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WITHDRAWN Identifying Fracture Networks Reactivated During Fluid Operations: Case Study from Coso Geothermal Field, California

Description: 

WITHDRAWN Identifying the faults and fractures reactivated during geothermal field operations can be challenging, especially considering the sites’ generally complex geology and stress fields. However, knowledge of which fractures rupture when provides important insight into the fluid flow within a field. The Coso Geothermal Field (CGF) in California experiences both natural and induced seismicity due to its tectonically active setting and 30+ years of fluid extraction and reinjection. Additionally, the induced seismicity can be correlated to both long-term normal production and shorter-term operational pauses, or so-called shut-ins. During shut-ins, the field experiences a rapid increase in pore pressure near production wellbores caused by the temporary stop in mass extraction.

Here, we analyze 15 years of daily operational data and seismic waveforms recorded on 24 local seismic stations with the goal to identify the structures reactivated during shut-ins at the CGF. Using a catalog of over 60,000 earthquakes with moment magnitudes between -0.4 and 3.8, we first relocate events using waveform correlated differential times and compute focal mechanisms. While shut-in seismicity generally occurs in different regions compared to the normal production seismicity, we find no significant difference in their focal mechanisms, implying similar stress fields are acting during both types of operations. Furthermore, we combine the focal mechanisms, earthquake relocations, and waveform similarities to infer fault planes within the field to minimize the location uncertainties caused by using a simple 1D velocity model in a geologically complex area. Understanding the relationship between operational parameters and the reservoir's seismic response can reveal critical factors that influence the stress field and the reservoir's productivity, guiding operators regarding future drilling sites.

Session: Mechanistic Insights into Fluid-induced Earthquakes from the Laboratory to the Field [Poster]

Type: Poster

Date: 4/15/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Joanna

Student Presenter: No

Invited Presentation: 

Poster Number: 96

Authors