Abstract

Geothermal exploration will help moving towards a low-carbon economy and provide a basis for green and sustainable growth. The development of new practical, reliable methods for geophysical characterisation of a reservoir has the potential to facilitate a broader application of deep geothermal energy. At the Groß Schönebeck in-situ laboratory, a unique vertical seismic profiling (VSP) dataset was recorded in two 4.3 km deep geothermal boreholes using fibre optic cables in early 2017. The experiment set-up consisted of 61 vibrator points organised in a spiral pattern around the well site to ensure a proper azimuth distribution in the target reservoir section. Data were processed using a standard workflow for VSP. As a result, a detailed 3-dimensional 0.75 × 1 × 4.5 km size image around the existing boreholes was created using the Kirchhoff migration algorithm with restricted aperture. The imaging resolved small-scale features in the reservoir essential for the future exploration of the geothermal research site. Borehole data with vertical resolution up to 16 m revealed the existing depth variations of the Elbe basis sandstone horizon at 4.08–4.10 km depth and indications of an unconformity in the area where we expect volcanic rocks. In addition, in the borehole data a complex interlaying with numerous pinch outs in the Upper Rotliegend reservoir section (3.8 to 4 km depth) was discovered. Thereby, we demonstrate that wireline fibre optic data can significantly contribute to exploration by providing an efficient and reliable method for deep geothermal reservoir imaging.

Highlights

  • Measurements with a fibre-optic cable installed in diverse environments are widely applied for seismic data acquisition for versatile research topics such as urban seismology (Dou et al, 2017; Spica et al, 2020b; Yuan et al, 2020), glacial studies (Booth et al, 2020; Brisbourne et al, 2021; Hudson et al, 2021), geothermal exploration (Li and Zhan, 2018; Lellouch et al, 2021), volcanology (Nishimura et al, 2021) and underwater seismology (Spica et al, 2020a; Lior et al, 2021)

  • At the Groß Schönebeck in-situ laboratory, a unique vertical seismic profiling (VSP) dataset was recorded in two 4.3 km deep geothermal boreholes using fibre optic cables in early 5 2017

  • Thereby, we demonstrate that wireline fibre optic data can significantly contribute to exploration by providing an efficient and reliable method for deep geothermal reservoir imaging

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Summary

Introduction

Measurements with a fibre-optic cable installed in diverse environments are widely applied for seismic data acquisition for versatile research topics such as urban seismology (Dou et al, 2017; Spica et al, 2020b; Yuan et al, 2020), glacial studies (Booth et al, 2020; Brisbourne et al, 2021; Hudson et al, 2021), geothermal exploration (Li and Zhan, 2018; Lellouch et al, 2021), volcanology (Nishimura et al, 2021) and underwater seismology (Spica et al, 2020a; Lior et al, 2021). Measurements with a fibre-optic cable installed along the casing or behind the tubing are widely and successfully applied for borehole seismic data acquisition. Since the studied geothermal reservoir zone is located at 50 a depth greater than 4 km and overlaid by Zechstein salt, it is a challenging target for exploration with conventional seismic methods

The distributed acoustic sensing vertical seismic profiling survey
Data preconditioning
Velocity model building and ray tracing
Data preparation for migration
Upper Rotliegend horizons
Elbe basis sandstone layer
The lower Rotliegend unconfomity 225
The Groß Schönebeck experiment
Data processing
Future geothermal exploration plans
Conclusions
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