GInGER (GravImetry for Geothermal ExploRation): A New Tool for Geothermal Exploration Using Gravity and 3D Modelling Software

Abstract

With the aim to determine fracture porosity in geothermal reservoirs, GInGER was developed for computing gravity effects of 3D geological units using high resolution DEM. Since the code builds up on seismic data, i.e. on fix distribution of geological structures, it allows for changing interactively the density of every structure, calculating the new gravity effect of the model in real time and comparing it with field measurements. The software was developed to sustain fracture porosity determination using micro-gravity measurements, i.e. based on an accurate geological model to characterize areas with a significant misfit between the model’s gravity effect and measurements. However this misfit can also be interpreted for other purposes such as reservoirs characterization, error map of the model, first modelling of geological structures which were not highlighted by other methods. In the presentation, we will exemplify the methodology and the capability of the software on two geothermal projects located in the Swiss Molasse Basin of Switzerland, the projects of St. Gallen and Eclépens. Both projects are targeting deep faults affecting aquifers at few kilometers of depth. In both cases a detailed 3D geological model was established. However, while for the St. Gallen project, we were able determine the increase of porosity due to the fault system at a depth of more than 4 km and a first modelling of a Permo-Carboniferous graben which was not modelled by the 3D seismic campaign, in Eclépens, we focus on sensitivity analysis on the available 3D geological model to optimize the field survey.