Hydraulic-Fracturing Induced Seismicity Driven by Accelerated Fault Creep

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

Models for injection-induced earthquakes typically incorporate effects of poroelastic diffusion and ascribe earthquake fault activation to elevated pore pressure or increased shear stress. In the case of hydraulic fracturing in shale, this paradigm is incompatible with underground experiments and rate-state frictional models, which predict stable sliding (aseismic slip) on faults that penetrate rocks with high total organic content (TOC) or elevated clay content. Here, we present a high-resolution microseismic dataset that monitored a hydraulic-fracturing treatment associated with a M_w4.1 induced earthquake in the Western Canadian Sedimentary Basin. This dataset shows the locations of the fault activated events nucleated above the injection depth, at a timescale that is likely too fast for pore-pressure diffusion, similar to other observations of induced seismicity in the region. Therefore, we develop an alternative model, wherein distal, unstable regions of a fault are progressively loaded by fluid-injection driven aseismic slip, and test it through rate-state modeling based on the real dataset. The rate of expansion of the associated slip front significantly outpaces pore-pressure diffusion and is consistent with observed timescales of earthquake nucleation. Our model predicts that dynamic (earthquake) rupture initiates when the slip front impinges on a fault region where rock composition favors slip-rate-weakening behavior. Dynamic weakening of the fault gouge is essential for a large earthquake to be induced, therefore carbonates are most susceptible. The magnitude of the event produced by the model is a very similar magnitude to the real earthquake, based on a data-derived geomechanical model and realistic input parameters. Improved understanding of fundamental processes of fault activation during hydraulic-fracturing is key to developing effective monitoring and mitigation strategies and could also help to inform models for natural earthquake triggering.

Presenting Author: David W. Eaton

Authors