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Assessing the Relative Contributions of Fluid Pressure and Elastic Stress to Induced Seismicity

Description: 

Induced seismicity may involve complex triggering mechanisms that significantly complicate subsurface energy extraction. While both pressure and elastic stress effects have been linked to induced events, the relative contribution of these effects to total seismic-moment-release remains to be understood. One key component in determining the importance of pressure vs. elastic stress effects are more robust constraints on crustal hydrology. We examine processes that govern fault hydrology and slip at various scales from centimeter lab-samples to kilometer reservoirs. We use tidal responses and lab core measurements to estimate permeability changes in a shallow geothermal reservoir near Winnemucca, Nevada, where geothermal operations take advantage of hydrothermally-altered and fractured rocks. The reservoir formed within a sequence of normal and strike slip fault in the basin and range tectonic province.

We integrate results from InSAR, pressure, temperature and seismicity analyses. We generate a high-resolution seismicity catalog based on waveform cross-correlations and relative event relocations. The seismicity with ML -2.0 to 1.0 forms spatial clusters close to injection wells, although reservoir deformation is dominated by compaction and pore-space collapse. We test reservoir cores from intact (porosity~0.4 %) and fractured phyllites (porosity~4%) as well as felsic intrusive rocks (7 – 15 %) and determine permeability and poroelastic coupling during stepwise pore (<40 MPa) and confining pressure changes (<45 MPa). Permeability values from seismicity migration are compared with direct permeability measurements from lab tests and tidal analysis. Corresponding peak fault zone permeability is ~50 milliDarcy at 1 km depth. These values suggest that direct pressure effects are likely limited to near-well regions. Deep and distant induced events associated with geothermal and hydrocarbon operations likely require more complex mechanisms such as poroelastic stress transfer and aseismic slip.

Session: De-risking Deep Geothermal Projects: Geophysical Monitoring and Forecast Modeling Advances

Type: Oral

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Thomas H. W. Goebel

Student Presenter: No

Invited Presentation: 

Authors