the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Earthquakes triggered by the subsurface undrained response to reservoir-impoundment at Irapé, Brazil
Abstract. The necessity to reduce carbon emissions to mitigate climate change is accelerating the transition from fossil fuels to renewable energy sources. Specifically, hydropower, in particular, has emerged as a prominent and safe renewable energy source but entails reservoir-triggered seismicity (RTS). This phenomenon causes significant challenges for safe reservoir management. Irapé, in Brazil, is a prominent RTS site where seismicity surged after reservoir filling, with a maximum event of magnitude 3.0 in May 2006, just six months after the start of reservoir impoundment. Despite more than a decade has passed since the seismicity occurred, the factors governing these earthquakes and their connection to subsurface rock properties remain poorly understood. Here, we attempt to understand the potential causes of RTS at Irapé dam, which is the highest dam in Brazil with 208 m, and the second highest in South America. Permeability and porosity measurements of cylindrical cores from hard and intact rock samples, which have been extracted near the RTS zone, by pitting 10 cm from the surface, reveal a low-permeability rock. Porosity values range from 6.340 to 14.734 %. Only 3 out of the 11 tested samples present permeability higher than the lowest measurable value of the apparatus (0.002 mD), with the highest permeability being 0.0098 mD. The undrained response of the low-permeability rock placed below the reservoir results in an instantaneous increase in pore pressure and poroelastic stress changes due to elastic compression, which brings potential faults located below the reservoir closer to failure conditions. According to our analytical calculations, the increase in 136 m of the reservoir-water level caused a 0.54 MPa pore pressure buildup at the depth of the Magnitude 3.0 earthquake, i.e., 3.88 km, resulting in an increase of 0.82 MPa in the vertical effective stress and a decrease of 0.34 MPa in the horizontal effective stress. These changes resulted in an increase in the deviatoric stress that led to fault destabilization, causing the RTS. The laboratory measurements and analytical calculations corroborate the hypothesis that the initial seismic activity was induced by the undrained subsurface response to the reservoir loading at Irapé.
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CC1: 'Comment on egusphere-2024-166', Giacomo Medici, 14 Mar 2024
General comments
Innovative geophysical research that supports new frontiers in the geo-energy transition. Please, cover my minor technical comments and suggestions to bring the impact out of your manuscript.
Specific comments
Line 12. The concept of hydro-power is unclear in the abstract. Please, revise this part of the manuscript.
Line 57. “Deep faults” unclear. Are you mentioning the concept of earthquakes and brittle/ductile transition which is quite deep? Please, revise the sentence.
Line 95. Clearly state the aim of your research and the 3 to 4 specific objectives of your research by using numbers (e.g., i, ii and iii).
Lines 98-107. Insert more information on the structural geology / tectonics of the area given the nature of the paper.
Lines 162-186. Did you back up the porosity crossing with another method (e.g., NMR)? Is it the measurement reliable?
Lines 162-186. Why so interested in vertical permeability with respect to the bedding planes? What about the horizontal one?
Lines 249-251. “On the other hand...pressurized”. Insert recent papers that discusses induced seismicity by rising pressure in the fracturing network of geothermal reservoirs.
- Gan, Q., Elsworth, D. (2014). Analysis of fluid injection‐induced fault reactivation and seismic slip in geothermal reservoirs. Journal of Geophysical Research: Solid Earth, 119(4), 3340-3353.
- Diehl, T., Kraft, T., Kissling, E., Wiemer, S. (2017). The induced earthquake sequence related to the St. Gallen deep geothermal project (Switzerland): Fault reactivation and fluid interactions imaged by microseismicity. Journal of Geophysical Research: Solid Earth, 122(9), 7272-7290.
- Medici, G., Ling, F., Shang, J. (2023). Review of discrete fracture network characterization for geothermal energy extraction. Frontiers in Earth Science, 11, https://doi.org/10.3389/feart.2023.1328397.
Lines 325-335. The conclusions are too short. Please better highlight the “take home” message and the “novelty” of your research.
Line 358. Please, integrate the relevant and recent literature suggested above.
Figures and tables
Fig. 1. Make the fault trace much more evident. Highlight where the fault is dipping.
Fig. 6. Permeability must be plotted in a log-scale. If you make this change correlation with porosity will be more evident.
Fig. 7. Insert approximate spatial scale.
Citation: https://doi.org/10.5194/egusphere-2024-166-CC1 -
RC1: 'Comment on egusphere-2024-166', Anonymous Referee #1, 03 Apr 2024
1-514: The manuscript discusses the impact of reservoir filling on induced seismicity and concludes, that the undrained response of the subsurface rather than pore pressure diffusion is triggering mechanism. Field, lab and modelling techniques are used to reach this conclusion. Recommendations on how to prevent future induced earthquakes through reservoir impoundment strategies are given.
The scientific significance of the manuscript is high with the topic remaining urgent and unresolved. The presentation quality is superb as the manuscript is very well structured and filled with visually pleasing and comprehensible figures. The use of the English language is impeccable throughout most parts; however, two sections fall below standard and need thorough revision. The list of references also needs revision as consistency is lacking. The scientific quality is high as well. Abundant and relevant references are included, established methods are applied, results are discussed and put into context, and recommendations for reservoir management strategies are given.Please mind these detailed comments for minor revision:
13: At what frequency? It sounds like it is always the case.
18: Great!
21: Delete comma
22: Numbers until twelve in letters?
23: Wording too complicated. Maybe "above the bottom threshold".
29: Traditionally I expect all effective stresses to decrease when pore pressure increases. Please make difference clearer in this sentence.
50: Great introduction
52: I'm confused by the variation in abbreviations: Mw, ~M and M. All the same?
59: Great
65: Thanks for the examples
68: What is the aim of the manuscript? It reads as if it was the forecasting of RTS hazard by interaction and analysis of drained and undrained responses.
77: Great reading flow
85: Great position of this paragraph
93: that = it
92: that = the
96: I really like the traditional structure of the manuscript
106: Language issues? Word order?
104: Reference?
105: ..sedimentation processes of passive margins associated with the deposition.. Language issues? Stands out against all other sentences.
108: Blue colour doesn't match well in image/legend
108: What indicates the line at the top left?
114: Number = word?
124: Maybe word it more carefully? "This leads us to investigate a causative relationship/ hypothesis"
132: Space in reference missing
147: Is this also true for the depth of the event (3.88km)? Maybe add information on faulting regime data source and depth.
155: Why is this differently spelled? km vs. -km. It occurs several times throughout the manuscript.
182: Maybe stay in present tense here, like everywhere else.
188: Delete second "an"
220: ..in these samples. I find this btw already an interesting result!
233: Maybe elaborate a little on the similarity of the rocks to make this argument more convincing for the reader.
276: I don't associate highly metamorphosed rock with good porosity. It reads as if the authors do. Maybe contrast better: "despite high porosity, the rock has low permeability. Therefore, …"
278: I like the idea with the integrated outcrop picture. However, I don't find the figure intuitive to an amateur reader: Is this is a side view or a top view? What does the irregular trapezium indicate? Are the angles of the sides relevant? What do the yellow circles indicate? Where do the arrows point? Where does the crystalline rock start? Why is the figure in this irregular box?
290: What is the problem? Please specify.
289: "Potential reservoir site". Make it more obviously a recommendation and summary.
289 cont.: These are conclusions and recommendations rather than discussion. Move to correct section please.
296: In the Irapé case the dam is already built and poro-perm measurements have been taken. Please make the distinction clearer between the existing project and potential future projects.
299-309: PARAGRAPH IS POORLY WRITTEN, PLEASE REWRITE . Vocabulary is insufficient and words seem to be missing. While the rest of the manuscript is carefully and beautifully composed, this paragraph seems to lack structure, aim and, frankly, language skills.
299: Is being employed or should be employed? Above, conditional tense is used, here not. Please adjust.
302: "effort have begun"? Maybe: Efforts have been made regarding... "infrastructure harm"? Maybe: damages… "loss and damages" of what?
300-302: Please rewrite. TLP does not initiate light and is not an approach or point. Maybe: According to the TLP green light permits operations without restriction, yellow light demands mitigation measures and red light appeals for regulatory intervention.
304: ensure??
305: can be revolved around??
307: promising what?
311: The figure is insufficiently included and introduced in the paragraph.
313-318: The description is great.
335: Manipulation of reservoir loading refers to the impoundment. Mind that the study also suggests mitigation and management strategies for risk of RTS (289-323) which is not mentioned here. Add?
359-513: LIST OF REFERENCES IS INCONSISTENT AND CONTAINS ERRORS, PLEASE REWRITE. - points missing - spaces missing - pages differently abbreviated - DOIs differently inserted - links inconsistently used - some spelling errors
Thank you for your efforts and good luck!
Citation: https://doi.org/10.5194/egusphere-2024-166-RC1 - AC1: 'Reply on RC1', Haris Raza, 12 Jul 2024
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RC2: 'Comment on egusphere-2024-166', Nikita Bondarenko, 24 May 2024
The article presents an analytical assessment of the undrained response impact on the state of stress change during reservoir impoundment and associated reservoir triggered seismicity. Authors present laboratory measured permeability and porosity to support the assumption of undrained response. The assessment is based on assumption of oedometer conditions and using analytical expression based on poroelastic relationships. However, a significant deficiency is that Equation 1 has only relation between horizontal stress and pore pressure. Even if the pore pressure is not changing (drained condition) the horizontal stress would change due to the change of vertical stress. This effect is expected to be the same order of magnitude or stronger than the effect of pore pressure change and therefore cannot be neglected. It is recommended that the calculations have to be updated or it should be explicitly shown that the term can be neglected (more details are available in specific comments in the attached file.
- AC2: 'Reply on RC2', Haris Raza, 12 Jul 2024
Status: closed
-
CC1: 'Comment on egusphere-2024-166', Giacomo Medici, 14 Mar 2024
General comments
Innovative geophysical research that supports new frontiers in the geo-energy transition. Please, cover my minor technical comments and suggestions to bring the impact out of your manuscript.
Specific comments
Line 12. The concept of hydro-power is unclear in the abstract. Please, revise this part of the manuscript.
Line 57. “Deep faults” unclear. Are you mentioning the concept of earthquakes and brittle/ductile transition which is quite deep? Please, revise the sentence.
Line 95. Clearly state the aim of your research and the 3 to 4 specific objectives of your research by using numbers (e.g., i, ii and iii).
Lines 98-107. Insert more information on the structural geology / tectonics of the area given the nature of the paper.
Lines 162-186. Did you back up the porosity crossing with another method (e.g., NMR)? Is it the measurement reliable?
Lines 162-186. Why so interested in vertical permeability with respect to the bedding planes? What about the horizontal one?
Lines 249-251. “On the other hand...pressurized”. Insert recent papers that discusses induced seismicity by rising pressure in the fracturing network of geothermal reservoirs.
- Gan, Q., Elsworth, D. (2014). Analysis of fluid injection‐induced fault reactivation and seismic slip in geothermal reservoirs. Journal of Geophysical Research: Solid Earth, 119(4), 3340-3353.
- Diehl, T., Kraft, T., Kissling, E., Wiemer, S. (2017). The induced earthquake sequence related to the St. Gallen deep geothermal project (Switzerland): Fault reactivation and fluid interactions imaged by microseismicity. Journal of Geophysical Research: Solid Earth, 122(9), 7272-7290.
- Medici, G., Ling, F., Shang, J. (2023). Review of discrete fracture network characterization for geothermal energy extraction. Frontiers in Earth Science, 11, https://doi.org/10.3389/feart.2023.1328397.
Lines 325-335. The conclusions are too short. Please better highlight the “take home” message and the “novelty” of your research.
Line 358. Please, integrate the relevant and recent literature suggested above.
Figures and tables
Fig. 1. Make the fault trace much more evident. Highlight where the fault is dipping.
Fig. 6. Permeability must be plotted in a log-scale. If you make this change correlation with porosity will be more evident.
Fig. 7. Insert approximate spatial scale.
Citation: https://doi.org/10.5194/egusphere-2024-166-CC1 -
RC1: 'Comment on egusphere-2024-166', Anonymous Referee #1, 03 Apr 2024
1-514: The manuscript discusses the impact of reservoir filling on induced seismicity and concludes, that the undrained response of the subsurface rather than pore pressure diffusion is triggering mechanism. Field, lab and modelling techniques are used to reach this conclusion. Recommendations on how to prevent future induced earthquakes through reservoir impoundment strategies are given.
The scientific significance of the manuscript is high with the topic remaining urgent and unresolved. The presentation quality is superb as the manuscript is very well structured and filled with visually pleasing and comprehensible figures. The use of the English language is impeccable throughout most parts; however, two sections fall below standard and need thorough revision. The list of references also needs revision as consistency is lacking. The scientific quality is high as well. Abundant and relevant references are included, established methods are applied, results are discussed and put into context, and recommendations for reservoir management strategies are given.Please mind these detailed comments for minor revision:
13: At what frequency? It sounds like it is always the case.
18: Great!
21: Delete comma
22: Numbers until twelve in letters?
23: Wording too complicated. Maybe "above the bottom threshold".
29: Traditionally I expect all effective stresses to decrease when pore pressure increases. Please make difference clearer in this sentence.
50: Great introduction
52: I'm confused by the variation in abbreviations: Mw, ~M and M. All the same?
59: Great
65: Thanks for the examples
68: What is the aim of the manuscript? It reads as if it was the forecasting of RTS hazard by interaction and analysis of drained and undrained responses.
77: Great reading flow
85: Great position of this paragraph
93: that = it
92: that = the
96: I really like the traditional structure of the manuscript
106: Language issues? Word order?
104: Reference?
105: ..sedimentation processes of passive margins associated with the deposition.. Language issues? Stands out against all other sentences.
108: Blue colour doesn't match well in image/legend
108: What indicates the line at the top left?
114: Number = word?
124: Maybe word it more carefully? "This leads us to investigate a causative relationship/ hypothesis"
132: Space in reference missing
147: Is this also true for the depth of the event (3.88km)? Maybe add information on faulting regime data source and depth.
155: Why is this differently spelled? km vs. -km. It occurs several times throughout the manuscript.
182: Maybe stay in present tense here, like everywhere else.
188: Delete second "an"
220: ..in these samples. I find this btw already an interesting result!
233: Maybe elaborate a little on the similarity of the rocks to make this argument more convincing for the reader.
276: I don't associate highly metamorphosed rock with good porosity. It reads as if the authors do. Maybe contrast better: "despite high porosity, the rock has low permeability. Therefore, …"
278: I like the idea with the integrated outcrop picture. However, I don't find the figure intuitive to an amateur reader: Is this is a side view or a top view? What does the irregular trapezium indicate? Are the angles of the sides relevant? What do the yellow circles indicate? Where do the arrows point? Where does the crystalline rock start? Why is the figure in this irregular box?
290: What is the problem? Please specify.
289: "Potential reservoir site". Make it more obviously a recommendation and summary.
289 cont.: These are conclusions and recommendations rather than discussion. Move to correct section please.
296: In the Irapé case the dam is already built and poro-perm measurements have been taken. Please make the distinction clearer between the existing project and potential future projects.
299-309: PARAGRAPH IS POORLY WRITTEN, PLEASE REWRITE . Vocabulary is insufficient and words seem to be missing. While the rest of the manuscript is carefully and beautifully composed, this paragraph seems to lack structure, aim and, frankly, language skills.
299: Is being employed or should be employed? Above, conditional tense is used, here not. Please adjust.
302: "effort have begun"? Maybe: Efforts have been made regarding... "infrastructure harm"? Maybe: damages… "loss and damages" of what?
300-302: Please rewrite. TLP does not initiate light and is not an approach or point. Maybe: According to the TLP green light permits operations without restriction, yellow light demands mitigation measures and red light appeals for regulatory intervention.
304: ensure??
305: can be revolved around??
307: promising what?
311: The figure is insufficiently included and introduced in the paragraph.
313-318: The description is great.
335: Manipulation of reservoir loading refers to the impoundment. Mind that the study also suggests mitigation and management strategies for risk of RTS (289-323) which is not mentioned here. Add?
359-513: LIST OF REFERENCES IS INCONSISTENT AND CONTAINS ERRORS, PLEASE REWRITE. - points missing - spaces missing - pages differently abbreviated - DOIs differently inserted - links inconsistently used - some spelling errors
Thank you for your efforts and good luck!
Citation: https://doi.org/10.5194/egusphere-2024-166-RC1 - AC1: 'Reply on RC1', Haris Raza, 12 Jul 2024
-
RC2: 'Comment on egusphere-2024-166', Nikita Bondarenko, 24 May 2024
The article presents an analytical assessment of the undrained response impact on the state of stress change during reservoir impoundment and associated reservoir triggered seismicity. Authors present laboratory measured permeability and porosity to support the assumption of undrained response. The assessment is based on assumption of oedometer conditions and using analytical expression based on poroelastic relationships. However, a significant deficiency is that Equation 1 has only relation between horizontal stress and pore pressure. Even if the pore pressure is not changing (drained condition) the horizontal stress would change due to the change of vertical stress. This effect is expected to be the same order of magnitude or stronger than the effect of pore pressure change and therefore cannot be neglected. It is recommended that the calculations have to be updated or it should be explicitly shown that the term can be neglected (more details are available in specific comments in the attached file.
- AC2: 'Reply on RC2', Haris Raza, 12 Jul 2024
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