Fluid-induced seismicity: insights from laboratory experiments and implications for geohazard management systems

Abstract

Fluid-induced seismicity: insights from laboratory experiments and implications for geohazard management systems

By Fadul Dawood

Abstract

Fluid-induced seismicity is a significant geohazard in industrial activities involving subsurface fluid injection, such as hydraulic fracturing, carbon sequestration, wastewater disposal, and enhanced geothermal systems. Current risk management strategies often rely on empirical relationships between fluid injection volumes and cumulative seismic moment. However, field observations show that some induced earthquakes exceed forecasted maximum magnitudes, highlighting limitations in existing predictive models. This thesis investigates the correlation between the spatial and temporal evolution of faulting and measured physical properties of shale reservoir and underburden rocks, and seismic parameters from laboratory earthquakes.
Two experimental sets were conducted. First, intact core samples from the Horn River Basin shale in British Columbia, Canada, were characterised for their elastic moduli, ultrasonic wave velocity, and seismic anisotropy. These samples were loaded to failure under reservoir conditions in a triaxial apparatus, with acoustic emissions (AE) monitoring. Three deformation stages were observed: (i) an elastic stage with low AE rates, relatively small magnitudes, and distributed seismic events; (ii) a prefailure stage with increasing AE rates and moderate relative magnitudes AE events; and (iii) a failure stage with high AE rates, larger magnitudes, and AE localization. Progressive deformation was associated with decreases in the frequency-magnitude distribution parameter, b-value and P-wave velocity. AE events location shows that the evolution of seismic parameters at the transition between pre- to co-failure corresponds to the development of a larger, throughgoing fault.
In the second set, fluid was injected into a composite sample consisting of shale overlying a granite sawcut, simulating a pre-existing fault in the reservoir underburden. Fault reactivation patterns were strongly influenced by the strength heterogeneity of the composite sample. Initially, complex conjugate faulting developed in the underburden. At constant pore pressure, AE locations show progressive fault reactivation and throughgoing fault growth into the reservoir. The development of the throughgoing fault was accompanied by a reduction in P-wave velocity, an increase in seismicity rate, and larger seismic event magnitudes. Progressive fault reactivation and growth were also associated with a reduction in the b-value. The results reveal a clear relationship between the evolving fault structure, its growth, and the magnitudes of associated seismic events.
These findings demonstrate that real-time monitoring of systematic changes in physical properties and seismic parameters can inform proactive risk mitigation strategies, offering a more comprehensive approach to managing fluid-induced seismicity.