the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Sep 2024
Lithologically constrained velocity–density relationships and vertical stress gradients in the North Alpine Foreland Basin, SE Germany
Abstract. We systematically analysed density and velocity data from 41 boreholes to establish velocity-density relationships for the main lithological units in the North Alpine Foreland Basin in SE Germany. We applied these relationships to velocity data and spliced the resulting density values with actual density data and a shallow density model to retrieve complete density profiles along 55 deep wellbores, which at least penetrated the Cenozoic section in the study area. We integrated density profiles to vertical stress to investigate the spatial distribution of vertical stress gradients. Thereby, we observed an eastward decrease of vertical stress gradients, which correlates well with the geological configuration of the North Alpine Foreland Basin in SE Germany. Thereby, vertical stress gradient profiles can be reasonably estimated as a function of true vertical depth below ground level TVD in the western, central, and eastern parts of the study area using a power law relationship:
West: 21 MPa/km + (TVD/325)1/1.80, R² = 0.98
Central: 21 MPa/km + (TVD/410)1/1.93, R² = 0.99
East: 21 MPa/km + (TVD/531)1/1.95, R² = 1.00
In addition, we also investigated the distribution of vertical stress gradients at the top of Upper Jurassic carbonates, an important aquifer for deep geothermal energy production. Our study, therefore, provides a valuable resource for future geophysical, geomechanical, and geological studies in the North Alpine Foreland Basin, both in a fundamental and applied research context.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1984 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1984 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2024-2692', Giacomo Medici, 30 Sep 2024
General comments
Very good research in the field of geophysics with insights on geothermal energy. Please, consider the minor points to improve the manuscript.
Specific comments
Line 6. “We systematically analysed density and velocity data from 41 boreholes”. Using...please specify the technique/tool, this point needs to be clear in the abstract.
Lines 35-37. “Acoustic wave velocity through rocks or its inverse, the acoustic slowness, correlates well with density and porosity of different rock types. Several authors have investigated this correlation and established relationships that are widely used in geophysics and rock physics applications”. Please, add review papers that describes the geophysical techniques that contribute to determine the porosity and storage properties in deep aquifers:
- Medici G., Ling F., Shang J. 2023. Review of discrete fracture network characterization for geothermal energy extraction. Frontiers in Earth Science, 11, 1328397.
- Zhang, J. (2011). Pore pressure prediction from well logs: Methods, modifications, and new approaches. Earth-Science Reviews, 108(1-2), 50-63.
Line 42. “reduction of porosity”. Are you talking about the porosity of the matrix or the fractures? Please, specify. Indeed, in some sedimentary basins and rocks the fractures can still play a role on flow and storage of fluids at relatively elevated depths.
Line 57. Please, clarify the specific objectives of your research by using numbers (e.g., i, ii, and iii).
Line 138. “78 deep oil and gas wells”. Please, specify the depth range. How deep are the wells?
Lines 425-432. I can see 4 bulletin points. Therefore, your specific objectives should be 4.
Lines 454-560. Please, integrate relevant literature on the use of geophysics in deep aquifers.
Figures and tables
Figure 1. Vertical scale is unclear.
Figure 5. Make the letters "a", "b", and "c" larger.
Figure 5c. The density profiles are noisy. But, I can see an unreal spike at 4100 TVD(m) that should be deleted from the dataset.
Citation: https://doi.org/10.5194/egusphere-2024-2692-CC1 - AC3: 'Reply on CC1', Michael Drews, 14 Feb 2025
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RC1: 'Comment on egusphere-2024-2692', Anonymous Referee #1, 18 Dec 2024
The topic of the manuscript is very interesting for the local geology as well as a reproducible approach for other basin setting for which heterogeneous boreholes information are available. The manuscript is generally well written, clear and concise. Only the Abstract needs significantly improvement. In fact, the abstract struggles to summarize the study effectively and comprehensively. It is not clear that there is and what is the difference between the datasets used to calibrate (A) and to derive the profiles (B). Nor is the methodology clear (sonic velocity or seismic interval velocity). There is not enough information on the stratigraphy of the area. These should be few, synthetic but are essential to understand the logic of the work. The importance of the Top of Jurassic boundary and its relationships with the rest of the stratigraphy should be presented and highlighted. On the contrary, the formulas do not really need to be included in the abstract. possibly only the value of R2. For the rest, it's a pleasure to read a well-crafted manuscript with well-defined objectives from the beginning. I have only one major concern about Figure 1, which needs to be completely redrawn. This and other minor suggestions are indicated in the annotated pdf.
Finally, I recommend publication once the (few) comments above have been addressed.
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AC1: 'Reply on RC1', Michael Drews, 14 Feb 2025
Dear Reviewer RC1,
Many thanks for your time and constructive feedback.
We replied to your general comments in the file: Reply_General_Comments_Reviewer#1.pdf
We replied point-by-point to your additional comments in the annotated pdf: Reply_Manuscript_Comments_Reviewer#1.pdf
We hope the implemented changes improved the manuscript as intended and that our replies clarify all open questions.
Kind regards,
Michael Drews, Peter Obermeier and Florian Duschl
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AC1: 'Reply on RC1', Michael Drews, 14 Feb 2025
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RC2: 'Comment on egusphere-2024-2692', Anonymous Referee #2, 19 Dec 2024
This paper is well written, and the data could be of interest but it lacks physics and perspectives to fully understand its importance.
- First, the authors state that their new vertical stress gradients really improve the estimate of vertical stress but they never compare their model with a model using a linear trend. I guess their main results should be to show how wrong we are we use a simplistic equation.
- Then none of their equations are discussed in terms of physics, or their implication in term of geological processes. Using a power law implies a certain evolution type with depth. Authors don't justify neither the form of eq. 2.
- the principal explanation for outliers in bulk density is overpressure. But there are many others factors that can be important, as cementation, variation of stress paths, and they are barely disuccsed;
I've put more comments in the files attached.
for all this reasons I recommend majors revision
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AC2: 'Reply on RC2', Michael Drews, 14 Feb 2025
Dear Reviewer RC2,
Many thanks for your time and constructive feedback.
We replied to your general comments in the file: Reply_General_Comments_Reviewer#2.pdf
We replied point-by-point to your additional comments in the annotated pdf: Reply_Manuscript_Comments_Reviewer#2.pdf
We hope the implemented changes improved the manuscript as intended and that our replies clarify all open questions.
Kind regards,
Michael Drews, Peter Obermeier and Florian Duschl
-
AC2: 'Reply on RC2', Michael Drews, 14 Feb 2025
Interactive discussion
Status: closed
-
CC1: 'Comment on egusphere-2024-2692', Giacomo Medici, 30 Sep 2024
General comments
Very good research in the field of geophysics with insights on geothermal energy. Please, consider the minor points to improve the manuscript.
Specific comments
Line 6. “We systematically analysed density and velocity data from 41 boreholes”. Using...please specify the technique/tool, this point needs to be clear in the abstract.
Lines 35-37. “Acoustic wave velocity through rocks or its inverse, the acoustic slowness, correlates well with density and porosity of different rock types. Several authors have investigated this correlation and established relationships that are widely used in geophysics and rock physics applications”. Please, add review papers that describes the geophysical techniques that contribute to determine the porosity and storage properties in deep aquifers:
- Medici G., Ling F., Shang J. 2023. Review of discrete fracture network characterization for geothermal energy extraction. Frontiers in Earth Science, 11, 1328397.
- Zhang, J. (2011). Pore pressure prediction from well logs: Methods, modifications, and new approaches. Earth-Science Reviews, 108(1-2), 50-63.
Line 42. “reduction of porosity”. Are you talking about the porosity of the matrix or the fractures? Please, specify. Indeed, in some sedimentary basins and rocks the fractures can still play a role on flow and storage of fluids at relatively elevated depths.
Line 57. Please, clarify the specific objectives of your research by using numbers (e.g., i, ii, and iii).
Line 138. “78 deep oil and gas wells”. Please, specify the depth range. How deep are the wells?
Lines 425-432. I can see 4 bulletin points. Therefore, your specific objectives should be 4.
Lines 454-560. Please, integrate relevant literature on the use of geophysics in deep aquifers.
Figures and tables
Figure 1. Vertical scale is unclear.
Figure 5. Make the letters "a", "b", and "c" larger.
Figure 5c. The density profiles are noisy. But, I can see an unreal spike at 4100 TVD(m) that should be deleted from the dataset.
Citation: https://doi.org/10.5194/egusphere-2024-2692-CC1 - AC3: 'Reply on CC1', Michael Drews, 14 Feb 2025
-
RC1: 'Comment on egusphere-2024-2692', Anonymous Referee #1, 18 Dec 2024
The topic of the manuscript is very interesting for the local geology as well as a reproducible approach for other basin setting for which heterogeneous boreholes information are available. The manuscript is generally well written, clear and concise. Only the Abstract needs significantly improvement. In fact, the abstract struggles to summarize the study effectively and comprehensively. It is not clear that there is and what is the difference between the datasets used to calibrate (A) and to derive the profiles (B). Nor is the methodology clear (sonic velocity or seismic interval velocity). There is not enough information on the stratigraphy of the area. These should be few, synthetic but are essential to understand the logic of the work. The importance of the Top of Jurassic boundary and its relationships with the rest of the stratigraphy should be presented and highlighted. On the contrary, the formulas do not really need to be included in the abstract. possibly only the value of R2. For the rest, it's a pleasure to read a well-crafted manuscript with well-defined objectives from the beginning. I have only one major concern about Figure 1, which needs to be completely redrawn. This and other minor suggestions are indicated in the annotated pdf.
Finally, I recommend publication once the (few) comments above have been addressed.
-
AC1: 'Reply on RC1', Michael Drews, 14 Feb 2025
Dear Reviewer RC1,
Many thanks for your time and constructive feedback.
We replied to your general comments in the file: Reply_General_Comments_Reviewer#1.pdf
We replied point-by-point to your additional comments in the annotated pdf: Reply_Manuscript_Comments_Reviewer#1.pdf
We hope the implemented changes improved the manuscript as intended and that our replies clarify all open questions.
Kind regards,
Michael Drews, Peter Obermeier and Florian Duschl
-
AC1: 'Reply on RC1', Michael Drews, 14 Feb 2025
-
RC2: 'Comment on egusphere-2024-2692', Anonymous Referee #2, 19 Dec 2024
This paper is well written, and the data could be of interest but it lacks physics and perspectives to fully understand its importance.
- First, the authors state that their new vertical stress gradients really improve the estimate of vertical stress but they never compare their model with a model using a linear trend. I guess their main results should be to show how wrong we are we use a simplistic equation.
- Then none of their equations are discussed in terms of physics, or their implication in term of geological processes. Using a power law implies a certain evolution type with depth. Authors don't justify neither the form of eq. 2.
- the principal explanation for outliers in bulk density is overpressure. But there are many others factors that can be important, as cementation, variation of stress paths, and they are barely disuccsed;
I've put more comments in the files attached.
for all this reasons I recommend majors revision
-
AC2: 'Reply on RC2', Michael Drews, 14 Feb 2025
Dear Reviewer RC2,
Many thanks for your time and constructive feedback.
We replied to your general comments in the file: Reply_General_Comments_Reviewer#2.pdf
We replied point-by-point to your additional comments in the annotated pdf: Reply_Manuscript_Comments_Reviewer#2.pdf
We hope the implemented changes improved the manuscript as intended and that our replies clarify all open questions.
Kind regards,
Michael Drews, Peter Obermeier and Florian Duschl
-
AC2: 'Reply on RC2', Michael Drews, 14 Feb 2025
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Peter Obermeier
Florian Duschl
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1984 KB) - Metadata XML