Exploration and Monitoring with Distributed Acoustic Sensing at the EGS Site Groß Schönebeck

Abstract

Vertical seismic profiling has been performed at the Groß Schönebeck site in order to gain more detailed information on the structural setting and geometry of the geothermal reservoir. Data acquisition was performed using the novel method of distributed acoustic sensing (DAS), using hybrid wireline fiber-optic sensor cables deployed in two 4.3 km deep wells. During the four-day survey, data for 61 source positions was acquired. From the recorded data, accurate time-depth relationships, velocity and reflection profiles along the wells were derived. We show that structural elements near the boreholes can be imaged with high resolution, despite gaps in the data due to sparse coverage exist. The DAS method has enabled measurements at elevated temperatures up to 150 °C and has led to significant time and cost savings compared to deployment of a conventional geophone chain. Important new experiences for application of this non-standard method of acquisition have been gathered.