Cement-Formation Debonding Due to Temperature Variation in Geothermal Wells: An Intensive Numerical Simulation Assessment^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors present a comprehensive analysis of the failure criteria of casing and cement systems in geothermal wells, highlighting the unique challenges they face compared to conventional oil and gas wells. The use of finite element methodologies and cohesive zone models to simulate the cooling and heating processes of the wellbore is a valuable approach to understanding the integrity issues of geothermal wells. The results of the study on the different failure modes during the cooling and heating phases, as well as the effect of interfacial shear strength (IBSS) values ​​on cement failure are particularly insightful. I would also like to note that the authors critically evaluate the results obtained. The final part of the study concludes that modifying the operation and construction of geothermal wells to maintain temperature differentials below critical levels is critical to preventing cement failure, a practical recommendation for industry professionals.

 

Critical comments.

1. The authors' article is very interesting, however, I have a fundamental question. The authors demonstrated the results of this study in their paper https://onepetro.org/ARMAUSRMS/proceedings-abstract/ARMA23/All-ARMA23/ARMA-2023-0863/532143 Please clarify whether this publication is a copy of previously published materials.

2. It is necessary to supplement the text with the following explanation. It is necessary to specify the object of the study. The fact is that the extraction of mineral water from high-temperature springs has similar studies. However, you do not consider them in your work. Why? And what exactly do you extract? For example, for high-thermal mineral springs (drinking), tubing with insulating material is used. And for them, casing columns are not of fundamental importance. Thus, the statement of the problem is slightly confusing. For this reason, the introduction must be redone.

 

Comments.

 

1. Page 3. Text "the IBTS and IBSS of the cement sheath, which can lead to the creation of micro annuli, using a finite element analysis approach." it is necessary to add "Within the framework of this task, it is planned to solve the following tasks ………1, 2, 3 …"

2. Page 3 and further. "." is used as a divider instead of "," (o 2.000 mm)

3. Figures 8, 9, 16 the text in the figures is difficult to read.

 

4. Commas are missing in the text.

 

5. the References section must include the work doi.org/10.1109/SCM50615.2020.9198816

6. The design of the References section does not correspond to the format of the journal.

 

Conclusion the work is interesting and can be accepted for publication after the indicated deficiencies are corrected.

Author Response

Reviewer 1

Critical comments.

1. The authors' article is very interesting, however, I have a fundamental question. The authors demonstrated the results of this study in their paper https://onepetro.org/ARMAUSRMS/proceedings-abstract/ARMA23/All-ARMA23/ARMA-2023-0863/532143 Please clarify whether this publication is a copy of previously published materials.

Thank you for the comment

This is the extension of the previous work. In the ARMA paper we showed the effect of pressure on casing cement deboning. The finite element model shown in that paper is also not the same as the one used for this paper. This paper deals with the temperature effect on casing-cement debonding, not the pressure.

2. It is necessary to supplement the text with the following explanation. It is necessary to specify the object of the study. The fact is that the extraction of mineral water from high-temperature springs has similar studies. However, you do not consider them in your work. Why? And what exactly do you extract? For example, for high-thermal mineral springs (drinking), tubing with insulating material is used. And for them, casing columns are not of fundamental importance. Thus, the statement of the problem is slightly confusing. For this reason, the introduction must be redone.

Thank you for the comment

Our  paper focuses on the casing-cement debonding in geothermal wells. Geothermal wells consider tubingless completion as being the best solution to obtain high flow rates, hence an insulated tubing is not used. As we have shown in our introductory part, many geothermal wells falls under this category.

Comments.

1. Page 3. Text "the IBTS and IBSS of the cement sheath, which can lead to the creation of micro annuli, using a finite element analysis approach." it is necessary to add "Within the framework of this task, it is planned to solve the following tasks ………1, 2, 3 …"

Thank you for the comment

The correction has been made accordingly, and a framework has been added in text

2. Page 3 and further. "." is used as a divider instead of "," (o 2.000 mm)

Thank you for the comment

Figures 2 and 3 have been fixed.

We follow the English system and comma “,” is used for divider, whereas point “.” Is used ss decimal. Thank you for spotting this in Figures 2 and 3. We have fixed that.

 

3. Figures 8, 9, 16 the text in the figures is difficult to read.

Thank you for the comment.

The correction has been made accordingly.

 

4. Commas are missing in the text.

 Thank you for the comment.

The manuscript has been revised

5. the References section must include the work doi.org/10.1109/SCM50615.2020.9198816

Thank you for the comment.

We have carefully revised your recommended paper, and unfortunately, that paper has nothing to do with our work. It will be unethical to include references that do not relate to our study.

6. The design of the References section does not correspond to the format of the journal.

Thank you for the comment

The reference will be designed according to the journal outline after the acceptance of the paper

 

Reviewer 2 Report

Comments and Suggestions for Authors

(1) The abstract mentions that "Type I debonding occurs first during cooling," but it does not specify the temperature threshold at which this occurs. Please provide explicit temperature values in the abstract for clarity.

(2) On page 2, the study employs "an intensive finite element methodology," yet the selection criteria for the 36 models are not detailed. Please justify the choice of these models and explain how they represent a comprehensive assessment of the problem.

(3) The material properties for cement and steel are listed in Table 2, but there is no discussion on how these values were derived or if they are representative of real-world applications. Please provide a reference to the source of these values or explain the rationale behind their selection.

(4) Figures such as Figure 7 show the "Impact of temperature variation on the magnitude of gap size" without any statistical analysis. Please include error analysis or confidence intervals to ensure the reproducibility of the results. Figure 8  and Figure 9 lack the legends of colorbars and the labels are not clear.

 (5) The study simulates cooling and heating processes with a ΔT of 300°C. It should be clarified whether this ΔT is based on observed geothermal well data or is a theoretical extreme. If the latter, please discuss the relevance of these simulations to real-world scenarios.

 (6)The paper states that "Type I debonding occurs first during cooling," but the depth of analysis into why this occurs before Type II debonding is not sufficiently explored. A more detailed explanation of the mechanics behind this phenomenon would be beneficial.

(7) The conclusion mentions the need for "alternative well operation strategies," but it does not offer specific strategies or a discussion on how these might be implemented. Please provide actionable recommendations based on your findings.

 (8) While the Cohesive Zone Model (CZM) is employed, the paper does not discuss its limitations or assumptions. A subsection addressing the limitations of the CZM and how they might affect the study's outcomes would be appropriate.

 (9) The paper evaluates IBSS values at differential temperatures but does not elaborate on how these temperatures affect the bonding mechanism at a material level. Please provide a more detailed chemical or physical explanation.

(10) The data presentation in tables such as Table 4 could be improved with the inclusion of standard deviations or other measures of variability, especially given the significant implications of the ΔT values reported.

(11) The term "debonding" is used throughout the paper, but it is not defined until later sections. For clarity, especially for readers unfamiliar with the term, please define key terms such as "debonding" and "micro-annuli" in the introduction.

(11) The references cited are crucial for grounding the study's findings. Please ensure that the most current and relevant literature is included, and consider updating references that may be outdated.

Comments on the Quality of English Language

Technical Terminology:

The manuscript utilizes specialized technical terms appropriately, indicating a strong command of the subject matter. However, some acronyms are introduced without prior definition (e.g., CZM, IBSS, IBTS), which may require clarification for readers outside the immediate field.

 

Consistency in Usage:

There is a need for consistency in the usage of terms. For example, the term "debonding" is used frequently but lacks an initial definition, which could confuse readers not familiar with the term.

 

Sentence Structure:

The manuscript exhibits a mix of complex and simple sentence structures, which is generally effective. However, there are instances of overly long sentences that could be split for improved readability.

 

Grammar and Punctuation:

The grammar is mostly correct, but there are occasional errors, particularly with subject-verb agreement and the use of articles. Punctuation, especially with lists and parenthetical statements, should be reviewed for correctness.

 

Active vs. Passive Voice:

The passive voice is used extensively throughout the manuscript. While appropriate for some sections, the use of active voice could enhance the clarity and engagement of the writing in others.

Author Response

Reviewer 2

1. the credibility of the simulation results can be enhanced by adding experimental data.

Thank you for the comment

The focus of the paper was not on the validation of any experiment with the simulation. Instead, it is focused on examining how differential temperature affects various types of debonding by deploying the finite element analysis approach. Finite Element method and Ansys as simulator are well known numerical simulation tools and do not require experimental validation every time. However, as result of this paper we are working on a possible experimental setup.

2. The research under different stratigraphic properties and pressure conditions can be further expanded to improve the applicability of the model.

Thank you for the comment

The paper's focus was not on using different lithological properties and assessing their impact on the debonding but was on the differential temperature. However, future studies will analyze the impact of the formation properties on the debonding. Please note that we demonstrated that a 2 m section can be used to model the casing-cement-rock interaction, and thus our approach is looking at that particular section, by neglecting the formation properties and in situ stresses, which we found to have less impact to our results. However, these conditions could be used for a different paper given the size and amount of the results.

3. Errors in figures: There is no Figure 2 in the text, and Figure 17 lacks the title of the figure.

Thank you for the comment

The correction has been made accordingly.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

The research work in this paper is instructive, but there are still the following points that can be further discussed.
1. the credibility of the simulation results can be enhanced by adding experimental data.
2. The research under different stratigraphic properties and pressure conditions can be further expanded to improve the applicability of the model.
3. Errors in figures:There is no Figure 2 in the text, and Figure 17 lacks the title of the figure.

Author Response

Reviewer 3

(1) The abstract mentions that "Type I debonding occurs first during cooling," but it does not specify the temperature threshold at which this occurs. Please provide explicit temperature values in the abstract for clarity.

Thank you for the comment

The correction has been made accordingly.

(2) On page 2, the study employs "an intensive finite element methodology," yet the selection criteria for the 36 models are not detailed. Please justify the choice of these models and explain how they represent a comprehensive assessment of the problem.

Thank you for the comment.

The paper already presents that 18 runs were conducted for temperature drops of about 100, 200, and 300°C, with the same procedure applied for the heating situation. Therefore, the total number of simulation runs is 36, as mentioned in the abstract. The reason for using such models is already present: “These temperature variations were chosen because the simulations involving 100 and 200°C temperature differential have led to the conclusion that differential temperature of 300°C will also cover the other two cases since the output parameters like gap, strain, or stress are linearly proportional with the temperature difference. This will be shown later.  While specific geothermal wells may have different conditions, this choice covers a wide range of them”

(3) The material properties for cement and steel are listed in Table 2, but there is no discussion on how these values were derived or if they are representative of real-world applications. Please provide a reference to the source of these values or explain the rationale behind their selection.

Thank you for the comment.

The values used in Table 2 are based on the extensive database that I am the curator at the university of Oklahoma we used median values as in a previous paper we have shown that these value work best to simulat cement.. We have included 2 references as per your recommendation.

(4) Figures such as Figure 7 show the "Impact of temperature variation on the magnitude of gap size" without any statistical analysis. Please include error analysis or confidence intervals to ensure the reproducibility of the results. Figure 8  and Figure 9 lack the legends of colorbars and the labels are not clear.

Thank you for the comment

As this is a simulation study and not an experimental one, putting an error bar with any statistical analysis is not possible. For the reproducibility of the result, if the same parameter is used in the CZM, then the results will be the same. Meanwhile, the legends of Figures 7 and 8 have been improved.

 (5) The study simulates cooling and heating processes with a ΔT of 300°C. It should be clarified whether this ΔT is based on observed geothermal well data or is a theoretical extreme. If the latter, please discuss the relevance of these simulations to real-world scenarios.

Thank you for the comment

The reason for having ΔT of 300°C has been added in the manuscript along with the relevant references.

(6) The paper states that "Type I debonding occurs first during cooling," but the depth of analysis into why this occurs before Type II debonding is not sufficiently explored. A more detailed explanation of the mechanics behind this phenomenon would be beneficial.

Thank you for the comment

Thank you for your comment. We already have stated that the tensile debonding will take place earlier particularly due to low IBTS values. This was also shown by Wise wt al, 2023, and other authors. The tensile debonding is very little investigated and as a result of this paper we are planning to dive deeper in the intimate phenomenon using laboratory experiments.

 

 (8) While the Cohesive Zone Model (CZM) is employed, the paper does not discuss its limitations or assumptions. A subsection addressing the limitations of the CZM and how they might affect the study's outcomes would be appropriate.

Thank you for the comment

The assumptions and limitations, along with the detailed discussion on these aspects, have already been presented in our previous studies, which are cited in this paper. Therefore, they are not repeated here in order to save space.

(9) The paper evaluates IBSS values at differential temperatures but does not elaborate on how these temperatures affect the bonding mechanism at a material level. Please provide a more detailed chemical or physical explanation.

Thank you for the comment

The focus of this paper was not on the effect of material on the bonding mechanism or assessing its chemical and physical alterations. However, this is a good suggestion, and in our upcoming paper, this analysis will be conducted.

(10) The data presentation in tables such as Table 4 could be improved with the inclusion of standard deviations or other measures of variability, especially given the significant implications of the ΔT values reported.

Thank you for the comment

As this is a simulation study and not an experimental one, therefore, putting a statistical analysis like standard deviation is not possible.

(11) The term "debonding" is used throughout the paper, but it is not defined until later sections. For clarity, especially for readers unfamiliar with the term, please define key terms such as "debonding" and "micro-annuli" in the introduction.

Thank you for the comment

The addition has been made accordingly.

(12) The references cited are crucial for grounding the study's findings. Please ensure that the most current and relevant literature is included, and consider updating references that may be outdated

Thank you for the comment

About 68% of the papers cited in the study are from 2019-2024, while only 32% were from before 2019.

Technical Terminology:

The manuscript utilizes specialized technical terms appropriately, indicating a strong command of the subject matter. However, some acronyms are introduced without prior definitions (e.g., CZM, IBSS, IBTS), which may require clarification for readers outside the immediate field.

Thank you for the comment

All acronyms were fully spelled out in the abstract, while their respective definitions were provided in the appropriate sections of the paper where further explanation was required.

Consistency in Usage:

There is a need for consistency in the usage of terms. For example, the term "debonding" is used frequently but lacks an initial definition, which could confuse readers not familiar with the term.

Thank you for the comment

The definition of debonding is placed in the early part of the introduction section

Sentence Structure:

The manuscript exhibits a mix of complex and simple sentence structures, which is generally effective. However, there are instances of overly long sentences that could be split for improved readability.

Thank you for the comment

The manuscript has been revised

Grammar and Punctuation:

The grammar is mostly correct, but there are occasional errors, particularly with subject-verb agreement and the use of articles. Punctuation, especially with lists and parenthetical statements, should be reviewed for correctness.

Thank you for the comment

The manuscript has been revised

Active vs. Passive Voice:

The passive voice is used extensively throughout the manuscript. While appropriate for some sections, the use of active voice could enhance the clarity and engagement of the writing in others.

Thank you for the comment

The manuscript has been revised

 

 

Reviewer 4 Report

Comments and Suggestions for Authors

The authors employed an intensive finite element methodology to analyze the debonding criteria of casing-cement systems in geothermal wells by examining over 36 independent models. The analysis revealed that Type I debonding occurs first during cooling, while Type II is the primary failure mode during heating. In general, the paper is innovative to a certain extent, but the novelty of the research expressed in writing is not obvious, and there are some shortcomings. Therefore, I suggest that the publication of the paper be reconsidered after major revision.

 

Specific review comments are as follows:

 

1 Keywords section: It is suggested to add the keyword 'numerical imulation', which is closely related to the paper.

2 The abstract part does not show the novelty of the paper, please add.

3 Introduction section: the third line of paragraph 3，“First is that in the geothermal well...... ” —It is suggested to provide relevant references.

4 Introduction section: the last paragraph，“Therefore, this study focuses on the effect of thermal variation on the IBTS and IBSS of the cement sheath, which can lead to the creation of micro annuli, using a finite element analysis approach....... ” —it is necessary to highlight this part of the content and elaborate on their strengths and weaknesses and innovation.

5 The introduction section is too long and it is recommended to streamline it a bit more.

6 Please redraw the part of figures and tables in the paper. The resolution of some figures is not up to the requirements, such as Figure 8 and Figure 9.

7 Please redraw the table in the text. It is suggested to have certain requirements on the format, such as a three-line table.

8 Chaper2.3 , “hence, an unconventional failure mode was utilized in this paper” —Please elaborate on what the unconventional failure mode is.

9 The first line of Table 1, Adjusted Values, needs to add units [mm], and check whether there are similar omissions in the whole paper.

10 Chaper2, “The above table and graphs show that the 2m casing/cement length can also represent a longer section of casing/cement”—Is there any theoretical basis for this view?Or can you provide relevant references?

11    Has the numerical simulation model established in the paper been verified?

12    The first paragraph of discussion, " To date, no detailed study has explored the CZM model for casing-cement and cement-formation contact in such depth."—It is suggested to provide relevant references.

13    The conclusions can be supplemented with some limitations and uncertainties in the study to provide comparisons.

14    What are future research plans based on this study?

Comments on the Quality of English Language

The writing level of the paper basically meets the requirements of journal publication！

Author Response

Reviewer 4

1. Keywords section: It is suggested to add the keyword 'numerical simulation’, which is closely related to the paper.

Thank you for the comment

The keyword 'numerical simulation is added

2. The abstract part does not show the novelty of the paper, please add.

Thank you for the comment. The novelty of the study has been added in the abstract

3 Introduction section: the third line of paragraph 3，“First is that in the geothermal well...... ” —It is suggested to provide relevant references.

Thank you for the comment

The reference has been added

4 Introduction section: the last paragraph，“Therefore, this study focuses on the effect of thermal variation on the IBTS and IBSS of the cement sheath, which can lead to the creation of micro annuli, using a finite element analysis approach....... ” —it is necessary to highlight this part of the content and elaborate on their strengths and weaknesses and innovation.

Thank you for the comment

We are not sure we have understood your comment. We have discuss about this in the discussions part.

5 The introduction section is too long and it is recommended to streamline it a bit more.

Thank you for the comment.

We tried to keep the introduction as short as possible. Still, as the reviewers already commented on the need for additional references for the paper, it is difficult to streamline it further. If we reduce the introduction, the reference count will decrease.

6 Please redraw the part of figures and tables in the paper. The resolution of some figures is not up to the requirements, such as Figure 7 and Figure 8.

Thank you for the comment

The correction has been made accordingly

7 Please redraw the table in the text. It is suggested to have certain requirements on the format, such as a three-line table.

Thank you for the comment

The correction has been made accordingly

8 Chaper2.3 , “hence, an unconventional failure mode was utilized in this paper” —Please elaborate on what the unconventional failure mode is.

Thank you for the comment

The unconventional approach was the use of selected nodes on casing-cement border and cement-rock interface.

The text has been added.

9 The first line of Table 1, Adjusted Values, needs to add units [mm], and check whether there are similar omissions in the whole paper.

Thank you for the comment

The correction has been made accordingly

10 Chaper2, “The above table and graphs show that the 2m casing/cement length can also represent a longer section of casing/cement”—Is there any theoretical basis for this view? Or can you provide relevant references?

Thank you for the comment

Simulations have shown that the gap remains nearly identical across all three cases (2, 10, and 100 m). Therefore, using a 2 m long casing instead of longer sections will reduce computational time while still accurately representing the behavior of longer casings. The proof of 2m being representative of other lengths was given through the simulation process, and hence, no reference is required.

11    Has the numerical simulation model established in the paper been verified?

Thank you for the comment

On the simulation side, the ANSYS simulation has verified that 2 m is representative of the other lengths. However, no experimental setup has been developed for the experimentation side to test this scenario.

12    The first paragraph of discussion, " To date, no detailed study has explored the CZM model for casing-cement and cement-formation contact in such depth."—It is suggested to provide relevant references.

Thank you for the comment

This sentence was written because no prior studies have explored the CZM model for casing-cement and cement-formation contact in such depth. This is also a key novelty of the paper, and therefore no reference is needed.

13    The conclusions can be supplemented with some limitations and uncertainties in the study to provide comparisons.

Thank you for the comment

Like any FEM study, there are limitations, but the main limitation of this study was neglecting the in situ stresses acting around the wellbore, which may impact the results positively.

14    What are future research plans based on this study?

Thank you for the comment

The future plan for this research is to have experimental validation with a setup that can endure the harsh conditions presented in this paper.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have corrected all the comments