| Abstract |
Since years, in Switzerland most of geothermal projects have not been success. Thônex well (1993) was almost dry; Basle (2006) encountered seismicity issues; Zurich-Trimmly (2012) was dry and St-Gall (2013) has encountered gas and seismicity issues. The only ones in operation are Riehen with a flow rate of 23 l/s at 65°C for district heating near Basle and Schlattingen for greenhouses heating. For the swiss population geothermal means seismicity, failure, and costly operations because most of them were drilled more than 2500 m deep and without exploration program. In 2014, after a preliminary phase of consultation between political, technical and administrative parties the State of Geneva and the local Utility Services SIG (Services Industriels de Genève) launched the GEothermie 2020 program aiming at developing in a short to medium time frame, a strategic roadmap to supply geothermal energy to the entire Canton (are of 282 Km2 and ca 482'500 inhabitants). The GEothermie 2020 project aims to develop a step-by-step approach whereby the uncertainties and risks associated with deep geothermal wells (see Basel and St. Gallen examples) will be mitigated by a careful gradual improvement of knowledge of the underground, first passing through the exploration of geothermal resources at shallow to medium depths and subsequently at greater depth. We are also working on the legal framework, communication and the development of a local market for geothermal heat. The Geothermie2020 program is a unique and special opportunity for the development of public and sustainable geothermal projects in Switzerland. This large project consists of three main phases, prospection, exploration and exploitation. The first phase is dedicated to both preliminary and detailed investigation where collection and examination of existing data have been followed by more in depth study with new data sets acquisition and interpretation (e.g. 2D, gravimetry, MT, etc.). The second phase started with a first exploration well GEo-01 which has been successfully drilled in 2018 in Satigny, north-west of Geneva city. Artesian water flow of 50 l/s and 34°C was the production of the well at final depth 744 m. This well is the most sucessfull swiss geothermal well since many years! Production units are mainly the faulted lower Cretaceous units at various depth from 460 m to 670 m. The final depth was 744 m and reached the Upper Jurassic. The drilling operation in the limestone units has been carried out with water circulation. Continuous water flow measurement and pressure test were done on surface. Because of inadequate well structure due to karstic features at 540 m, the logging program has not been performed deeper but thanks to continuous hydraulic tests on surface, we were able to localise the depth of the main water flow sources. Hydrocarbon have been encountered during the drilling phase and H2S is present in geothermal water. The second exploration well GEo-02 will start in september 2019. Goals are similar to GEo-01: testing a thrust system with revers fault in the lower Cretaceous and Upper Jurassic limestones, reaching the Kimmeridgien reef complex at 950m and improve our personal knowledge on carrying geothermal drilling project. Final depth will be 1130 m. The third and fourth exploration wells are planned for 2020-2021 and will reach 1500 m through the entire Malm. |