Surface Spills Associated with Oil and Gas Activities in Saskatchewan and Potential Impacts to Shallow Groundwater Resources

Abstract

Despite record oil production in Saskatchewan (SK), Canada over the last two decades, as well as emerging evidence of oilfield spills and concomitant public scrutiny, there has not been a detailed analysis conducted on the data surrounding the spatiotemporal distribution of spills, the identification of the source of spills, and the potential risks from spills to shallow groundwater supplies within the province. This lack of detailed analysis has contributed to the prevailing assumption within SK that oilfield spills are mainly associated with more recent high volume hydraulic fracturing (HVHF) activities, particularly in the Bakken Formation, as they are considered to be inherently riskier than older conventional extraction techniques (e.g., enhanced oil recovery (EOR)). The intent of this thesis is to provide a more informed understanding of the potential impacts associated with conventional and unconventional extraction activities as they pertain to shallow groundwater resources. This thesis draws primarily on the SK Upstream Oil and Gas Integrated Resource Information System (IRIS) Incident Report dataset. Descriptive and inferential statistics were employed to analyze temporal trends of the spills and oil and gas extraction activities from 1990 to 2019. Multiple regression analyses and geospatial modeling were applied to the spilled volumes to correlate their variability to the production intensity and analyze how these relationships vary spatially. The potential environmental risk of produced water (PW) spills was evaluated by characterizing the proximity of these incidents to water supply wells while considering surficial geologic properties and estimating the timescales over which contaminants will infiltrate the subsurface and be transported to shallow groundwater wells. There have been 24,878 oil and PW spills reported to the Saskatchewan Ministry of Energy and Resources totaling 4.10 x 105 m3. This includes a cumulative volume of spilled oil and PW of 9.20 x 104 m3 (22.5%) and 3.17 x 105 m3 (77.5%), respectively. Results of this thesis show that although there was a statistically significant increasing trend (p = 2e-05) in the Bakken producing well count from 1990 to 2019, there was no discernable pattern for spilled PW volumes (p = 0.1), which also holds true when comparing median spilled PW volumes pre and post Bakken HVHF boom (2006) (p = 0.2). Oil spillage had a statistically significant decreasing trend (p = 5e-04) overall with larger median spilled volumes before the beginning of the Bakken production boom as compared to after (p = 0.01). This indicates that Bakken oil production is not the predominant cause of surface spills. Additionally, multiple regression analysis revealed that total spilled volumes of PW and oil are closely and positively correlated with total production intensity volumes (R2 = 0.56 and R2 = 0.44, respectively) regardless of the method of production, further supporting that HVHF is not inherently riskier than conventional production in SK. In conjunction with the above results, this thesis determined that the majority of recorded groundwater wells (>50%) were located within 1 km of one or more PW spills. Just over 38% of these wells were shallow (0.3-20 m deep) which are most at risk for brine contamination from surface spills. While there is potential for brine contamination in all surficial features within the study area, areas with glacial tills (southeastern SK, hydraulic conductivity (K) range (10-11 - 10-7 m/s)) are less likely to experience contamination than areas with coarse-grained outwash sediments (west-central and west-southwestern SK, K range (10-5 - 10-3 m/s)). This conclusion was based on Darcy’s Law estimations of transit times through different surficial sediments; clay-rich till and glaciolacustrine deposits exhibited a time scale of thousands of years extending up to one million years while coarse-grained outwash sediments exhibited transit times of less than 10 years when the hydraulic gradient was relatively high (i = 0.1). The results of this thesis indicate that production from the Bakken is not the predominant source of surface spills in SK as is commonly assumed, that surface spills may also be associated with a variety and lengthy history of hydrocarbon exploration and production activities, and that long-term monitoring for potential brine contamination of drinking water resources should cover the full range of extraction activities. Not only will this analysis help decision-makers to focus on areas of concern that are most sensitive to saline contamination from PW spills through regulatory, preventative, and remedial efforts, but also addresses the issues from more than a century of oil and gas development.