Fault damage zone volume and initial salinity distribution determine  intensity of shallow aquifer salinisation in subsurface storage

Tillner, Elena; Langer, Maria; Kempka, Thomas; Kühn, Michael

doi:https://doi.org/10.5194/hess-20-1049-2016

Articles | Volume 20, issue 3

https://doi.org/10.5194/hess-20-1049-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-1049-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 3

Research article

|

08 Mar 2016

Research article |

| 08 Mar 2016

Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinisation in subsurface storage

Elena Tillner, Maria Langer, Thomas Kempka, and Michael Kühn

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Final revised paper (published on 08 Mar 2016)
Preprint (discussion started on 16 Jun 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C2484: 'Review of « Effective damage zone volume of fault zones and initial salinity distribution determine intensity of shallow aquifer salinization in geological underground utilization” submitted by M.Langer et al. to Hydrology Earth Systems Sciences (HESS)', Anonymous Referee #1, 10 Jul 2015
- AC C3536: 'Answers to comments of anonymous Referee #1', Elena Tillner, 09 Sep 2015
RC C2489: 'Review of the manuscript “Effective damage zone volume of fault zones and initial salinity distribution determine intensity of shallow aquifer salinization in geological underground utilization” by M. Langer et al.', Anonymous Referee #2, 10 Jul 2015
- AC C3543: 'Answers to comments of anonymous Referee #2', Elena Tillner, 09 Sep 2015
  - AC C3591: 'Answer comment - supplement', Elena Tillner, 10 Sep 2015
RC C2514: 'Review of the manuscript "Eective damage zone volume of fault zones and initial salinity distribution determine intensity of shallow aquifer salinization in geological underground utilization" by Langer et al.', Anonymous Referee #3, 13 Jul 2015
- AC C3575: 'Answers to comments of anonymous Referee #3', Elena Tillner, 09 Sep 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (23 Sep 2015) by Monica Riva

AR by Elena Tillner on behalf of the Authors (02 Dec 2015)

ED: Referee Nomination & Report Request started (28 Dec 2015) by Monica Riva

RR by Anonymous Referee #2 (18 Jan 2016)

Suggestions for revision or reasons for rejection

Review of the paper “Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinization in geological underground utilization”, by E. Tillner et al.
The revised version of the manuscript is significantly better than the original one. The authors have satisfactorily addressed all the comments made by the reviewers. For these reasons I recommend accepting the manuscript for its publication.
The authors have decided to be conservative and assume no compressibility and constant salinity without the fault. However, it is very interesting to see that when a gradient of salinity is considered within the fault, the salinization of the freshwater aquifer is significantly lower than in the conservative cases. This research is interesting to evaluate the risk of polluting freshwater aquifers as a result of fluid disposal. As future work, more realistic permeability distribution in the vertical direction of the fault would be of interest.
I only have some minor comments:
- Page 11, lines 30-31: the sentence “Hence, the duration of brine displacement into the shallow aquifer is shorter for all three scenarios.” is not very clear, shorter than what? I suggest rewriting this sentence.
- Page 15, line 19: Explain to what “these” refers to in “These range between 132 m…”, I guess it refers to “These depths range…”.
- Page 16, line 31: “focussing on” should be “focusing on” (there is an extra s).
- Table 3, last row, first column: “F1 2km Bc*” should be “F1 193km Bc*” (the length of the fault is not correct)
- Table 3, fifth row (F1 2km Bc*), seventh column (Salinization area): according to the text and by analyzing the overall response of the models, it seems that there is a typo in the salinization area of this model because it gives the largest area, but it should be the minimum. Thus, instead of 2.11*10^7, it may be 2.11*10^6.

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RR by Anonymous Referee #3 (02 Feb 2016)

Suggestions for revision or reasons for rejection

This is a review of the second version of the manuscript “Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinization in geological underground utilization”. In my opinion the authors have greatly improved the manuscript, and I only have some minor questions/concerns. I therefore recommend that the manuscript is accepted with minor revisions.
In the title (and later in the text) it is not clear what ‘geological underground utilization’ is supposed to mean. Why not just go with ‘geologic carbon storage’ instead, as this is the topic of the manuscript.
In the introduction I would delete the discussion about why the Person et al and Zhou et al papers come to slightly different pressure responses, because it doesn’t add to the topic of this paper. Also, it is not clear to me what Table 1 adds to the paper; I would delete it. If the table is to be retained, the authors need to make clear on which basis the different studies were chosen, as this table is not comprehensive when it comes to large domain studies or well/fracture leakage studies.
In the last paragraph of section 2, the authors talk about the displacement at the different faults. I am missing the context here. Why does the reader need to know the displacements?
The argument for using a single-phase model (bottom paragraph, page 7) by stating that otherwise CO2 might reach the fault is somewhat unconvincing. I think the argument is that the authors are not interested in CO2 leakage for this particular study. This, coupled with the argument that a brine injection is more conservative (as the authors write), is sufficient to justify running a single-phase model. However, now that the authors have done the comparison (see author’s responses), they could add a sentence, somewhat like ‘In addition, initial testing has shown that the difference in pressure response at the fault from using a two-phase model instead of a single-phase model, is small compared to other effects studied here.’
Page 9, line 22: the word ‘course’ is strange here; how about ‘location’?
Throughout the manuscript I would not use the names of the faults and formations, but would use simple descriptors such as ‘short fault’ for the 2km fault, ‘main adjacent fault’ for the full fault close to the injection, ‘surrounding faults’ for the three faults that are farther away, ‘storage aquifer’ for the Dethfurth Formation, ‘intermediate aquifer’ for the Muschelkalk Formation, and ‘shallow aquifer’ for Rupelian basal sands. I think this would make it easier to understand for folks who are not familiar with the site. Maybe add these descriptors to Table 2 for ‘translation’.
On page 17, in the section discussing brine leakage along abandoned wells, why is Birkholzer et al. (2011) not mentioned?
Both the ‘Summary and discussion’ and the ‘Conclusion’ sections start with a more-or-less long summary. I would delete the summary in one of them.
What does ‘pressure development’ mean?
Table 3: I would put the area where salinity is above the drinking water standard in km2. These areas are quite larger (on the order of tens of km2). This needs to be addressed.
Figure 3: why use global coordinates for display? I realize this commonly done, but the figure is not fitting in with other figures in the same coordinate system. Having such large numbers (e.g., 3440000) makes it difficult to judge distances?
Figure 4a): the order of magnitude difference between the two scales needs to be pointed out in the figure.
There are too many figures. I am sure all of them contain useful information, but the sheer number of figures washes out any details. It would be useful, if some of the figures could be combined to only show the most important features of the results.

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ED: Publish subject to technical corrections (11 Feb 2016) by Monica Riva

AR by Elena Tillner on behalf of the Authors (19 Feb 2016) Author's response Manuscript

Short summary

The degree of shallow aquifer salinisation triggered by fluid injection into deeper brine-bearing aquifers and brine upward migration through hydraulically conductive faults strongly depends on the regional depth of the freshwater-saltwater boundary, since displaced brines originate only from the upper fault damage zones in the study area. The highest local salinity increase in shallow aquifers occurs in case of closed model boundaries and low fault damage zone volumes.