Free gas transport in the subsurface: Analogues and applications

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We know free gas transport occurs in the shallow subsurface because one can see its expression as bubbles in springs, wetlands, geysers, and as free gas breakouts' during excavations and drilling. Yet we know little about free gas migration in the shallow', or non-saline, groundwater zone. There is almost no mention of free gas transport in groundwater textbooks, and virtually no conceptual diagrams in either textbooks or the published literature. It is consequently difficult to design effective field approaches to identify, monitor, and mitigate gas fluxes. In essence we don't know what free gas transport looks like' conceptually in the subsurface, nor do we know how to investigate or monitor for its occurrence.***Good scientific information on the nature and implications of free gas transport in the subsurface is hindering robust policy-making and public acceptability of development of two energy-related fields: carbon capture and storage (CCS) and fugitive methane gas migration (GM) around leaky petroleum wells***In CCS, supercritical phase CO2 is injected into deep geologic formations to curb anthropogenic releases to the atmosphere. Although a major environmental concern is free-phase gas leakage to surface, no field study has been conducted in this regard. More than 15 CCS operations exist, but none have been pushed to failure', and hence no free gas escape observed. ***Unconventional oil and gas development has transformed the world's energy supply, but is impeded in many jurisdictions due to public opposition. Migration of fugitive gases (mainly methane) from the vertical section of oil and gas boreholes and into freshwater aquifers has been identified as the major concern for groundwater quality. The most common evidence for gas migration is either surface casing vent flow' (inside the well casing) or surface-observable GM outside the casing. Regulators are currently struggling to define what GM means for water quality in freshwater aquifers that provide domestic well water supplies, and how GM be managed.***This work will study natural analogues where we know free gas transport in the shallow subsurface is occurring to improve our understanding of how to effectively detect, monitor, and remediate or manage free gases that are reaching fresh groundwater supplies and/or the ground surface. An extensive field program will be supported by specific lab studies. A parallel review of the distribution of non-hydrocarbon gases and abnormal pressuring in the Western Canadian Sedimentary Basin will provide regional context of free gas migration in recent geologic history.***The long term goals of this research are to develop a conceptual model that will guide free-gas migration investigations in the subsurface thus facilitating public understanding of energy industry activities, appropriate policy making, and efficient energy development that is environmentally responsible.*****