TY - GEN
T1 - Bimodal depth distribution of MEQs in the Newberry geothermal reservoir
AU - Fang, Y.
AU - Elsworth, D.
AU - Cladouhos, T.
N1 - Publisher Copyright:
Copyright (2014) ARMA, American Rock Mechanics Association
PY - 2014
Y1 - 2014
N2 - A bimodal depth distribution of fluid-injection-induced microearthquakes (MEQs) was observed in the 2012 stimulation phase of the Newberry Volcano Enhanced Geothermal System (EGS) Demonstration project in Oregon. During 7 weeks of hydraulic stimulation of well NWG 55-29, 90% of MEQs occurred in the shallow reservoir while few occurred adjacent to the expected deep stimulation zone. This enigmatic distribution of MEQs may have resulted from two alternative possible causes: (1) A segment of the casing may be damaged, the resulting leak introducing a new fluid source with the pressure triggering microseismicity in the shallow reservoir over the short term; or (2) fluid pressures may have migrated upwards from the deep injection zone to the shallow reservoir to induce local seismic events. Our analysis of the failure potential of the reservoir to fluid- injection indicates that the failure potential increases with reduced depth for a given wellhead pressure. The timing of pore-pressure diffusion suggests that upward-migration of fluid pressures from the injection zone cannot generate critical overpressures in the shallow zone of seismicity sufficiently quickly. This contention, favoring the role of a ruptured casing, is further supported by a coupled Thermal-Hydrological-Mechanical (THM) analysis and the observation (August 2013) that indeed the casing is damaged at shallow depth. Despite this, still unexplained remains the presence of seismicity at great depth, but absent at intermediate depth.
AB - A bimodal depth distribution of fluid-injection-induced microearthquakes (MEQs) was observed in the 2012 stimulation phase of the Newberry Volcano Enhanced Geothermal System (EGS) Demonstration project in Oregon. During 7 weeks of hydraulic stimulation of well NWG 55-29, 90% of MEQs occurred in the shallow reservoir while few occurred adjacent to the expected deep stimulation zone. This enigmatic distribution of MEQs may have resulted from two alternative possible causes: (1) A segment of the casing may be damaged, the resulting leak introducing a new fluid source with the pressure triggering microseismicity in the shallow reservoir over the short term; or (2) fluid pressures may have migrated upwards from the deep injection zone to the shallow reservoir to induce local seismic events. Our analysis of the failure potential of the reservoir to fluid- injection indicates that the failure potential increases with reduced depth for a given wellhead pressure. The timing of pore-pressure diffusion suggests that upward-migration of fluid pressures from the injection zone cannot generate critical overpressures in the shallow zone of seismicity sufficiently quickly. This contention, favoring the role of a ruptured casing, is further supported by a coupled Thermal-Hydrological-Mechanical (THM) analysis and the observation (August 2013) that indeed the casing is damaged at shallow depth. Despite this, still unexplained remains the presence of seismicity at great depth, but absent at intermediate depth.
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M3 - Conference contribution
AN - SCOPUS:84927128400
T3 - 48th US Rock Mechanics / Geomechanics Symposium 2014
SP - 534
EP - 542
BT - 48th US Rock Mechanics / Geomechanics Symposium 2014
A2 - Sterling, Ray
A2 - Detournay, Emmanuel
A2 - Pettitt, Will
A2 - Labuz, Joseph F.
A2 - Petersen, Lee
PB - American Rock Mechanics Association (ARMA)
T2 - 48th US Rock Mechanics / Geomechanics Symposium 2014: Rock Mechanics Across Length and Time Scales
Y2 - 1 June 2014 through 4 June 2014
ER -