Hydro-Mechanical-Seismological Modeling of Fluid-Induced Seismicity in
Fractured Nonlinear Poroelastic Media: Theory, Implementation and
Capabilities
Abstract
Decoupled hydro-shearing has been a decades-long paradigmatic mechanism
of fluid-induced seismicity. A surging alternative is coupled
hydro-mechanical triggering, largely based on the theory of linear
poroelasticity. Unfortunately, seismicity source fractures and their
geometric and physical alterations to a canonical poroelastic system are
rarely accounted for, and seismicity is typically forecasted using a
Coulomb stress rate model without producing catalogs. Here, I present a
new framework for modeling fluid-induced seismicity in arbitrarily
fractured nonlinear poroelastic media. The hydro-mechanical triggering
is modeled using our Jin & Zoback (2017,
https://doi.org/10.1002/2017JB014892) computational model that resolves
both fracture fluid storage and nonlinear flow in addition to full
poroelastic coupling. Seismological modeling is achieved stochastically
by generating stress drops based on the full inter-seismic poroelastic
stressing history. The two steps are sequentially coupled and advanced
in time via a new prediction-correction algorithm, allowing for fracture
stress updating and synthetic event catalog assembly. To demonstrate
model capabilities and effects of fractures and full coupling on
overpressure, stress and seismicity, I perform three microseismic-scale
numerical experiments by progressively adding fractures and poroelastic
coupling into a diffusion-only base model. Some previously unknown
mechanisms are elucidated. In contrast to existing models, my model
produces repeaters and linear clustering of seismicity. Poroelastic
coupling enhances the clustering, inhibits near-field seismicity over
time while increasingly favoring remote triggering, and overall
significantly reduces the event population. Meanwhile, some seismic
source statistical characteristics including the Gutenberg-Richter
scaling relation overall remain unaffected, and the curious -value
elevation for microseismicity can be attributed to a mechanical origin.