Geological Susceptibility to Hydraulic Fracturing-Induced Seismicity in the Montney Formation
Date
2022-05
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Abstract
This thesis focuses on induced (anthropogenic) seismicity related to hydraulic fracturing operations in the Montney Formation - a geological unit of Triassic age located in the Western Canada Sedimentary Basin. Originally a conventional oil and gas play, the Montney Formation is currently one of the most prolific unconventional resource plays worldwide. Documented cases of induced seismicity in the Montney play occur in distinct clusters, indicative of local variability of factors influencing the seismic activation potential (SAP). Notably, virtually all induced seismicity related to hydraulic fracturing, to date, has occurred in British Columbia despite similar levels of industrial activity in Alberta. This implies that geological trends may have a more significant impact on SAP than operational factors. This thesis presents several new methodologies for investigating the complex interplay between subsurface conditions and induced seismicity distribution. Three independent workflows, based on machine learning-based analysis, structural interpretation, and statistical inference, respectively, were developed to evaluate hypotheses regarding the influence of geological, geomechanical and structural controls of hydraulic fracturing-induced seismicity in the Montney Formation. First, a machine learning model was used to identify areas within the Montney that are characterized by the highest geological susceptibility to induced seismicity. The results suggest that distance to the Cordilleran deformation front and injection depth are the most important factors influencing the observed seismicity trends. Next, a multi-step workflow based on trend-surface analysis combined with geophysical data interpretation allowed major structural trends (structural corridors) to be delineated throughout the Montney play. The results of machine learning and structural interpretation were used to formulate hypotheses regarding geological factors influencing observed cluster characteristics of seismicity in the Montney. These hypotheses were independently tested using SimSeis – a newly developed tool for statistical inference based on a stochastic simulation approach. Using this tool, sets of synthetic catalogs are generated according to assumed spatial relationship(s) between geological susceptibility and/or mapped structural corridors and further compared against a Null hypothesis, corresponding to a random spatial association of induced seismicity with hydraulically fractured wells. While each of the alternative models performed significantly better than the Null hypothesis, a machine-learning model based on geological susceptibility achieved the best results. SimSeis is customizable and can be applied to investigate mechanisms that influence the distribution of induced seismicity distribution in other unconventional plays and thus enhance currently existing seismic-risk mitigation strategies.
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Keywords
induced seismicity, hydraulic fracturing, statistical analysis, machine learning, Montney Formation
Citation
Wozniakowska, P. G. (2022). Geological susceptibility to hydraulic fracturing-induced seismicity in the Montney Formation (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.