Changes in permeability caused by transient stresses: Field observations, experiments, and mechanisms

TLDR

Earthquake‑induced stress oscillations, even at strain amplitudes of 10⁻⁶, can temporarily increase permeability and fluid mobility in geological media, but the enhanced permeability usually recovers to prestimulated values over months to years. Monitoring permeability in geothermal systems with abundant seismicity and the flow response to local and regional earthquakes would help test proposed mechanisms and identify controls on permeability evolution. Permeability changes at such small stresses arise from unblocking pores by breaking permeability‑limiting colloidal deposits or mobilizing trapped droplets and bubbles, with recovery governed by pore reblocking or geochemical sealing.

Abstract

Oscillations in stress, such as those created by earthquakes, can increase permeability and fluid mobility in geologic media. In natural systems, strain amplitudes as small as 10 −6 can increase discharge in streams and springs, change the water level in wells, and enhance production from petroleum reservoirs. Enhanced permeability typically recovers to prestimulated values over a period of months to years. Mechanisms that can change permeability at such small stresses include unblocking pores, either by breaking up permeability‐limiting colloidal deposits or by mobilizing droplets and bubbles trapped in pores by capillary forces. The recovery time over which permeability returns to the prestimulated value is governed by the time to reblock pores, or for geochemical processes to seal pores. Monitoring permeability in geothermal systems where there is abundant seismicity, and the response of flow to local and regional earthquakes, would help test some of the proposed mechanisms and identify controls on permeability and its evolution.