Title:

The Effect of Fault Zone Development on Induced Seismicity

Authors:

Mark MCCLURE and Roland HORNE

Key Words:

induced seismicity, EGS, faults and fractures

Conference:

Stanford Geothermal Workshop

Year:

2012

Session:

Enhanced Geothermal Systems

Language:

English

Paper Number:

Mcclure

File Size:

423 KB

View File:

Abstract:

It is widely acknowledged that induced slip on preexisting fractures is responsible for both the induced seismicity and the permeability enhancement in Enhanced Geothermal Systems (EGS). At a given location, the character of the preexisting fractures can be classified along a spectrum from joints or crack-like faults to fully developed, thick faults with cataclasite fault cores. We reviewed data collected at seven projects around the world and found a striking variability in the character of the fractures and faults at each site. There was an excellent correlation between the degree of brittle fault formation and the maximum magnitude of seismic events induced by stimulation. For long term circulation in which injection rate exceeded production rate, the correlation was weaker, but still present. Our results suggest that characterization of fault development should receive more emphasis, both in seismic hazard estimation and in reservoir engineering and modeling. We discuss the interactions between frictional properties, lithology, depth, geological heterogeneity, and seismic hazard. For cases where only very small seismic events were induced, we offer alternative hypotheses to explain the mechanism of their generation. We conclude by discussing our findings in the context of induced seismic hazard analysis in general.


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