Induced seismicity in the Kiskatinaw area of Northeastern British Columbia, Canada: Empirical investigation of hydraulic diffusivity and induced seismic response of the fractured reservoir

Abstract

This empirical study investigates the mechanistic reasoning behind the occurrence of large magnitude fluid-injection-induced seismic events during hydraulic fracturing in the Kiskatinaw area. The data unveiled atypical non-parabolic spatio-temporal distributions of induced seismic event hypocenters—previously unreported in existing literature. These distributions were predominantly associated with larger magnitude events. Distinctly, our research delves into the concept of hydraulic diffusivity within fractured reservoirs, interpreting the observed patterns in these unique spatio-temporal hypocentral growth distributions. The study reveals that in unconventional fractured reservoirs of this region smaller seismic events are linked to active stages via low hydraulic diffusive and highly hydraulically connected, dispersed, fracture network, while larger magnitudes can associate with highly diffusive and concentrated fractured pathways with limited hydraulic connectivity. This was attributed to the contrasting storativity of connected fracture networks impacting fluid pressure propagation pace to hydraulically connected seismogenic faults. Furthermore, the data pointed to an inverse relationship between hydraulic diffusivity and the number of hydraulically connected structures to the active stage, leading to higher pressure build-ups and larger seismic event magnitudes at greater diffusivity levels. This understanding offers insights into the variances in seismic responses across stages and wells. Intriguingly, unlike standard hydraulic fracturing of unconventional reservoir models emphasizing on tensile fracture generation, our findings underscore the significant role of pre-existing natural fractures in inducing shear slip during fluid injection. The seismic energy release to hydraulic energy input ratio observed was considerably higher than in settings with more massive rocks, aligning with results reported for enhanced geothermal operations. Conclusively, fluid injection in certain fractured reservoirs of the KSSMA can lead to significant pressure buildup perturbations, causing larger seismic events, while in others, a multitude of smaller events prevails, highlighting the complex interplay of hydraulic diffusivity, fracture intensity, and connectivity in determining seismic responses.