Wireline distributed acoustic sensing allows 4.2 km deep vertical seismic profiling of the Rotliegend 150 °C geothermal reservoir in the North German Basin

Abstract

Abstract. We performed so-far-unprecedented deep wireline vertical seismic profiling at the Groß Schönebeck site with the novel method of distributed acoustic sensing (DAS) to gain more detailed information on the structural setting and geometry of the geothermal reservoir, which is comprised of volcanic rocks and sediments of Lower Permian age. During the survey of 4 d only, we acquired data for 61 source positions using hybrid wireline fiber-optic sensor cables deployed in two 4.3 km deep, already existing wells. While most of the recorded data have a very good signal-to-noise ratio, individual sections of the profiles are affected by characteristic coherent noise patterns. This ringing noise results from incomplete coupling of the sensor cable to the borehole wall, and it can be suppressed to a large extent using suitable filtering methods. After conversion to strain rate, the DAS data exhibit a high similarity to the vertical component data of a conventional borehole geophone. We derived accurate time–depth relationships, interval velocities, and corridor stacks from the recorded data. Based on integration with other well data and geological information, we show that the top of a porous and permeable sandstone interval of the geothermal reservoir can be identified by a positive reflection event. Overall, the sequence of reflection events shows a different character for both wells explained by lateral changes in lithology. The top of the volcanic rocks has a somewhat different seismic response in both wells, and no clear reflection event is obvious at the postulated base of the volcanic rocks, so that their thickness cannot be inferred from individual reflection events in the seismic data alone. The DAS method enabled measurements at elevated temperatures up to 150 ∘C over extended periods and led to significant time and cost savings compared to deployment of a conventional borehole geophone string. This wireline approach finally suggests significant implications for observation options in old wells for a variety of purposes.

3D deep geothermal reservoir imaging with wireline distributed acoustic sensing in two boreholes

“…Depth variations of this horizons are visible already in a small volume around the boreholes. The indication of these variations in lithological sequences is also present in the corridor stacks within this interval (Henninges et al, 2021).…”

“…In E GrSk 3/90, we recorded the planned 61 VPs and the maximum surveyed depth is at 4251 m MD. Nevertheless, recorded datasets from this borehole have inconsistent amplitudes caused by unknown reasons, which requires further investigations (Henninges et al, 2021).…”

Dynamic motion monitoring of a 3.6 km long steel rod in a borehole during cold-water injection with distributed fiber-optic sensing

“…Johannessen et al (2012) introduced the potential and capabilities for acoustic in-well monitoring applications based on DAS systems which range from, e.g., flow measurements, sand detection, gas breakthrough and leak detection to vertical seismic profiling (VSP). Daley et al (2013), Mateeva et al (2014), Harris et al (2016), Daley et al (2016) and Henninges et al (2021) compare traditional geophone with DAS recordings acquired during a vertical seismic profiling campaign (VSP). Götz et al (2018) report on a multi-well VSP campaign at a carbon dioxide storage site by using only one single DAS interrogator.…”

Distributed Acoustic Sensing in Volcano-Glacial Environments - Mount Meager, British Columbia

“…The broadband response of DAS can aid to recover a wide range of signals in various applications (Jousset et al, 2018;Lindsey et al, 2020;Paitz et al, 2020). DAS has initially been used for vertical seismic profiling in hydrocarbon and geothermal exploration (Mateeva et al, 2014) and has subsequently been adapted to a wider range of seismological applications (Henninges et al, 2021;Lindsey et al, 2017;Martin et al, 2017;Walter et al, 2020;Zhan, 2020).…”