Inverse flow zone characterization using distributed temperature sensing in a deep geothermal production well located in the Southern German Molasse Basin

Abstract

Abstract. The localization and characterization of hydraulically active zones in a geothermal well is a major task in understanding the hydro geothermal reservoir. This is often done based on interpretations of spinner flow meter measurements that are performed at the end of the well test while injecting cold water. Once a production well is equipped with an electric submersible pump, data collection inside the reservoir and monitoring of the flow zones is usually barely possible. In a 3.7 km (MD) deep geothermal production well in Munich, Germany, it was successfully demonstrated in 2019 that a permanently installed optical fiber cable could close this measurement gap. We used this fiber-optic monitoring system to collect distributed temperature data once the well was set into production. We inversely modeled the inflow from the formation into the borehole from the production temperature data with an energy and mass balance model. The derived flow profile correlates with previous flow meter analysis and indicates that a karstified region at the very top of the reservoir is the driving factor for hydraulics and obtained production temperature. Qualitatively, the two profiles acquired by distributed temperature sensing (DTS) and flow meter are matchable, yet the production inflow profile by DTS logging is more differentiated compared to spinner flow meter logs interpretation during injection.