NANT and DERT Multiphysics Experiments: Fast, Affordable, High-Resolution Prospection Methods for Geothermal Systems

“The growth of the geothermal sector requires innovative methods to reduce exploration costs whilst minimizing uncertainty during subsurface exploration. In order to support the expanding need for renewable energy, we need innovative, quickly-processed, logistically flexible and affordable high-resolution geophysical methods. To address such a demand, we integrate high-resolution Nodal Ambient Noise Tomography (NANT) and Deep Electrical Resistivity Tomography (DERT) to investigate geothermal systems. NANT and DERT have a penetration depth of up to 5 km and 1.5 km, respectively and complementary resolutions. We have jointly deployed these methods in various sites across the globe including Switzerland, Italy, Indonesia, and the Caribbean to prospect different geological settings including sedimentary and volcanic domains. Inversions have been performed in urbanized areas, jungles both in high and middle enthalpy systems. These datasets allowed geothermal operators to save exploration costs while reducing subsurface uncertainty.

We present the results of a recent acquisition performed in Guadaloupe that aims to showcase why such an affordable approach will revolutionize the acquisition in logistically complex regions. Experiments last less than 10 days and delivery of 3D velocity and resistivity cubes is done within a few months.

As a study case, we deployed 48 3-component 5 Hz nodal geophones around the summit crater and the base of La Soufriere in October 2023, recording passive seismic data at a sample frequency of 250 Hz for a month. Simultaneously, a campaign for electrical resistivity was carried out, offering the chance to compare the 3D seismic velocity and electrical resistivity models. Geophysical data acquisition is typically coupled with geochemical analyses of deep-sourced fluids (gas and water) sampled from surface hydrothermal manifestations. This allows us to characterize the signature of the fluids and deeper reactions. Ultimately, aerial photogrammetry with thermal cameras is a powerful tool to identify surface thermal anomalies and, on a broader scale, potential trends and orientation of fluid migration pathways related to tectonic discontinuities. Our results show how such an affordable, agile and deep-penetrating multiphase multiphysics workflow, combined with geochemical fluid analyses and remote sensing approaches, can boost the geothermal sector with very limited investments without trading on subsurface uncertainty.”