Numerical Modeling and Simulation of Thermal Effect-Driven Bottom Hole Pressure Variation and Control Technology During Tripping-Out in HTHP Ultra-Deep Wells

Comments 1: The literature review is comprehensive, but readability could be improved. Rather than listing prior work, the section should be reorganized to evaluate and summarize previous studies, highlight their contributions, and clearly identify knowledge gaps.

Response 1: Thank you for the valuable suggestions on the literature review! We have restructured this section to move beyond mere enumeration of previous studies. We now classify and evaluate existing research, summarize the core contributions of each literature, and clearly identify the current research gap—i.e., the lack of quantitative analysis on the coupling mechanism between thermal effects and BHP during ultra-deep well tripping out, as well as pressure control methods adapted to narrow safe density windows. This revision enhances the readability and logical coherence of the review.

Comments 2: The core temperature model (Eqs. 1–4) is adapted from literature without derivation. While citing Mao et al. is appropriate, a brief physical interpretation of each term should be provided. In addition, definitions for all symbols should be included immediately after each equation, not only in the Abbreviations table.

Response 2: Thank you for your attention to model derivation and terminology explanation! We have supplemented brief physical interpretations for the core temperature model (Equations 1-4), clarifying the physical significance of each equation. Additionally, we have provided definitions of all symbols immediately following each equation, rather than solely listing them in the abbreviation table, ensuring readers can intuitively understand the meaning of terms while maintaining academic rigor.

Comments 3: The SOP solution scheme is introduced, but no grid-independence or time-stepping sensitivity analysis is presented. Such studies are recommended, or at least a discussion of numerical stability and accuracy should be added.

Response 3: Thank you for reminding us of numerical stability and accuracy issues! We have supplemented grid independence analysis (axial grid step sizes: 10m, 5m, 1m) and time step sensitivity analysis (10s, 5s, 1s). The results show that the calculation deviations of bottom hole temperature (BHT) at 2910m and 9026m are both ≤0.17%, proving that grid and time step have no significant impact on the results. We have also added discussions on numerical stability and accuracy in the manuscript to ensure the reliability of model calculations.

Comments 4: The model is not validated against physical measurements. Although pressure and temperature data are unavailable during tripping-out, validation against measured values at the end of drilling (the start of tripping) would strengthen confidence in the modelling. If LWD data are available, such validation is strongly recommended.

Response 4: Thank you for emphasizing the importance of model validation! Due to the difficulty in obtaining measured data during tripping out, we have validated the model using temperature data at the end of drilling (before tripping out) combined with the industry-recognized Drillbench software. The deviation of the initial temperature field is less than 3℃, which enhances the model's credibility. Currently, there is no logging while drilling (LWD) data for this well; if relevant measured data can be obtained in the future, we will further supplement the validation to improve the model's persuasiveness.

Comments 5: The distinction between the proposed technology and the existing “weighted mud cap method” (lines 323–332) is unclear. The authors should explicitly explain how their approach differs and what advantages it offers Specific comments

Response 5: Thank you for pointing out the need to clarify the differences and advantages of the proposed method! We have clearly defined the core differences between our method and the traditional "heavy slug method": ① Different design objectives: The traditional method only compensates for swabbing pressure and does not consider the dynamic BHP changes caused by thermal effects; our method focuses on the synergistic effect of thermal effects and swabbing pressure to achieve precise BHP regulation. ② Different implementation methods: The traditional method involves one-time injection of heavy slug before tripping out, while our method dynamically and alternately supplements two types of drilling fluid during tripping out. ③ Core advantages: Our method can control BHP fluctuation within 0.339MPa, avoiding pressure surges caused by one-time injection, which is more suitable for the narrow safe density window of ultra-deep wells and effectively reduces the dual risks of lost circulation and kick. Relevant comparative analysis has been added to the manuscript.

Comments 6: Table 2. Move Conductor Casing up to before Surface Casing.

Response 6: Thank you for the suggestion! In accordance with the design logic of wellbore structure, we have moved "Conductor Casing" before "Surface Casing" in Table 2, standardizing the order of wellbore structure to facilitate readers' understanding.

Comments 7: Table 3. Please provide references for the data origin.

Response 7: Thank you for the rigorous requirement! The thermal physical parameters of materials such as drilling fluid and casing in Table 3 are derived from the field design plans provided by Southwest Oil & Gas Field, which are actual engineering data (not publicly available yet). We have supplemented the data source description in the manuscript to ensure its credibility.

Comments 8: Figure 6. How the grid size and time step were determined?

Response 8: Thank you for the inquiry! The grid size and time step in Figure 6 are determined through sensitivity analysis: the axial grid step size is set to 5m, the formation radial direction extends to the disturbance boundary (10m) at equal intervals of 0.5m, and the time step is set to 10s. This parameter combination ensures both calculation accuracy (deviation ≤0.17%) and computational efficiency. The detailed basis for this determination has been supplemented in the manuscript.

Comments 9: Tables 6 and 7. Review and correct errors; some of the values appear inconsistent.

Response 9: Thank you for pointing out the numerical inconsistency! We have carefully reviewed Tables 6 and 7, corrected the inconsistent numerical values, and ensured data accuracy to avoid misleading readers.

Comments 10: Figure 8 and other multiple-plot figures. Label each subplot clearly (e.g. Figure 8a, 8b, etc)

Response 10: Thank you for the suggestion! We have added clear labels (e.g., Figure 8a, Figure 8b) to Figure 8 and all other multi-subfigure diagrams.

Comments 11: Figures 8-10. Specify the tripping rate used (e.g. 400m/h)?

Response 11: Thank you for the reminder! We have clearly annotated the adopted tripping speed (400m/h) in Figures 8-10.

Comments 12: Conclusions section. Rewrite to emphasize the key findings and new insights from the modelling work. The proposed weighted drilling fluid supplementation method has not yet been field-tested or validated, so it should not be presented as a definitive finding. Instead, it should be framed as a promising concept requiring further investigation.

Response 12: Thank you for the optimization suggestions on the conclusion! We have rewritten the conclusion to highlight core findings and new insights: ① Quantified the impact of thermal effects on BHP during tripping out of HTHP ultra-deep wells (BHT increased by 72.6℃ and BHP decreased by 2.410MPa at 9026m); ② Reveaed the differences in temperature-pressure coupling mechanisms between shallow wells and ultra-deep wells; ③ Clarified that the proposed weighted drilling fluid supplementation method is a promising technical idea that has not yet undergone field testing. Future research should further verify and optimize it through field experiments, avoiding definitive statements to maintain academic rigor.

Comments 1: The abstract is difficult to follow and lacks a standard structure. Please rewrite it into three clear paragraphs:

(1) A short introduction to the problem,

(2) A brief description of the approach or methodology, and

(3) A concise summary highlighting the novelty and key findings.

Response 1: Thank you for the valuable comments from the reviewers! In response to your requirements, we have rewritten the abstract into a three-paragraph structure:The first paragraph clarifies the core challenges of BHP control during tripping out of hole in HTHP ultra-deep wells;The second paragraph summarizes the research route of "modeling + case calculation + technology proposal";The third paragraph condenses the innovations of the weighted drilling fluid supplement method and the core result that BHP fluctuation is ≤ 0.339 MPa, resulting in a clearer logic.

Comments 2: The first paragraph in the introduction part is not clear; what message you want to deliver with it, please restructure

Response 2: Thank you for the reviewers' valuable comments on the identified issues! We have reorganized the first paragraph of the introduction, clearly conveying the logical chain of "the strategic importance of deep and ultra-deep well resources → the challenges of BHP control during tripping out of hole in ultra-deep wells → the risks induced by thermal effects", making the core information more straightforward and comprehensible.

Comments 3: Is it necessary to have Fig.1 1? I do not see the point behind it

Response 3: Thank you for the reviewers' attention! Considering that readers without field experience may confuse the "drilling operation" and "tripping out of hole" conditions, Figure 1 intuitively presents the core differences between the two to facilitate quick understanding of the research scenario. Therefore, we retain Figure 1 and supplement the figure caption to clearly illustrate its purpose.

Comments 4: As far as I understood from your claim part (Last paragraph in the introduction), that you try to numerically evaluate the impact of the bottom hole temperature in the bottom hole pressure while tripping out to reduce the risk of influx, however, in the real world, usually we pump high-density mud pill prior to tripping out to compensate for any reduction in BHP while tripping. Your work is mainly for understanding the impact, not to propose a solution, so I would recommend that you to specify the problem you try to solve in a better way

Response 4: Thank you for the reviewers' in-depth inquiry! The core of this study is to address the limitations of the traditional "heavy slug" technology: this technology only compensates for swabbing pressure but fails to consider the thermal effect-induced bottom hole pressure (BHP) loss caused by the long tripping-out cycle and large temperature difference in ultra-deep wells. Direct application of this traditional technology is prone to exceeding the formation fracture pressure. Therefore, we quantified the impact of thermal effects on BHP through modeling and proposed a weighted drilling fluid supplement method, which caters to the operational requirements of narrow safe density windows.

Comments 5: I would recommend you add 2 sections after the introduction: first, call it Study objective, under this title, list the main objective of the study; second, Methodology, under this title, give a brief overview of the methods and processes used.

Response 5: Thank you for the reviewers' constructive suggestions! In accordance with your requirements, we have added two new chapters: the "Research Objectives" chapter clarifies three core purposes, and the "Research Methodology" chapter outlines the complete process including data collection, model development, numerical computation, and technical validation, making the research framework more explicit.

Comments 6: The date presented in Table 2, can be integrated into fig 2

Response 6: Thank you for the reviewers' optimization suggestions! We have integrated the thermal physical properties of materials in Table 2 into Figure 2 (Wellbore Structure Schematic Diagram), presenting them in a correlative manner of "structure + parameters". This avoids the redundancy of a separate table and makes the information more intuitive and comprehensible.

Comments 7: The Specific heat capacity and Thermal conductivity of the drilling fluids, cement, casing, etc, which are shown in Table 3, from where did you get them?

Response 7: Thank you for the reviewers' rigorous requirements! The thermal physical property parameters of materials such as drilling fluid and casing in Table 3 are derived from the field design plans provided by Southwest Oil & Gas Field, which are actual engineering data (not publicly available yet). We have supplemented the data source description in the manuscript to ensure its credibility.

Comments 8: Since you consider the tripping out operation, why do you present the drilling parameters (the ones in Table 4)

Response 8: Thank you for the reviewers' inquiry! This study requires the "temperature field at the end of drilling operation" as the initial condition for tripping out of hole. The drilling parameters in Table 4 are specifically used to compute this initial temperature field, serving as the foundation for subsequent thermal effect analysis. Thus, the table is retained.

Comments 9: Did you conduct sensitivity analysis for the mesh? You have to do it , to see the impact.

Response 9: Thank you for the reviewers' reminder! We have supplemented the grid sensitivity analysis: by batch-adjusting the axial grid step sizes (10m, 5m, 1m), the calculation deviations of BHT at 2910m and 9026m are ≤0.13% and ≤0.07% respectively; combined with the time step analysis (10s, 5s, 1s), the BHT deviation is ≤0.17%. These results indicate that the grid and time step have no significant impact on the outcomes. The finally determined parameters ensure computational reliability, and the relevant content has been added to the manuscript.

Comments 10: You need to conduct a sensitivity analysis for the other input as well. because you did not consider the uncertainty for the input data

Response 10: Thank you for the reviewers' suggestion! During the tripping out of hole condition, the drilling fluid circulation ceases. We have conducted a sensitivity analysis on the core influencing factor "tripping speed" (results presented); the remaining parameters are all actual case parameters of Well PS6. After verification, these parameters fall within the engineering reasonable range and have no significant interference with the core laws, thus no additional elaboration is provided.

Comments 11: Table 6, (Efficiency () , is it tripping speed ? please use tripping speed

Response 11: Thank you for the reviewers' pointing out the typo! We have uniformly corrected the "Efficiency ()" in Table 6 to "tripping speed", ensuring consistent expression throughout the manuscript and eliminating ambiguity.

Comments 12: You should clearly present the initial boundaries of the model

Response 12: Thank you for the reviewers' reminder! We have clearly supplemented the initial and boundary conditions of the model in the manuscript, including the initial temperature following the geothermal gradient, temperature continuity at the drill bit, and constant temperature of drilling fluid supplementation at the wellhead. These supplements ensure the model's integrity, and the relevant content has been updated.

Comments 13: You need to do additional simulations to come up with a good conclusion.

Response 13: We appreciate the valuable suggestions from the reviewers! By comparing the temperature field and bottom-hole pressure (BHP) variations during tripping-out at 2910m and 9026m in Well PS6, we have confirmed the core conclusion that thermal effects exert a more significant impact on BHP during tripping-out in ultra-deep wells, and the existing simulations are sufficient to support the research arguments.

Currently, we have not identified additional simulation directions more relevant to the theme of this study. If the reviewers consider that specific scenarios (such as different working conditions and parameter combinations) need to be supplemented, we are more than willing to make improvements in accordance with your guidance to further enhance the reliability of the conclusions.

Comments 14: The other important point is the validation of your model. I do not see it anywhere. You have to validate it

Response 14: Thank you for the reviewers' emphasizing the importance of validation! Due to the difficulty in obtaining measured data for the tripping out of hole condition in ultra-deep wells, we adopted the industry-recognized Drillbench software for indirect validation: by comparing the circulating temperature field at the initial moment of tripping out of hole, the deviation is less than 3℃, which verifies the computational accuracy of the model. This validation process has been added to the manuscript.

Comments 15: Why you considered 10hr as mix time?

Response 15: Thank you for the reviewers' inquiry! The 10 hours refers to the total tripping out operation time at 2910m depth, which is calculated as the sum of the net tripping time (based on a tripping speed of 400m/h) and the auxiliary operation time (such as drill string disconnection and drilling fluid supplementation). Since this study focuses on the impact of thermal effects throughout the entire tripping out process, the calculation time is set to 10 hours, which is consistent with the actual engineering scenario.

Comments 16: Try to find a better way to present your results, for example, the one shown in Figure 8 , it is not easy to get any conclusion out of them. For example, you can present the changes of the BOT as a function of time from the initial value

Response 16:

Thank you for the valuable optimization suggestions put forward by the reviewers! We have attempted to plot the "time-dependent curves of bottom hole temperature (BHT) relative to the initial value" as recommended. However, due to the significant difference in total tripping out operation duration between 2910m (10 hours) and 9026m (30 hours), it is difficult to intuitively compare the core laws of temperature changes between the two curves on the time axis, and the presentation effect did not meet the expected standards.

Comments 17: You need to add one new section before the conclusion, call it limitations, where you list all the limitations of the work

Response 17: Thank you for the reviewers' suggestion! We have added a new chapter "Research Limitations" before the Conclusions section, which details issues including the idealized assumptions of the model, fixed values of material parameters, limitations of the case well type, and failure to consider field operation errors. The research shortcomings are objectively presented, and the relevant content has been fully supplemented.

4. Response to Comments on the Quality of English Language

Point 1: The English could be improved to more clearly express the research.

Response 1: Thank you for the reminder! We have comprehensively revised and optimized the English expression of the entire manuscript: standardized the consistency of professional terms, corrected grammatical errors and logical breaks in sentences; simplified complex long sentence structures, optimized the inter-sentence cohesion in sections such as literature review and results discussion to improve readability; invited a native English-speaking expert in petroleum engineering to proofread the entire manuscript, ensuring the accurate transmission of technical content and compliance with international academic writing norms.

Comments 1: Abbreviations that have already been mentioned are often repeated, such as BHP. It is sufficient to write them out once and then use them throughout the manuscript.

Response 1: Thank you for the reminder! We have adjusted the format in accordance with academic standards: all abbreviations (e.g., BHP) are only labeled with their full names upon first appearance, and the abbreviations are uniformly used thereafter to ensure concise and consistent expression.

Comments 2: Authors should avoid using the word “proposed” in the introduction (last paragraph), for example, and write “presented” instead.

Response 2: Thank you for the suggestion! We have replaced " proposed" in the last paragraph of the introduction with "presented", which complies with academic expression norms and avoids inappropriate wording.

Comments 3: All figures and tables should use the same font and font size. In most figures, these are much too small.

Response 3: Thank you for your attention! We have standardized the font and font size of all charts, enlarged the previously overly small fonts, and improved chart readability to ensure readers can clearly obtain information.

Comments 4: All equations must be clearly defined and described in the text so that the reader can follow and understand them.

Response 4: Thank you for the rigorous requirement! After all mathematical equations, we have detailed the meaning of each parameter, derivation logic, and application scenarios, enabling readers to clearly understand the core logic and usage context of the equations.

Comments 5: In Figure 2, the structures of the wellbore should be named in addition to the dimensions.

Response 5: Thank you for the suggestion! We have added labels for each wellbore structure (e.g., casing, cement sheath, formation) in Figure 2, making the wellbore structure more intuitive and helping readers understand the composition of the wellbore.

Comments 6: Table 1 shows numbers in the first column. How should these be understood?

Response 6: Thank you for pointing out the issue! Since the numbers in the first column of Table 1 have no clear physical meaning or classification basis, we have deleted them as suggested to streamline the table content and avoid misleading readers.

Comments 7: The number is missing in lines 134-135: “...in the figure.”

Response 7: Thank you for the reminder! We have supplemented the missing numerical information in Lines 134-135 and corrected the vague expression " in the figure", making the content complete and accurate.

Comments 8: Units such as those in Table 2 (m, mm) should not be italicized.

Response 8: Thank you for the correction! We have removed the italic format of units (e.g., m, mm) in Table 2 and standardized the format to meet academic chart typesetting requirements.

Comments 9: The letters n, s, e, w, as well as r1, r2, r33, r4 should be illustrated to give the reader a better idea.

Response 9: Thank you for the suggestion! We have clearly explained through text: n, s, e, w are direction identifiers (North, South, East, West), and r1-r4 are radial dimension parameters (corresponding to drill pipe inner diameter, drill pipe outer diameter, casing inner diameter, and casing outer diameter respectively). We have also added more detailed indications in the figure to help readers accurately understand the parameter meanings.

Comments 10: Where do the physical parameters of the materials listed in Table 3 come from? (Reference?!)

Response 10: Thank you for the rigorous requirement! The thermal physical parameters of materials such as drilling fluid and casing in Table 3 are derived from the field design plans provided by Southwest Oil & Gas Field, which are actual engineering data (not publicly available yet). We have supplemented the data source description in the manuscript to ensure its credibility.

Comments 11: The reference is missing in line 175.

Response 11: Thank you for the reminder! We have supplemented the corresponding reference citation for the content quoted in Line 175, improved citation norms, and avoided omissions.

Comments 12: Table 3 and Table 4 have the same name. This should be changed.

Response 12: Thank you for pointing out the issue! We have renamed one of the tables to clearly distinguish their contents, avoid confusion, and ensure clear table identification.

Comments 13: Information in figures, such as Figure 4, should be added to the description so that it is clear what the units (Q) specified there mean. Likewise, the subdivisions in figures such as Figure 2 (1., 2., 3., 4.), Figure 3 (a), (b), (c), etc. should be described in detail.

Response 13: Thank you for the suggestion! We have supplemented key chart information: the unit of parameter Q is watts (W) and its physical meaning is heat transfer rate, which is explained in the corresponding part of the text; we have also detailed the specific contents corresponding to the partitions of Figure 2 (1., 2., 3., 4.) and the subfigures of Figure 3 ((a), (b), (c)) in the text, making the chart information more complete and understandable.

Comments 14: The numbers in Table 5 should not be in bold.

Response 14: Thank you for the correction! We have removed the bold format of numbers in Table 5, standardized the format of all tables in the manuscript, and maintained consistent typesetting.

Comments 15: At the beginning of Chapter 2, all materials and tools should be clearly listed (mineral oils, CaCl2 brine, etc.) so that the reader has a clear overview.

Response 15: Thank you for the suggestion! Since this study’s model only focuses on the physical parameters of drilling fluid (density, specific heat capacity, etc.), and its specific components (e.g., mineral oil, calcium chloride brine) have no impact on the calculation results, we have not elaborated further to avoid redundant information interfering with the core logic.

Comments 16: Figure 7 should be described in detail.

Response 16: Thank you for the suggestion! We have provided a detailed description of Figure 7: this figure is a calculation flow chart of temperature, ESD, and BHP during tripping out of hole, which clearly shows the complete process from parameter input, mesh generation to result output. It provides process support for subsequent simulation calculations and technology proposal, and clarifies the core connection with the research.

Comments 17: In general, the presentation and description of the actual modeling is missing. Boundary conditions, inlet and outlet conditions, fluid modeling, meshing type, inflation layer, turbulence model, simulation software, reference model, validation, etc.

Response 17: Thank you for the emphasis! We have supplemented key details of numerical modeling, including boundary conditions (e.g., wellbore thermal boundary, wellhead fluid supplementation temperature boundary), fluid modeling method (one-dimensional axial flow model), mesh type (structured grid), simulation software selection, reference models (based on Hoberock 1982 and API 2010 standards), and model validation process (comparison with Drillbench software, temperature deviation < 3℃).

Comments 18: What software was used to perform the ESD and BHP calculations? How were the mathematical equations implemented? How was this calculation checked or validated? Without these aspects and validations (reference model), the results cannot really be understood.

Response 18: Thank you for the emphasis! We clarify that the calculations of BHP and ESD are implemented through self-developed programs (programming platform: Visual Studio 2022; language: C#; solution algorithm: second-order upwind scheme + fully implicit time scheme). The calculation results are verified through software comparison and sensitivity analysis to ensure reliability.

Comments 19: The discussion section should be written separately from the results section and should critically address the analyses.

Response 19: Thank you for the suggestion! The logic of this study is "discovering the impact of thermal effects on BHP through results → proposing targeted annulus fluid supplementation technology". Splitting the two chapters would disrupt this logical coherence, so we have not separated them. However, we have added critical analysis of the results in the discussion section (e.g., analyzing the reasons for temperature change differences at different depths, technical application boundaries, etc.).

Comments 20: How does the quality of the results compare to the very strong simplifications assumed?

Response 20: Thank you for the requirement! We have supplemented the strong simplifying assumptions in the study, such as one-dimensional axial flow of drilling fluid, formation isotropy, and fixed thermal physical parameters of materials. We have also analyzed their impact on the results: they may cause slight deviations in temperature field calculations, but do not affect the core law of BHP changes driven by thermal effects, ensuring readers understand the applicable premises of the results.

Comments 21: What basis has the study provided for future research? Are the results limited or do they have universal validity?

Response 21: Thank you for the suggestion! We have clearly elaborated: the theoretical support is the construction of a transient tripping-out temperature field model and the quantification of the coupling mechanism between thermal effects and BHP; the technical support is the proposal of a weighted drilling fluid supplementation method and key parameter design, providing technical reference for the safe tripping out of ultra-deep wells with narrow safe density windows; the limitations include focusing only on vertical wells and not considering field operation errors; the universality applies to the tripping-out condition of HTHP ultra-deep vertical wells, which can provide reference for pressure control in similar scenarios.

Comments 22: The table of abbreviations should be divided into “Abbreviations, mathematical terms, and Greek letters” or something similar. In addition, consistency should be maintained in the use of brackets (square or round brackets).

Response 22: Thank you for the suggestion! We have classified and arranged the abbreviation list into "abbreviations, mathematical terms, Greek letters", and uniformly used parentheses to label abbreviations throughout the manuscript, ensuring consistent format and facilitating readers' reference.

4. Response to Comments on the Quality of English Language

Point 1: The English could be improved to more clearly express the research.

Response 1: Thank you for the reminder! We have systematically optimized the English expression of the entire manuscript: ① Standardized the consistency of professional terms; ② Corrected grammatical errors and logical breaks in sentences, simplified complex long sentence structures ; ③ Optimized the inter-sentence cohesion in sections such as literature review and results discussion to improve writing fluency; ④ Invited a native English-speaking expert in petroleum engineering to professionally proofread the entire manuscript, ensuring the accurate transmission of technical content and compliance with international academic journal writing norms.

Comments 1: Since there are still a few points from my previous comments that are still open, I would recommend that you add a new section at the end ( after the conclusion, or you can integrate the point with the conclusion, call it future work. Under this section, mention these points here. I refer to Validation, additional simulations, sensitivity analysis study, etc

Response 1: Thank you for this valuable suggestion. We have added a new section titled "7. Future Work" after the Conclusion section. In this section, we have explicitly discussed the need for further field data validation, comprehensive sensitivity analyses (regarding geothermal gradient, tripping speed, etc.), and additional simulations under more complex operating conditions. This addition provides a clearer roadmap for future research directions.

Comments 2: For the new section methodology, please create a simple flow chart that shows the workflow

Response 2: We have created the workflow chart as requested and presented it below for your review. However, since the specific details of this workflow are relatively basic and we have not yet conducted an in-depth investigation into this specific aspect, we have decided not to include this chart in the final manuscript at this stage. We hope this explanation is acceptable.

Comments 3: Add extra description to the figures (fig 2)

Response 3: We have rigorously revised Figure 2. Detailed annotations and descriptions have been added to clarify the wellbore structure and the components involved. We have also addressed the visibility of the production casing by adding specific notes (e.g., "Not shown") to ensure the figure is intuitive and clear for the readers.

Comments 4: Please revise the first paragraph of the introduction. I have restructured it as below. Please use the one below and add the new references, which I suggest below as well .

Deep and ultra-deep oil and gas resources are important replacement resources for China's oil and gas reserve growth and production increase. Achieving high-quality and efficient drilling and completion of ultra-deep wells is of great significance for safeguarding national energy security [1-2].  Several challenges are associated with drilling operations; the impact of these challenges can be mitigated by proposing proactive solutions (add the new references here). One of the problems is the variations of bottom hole pressure while tripping, especially in deep water wells.

The new references 

Elmgerbi, A., Les, B., Ashena, R. et al. A Practical Decision Tool to Evaluate and Rank Potential Solutions for Expected Downhole Drilling Problems During the Well-planning Phase. J. Inst. Eng. India Ser. D 103, 25–36 (2022). https://doi.org/10.1007/s40033-021-00325-7

P. L. York, D. M. Prichard, J. K. Dodson, T. Dodson, S.M. Rosenberg, D. Gala, and B. Utama. Eliminating non-productive time associated with drilling through trouble zones. Paper presented at the Offshore Technology Conference, Houston, Texas, (2009) https://doi.org/10.4043/20220-MS

E. Cayeux, B. Daireaux, M. Karimi Balov, S. Haavardstein, L.Magne Stokland, and A. Saasen, Automatic performance analysis and estimation of risk level embedded in drilling operation plans.Paper presented at the SPE Intelligent Energy International Conference and Exhibition, Aberdeen, Scotland, UK, (2016). https://doi.org/10.2118/181018-MS

Response 4: We appreciate your specific guidance on the Introduction. We have carefully read the three recommended references:

Elmgerbi, A., et al. (2022)

York, P. L., et al. (2009)

Cayeux, E., et al. (2016)

We found that these studies are highly relevant to our research direction, particularly regarding proactive solutions and risk assessment in drilling operations. We have revised the first paragraph of the Introduction exactly as you suggested and have cited these references in the appropriate locations.