For the safe and sustainable use of deep geothermal wells, construction must proceed as intended. An integer well ensures that all fluids within the borehole are always under control. One of the most critical steps is the cementing of the casings. Despite extensive experience in the petroleum industry, challenges with well integrity are a worldwide phenomenon. One reason could be that conventional measurement methods can only verify the success of cementing once the cement job has been completed. In contrast, distributed fiber optic sensing methods can monitor the entire cementing process along the entire drilling path.
This data set contains the results of the Distributed Temperature Sensing (DTS) and the derived product "vibrational energy" of a Distributed Dynamic Strain Sensing (DDSS or DAS) of the whole cementing process. We collected this data during the primary cementing of an injection well's 874m surface casing at the geothermal site Schäftlarnstr, Munich. We measured the cement placement and 24 hours of the early hydration.
We obtained the data with a fiber optic cable permanently deployed behind the casing. The cable contained Multi-Mode fibers (for DTS) and Single-Mode fibers (for DAS). Table 1 in the data description document shows the units used and the key parameters of our measurement.
In the first step, we allocated each channel to its depth in the borehole. We used a cold spray (for DTS) and a tap test (for DAS) to locate the entry to the borehole. To obtain the vibrational energy of the DAS data, we summarized the raw dynamic strain with a Root Mean Square (RMS) in a window of 60 seconds. We calculated the vibrational energy for a wide range of different frequency ranges (Butterworth bandpass). The data are provided in csv formats and further explained in the data description document.
Acknowledgement:
GFK-Monitor is funded by the Federal Ministry for Economic Affairs and Climate Action via the Project Management Jülich (PTJ) (funding code: 03EE4036, project duration: July 1, 2022 - June 30, 2025). The fiber optic infrastructure was provided by GAB (Geothermie Allianz Bayern): Funded by: Bayerisches Staatsministerium für Wissenschaft und Kunst (Hauptgebäude: Salvatorstraße 2, 80333 München).
An extensive vertical seismic profiling (VSP) survey using wireline distributed acoustic sensing (DAS) technology was carried out between the 15th and 18th of February 2017 at the geothermal in-situ laboratory Groß Schönebeck, Germany. Borehole measurements were recorded in two 4.3 km deep wells E GrSk 3/90 and Gt GrSk 4/05. Two hybrid fibre optics cables were freely lowered inside the wells to form dense receiver arrays. As a seismic source, four heavy vibroseis trucks were used. The survey consisted of 61 source positions distributed in a spiral pattern around the target area.
This data publication consists of raw uncorrelated seismic data acquired for 3D seismic imaging purposes. Supplementary information such as well trajectories, source point coordinates, and the pilot sweep data is also provided. Data related to zero-offset measurements can be found in Henninges et al. (2021, https://doi.org/10.5880/GFZ.4.8.2021.001).
Further details on the survey design and data acquisition parameters can be found in Henninges et al. (2021, https://doi.org/10.5194/se-12-521-2021); Martuganova et al. (2021, 2022). Information on high-resolution 3D reflection seismic acquisition campaign carried out at Groß Schönebeck in February–March 2017 can be found in Krawczyk et al. (2019); Bauer et al. (2020); Norden et al. (2022). The 3D DAS VSP processing workflow, 3D DAS imaging results, and comparison with 3D surface seismics are presented in Martuganova et al. (2022).
Understanding physical processes prior and during eruptions remains challenging, due to uncertainties about subsurface structures and undetected processes within the volcano. Here, the authors use a dedicated fibre-optic cable to obtain strain data and identify volcanic events and image hidden near-surface volcanic structural features at Etna volcano, Italy. In the paper Jousset et al. (2022), we detect and characterize strain signals associated with explosions, and we find evidences for non-linear grain interactions in a scoria layer of spatially variable thickness. We also demonstrate that wavefield separation allows us to incrementally investigate the ground response to various excitation mechanisms, and we identify very small volcanic events, which we relate to fluid migration and degassing. We recorded seismic signals from natural and man-made sources with 2-m spacing along a 1.5-km-long fibre-optic cable layout near the summit of actives craters of Etna volcano, Italy. Those results provide the basis for improved volcano monitoring and hazard assessment using DAS. This data publication contains the full data set used for the analysis. This data set comprises strain-rate data from 1 iDAS interrogator (~750 traces), velocity data from 15 geophones and 4 broadband seismometers, and infrasonic pressure data from infrasound sensors. For further explanation of the data and related processing steps, please refer to Jousset et al. (2022). Waveform data are available from the GEOFON data centre, under network code 9N.
In January 2020, a swarm of earthquakes started under Thorbjorn volcano, Reykjanes, SW Iceland, associated to the uplift of up to 0.5 cm per day. Concern in Iceland was growing and the Iceland Meteorological Office suggested at that time that possibly magma intruded in the crust at shallow depth (3 to 9 km). The first eruption occurred on 19.03.2021, followed by many others in the foolwing years. The GFZ started a seismological Hazard and Risk Team (HART), as soon as February 2020 in cooperation with IMO, ISOR and the University of Iceland. The interrogator was located in Grindavik and was connected to a standard telecom cable. The full data dataset of this 5J network comprise 250 Tb of raw data. The standard infrastructure is not designed for such large data set. Therefore, we implement here several datasets, corresponding to several processing and associated publications. Specific full data set is available upon request to the authors. In Flovenz et al., 2022, the data subset comprise a selection of wave-forms recorded along an optical fibre of 21 km length. The subset consists of 40 channels at 100 Hz (spatially stacked 9x). The whole time period from January until August 2020 is covered, with a total size of 496 GB. The data is MiniSEED at 4096 bytes record length with STEIM2. In Maass et al., 2024, the data subset consists of two sections of contiguous channels (1701-2000 and 3921-4218, spatial sampling 4 meters) of dynamic strain rate down sampled at 5 Hz. The whole time period from January until August 2020 is covered, with a total size of 340 GB. The data is MiniSEED at 4096 bytes record length with STEIM2.