ALBERT

Description: To allow sustainable development and operation of deep geothermal wells, it is crucial to have a good understanding of the reservoir characteristics and its changes over time. Distributed fiber optic sensors are becoming more common, as these allow in-situ data collection of spatio-temporal temperature and/or acoustic data in harsh downhole environments. In Germany’s largest geothermal project, a fiber-optical cable was permanently deployed to total depth together with a pressure sensor located 50m above the reservoir. Additionally a second fiber-optical cable was cemented in the top-section. This poster describes the planning and installation, and provides an outlook on the expected data.

Description: Fiber optic sensing has gained importance for wellbore monitoring and reservoir characterization in geothermal fields as it allows continuous, spatially highly resolved measurements. Distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) technologies, among others, enable monitoring of flow regimes and heat transport inside the wellbore to describe the dynamical behavior of the reservoir. The technically challenging installation of a permanent fiber optic monitoring system in a geothermal production well over the entire wellbore length was conducted for the first time at the geothermal site Schäftlarnstraße in Munich, Germany. One cable with two DAS fibers, two DTS fibers, and one fiber for a downhole fiber optic pressure/temperature gauge were clamped to ¾-in. sucker rods and installed to 3.7 km measured depth to collect data from the wellbore after drilling, during testing, and during operations. We present DTS profiles during 3 months of well shut-in and show the results of two cold water injection tests conducted to localize inflow zones in the reservoir and to test the performance of the fiber optic setup. A vertical displacement in temperature peaks of approximately 1.5 m was observed during the injection tests, presumably resulting from thermal contraction of the sucker rod–cable setup. This was verified by analyzing the strain information from the DAS records over 1 h of warm-back after cold water injection with the calculated theoretical thermal contraction of DTS of the same period. We further verified the flowmeter measurements with a gradient velocity analysis of DTS profiles during injection. Intake to the major inflow zone was estimated to 93.5% for the first injection test, respective 94.0% for the second, intake of flowmeter was calculated to 92.0% for the same zone. Those values are confirmed by analyzing DTS profiles during the warm-back period after the well was shut.

Description: Für eine erfolgreiche Umsetzung der Wärmewende sind unter anderem kom- munale Energieversorger in der Verant- wortung. Deutschlands größte und 2021 in Betrieb genommene Geothermiean- lage »Schäftlarnstraße« der Stadtwerke München (SWM) mit drei geothermalen Dubletten in München-Sendling soll dazu beitragen, bis 2035 eine Klimaneutralität zu erreichen und den Bedarf an Wärme in München CO2-neutral zu decken. Zur strukturellen Überwachung der Bohrloch- konstruktion und zur Unterstützung einer sicheren und nachhaltigen Bewirtschaf- tung der Wärmequelle wurde bereits im Jahr 2019 ein Glasfaserkabel in einer der Produktionsbohrungen bis Endteufe eingebracht.