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

Martuganova, Evgeniia; Stiller, Manfred; Norden, Ben; Henninges, Jan; Krawczyk, Charlotte M.

doi:https://doi.org/10.5194/se-13-1291-2022

Articles | Volume 13, issue 8

https://doi.org/10.5194/se-13-1291-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Fibre-optic sensing in Earth sciences

https://doi.org/10.5194/se-13-1291-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 8

Research article

|

22 Aug 2022

Research article |

| 22 Aug 2022

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

Evgeniia Martuganova, Manfred Stiller, Ben Norden, Jan Henninges, and Charlotte M. Krawczyk

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Final revised paper (published on 22 Aug 2022)
Preprint (discussion started on 15 Nov 2021)

Interactive discussion

Status: closed

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)

Citation: https://doi.org/10.5194/se-2021-138-RC1
- 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
  
  Citation: https://doi.org/10.5194/se-2021-138-AC1
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.

Citation: https://doi.org/10.5194/se-2021-138-RC2
- 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
  
  Citation: https://doi.org/10.5194/se-2021-138-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Evgeniia Martuganova on behalf of the Authors (30 Apr 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (02 May 2022) by Gilda Currenti

RR by Anonymous Referee #1 (09 May 2022)

RR by Anonymous Referee #3 (18 Jul 2022)

Suggestions for revision or reasons for rejection

Dear Authors,

Thank you for submitting your interesting work to Solid Earth. Indeed, applying novel methods, such as DAS, to carbon-neutral energy projects, such as geothermal, are of great interest and importance.

The paper demonstrates the successful application of 3D DAS VSP imaging using wireline fibres. In addition, the authors did great work addressing the issues and challenges related to such dataset and showed the value of the received image for a decision on further wells placement for harvesting geothermal energy.

The paper is well written, the abstract is to the point, and the conclusion provides a complete summary of the presented work. Especially I want to praise the authors for their work on the quality of illustrations and detailed explanation of the processing steps in Table 1.

Below is the minor suggestions which may further improve this work:

24-25: "measure particle displacement" -- despite the usage of the hDVS system, it is commonly assumed that DAS measures strain change or strain rate. Please clarify.

47: it would be beneficial to mention reservoir temperature in the considered case to understand if high-temperature geophones could be used or not.

111: it would be great if authors could bring their hypothesis on "unknown reasons"

Figure 2: it could be beneficial to highlight the changes in the seismograms, which the reader should pay attention to between processing steps.

157: were Thomsen's parameters chosen only based on DAS VSP data, or some logs were used to estimate them? Please elaborate.

Figure 3, 4b, 5, 6: North arrow is confusing. Consider changing the north arrow on 3D plots or using northing and easting if x and y coordinates match these orientations. Also, some figures have "N" on top of the arrow; some do not.

304: "constelation fibres' -> "engineered fibres", as constelation is a trademark

325: "geothermal fiel, which are limitd to the depth up to 600 m." -> "geothermal field, which are limited to the depth of 600 m."

399: 'borehole seismics" -> "borehole seismic"

I recommend accepting the paper for publication after incorporating these minor suggestions.

Hide

ED: Publish subject to minor revisions (review by editor) (18 Jul 2022) by Gilda Currenti

AR by Evgeniia Martuganova on behalf of the Authors (23 Jul 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (25 Jul 2022) by Gilda Currenti

ED: Publish as is (25 Jul 2022) by Susanne Buiter (Executive editor)

AR by Evgeniia Martuganova on behalf of the Authors (29 Jul 2022) Manuscript

Short summary

We demonstrate the applicability of vertical seismic profiling (VSP) acquired using wireline distributed acoustic sensing (DAS) technology for deep geothermal reservoir imaging and characterization. Borehole DAS data provide critical input for seismic interpretation and help assess small-scale geological structures. This case study can be used as a basis for detailed structural exploration of geothermal reservoirs and provide insightful information for geothermal exploration projects.