Coupled Thermo-Hydro-Mechanical Effects on Injection-Induced Seismicity
in Fractured Reservoirs
Abstract
With the urgent necessity of geo-energy resources to achieve carbon
neutrality, fluid injection and production in the fractured media will
significantly increase. Applications such as enhanced geothermal
systems, geologic carbon storage, and subsurface energy storage involve
pressure, temperature, and stress changes that affect fracture stability
and may induce microseismicity. To eventually have the ability to
control induced seismicity, it is first necessary to understand its
triggering mechanisms. To this end, we perform coupled
thermo-hydro-mechanical (THM) simulations of cold water injection and
production into a rock containing two fracture sets perpendicular
between them. The permeability of fractures being four orders of
magnitude higher than the one of the rock matrix leads to preferential
pressure and cooling advancement, which induce stress changes that
affect fracture stability. We find that the fracture set that is
oriented favorably to undergo shear slip in the considered stress regime
becomes critically stressed, inducing microseismicity. In contrast, the
fracture set that is not favorably oriented for shear remains stable.
These results contrast with those obtained for an equivalent porous
media that does not explicitly include fractures in the model, which
fails to reproduce the direction-dependent stability of fractures
present in the subsurface. We contend that fractures should be directly
embedded in the numerical models when inhomogeneities are of the spatial
scale of the reservoir to enable reproducing the THM coupled processes
that may lead to induced microseismicity.