Investigating factors associated with fugitive gas migration in Northeast British Columbia, Canada

• Main Author: Sandl, Elyse
• Format: Text
• Language: English
• Published: University of British Columbia 2020
• Subjects: Canada; British Columbia; Fort Nelson
• Online Access: https://dx.doi.org/10.14288/1.0389605; https://doi.library.ubc.ca/10.14288/1.0389605

Oil and gas wells are engineered with barriers to prevent fluid movement along the wellbore. If the integrity of one or more of these barriers fails, it may result in subsurface leakage of natural gas outside the well casing, a process termed fugitive gas migration (GM). Knowledge of the occurrence and causes of GM is essential for effective management of the potential risks of GM. In BC, oil and gas producers are required to report well drilling, completion, production, and abandonment records for all oil and gas wells to the provincial regulator. This well data provides a unique opportunity to identify well characteristics associated with higher likelihoods for GM to develop. Here I employ multilevel logistic regression to understand the associations between various well attributes and reported occurrences of GM, found in 0.6% of the 25,000 oil and gas wells in BC. My results indicate that there is no meaningful association between the occurrence of GM and hydraulic fracturing or directional drilling. Overall there appears to be no engineering attribute in the study database that is conclusively associated with GM. The best predictors of GM are indicators of well integrity loss, such as surface casing vent flow, remedial treatments, and blowouts, and geographic location. I ascribe the spatial clustering of GM cases to the local geologic environment, and I speculate that there are links between particular intermediate gas-bearing formations and GM occurrence in the Fort Nelson Plains area. The results of this study suggest that oil and gas wells in high GM occurrence areas and those showing any attribute associated with integrity failure, such as surface casing vent flows, should be prioritized for monitoring to improve the detection of GM.