Feasibility Study of Controlled-Source Electromagnetic Method for Monitoring Low-Enthalpy Geothermal Reservoirs

• Published in: Applied sciences 2023-08, Vol.13 (16), p.9399
• Main Authors: Eltayieb, Mahmoud, Werthmüller, Dieter, Drijkoningen, Guy, Slob, Evert
• Format: Article
• Language: English
• Subjects: Analysis; Cold; CSEM monitoring; Electric fields; Electric properties; Electromagnetism; Energy; Feasibility studies; feasibility study; geothermal energy; Geothermal power; Geothermal resources; Investigations; low-enthalpy reservoirs; Methods; Netherlands; Permeability; Reservoirs; Steel pipes; sustainable utilization; Temperature; TU Delft campus geothermal project
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app13169399

Tracking temperature changes by measuring the resulting resistivity changes inside low-enthalpy reservoirs is crucial to avoid early thermal breakthroughs and maintain sustainable energy production. The controlled-source electromagnetic method (CSEM) allows for the estimation of sub-surface resistivity. However, it has not yet been proven that the CSEM can monitor the subtle resistivity changes typical of low-enthalpy reservoirs. In this paper, we present a feasibility study considering the CSEM monitoring of 4–8 Ω·m resistivity changes in a deep low-enthalpy reservoir model, as part of the Delft University of Technology (TU Delft) campus geothermal project. We consider the use of a surface-to-borehole CSEM for the detection of resistivity changes in a simplified model of the TU Delft campus reservoir. We investigate the sensitivity of CSEM data to disk-shaped resistivity changes with a radius of 300, 600, 900, or 1200 m at return temperatures equal to 25, 30, …, 50 °C. We test the robustness of CSEM monitoring against various undesired effects, such as random noise, survey repeatability errors, and steel-cased wells. The modelled differences in the electric field suggest that they are sufficient for the successful CSEM detection of resistivity changes in the low-enthalpy reservoir. The difference in monitoring data increases when increasing the resistivity change radius from 300 to 1200 m or from 4 to 8 Ω·m. Furthermore, all considered changes lead to differences that would be detectable in CSEM data impacted by undesired effects. The obtained results indicate that the CSEM could be a promising geophysical tool for the monitoring of small resistivity changes in low-enthalpy reservoirs, which would be beneficial for geothermal energy production.