Hydraulic Testing and Reservoir Characterization of the Taufkirchen Site in the Bavarian Molasse Basin, Germany

Abstract

The geothermal project Taufkirchen in Southern Bavaria (Germany, south of Munich) is expected to produce energy equivalents of 40 MWth and 4 MWel with an anticipated thermal water production rate of 120 l/s at a temperature of 133 °C. Extensive hydraulic well testing in various configurations was carried out to hydraulically characterize the thermal aquifer situated in porous-fractured limestones of the Malm formation. The first well of the doublet reached its target by end of 2011 with a total depth of 4259 m (MD). Subsequent well logging and testing was carried out to investigate well conditions, well productivity and reservoir properties. The initial expectations were not fully met. A second well of 3933 m (MD) was drilled in 2012. Initial hydraulic tests indicated the productivity of this well was twice as high compared to the first well. The success of a geothermal well is usually rated in terms of productivity and injectivity index, respectively, specifying the production/injection rate as function of the differential pressure applied (e.g. liters per seconds per bar). The instant short-term well productivity can be assessed relatively quickly by means of airlift or pump tests. The results obtained at that early stage are preliminary and may not reveal the full sustainable potential of the reservoir. Additional hydraulic testing is designed to obtain a more comprehensive data set which can be interpreted towards a profound understanding of the reservoir characteristics. Careful test layout is essential with regard to test quality and prerequisite for sound test interpretation. A good understanding of the thermal reservoir improves predicting of long-term thermal water extraction rates and the dimensioning of the power plant. It may also provide the necessary information to undertake well improvement measures or to plan additional wells. The influence of thermal effects, borehole skin and rate dependent friction loss on test interpretation is shown using the examples of two circulation tests conducted at the Taufkirchen site. Sensitive issues of test design and test-setup are identified and proposals for optimized test configuration in comparable aquifers are presented.