Injection-induced fault slip assessment in Montney Formation in Western Canada

Abstract

Hydraulic stimulation to enhance energy extraction from geothermal and unconventional resources is typically accompanied by seismicity because injection changes pore pressures and temperatures, facilitating slippage of fractures and faults. Induced seismicity carries potential risk if events are large enough to damage infrastructure. The uncertainty invariably associated with the state of stress measurements and subsurface geomechanics parameters affects the analysis of fault slip and seismicity induced resulting from hydraulic fracturing. In this study, a probabilistic approach is used to assess the slip tendency of known faults crossing the compartmentalized Montney Formation of western Alberta and northeastern British Columbia. We first divide the formation into four different stress areas based on pore pressure deviations from hydrostatic. In each stress area, geomechanics parameters are expressed as probability distributions using multivariable datasets from borehole petrophysical data to injection-induced focal mechanisms. Monte Carlo simulations are applied to assess the potential slip tendency of local faults. We display the cumulative distribution function of critical pore pressure to cause slip on each fault by using analyses of the parameters of the Mohr–Coulomb shear failure criterion and local tectonic stress state. The results provide useful input for seismic hazard assessment and risk mitigation for local faults affected by high-rate fluid injection.

Probabilistic assessment of induced seismicity at the Alberta No. 1 geothermal project site

“…First, extrinsic parameters that can be controlled, such as injection pressure, flow rate, viscosity, volume, and type of fluid, and second, subsurface intrinsic parameters that are uncontrollable. These intrinsic parameters may include stress state and pore pressure, size and density of fissures and fractures, fault orientation and frictional strength, steady-state coefficient of friction, rock permeability, and compressibility, as well as other geomechanical parameters such as brittleness and deformation properties (Yaghoubi et al 2022). However, substantial levels of inherent uncertainty are associated with the value of each in-trinsic parameter.…”

Pore Pressure Diffusion and Onset of Induced Seismicity

“…If the changes in background stresses and fault frictional properties are small, then pore pressure change is the main factor controlling slip tendency. In hydraulic fracturing operations where pore pressure changes are significant, often on par with or exceeding the hydrostatic pressure, slip tendency analysis is particularly useful and insightful (Moeck et al., 2009; Shen et al., 2019; Yaghoubi et al., 2022). In wastewater injection cases, however, the pressure changes are much smaller, and the resulting changes in slip tendency also are much smaller (e.g., Vacadda et al., 2021).…”

Injection-induced basement seismicity beneath the Raton Basin: constraints from refined fault architectures and basin structure

“…Increasingly evidence for aseismic deformations has been identified around wastewater injection [30], hydraulic fracturing [31,32] and geothermal exploitation [33]. Such aseismic processes explain seismicity occurring beyond the spatial-temporal stress perturbation via pore-fluid pressure increase and poroelastic effects.…”