Seismic Node Arrays for Enhanced Understanding and Monitoring of Geothermal Systems

Abstract

Harnessing geothermal energy will likely play a critical role in reducing global CO2 emissions. However, exploration, development, and monitoring of geothermal systems remain challenging. Here, we explore how recent low-cost seismic node instrumentation advances might enhance geothermal exploration and monitoring. We show the results from 450 nodes deployed at a geothermal prospect in Cornwall, United Kingdom. First, we demonstrate how the nodes can be used to monitor the spatiotemporal and size distribution of induced seismicity. Second, we use focal mechanisms, shear-wave source polarities, and anisotropy to indicate how the dense passive seismic observations might provide enhanced insight into the stress state of the geothermal systems. All the methods are fully automated, essential for processing the data from many receivers. In our example case study, we find that the injection-site fracture orientations significantly differ from that of the crust above and the regional stress state. These observations agree well with fracture orientations inferred from independent well-log data, exemplifying how the nodes can provide new insight for understanding the geothermal systems. Finally, we discuss the limitations of nodes and the role they might play in hybrid seismic monitoring going forward. Overall, our results emphasize the important role that low-cost, easy-to-deploy dense nodal arrays can play in geothermal exploration and operation.