Risk Assessment Method for Analyzing Borehole Instability Considering Formation Heterogeneity

Round 1

Reviewer 1 Report

The manuscript titled "Risk assessment method of borehole instability considering formation heterogeneity" presents an approach to address the issue of parameter uncertainty in borehole stability analysis. The authors established a wellbore stability model to calculate wellbore stability reliability. The paper's objectives, methodology, and findings are clearly stated, and the results provide valuable insights.

1. As we know, there are so many kinds of strength criteria, why do the authors chose Modified Lade criterion?

2. The abstract could be revised to provide a more concise summary of the objectives, methodology, and key findings.

3. Consistently use either "borehole" or "wellbore" throughout the manuscript to avoid confusion.

4. In some parts of the paper, acronyms are used without prior definition. Please ensure that all acronyms are defined when first introduced.

5. References are appropriately cited throughout the manuscript, but it is recommended to check for consistency in formatting and punctuation to conform to the chosen citation style.

After addressing the above comments, the paper could be considered for publication.

Author Response

1. As we know, there are so many kinds of strength criteria, why the authors identified only Modified Lade criterion?

Response: The modified Lade criterion takes the intermediate principal stress into account, and has a high prediction accuracy for rock strength. It also meets the requirements of smooth and convex, and is convenient for application in numerical calculation.

2. The abstract could be revised to provide a more concise summary of the study's objectives, methodology, and key findings.

Response: The abstract has been revised according to the four-element specification in the manuscript.

3. It is advisable to consistently use either "borehole" or "wellbore" throughout the manuscript to avoid confusion.

Response: The "wellbore" has been revised to "borehole" entirely in the manuscript.

4. In some parts of the paper, acronyms are used without prior definition. Please ensure that all acronyms are defined when first introduced.

Response: All acronyms have been defined when first introduced in the manuscript.

5. References are appropriately cited throughout the manuscript, but it is recommended to check for consistency in formatting and punctuation to conform to the chosen citation style.

Response: References have been revised for consistency in formatting and punctuation to conform to the chosen citation style.

6. Two articles related to wellbore stability are recommended: ①Influence of multi-planes weakness on unstable zones near wellbore wall in a fractured formation. Journal of Natural Gas Science and Engineering, 93(3), 104026. ②Parametric sensitivity study of wellbore stability in transversely isotropic medium based on poly-axial strength criteria. Journal of Petroleum Science and Engineering, 197(3), 108078.

Response: The provided articles has been carefully studied and cited in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Overall Comments:

This paper presents a study on the establishment of a risk assessment model for borehole instability using the Monte Carlo method, analyzing the impact of uncertainty from individual influencing factors on borehole stability, as well as the influence of uncertainty coupling from multiple factors on borehole stability reliability. Overall, the research appears to be comprehensive and well-structured, with potentially significant implications for practical drilling engineering. However, there are some areas where the paper could be improved,

1. While discussing the influence of various factors on borehole stability, the paper identifies rock cohesion as the most sensitive factor for borehole collapse and instability. However, it does not delve into the reasons behind this sensitivity. A more in-depth discussion on this aspect would strengthen the paper's arguments.
2. I would like to suggest to add research findings and novelty to the abstract.
3. Introduction: Authors must include the most recent research works to find the knowledge gaps and to depict the comprehensive importance of the current study.
4. The meaning of Figure 1 should be explained in more detail.
5. The paper mentions that the established risk assessment model can analyze the effects of geo-mechanical parameter uncertainty on borehole stability, yet detailed analyses are not provided. Providing more information on this aspect would strengthen the paper's contributions.
6. The language and structure of the paper are generally clear, and the figures and data effectively support the arguments made. However, some sentences could be rephrased for improved readability. For instance, "The research results showed that, (1)…" could be revised to "Our research yielded the following findings: First,…".

In conclusion, this paper addresses an interesting and significant topic, utilizing the Monte Carlo method to assess risks associated with borehole instability. While there are areas for improvement, as outlined above, the overall research appears to be noteworthy. I recommend that the authors consider the suggested revisions to enhance the paper's clarity and depth.

Minor editing of English language required.

Author Response

1. While discussing the influence of various factors on borehole stability, the paper identifies rock cohesion as the most sensitive factor for borehole collapse and instability. However, it does not delve into the reasons behind this sensitivity. A more in-depth discussion on this aspect would strengthen the paper's arguments.

Response: A more detailed examination of this aspect has been discussed in the manuscript.

2. I would like to suggest to add research findings and novelty to the abstract.

Response: The research findings and novelty have been added in the manuscript.

3. Introduction: Authors must include the most recent research works to find the knowledge gaps and to depict the comprehensive importance of the current study.

Response: The most recent research works have been added and depicted in the manuscript.

4. The meaning of Figure 1 should be explained in more detail.

Response: The Figure 1 has been explained in detail.

5. The paper mentions that the established risk assessment model can analyze the effects of geo-mechanical parameter uncertainty on borehole stability, yet detailed analyses are not provided. Providing more information on this aspect would strengthen the paper's contributions.

Response: Detailed analyses have been provided in the manuscript.

6. The language and structure of the paper are generally clear, and the figures and data effectively support the arguments made. However, some sentences could be rephrased for improved readability. For instance, "The research results showed that, (1)…" could be revised to "Our research yielded the following findings: First,…".

Response: Some sentences have been rephrased to improve readability in the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper established a wellbore stability model based on the reliability theory, which shed light on the influences of the uncertainty of input parameters on the wellbore stability. The idea is novel and important. My detailed comments are as follows:

(1)    Add the newest papers about the topic. Two papers must be added at least.

a)      Optimizing the Wellbore Trajectory of Directional Wells Considering Wellbore Stability Subjected to the Non-Independence and Uncertainty of Geomechanical Parameters

b)     Combined effect of anisotropy and uncertainty on the safe mud pressure window of horizontal wellbore drilled in anisotropic saturated rock

(2)    Technical terms must be unified, such as wellbore/borehole stability, rupture/fracture pressure.

(3)    What’s the difference between your paper and reference ‘Ma, 2021’? Please clarify it.

Your manuscript needs careful editing and particular attention to English grammar, spelling, and sentence structure. You used ‘In order to’ twice in adjacent two sentences.

Author Response

(1) Add the newest papers about the topic. Two papers must be added at least.

Response: The newest papers about the topic have been carefully studied and cited in the manuscript.

(2) Technical terms must be unified, such as wellbore/borehole stability, rupture/fracture pressure.

Response: The technical terms have been unified; the "wellbore" has been revised to "borehole" entirely in the manuscript; and the " rupture" has been revised to "fracture" entirely in the manuscript.

(3) What’s the difference between your paper and reference ‘Ma, 2021’? Please clarify it.

Response: The variation coefficient of the output value of the predicted borehole collapse pressure and fracture pressure is used to evaluate the sensitivity of borehole stability to each influencing factor in our study, which is different with the reference ‘Ma, 2021’.

Author Response File: Author Response.pdf

Reviewer 4 Report

This work is a compelling exploration of parameter uncertainty, carrying significant implications for well design and construction. This reviewer has only a few suggestions to enhance the quality of the manuscript.

1. The first two paragraphs provide a comprehensive overview of the significance of borehole instability. This reviewer reccomends including citations to support some of the statements and for the statistics mentioned in them. 

2. Please revise your figure numbering (there are two Figure 2) and address the issue of inconsistent font sizes. Also, note that 'Wells' should not be capitalized.

3. In the discussion, the authors should thoroughly compare the results within earlier works mentioned in the literature review, stating whether their findings are in agreement.

Author Response

1. The first two paragraphs provide a comprehensive overview of the significance of borehole instability. This reviewer recommends including citations to support some of the statements and for the statistics mentioned in them.

Response: The references supporting some of the statements and for the statistics have been cited in the first two paragraphs.

2. Please revise your figure numbering (there are two Figure 2) and address the issue of inconsistent font sizes. Also, note that 'Wells' should not be capitalized.

Response: The figure numbering, inconsistent font sizes and 'Wells' have been revised in the manuscript.

3. In the discussion, the authors should thoroughly compare the results within earlier works mentioned in the literature review, stating whether their findings are in agreement.

Response: The results within earlier works mentioned in the literature review have been added in the manuscript.

Author Response File: Author Response.pdf

Reviewer 5 Report

The authors in this paper created a wellbore stability model that takes into account the uncertainty of the input parameters. To do this, they used the Monte Carlo method to calculate the reliability of wellbore stability at different drilling mud densities, assessed the sensitivity of wellbore instability to one parameter, and investigated the window of safe drilling mud density at different reliability of wellbore stability under multi-parameter uncertainties. From a practical point of view, the authors obtained the following important results: the uncertainty of rock adhesion has a great influence on the rupture pressure of vertical and horizontal wells. The authors found that under multi-parameter uncertainty, the overall trend of the analysis results is consistent with conventional well stability results, but the safe mud density window is further narrowed, indicating that the calculation of the safe mud density window is consistent with the traditional well stability analysis method. will significantly increase the risk of well instability. Uncertainty assessment determines the uncertainty associated with the minimum required mud pressure to make more reliable decisions during drilling operations. In general, one can positively evaluate the work for publication in the journal. Authors need to take into account some recommendations:

1) In the conclusion and abstract, the authors need to indicate ways for further development and application of approaches.

2) English language needs improvement in some places.

3) A number of new articles can be added to the reference list, for example

Galkin, V.I., Martyushev, D.A., Ponomareva, I.N., Chernykh, I.A. Developing features of the near-bottomhole zones in productive formations at fields with high gas saturation of formation oil. Journal of Mining Institute. 2021. V.249. pp. 386-392. https://doi.org/10.31897/PMI.2021.3.7

Popov, S.N., Chernyshov, S.E., Krivoshchekov, S.N. Comparative analysis of the analytical and numerical methods for calculating the stress-strain state of the near-wellbore zone based on the elastic model taking into account the main structural elements of the well. Bulletin of the Tomsk Polytechnic University, Geo Assets Engineering, 2023, 334(5), pp. 94–102. https://doi.org/10.18799/24131830/2023/5/3961

English language needs improvement in some places.

Author Response

1) In the conclusion and abstract, the authors need to indicate ways for further development and application of approaches.

Response: Further development and application of the approaches has been added in the conclusion and abstract.

2) English language needs improvement in some places.

Response: The language problems of the manuscript have been checked and modified, which makes sure that the manuscript is free of grammatical, spelling and other common errors.

3) A number of new articles can be added to the reference list.

Response: The provided articles has been carefully studied and cited in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The paper has been revised well.