the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
3D deep geothermal reservoir imaging with wireline distributed acoustic sensing in two boreholes
- 1Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences,14473 Potsdam, Germany
- 2Department of Applied Geophysics, Technische Universität Berlin,10587 Berlin, Germany
- 1Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences,14473 Potsdam, Germany
- 2Department of Applied Geophysics, Technische Universität Berlin,10587 Berlin, Germany
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.
Evgeniia Martuganova and Charlotte M. Krawczyk
Status: final response (author comments only)
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RC1: 'Comment on se-2021-138', Anonymous Referee #1, 26 Dec 2021
The authors present results of a VSP experiment for geothermal explorations using DAS. This is an interesting topic and of great societal interest. The paper is generally well written and figures are broadly all relevant and of good quality.
Be fore final publications I recoment that the authors clarify the overall purpose of the paper: Is it a DAS paper, a processing paper, or interpretation paper. I feel it is more of the latter. The overall question(s) that are adressed should be stated more explicitly in the introduction. Notably why and how VSP can help to make geothermal energy production in that particular area a success. Also, what are recommendations for future sites, both in similar and different geological settings. This would IMHO increase the "citability" of the manuscript.
Minor comments:
Line 16: Referenced Spica 2020b before Spica 2020a
Line 25: The well is probably "completed", not just "drilled" ?
L27: "...rarely found in [peer-reviewed] literature"...
L30: Add comment on how your work will contribute to geothermal exploration. What questions for decission makers are you adressing? What scientific quesitons are you adressing?
Figure 1: The world map is too small. It is hard to localise the site geographically
L63: "optimal" SNR. Is that optimum subjectively chosen? is there a quantitative approach to find the optimum? Is this published earlier and you could reference a figure?
L81: Please comment on if there are any DAS-specific steps neccesary (beside the polarity flip). strain(rate) data may be quite different from usual velocity data. Explicitly stating that no additional steps are required may help to promote this technology.
Table1: What do you mean by data conditioning?
L100: add references for Burg convolution and TF-attenuation
L104: "slapping" of the cable. Do you mean that loose bits of the cable are dangling around in the tubing and cause these signals. IT might need some additional explanation here.
L119: "iteratively optimised" was that a manual or automatic process?
L123: Was the ray tracing done in the anisotropic velocity model? Is it worth mentioning a reference to that ray tracer? is it publicly available?
L134: "cleanest": subjectively or objectively?
Figure 4: The legend and text is too small
Figure 5: 3D figures are difficult to understand in paper form. is that really neccesary here? would simple 2D slices be better?
L191: the "Green arrow" is very hard to identify in the figure 6 (as are the other markers.
L205: Why is that sandstone formation chosen as target formation? What do you expect to find with VSP that wasn't known from seismics? did you find this? I suspect faults are relevant for reservoir integrity. What is known about faults in the area and can you in this paper help to comment on risks for geothermal production? I suspect the plan is for hydraulic stimulation? Any risk for fault reactivation and major EQs?
L271: Contractions shouldn't (sorry, should not) be used in scientific writing
L324: it would be beneficial to posiiton your work in the broader geothermal exploraiton picture. Do you recoomend VSPs for all sites? What can be gained? What geological setting would justify it? Was DAS an adequate tool? Any lessons learned (in design, acquisition parameters, or processing)
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AC1: 'Reply on RC1', Evgeniia Martuganova, 30 Apr 2022
Dear reviewer,
Thank you for your comments and suggestions that helped to improve the paper. In a separate attachment, we include the original comments followed by our reply. After this, the revised manuscript (marked-up copy) with the changes highlighted is appended.
On behalf of all co-authors,
Yours faithfully,
Evgeniia Martuganova
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AC1: 'Reply on RC1', Evgeniia Martuganova, 30 Apr 2022
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RC2: 'Comment on se-2021-138', Anonymous Referee #2, 02 Mar 2022
Thank you for your submission. The manuscript shows an important application of seismic imaging at a geothermal site using distributed acoustic sensing (DAS). The manuscript shows a migrated 3D volume using DAS vertical seismic profiling and provides structural and stratigraphic interpretation of the main reflectors. This is one of the few applications using 3D VSP with DAS for characterization of geothermal sites.
Overall, the manuscripts shows the necessary figures for its claims. However, I would suggest also adding a synthetic seismogram using well logs if possible. Additionally, I believe the paper needs careful proof reading to improve the readability and clarity. More especifically, the introduction should contain clear objectives, the claim and main manuscript outcomes. More work is needed in the literature overview to describe the previous research using DAS in geothermal sites and their achievements. Furthermore, I have added specific comments in the attached pdf.
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AC2: 'Reply on RC2', Evgeniia Martuganova, 30 Apr 2022
Dear reviewer,
Thank you for your comments and suggestions that helped to improve the paper. In a separate attachment, we include the original comments followed by our reply. After this, the revised manuscript (marked-up copy) with the changes highlighted is appended.
On behalf of all co-authors,
Yours faithfully,
Evgeniia Martuganova
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AC2: 'Reply on RC2', Evgeniia Martuganova, 30 Apr 2022
Evgeniia Martuganova and Charlotte M. Krawczyk
Evgeniia Martuganova and Charlotte M. Krawczyk
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