Field investigation of surface casing vent flow and gas migration around leaky petroleum wells

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Leaky wells represent one of the greatest environmental liabilities to the oil and gas industry. Furthermore, this liability can be transferred to the public purse when wells become "orphaned" (i.e. no legally responsible or financially able party exists to manage abandonment), which is occurring more frequently in the current economic climate. Leaky wells can exhibit surface casing vent flow (SCVF), where gas (primarily methane) leaks inside the well casing(s), and/or gas migration (GM), where gas migrates from the target or intermediate zone, or through a hole in the well casing at some depth, to the ground surface. In particular, the extent of GM is not well delineated, gas transport pathways are not well understood, and remediation efforts are rarely successful on the first attempt (or second or third). There is a clear need for research to i) increase knowledge about how gas moves in the subsurface and ii) to develop best practices to monitor and guide remediation attempts around leaky wells.In collaboration with industry partners and gas migration service providers, this project will comprise a series of investigations at select leaky well sites, starting broad in scope (non-intrusive investigations at 5-6 wells) before focusing on one well site to conduct a comprehensive detailed study informed by the previous investigations. A variety of gas migration assessment approaches will be employed in the first part of the project, as per management practices of individual gas migration service providers, which will allow comparison of methods and techniques while providing data on SCVF/GM. This information will then be used to conduct a detailed subsurface investigation, including drilling, coring, geophysics, extensive groundwater sampling, among others. The end result will be a comprehensive conceptual model of subsurface gas transport (the first of its kind) as well as the development of a numerical model and guidelines for best management practices regarding monitoring and remediation of leaky wells.