Seismic Methods for Geoenergy-Related Site Investigations in Crystalline Rocks: Case Study from Pirkkala, Finland

Abstract

Summary Geophysical methods can help to determine the best possible location for geothermal wells and have the potential of fracture mapping in hardrock environments. High-resolution active seismics can provide required meter-scale information in this context while passive seismics enables fast and cost-effective reconnaissance. This survey consisted of active reflection seismic profiles acquired using planted geophones and a newly developed, state-of-the-art nodal seismic landstreamer, small-scale passive seismic array, as well as zero-offset VSP acquired using Distributed Acoustic Sensing (DAS). The study clearly illustrates how the integration of various seismic methods allows for a comprehensive assessment of the subsurface conditions at a geoenergy site in hardrock environment. Despite challenges such as low data quality of certain measurements, correlations between different datasets have been established, enhancing the reliability of the results. The identification of thermal anomalies and fracturing inferred from seismic and drilling data at specific depths suggests areas of enhanced heat transfer and potential targets for optimized geoenergy well placement. Overall, this study demonstrates the effectiveness of seismic methods for characterizing geological formations in crystalline rock environments in urban areas and assessing their suitability for geoenergy applications.