In geothermal well doublets, relatively cold water is injected through one well into a geothermal reservoir to produce hot water from the other well. The volume of the cold water around the injection well increases over time and results in a thermal breakthrough, which diminishes the economic benefit of geothermal energy. Thus, it is necessary to trace the time-lapse change in the volume of the cold water to monitor geothermal reservoirs efficiently. The electrical resistivity of the geothermal reservoir is found to change where the cold water is localized due to temperature change. In principle, the controlled-source electromagnetic (CSEM) method can be used to get information about such changes in electrical resistivity.
So far, I investigated the feasibility of monitoring a synthetic model of the Delft geothermal project (DAPwell) using CSEM forward modeling. In 1D numerical experiments, the optimal source frequency, as well as the optimal survey configuration, are investigated. In a 3D setting, I studied the change in the time-lapse electric field response due to various radii of the cold front. I also examined the optimal source receiver offset. Moreover, I investigated the influence of different sources of noise in addition to the borehole steel casing on the time-lapse signal.
The results suggest that monitoring the DAPwell geothermal reservoir using the land CSEM method is feasible. For future work, I am going to use a fluid flow model to build a more realistic geoelectric model and apply the methods developed to it.