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Schlagwörter:
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Zusammenfassung:
Several target reservoirs for Enhanced Geothermal Systems comprise hot, dry rock lithologies characterized by low matrix permeability. To improve the permeability of these formations and thus to increase the productivity of power plants, hydraulic stimulation is a common practice. For this purpose, water is injected into the reservoir, causing a local change in the effective stress state that can potentially trigger fault slip seismicity. However, seismicity can be triggered even during normal operation, as in the case of the Blue Mountain geothermal field, Nevada, USA. Here, a significant increase in microseismic activity is observed during the annual maintenance shutdown of the power plant pumps, suggesting more complex processes, such as poroelastic stress transfer, contributing to seismicity. To better understand induced seismicity and explore the underlying mechanisms, we conducted triaxial experiments on intact and faulted reservoir rock samples from the DB2 well at the Blue Mountain geothermal site and determined the effective pressure sensitivity of flow and poroelastic properties over a range of pore (<40 MPa) and confining (<50 MPa) pressure conditions. Laboratory results are compared with permeability estimates previously determined from tidal responses in idle wells, supplemented by a seismicity catalog of continuous waveforms records from 2016 to 2019 to identify seismicity migration patterns associated with operational changes. The integration of cross-scale field and laboratory data aims to improve the characterization of the permeability structure of the fault zone at Blue Mountain and to better understand the coupling between matrix permeability, fault zone hydrology and mechanical behavior.
