Application Of The Gravity Method To Constrain Geological Structures Of Geothermal Interest In The Geneva Basin

Abstract

This study focuses on the processing and analysis of public gravity data from the gravity Atlas of Switzerland to evaluate the possibility to use gravity data as a standard subsurface investigation toolinthe Geneva Canton toconstrainthemain geological features, which can be associated with low to medium temperature geothermal resources at different ranges of depth. The Geothermie 2020 program developed by Services Industriels de Genève (SIG) and the Geneva Canton, aims at exploring the subsurface to tap geothermal resources for heat production and storage, and power production. Therefore shallow aquifers, as well as deep targets need to be investigated to identify potential areas of interests where detailed geophysical surveys and drilling of exploration wells can be carried out. We identified 4 main formations that are both geothermal relevant and show significant density variations which can be constrained by the gravity method: shallow quaternary deposit, Tertiary Molassic sediments, Mesozoic carbonates and deeper crystalline basement with embedded Permo-Carbonifer troughs. The processing workflow focuses on the calculation of the Complete Bouguer Anomaly (CBA), from which a regional trend is removed to produce a residual gravity anomaly to enhance the signal from geological structures of interest, followed by the calculation of the vertical derivatives, horizontal gradient and directional derivatives, and finally by the filtering employing Butterworth bandpass filters at increasing bandwidth to produce a number of residual anomalies. The results, which are interpreted according to the available geological data, show the potential of the gravity method in delineating both shallow geological features and deeper structures related to the Mesozoic sequence and to the Permo-Carbonifer sediments filling the troughs that locally cut the crystalline basement.

AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019