A model for induced seismicity caused by hydrocarbon production in the Western Canada Sedimentary Basin

Abstract

Over the past three decades, a significant number of small-magnitude and shallow earthquakes have occurred in the Western Canada Sedimentary Basin and are located along its western flank near areas of oil and gas production. One of the better documented examples is the swarm of earthquakes associated with the Strachan field, in the Alberta foothills. A model based on Segall's poroelastic theory is developed to account for the occurrence of earthquakes below the Strachan reservoir. Using this methodology, we show that the earthquake of 19 October 1996, underneath the Strachan field, was most probably triggered by gas extraction. The numerical model also implies that gas extraction would cause subsidence and localized changes in in situ stress magnitudes. There is a strong correlation between rates of production and the number of seismic events, but the onset of major seismic activity postdates the commencement of production by approximately 5 years. Poroelastic modelling can account neatly for this observed delay. The modelled stress changes due to gas extraction point to a regime which favours reverse or thrust faulting that is compatible with stress magnitude measurements in the area. The proposed mechanism involves volume changes which decrease the vertical stress S v and increase the larger horizontal stress S Hmax . The mean stress increase beneath the reservoir appears to be small, but increasing the deviatoric stress permits Mohr-Coulomb failure. As a result, the initially high rate and long history of gas extraction appear likely to be the main trigger for the seismicity beneath the Strachan field.Résumé : Au cours des trois dernières décennies, un nombre important de tremblements de terre de faible magnitude et de faible profondeur sont survenus dans le Bassin sédimentaire de l'Ouest du Canada, et localisés le long de son flanc occidental, à proximité de régions productrices de pétrole et de gaz. L'un des exemples le mieux documenté est représenté par le groupe de tremblements de terre associé au champ de Strachan, dans les Foothills de l'Alberta. Un modèle fondé sur la théorie poroélastique de Segall a été élaboré pour expliquer les événements de tremblements de terre sous le réservoir de Strachan. Nous démontrons par cette approche que la cause la plus probable de déclenchement du tremblement de terre du 19 octobre 1996, sous le champ de Strachan, serait l'extraction du gaz. Le modèle numérique révèle en plus que l'extraction du gaz serait responsable d'un phénomène de subsidence et des changements apparus localement dans la grandeur des contraintes in situ. On observe une forte corrélation entre les taux de production et le nombre d'événements sismiques, mais le début de l'activité sismique significative n'a débuté que cinq années approximativement après le commencement de la production. La modélisation poroélastique rend compte nettement de ce délai observé. La modélisation des changements des contraintes engendrés par l'extraction du gaz pointe un régime qui favorise le développement de failles cheva...

Did Anthropogenic Activities Trigger the 3 April 2017 Mw 6.5 Botswana Earthquake?

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Isolated cases of remote dynamic triggering in Canada detected using cataloged earthquakes combined with a matched‐filter approach

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Monitoring performance using synthetic data for induced microseismicity by hydrofracking at the Wysin site (Poland)

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