Novel Approach for the Exploration of the Muschelkalk Aquifer in Switzerland for the CO2-free Production of Vegetables

Abstract

In Switzerland, the Grob vegetable gardening and cultivation company, with around 7 ha of greenhouses in Schlattingen, produces different types of vegetables (mainly cherry tomatoes) more or less all year round. The heating of the greenhouses requires about 20,000 MWh of energy per year. Using a mix of fossil fuels (80 % gas and 20 % oil) currently produces annual CO2 emissions of about 5,000 tons, which should be substituted by the use of geothermal energy. Because of the lack of detailed data in the region of Schlattingen it was decided, in cooperation with Canton Thurgau, to conduct an intensive investigation program in a first vertical borehole (1,508 m bgl), including drilling into the basement with partial coring. The geological and hydrogeological data acquired were used to prepare a geological and finite element hydrothermal model of the Muschelkalk aquifer for the planning of a second inclined borehole. On this basis it was decided to select a novel approach with an almost 800 m long horizontal drilling section in the Muschelkalk aquifer and a total length of 2,013 m to explore as many tectonic structures as possible to increase the chances of success for a higher flow rate. Using a rotary steerable system (RSS), the horizontal drill paths could be implemented into the 33 m thick aquifer (1,112 to 1,145 m bgl).