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Hui, Gang (University of Calgary, Alberta, Canada) | Chen, Shengnan (University of Calgary, Alberta, Canada) | Gu, Fei (PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China)
Abstract Two earthquakes with the moment magnitude of 3.9 and 4.1 occurred in January 2015 and January 2016 near the Crooked Lake region, Alberta. Both earthquakes were attributed to the hydraulic fracturing operations of three horizontal wells located at the same well-pad. The underlying mechanisms of both earthquakes are still unclear and required to be investigated to mitigate risks of future seismicity in this region. In this study, the coupled simulations of the fluid flow and geomechanics were conducted to characterize the temporal and spatial evolution of pore pressure diffusion and stress perturbation during and after hydraulic fracturing operations. The Coulomb Failure Stress along the pre-existing fault near the horizontal wells were then calculated to study the reactivation of the fault. Sensitivity analysis was finally conducted to understand the effects of the fault's orientation, injection layer permeability, and distance between the fault and hydraulic fractures on the induced seismicity. The results showed that one North-South-oriented fault was activated twice after the sequential fracturing operations of three horizontal wells in 2015 and 2016. The Mw 3.9 earthquake was triggered by the stress and pore pressure changes that activated the fault in the basement. The relatively long-time interval between the stimulation and the induced earthquake was attributed to the low permeability and geomechanics property from the injection layer to the fault. The subsequent Mw 4.1 event was triggered by the direct connection between the hydraulic fractures, natural fractures, and the fault. Sensitivity analysis has suggested that the activation of faults were susceptible to the proximity between stimulated well and seismogenic faults, low permeability of the injection layer, and the low angle between the fault strike and the maximum horizontal stress.
Eyre, Thomas (University of Calgary) | Eaton, David (University of Calgary) | Zecevic, Megan (University of Calgary) | Venieri, Marco (University of Calgary) | Weir, Ronald (University of Calgary) | Lawton, Donald (University of Calgary) | Garagash, Dmitry (Dalhousie University)
Earthquakes induced by hydraulic fracturing are typically believed to be caused by elevated pore pressure or increased shear stress. However, according to a recent study, these mechanisms are incompatible with experiments and rate-state frictional models that predict stable sliding (aseismic slip) for faults with high clay content or total organic carbon, as well as observations of the timings and locations of the seismicity. An alternative model was therefore proposed, in which distal, unstable regions of a fault are loaded by aseismic slip on stable regions of the fault stimulated by hydraulic fracturing. This model has significant implications in terms of mitigating induced seismicity, as it suggests that there may be a potentially measurable deformation signal tens of hours before earthquake nucleation. However, the conclusions of that study were based on a relatively small number of events from a small local broadband network. In this study we integrate a high-resolution microseismic dataset from the same treatment with that previous work, and demonstrate that the microseismic data provides an even more compelling case that aseismic slip plays a role in induced seismicity. Presentation Date: Monday, October 12, 2020 Session Start Time: 1:50 PM Presentation Time: 2:15 PM Location: 360A Presentation Type: Oral
ABSTRACT: An integrated approach is proposed to identify possible triggering mechanisms of the induced seismicity by analyzing a seismicity sequence in the Duvernay Formation. Based on a case study, we establish linkages between regional faults, an induced seismicity sequence, and hydraulic fracturing operations. It is shown that 20 induced seismicity events with magnitude larger than 1.5 were detected by regional seismological networks, with depth ranging from 2,313m to 3,850m below the sea level. Four faults are identified using the ant-tracking technique. Their distributions are consistent with previously published focal mechanisms. The finite-element model based on the reservoir geomechanics and geophysics is built to calculate the stress and pore pressure changes due to the fracturing in the low permeability shale play. As the fracturing stimulation operations continued, four faults were reactivated and the Coulomb stress changes during hydraulic fracturing reach 6.7~10.7 MPa, far beyond what is required to reactivate these faults. Our results are indicative of a direct connection between hydraulic fractures and nearby faults, leading to induced seismicity in Duvernay Formation.
Recordings of the seismic activity used to be rare in the Western Canada Sedimentary Basin (WCSB) and most of the recorded ones located in the fold-and-thrust belt of the Rocky Mountains (Zhao, 2018). However, a noteworthy increase in the induced seismicity has been reported in the WCSB since 2009, when the combination of the horizontal drilling and the multistage hydraulic fracturing technologies was adopted to develop the unconventional tight/shale reservoirs in this area (Atkinson et al., 2016). It is believed that the recent rise in induced seismicity has been largely attributed to the hydraulic fracturing operations (Schultz, et al. 2017). For example, researchers have correlated the hydraulic fracturing operations to the recent induced seismicity both temporally and spatially in western Canada (Schultz, et al., 2015), such as the clusters of induced seismicity with a maximum magnitude of Mw 3.6, between Oct. 25 and Dec. 15 in 2016 in the Fox Creek area, Alberta (Eaton, et al., 2018) and the earthquake with magnitude of Mw 4.5 on Nov. 29, 2018 in the Fort St. John region, British Columbia (Natural Resources Canada, 2018).
Rodríguez-Pradilla, Germán (School of Earth Sciences, University of Bristol, UK.) | Eaton, David (Department of Geoscience, University of Calgary, Canada.) | Popp, Melanie (geoLOGIC Systems Ltd., Calgary, Canada.)
Abstract The goal of this work is to calibrate a regional predictive model for maximum magnitude of seismic activity associated with hydraulic-fracturing in low-permeability formations in the Western Canada Sedimentary Basin (WCSB). Hydraulic fracturing data (i.e. total injected volume, injection rate, and pressure) were compiled from more than 40,000 hydraulic-fractured wells in the WCSB. These wells were drilled into more than 100 different formations over a 20-year period (January 1st, 2000 and January 1st, 2020). The total injected volume per unit area was calculated utilizing an area of 0.2° in longitude by 0.1° in latitude (or approximately 13x11km, somewhat larger than a standard township of 6x6 miles). This volume was then used to correlate with reported seismicity in the same unit areas. Collectively, within the 143 km area considered in this study, a correlation between the total injected volume and the maximum magnitude of seismic events was observed. Results are similar to the maximum-magnitude forecasting model proposed by A. McGarr (JGR, 2014) for seismic events induced by wastewater injection wells in central US. The McGarr method is also based on the total injected fluid per well (or per multiple nearby wells located in the same unit area). However, in some areas in the WCSB, lower injected fluid volumes than the McGarr model predicts were needed to induce seismic events of magnitude 3.0 or higher, although with a similar linear relation. The result of this work is the calculation of a calibration parameter for the McGarr model to better predict the magnitudes of seismic events associated with the injected volumes of hydraulic fracturing. This model can be used to predict induced seismicity in future unconventional hydraulic fracturing treatments and prevent large-magnitude seismic events from occurring. The rich dataset available from the WCSB allowed us to carry out a robust analysis of the influence of critical parameters (such as the total injected fluid) in the maximum magnitude of seismic events associated with the hydraulic-fracturing stimulation of unconventional wells. This analysis could be replicated for any other sedimentary basin with unconventional wells by compiling similar stimulation and earthquake data as in this study.
Lavoie, V. (Paramount Resources) | Willson, S. M. (Apache Corporation) | Sturm, C. (Apache Corporation) | Lee, J. (Paramount Resources) | Purdue, G. (Paramount Resources) | Dempsey, D. (University of Auckland)
ABSTRACT: A workflow is presented to assess potential induced seismicity (IS) hazard associated with multi-well pad hydraulic fracturing stimulation, comprising steps of increasing sophistication which span easy-to-implement simple analytical screening tools to the application of a newly-developed model capable of calibrated forecasts of IS occurrence. The first level of hazard assessment takes a simplified fault description to determine stress changes required for the fault to become critically stressed. This permits a ‘traffic light’ screening of faults depending upon their slip potential. Extended analyses then incorporate fault surface topography and perturbations in stress and pressure caused by hydraulic fracturing operations. Potential IS event size is estimated using a fault size-magnitude relationship. These simplified assessments of fault slip potential are complemented by a more advanced consideration of fault rupture, fractal stress heterogeneity and evolving stress and pore pressure distributions. The advanced model provides a good qualitative match between the simulated and observed microseismic events occurring during well stimulation. Using the existing pad as a calibration point, ‘what-if’ scenarios are presented to assess operational procedures to minimize IS hazard and to assess IS potential in new areas ahead of well pad drilling and completion.
It is now well-established that under certain geologic conditions the deep disposal of large volumes of water produced as part of oil and gas operations can trigger induced seismicity, IS (Ellsworth, 2013; Frohlich et al., 2014; Rubinstein and Babaie Mahani, 2015; Weingarten et al., 2015). More recently, there is also a growing awareness that hydraulic fracturing operations, too, can sometimes induce seismicity (Holland, 2011, 2013; B.C. Oil and Gas Commission, 2012, 2014; Davies et al., 2013; Friberg et al., 2013; Clarke et al., 2014; Skoumal et al., 2015; Atkinson, et al., 2016; Bao and Eaton, 2016; Schultz et al., 2017, 2018), even though the number of wells potentially associated with IS is exceptionally small - Table 1. However, within the Western Canada Sedimentary Basin, hydraulic fracturing has caused some of the largest IS events (Atkinson et al, 2016), and this has led the Alberta Energy Regulator (AER) to impose operational ‘traffic light’ protocols aimed at minimizing the risk of induced seismicity (AER, 2015, Figure 1).