High-Resolution Imaging of Geothermal Flow Paths Using a Cost-Effective Dense Seismic Network

This project successfully developed an advanced, low-cost, automated seismic imaging system that used small earthquakes to form high-resolution images of underground distributions of steam and water flow paths in producing geothermal fields, and demonstrated the practical implementation of this technology in an operating geothermal field. The project advanced the technology by integrating the components into a system that can be cost-effectively, reliably, and routinely used in operating geothermal fields to provide images of the movement of fluids in space with a fast-turnaround time from data collection to processing, imaging, and rock physics interpretations. The project demonstrated the technology at The Geysers geothermal reservoir in northern California, where a 91-station low-cost seismic network was installed over a 5 x 5 kilometer study area. The project team acquired and processed seismic data from more than 17,000 micro-seismic events and generated images of seismic velocities representing reservoir flow paths. Correlation of the seismic velocities with known water injection and steam production volumes allowed the team to calibrate the seismic data, which can now be applied throughout the reservoir where borehole data are unavailable. The seismic velocities and resulting calculated rock properties, together with reservoir data derived from observations in boreholes, allow interpretation of the seismic images to identify water and steam saturated zones, fluid pathways, and fractured or solid rock. This information allows the reservoir operator to develop a better drilling program that minimizes drilling of unsuccessful wells, resulting in reduced costs and lower electricity rates for California ratepayers.