British Columbia (Canada) Ministry of Energy, Mines, and Low Carbon Innovation released their report (#2021-16) in May, 2021. They reported that rapid expansion of unconventional gas extraction has been accompanied by environmental concerns related to fugitive gas due to wellbore integrity failure of energy wells, principally in the United States (Vidic et al., 2013).
The risks associated with fugitive gas migration (GM) include deterioration of groundwater quality, increase in greenhouse gas emissions, and explosive hazards in confined spaces. Northeastern British Columbia (NEBC) hosts some of the world’s largest unconventional gas reservoirs, which contribute more than 60% of the province’s total gas production as of 2016 (Adams and Balogun, 2016). However, no assessments of baseline groundwater quality were conducted prior to energy resource development, and therefore groundwater dissolved natural gas conditions were poorly understood on a regional scale.
This project, conducted through the Energy and Environment Research Initiative (EERI) at the University of British Columbia and performed in complement to two other projects (see (here) and (here)), aspires to address knowledge gaps about environmental impacts and environmental fate of GM in geology typical of NEBC.
The principal research objective is to characterize groundwater quality in the Peace Region of NEBC, an area of active oil and gas development, with a specific focus on the distribution, concentration, and origin of dissolved hydrocarbons, principally methane. The project objectives were achieved by the installation of and sampling from a network of 29 monitoring wells (MW) distributed through the Peace Region at locations determined by criteria described
in earlier Geoscience BC reports (Allen et al., 2021; B. Ladd et al., 2020). Results from this project will inform appropriate groundwater monitoring strategies in light of continued oil and gas development for the region.
In this activities report, the university authors provided the motivation, background, and information on the project progression as well as summaries of their principal findings, which are fully described in peer-reviewed journal publications and student theses, some under preparation. These knowledge products include:
• An overview of fugitive gas in northeastern BC, and preliminary results from this project in the context of the wider EERI program.
• A study focusing on determining the distribution and sources of dissolved natural gas, principally methane, based on sampling from the newly installed monitoring network of 29 wells, and from domestic wells across the Peace Region.
• A study quantifying recharge mechanisms of a buried-valley groundwater system using a steady-state groundwater flow model.
• A manuscript describing regional-scale and local-scale methane characterization studies, as well as the buried-valley recharge study mentioned above.
• A study of the geochemical composition of subsurface materials in NEBC and how fugitive gas could affect groundwater quality.
• A study investigating the petrophysical properties of sedimentary formations encountered during drilling across the Peace Region to better constrain how mobile any fugitive gas may be in the shallow subsurface.
Principal findings:
• Productive groundwater zones are typically found at base of quaternary sediments or the fractured top of bedrock (Goetz, 2021).
• Median groundwater total dissolved solids (TDS) content in samples from the monitor-well network was approximately 1800 mg/L, ranging from a minimum of 489 mg/L to a maximum of approximately 5997 mg/L (water TDS is considered excellent if it is less than 300 mg/L; water
with TDS > 1200 mg/L is considered unacceptable for human consumption) (Allen, 2021).
• Spatially averaged groundwater recharge rates in the Sunset Paleovalley, a system representative of NEBC, were estimated to be 16 mm per year; groundwater flow was slow - residence times averaged 2900 years (A. M. Goetz et al., 2021).
• Dissolved methane is ubiquitous in groundwater; concentrations in most samples are less than 0.1 mg/L. Concentrations greater than 1 mg/L were found in only 3 of 29 monitoring-well samples (Allen, 2021; Goetz, 2021 and Goetz et al 2021 in preparation).
• Stable carbon isotopes, and the concentrations of methane, ethane and propane, indicate a biogenic origin of natural gas from all but one sample from the monitoring-well network (Allen, 2021; Goetz, 2021 and Goetz et al 2021 in preparation).
• Dissolved natural gas concentrations were not correlated with proximity of monitoring well to energy wells (Allen, 2021; Goetz, 2021 and Goetz et al 2021 in preparation).
• Methane concentrations in groundwater samples collected from the water-supply wells for the town of Hudson’s Hope ranged from between 24.7 to 95.9 mg/L. No higher-chain hydrocarbons were detected in the samples. Stable-carbon isotopes suggest that the methane is thermogenic. The methane is not related to energy development; the most likely origin is the Gething Formation coalbeds, which underlie the town’s buried-valley water-supply aquifer (Goetz, 2021).
• The highest methane concentration from monitoring-well network samples was 32.0 mg/L in well EERI 16. Isotopes and wetness indicate that the gas is thermogenic. There are two potential explanations for origin of the gas:
1) proximal energy wells, 3 of which are less than 200 m from EERI 16, although there are no reports of surface casing vent flow, gas migration, or abandoned well leaks;
2) natural geologic pathways, associated with faulting, could connect the sampling depth to a deeper gas source. Further investigation is required to distinguish between these explanations (Allen, 2021; Goetz, 2021 and Goetz et al 2021 in preparation).
• Water quality results from samples from domestic water wells were statistically equivalent to those from samples collected from newly installed monitoring wells (Allen, 2021 and Goetz et al in preparation).
Ultimately, the data and knowledge resulting from this project have allowed us to comprehensively assess regional groundwater natural gas conditions in the Peace Region, northeastern BC. Findings from the various research outputs will help support policy making by regulators and provide technical guidance for groundwater protection and GM, including informing groundwater monitoring strategies.
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