CHARACTERISTICS, MAGNITUDES AND IMPACTS OF PETROLEUM WELL INTEGRITY ISSUES IN ALBERTA

CH₄ emissions, migration or contamination from petroleum activities, including surface casing vent flow (SCVF), gas migration (GM) and aquifer contamination due to well integrity issues can impact: safety, climate, groundwater resources, crop and plant health, human health and business performance. SCVs coupled with improvements in well design, construction and regulatory compliance typically suppress gas migration and aquifer contamination, such that groundwater impacts are uncommon, although exceptions occur. Likewise, safety impacts are now uncommon. Well integrity issues affect about 10,000 of the approximately ¾ of a million wells in Alberta and these emit, on average about 13 m³/day, making climate impacts a key concern, that accounts for about 20% of Alberta’s upstream methane emissions.

Plant impacts associated with pipeline leaks mimic GM issues. Impacts are rarely due to CH₄ asphyxia, but more commonly, leaks are indirectly due to CO₂ induced stress or asphyxia due to vadose zone microbial oxidation of migrating gas. The effects of anthropogenic and natural CH₄ seepage on vegetation and crops are indistinguishable. Where microbial oxidation of CH₄ produces CO₂, vegetation can also be impacted by groundwater chemistry changes and inorganic chemical reactions among CO₂, groundwater, minerals and vegetation. There have been several attempts to determine correlations between GM CH₄ flux and plant health impacts. While variable plant health and growth effects occur, including improvements in some species at low gas migration rates, detrimental impacts and even plant mortality occur at higher leakage rates. However, no quantitative recommendations related to gas migration rate exist because impacts are complicated by independent factors including, but not limited to, soil composition and characteristics, meteorological conditions, the microbial flora, and the plant species. There are several “sinks” where CH₄ is oxidized, in the atmosphere, oceans and in the vadose zone of soils. The effectiveness and efficiency of the microbial soil sink plays an important role in the rates of microbial CH₄ oxidation. The microbial soil CH₄ sink can be affected adversely by agricultural and land use practices including the efficiency and vitality of vadose zone microbial CH₄ oxidation.