Influence of Temperature on Permeability Evolution

ABSTRACT: Shear reactivation of faults and fractures in the shallow crust is a primary mechanism modulating permeability evolution as a result of fault reactivation and dilation. However, details of the relationship between permeability change (Δk) and seismic moment (M0) remain poorly constrained. We conduct a series of shear reactivation experiments using a single inclined fracture (SIF) transecting cylindrical samples of Westerly granite in zero-axial-displacement mode at different temperatures. Shear reactivation is triggered by stepwise incrementing fluid pressures at an average rate of 0.05MPa/min and with displacement driven by the strain energy stored in the axial piston. Within each pressure increment we measure concurrent histories of shear displacement, permeability change and acoustic emissions (AE). Absolute calibrated seismic moments are derived from these AE events and related to evolving steady state permeabilities. Successive experiments probe the Δk-M0 response at 24°C, 69°C and 111°C to investigate the impact of temperature on the correlation between incremental permeability change and seismicity. We relate permeability change to seismic moment as Δk = ωM0 for Westerly granite samples at each temperature using a linear relationship, where this constant scaling multiplier (ω) decreases with increasing temperature. We propose a mechanistic model that defines the observed link between permeability increase and seismic moment. The influence of temperature is explained through displacement, shear stress drop and shear dilation angle. Our findings suggest that elevated temperatures decrease shear displacement and shear stress drop but increase shear dilation, which consequently results in a decreased linear coefficient linking permeability increase and seismic moment.