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Induced Seismicity: Traffic
Mitigation of Induced Seismicity that is Triggered by Hydraulic Fracturing
The increased use of hydraulic fracturing in recent decades has resulted in public concern over induced seismicity. Regulatory agencies have identified that these man-made earthquakes can be caused by either wastewater disposal or hydraulic fracturing, with the latter being an increasingly common source in Western Canada. Induced seismicity is regulated in Western Canada through programs including the ‘Traffic Light System’ which informs operational responses to induced seismic events depending on the local magnitude.
While the structure of these regulations focuses on the seismic magnitude, it is becoming increasingly evident that determination of ground motion is more important for estimating potential psychological or physical damages. We completed seismic wave propagation simulations within the Western Canada Sedimentary Basin, which confirmed previous finding in scientific literature demonstrating the importance of considering ground motion as opposed to magnitude in the regulation of induced seismic events. The propagation of historic induced seismic events was simulated utilizing the modelling software SPECFEM 3D Cartesian, in consideration of varying sediment types and thicknesses, to generate shaking maps and waveforms at receivers, demonstrating the variations in potential damages. This technique theoretically demonstrates that induced seismic activity causes different levels of ground motion, and therefore damages, depending on the impedance and thickness of sediments, with potential application to improve the existing induced seismicity regulation in Western Canada.
We present recommendations to utilize ground motion as a parameter for determining thresholds for the Traffic Light System instead of earthquake magnitude. Thresholds that account for the exposure and vulnerability of individuals to the ground shaking will provide more protection to personal well-being compared to the current system. Our recommendations would provide greater protection in more vulnerable areas, and higher tolerances for shaking in remote areas. This flexibility provides benefits to both private industry and the public.
Hydraulic Fracturing: Freshwater
Reducing freshwater in hydraulic fracturing: An analysis of fracturing fluids used in the Montney Formation in Alberta and policy recommendations for freshwater reduction
Hydraulic fracturing is a water-intensive method of oil and gas extraction from unconventional reservoirs. In Alberta, hydraulic fracturing operations are performed primarily within the Montney Formation. The rapid expansion in the employment of this technique over the last few years has led to a growing demand for freshwater by industry. The extraction of large amounts of fresh water from natural sources, such as aquifers and rivers, can impact the health of these sources, especially sensitive aquatic ecosystems, and limit the availability of potable water supply to nearby communities. Many existing water management policies and regulations for the oil and gas industry were developed for conventional production methods and have been applied to hydraulic fracturing. This can be problematic since conventional methods use freshwater in different ways and in different quantities than hydraulic fracturing. Responsible and sustainable development of hydraulic fracturing projects requires solutions to reduce the necessity of freshwater use through the development of policy to encourage the use of alternative fracturing fluids.
We conducted a study on 598 stimulated wells in the Montney Formation in Alberta to assess both water usage and the efficiency of hydraulic fracturing fluids (HFF) by comparing the injected water volumes with the first 12 months of production. The HFF were divided into four categories based on their main carrier fluid: water-based, oil-based, energized gas, and energized cryogenic. According to the statistical analysis, wells using energized cryogenic HFF showed the highest barrel of oil equivalent (BOE) production among the four categories. We found that energized cryogenic wells allowed for approximately 20% higher BOE production with 80% less water consumption compared to water-based wells.
Here, we examine freshwater use in hydraulic fracturing in Alberta and relevant policy that could be introduced to support alternate technologies for the reduction of freshwater use in fracking.
Hydraulic Fracturing: Disposal
Risks and Mitigations for Hydraulic Fracturing Wastewater Disposal Operations in Western Canada
In western Canada, most hydraulic fracturing wastewater is disposed of in deep injection wells. Risks associated with the disposal activity concern both the public and the petroleum industry, as these risks may impact the surface environment. The objective of this study is to suggest technical and policy measures to mitigate the risks associated with groundwater contamination during wastewater disposal activities related to hydraulic fracturing. To identify and evaluate the risks, we have performed extensive scientific and policy literature reviews. Also, we conducted interviews with professionals in the oil and gas industry for this study. Risks associated with the disposal activity are identified and further categorized into hydrogeological, geological, and mechanical risks. In Alberta, the geological risks are considerably low, and the mechanical risks are well-controlled with current regulations and legislation. Hydrogeological risks, however, are difficult to quantify and may lack control measures because the level of uncertainty in long-term groundwater transport is high. The hydraulic fracturing water cycle is then studied to determine practices that can reduce the risks associated with water contamination. This water cycle is composed of four stages, including water sourcing, hydraulic fracturing and well completion, treatment of flowback water, and recycling or disposal of water. Decisions for each stage are made primarily based on regulatory and economic factors, including the cost of transport, storage, and treatment of water. By analyzing the water cycle, we have concluded that the most effective and feasible practices to reduce the risks are intensive monitoring of groundwater in the vicinity of disposal sites, and increasing the recycled water ratio in hydraulic fracturing operations. To promote the latter practice, we recommend updating regulations to encourage water recycling and implementing government-initiated water recycling incentive programs in hydraulic fracturing operations.
Induced Seismicity: Prediction
Mitigation of Induced Seismicity that is Triggered by Hydraulic Fracturing
Development of low-permeability hydrocarbon resources has increased during the past decade. In some areas, injection-induced seismicity has become a growing concern in the application of hydraulic fracturing of low-permeability reservoirs.
We examine the current state of knowledge in evaluating the seismic hazard of a geological formation or region; focus is given to the Duvernay Formation in Alberta, Canada. In literature, we find that factors such as pre-existing faults and permeable pathways for pressure diffusion and stress transfer, proximity to crystalline basement and reefs, as well as high rates of natural seismicity and pore fluid overpressures are potential indicators of seismic susceptibility.
We utilize 2D geomechanical modeling to gain insight into the impact of fault orientation relative to the minimum (θmin) and maximum (θmax) stresses, along with fault reactivation through hydraulic fracturing (HF). We find that during HF treatments, fracture growth is hindered for the critically angled fault (30°N from θmax) relative to the stable fault orientation (90°N from θmax). Moreover, a stable fault acts as a hydraulic conduit for injected fluids, whereas a critically angled fault acts as a fluid sink. Greater displacement magnitudes occur for critically angled faulaats, thus, greater fault slip occurs.
We examine two mitigation practices of skipping stages and HF at half the injection spacing. Skipping stages reduces the total injected volumes, whereas decreasing the injection spacing reduces the length of fracture growth. We find that for the critically angled fault effectiveness of mitigation methods is greatly reduced.
Finally, we summarize current policies and outline possible policy measures that could help minimize the risk of induced seismicity. Moving forward, we suggest that regulators establish minimum pre-operation induced seismicity risk assessment criteria to form a baseline of assessment. Additionally, we recommend that regulators explore expanding induced seismicity regulations to areas near population centers and critical infrastructure to lower the risk of high impact events.
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