells are not significant sources of wellbore leakage and atmospheric emissions, although these are not carefully monitored and they were not generally constructed with comparable regard for wellbore integrity. Leaking petroleum wellbores are identified, regularly monitored and serious leaks are remediated. The success of the monitoring and reporting strategy is illustrated by the declining SCVF/GM emissions with time, despite the increase in the number of petroleum wells. Whether other potential sources of natural and anthropogenic methane emissions, such as water wells, agricultural activities, landfills, or the agricultural degradation of the soil methane sink should be subject to similar monitoring and remediation strategies is outside the scope of this report, but it appears that SCVF/GM methane emissions were incorrectly inventoried in 2010 and that, despite their being the best characterized and most comprehensively and regularly monitored methane emission sources they have also been one of the targets of the earliest emissions reductions strategies. This emphasis on wellbore SCVF/GM does not reflect the relative importance of their emissions contributions.
Wellbore SCVF/GM leakages are clearly the most comprehensively monitored, reported and the most aggressively remediated sources of Canadian methane emissions. Other sources should emulate the monitoring and remediation example provided by SCVF/GM monitoring and remediation actions. A uniformly described Canadian methane leakage sources database from both natural and anthropogenic sources would be useful and informative for both GHG mitigation and policy formulation.
# 15-SGRC-09