Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs

Round 1

Reviewer 1 Report

I have gone carefully through the manuscript. The subject is interesting and the authors have done an insightful study. The manuscript can be considered for publication after addressing the following concerns:

- The Abstract should contain answers to the following questions: What problem was studied and why is it important? What methods were used? What are the important results? What conclusions can be drawn from the results? What is the novelty of the work and where does it go beyond previous efforts in the literature? Please include specific and quantitative results in your Abstract, while ensuring that it is suitable for a broad audience.

 

- The Introduction should make a compelling case for why the study is useful along with a clear statement of its novelty or originality by providing relevant information and providing answers to basic questions such as: What is already known in the open literature? What is missing (i.e., research gaps)? What needs to be done, why and how? Clear statements of the novelty of the work should also appear briefly in the Abstract and Conclusions sections.

- Good sensitivity analyses have been performed and the results are amazing. Which factor would play the most important role?

- How about the effect of reservoir parameters like permeability on the obtained pressure? especially after shut-in time?

- The authors have studied the effect of fracture complexity on the bottom hole pressure. Does this factor support the main characteristics of a fracture network? Characteristics such as fracture intensity, orientation, width, etc.

- How about the model or results validation and verification? How one can confirm that the obtained results are reliable?

-  What are the future developments for this study? Please discuss this in the manuscript.

Author Response

Dear reviewer：

Thank you for your letter and comments concerning our manuscript entitled “Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs” (ID: sustainability-2486455).

The main corrections of the paper and the responses to the reviewers' comments are as follows, in which the revised content is marked in red, and the newly added content is marked in blue.

1. Comment: The Abstract should contain answers to the following questions: What problem was studied and why is it important? What methods were used? What are the important results? What conclusions can be drawn from the results? What is the novelty of the work and where does it go beyond previous efforts in the literature? Please include specific and quantitative results in your Abstract, while ensuring that it is suitable for a broad audience.

Response: Since most of the studies focus on the separate design of fracturing, shut-in and production, the tight oil and gas recovery is not high. Therefore, this paper innovatively reveals the pressure transfer law during shutting in well based on the integration of fracturing, shut-in and production. The influence law of fracturing fluid volume, shut-in time, reservoir original formation pressure and fracture network complexity on the effect of well shut-in was studied to optimize the shut-in system. Specific quantitative results in response to the comments made by the expert are presented in the abstract of this paper.

2. Comment: The Introduction should make a compelling case for why the study is useful along with a clear statement of its novelty or originality by providing relevant information and providing answers to basic questions such as: What is already known in the open literature? What is missing (i.e., research gaps)? What needs to be done, why and how? Clear statements of the novelty of the work should also appear briefly in the Abstract and Conclusions sections.

Response: Most of the research focus on the separate design of fracturing and well shut-in, and few scholars have conducted comprehensive research on both, which is difficult to meet the requirements of actual oil and gas development. Therefore, this paper innovatively establishes a systematic model integrating geological model, hydraulic fracture extension model, shut-in and production model of the target block, and optimizes the design of production enhancement method after shutting in well according to reservoir characteristics.

3. Comment: Good sensitivity analyses have been performed and the results are amazing. Which factor would play the most important role?

Response: In this study, the influence law of fracturing fluid volume, shut-in time, reservoir original formation pressure and fracture network complexity on the effect of well shut-in was studied. In actual production, reservoir pressure and fracture network complexity have a significant impact but these properties cannot be changed. Fracturing fluid volume and the shut-in time can be designed in advance to maximize the reservoir active area.

4. Comment: How about the effect of reservoir parameters like permeability on the obtained pressure? especially after shut-in time?

Response: In this paper, the transfer law of pressure in this reservoir during shutting in well is investigated using Block M as an example. This block is a tight reservoir, and the theoretical geological model with a reservoir permeability of 0.13 mD was established in the modeling, and the change of the permeability of the tight reservoir was not taken into account too much.

5. Comment: The authors have studied the effect of fracture complexity on the bottom hole pressure. Does this factor support the main characteristics of a fracture network? Characteristics such as fracture intensity, orientation, width, etc.

Response: When studying the influence law of fracture complexity on reservoir pressure transfer during shutting in well, the natural fractures need to be designed in the modeling. In the design, the parameters of natural fractures, such as fracture width and orientation, are set according to the actual data of the reservoir.

6. Comment: How about the model or results validation and verification? How one can confirm that the obtained results are reliable?

Response: In this study, actual data from the study area were used for modeling of fracturing and well shut-in, and finally production simulation of the model was carried out. Since no history matching was done, there was no model validation process. The conclusions of this study are in line with the general understanding and laws, and can be well explained based on the actual oilfield, with a certain degree of persuasiveness.

7. Comment: What are the future developments for this study? Please discuss this in the manuscript.

Response: Additions have been made to the manuscript based on expert comments. In the future, the numerical simulation results in this paper, combined with the indoor experimental means, can more accurately reflect the actual oilfield site and formulate the optimal design of fracturing and well shut-in solutions. As an important link in the integration of geological engineering, this research is expected to make a greater contribution to the sustainable development of oil and gas and to ensure a stable supply of energy security.

 

Special thanks to you for your good comments.

Yours sincerely,

Le Yan

Author Response File: Author Response.pdf

Reviewer 2 Report

Taking the tight oil reservoir in Block M as an example, this paper uses an integrated fracturing development software platform to build a geological model of the target block, and then conducts fracture propagation, shut-in, and production simulation on this basis. The changes of reservoir pressure field in the process of shut-in are analyzed, and the influence laws of fracturing fluid volume, shut-in time, original formation pressure and fracture network complexity on shut-in effect are studied. The results show that the retention of fracturing fluid increases, the pore pressure near the fracture matrix increases, and the diffusion distance of fracturing fluid to the far fracture matrix increases. The overall quality of the manuscript is good, but it needs to be improved in the following aspects.

 

Line 12: In this paper, the law of pressure transfer in the shut-in stage after fracturing is studied by numerical simulation. But the content of sustainability is not reflected much in the article, it may be possible to discuss the influence of pressure change on formation stability after shut-in.

 

Line 94: Figure 1 and Figure 2 can be placed in a row.

 

Line 121: Please improve the quality of Figure 3 to ensure clarity. Do the same for other similar images.

 

Line 160: Table 3 needs to be completed in accordance with the three-line table when   changing the page. You might refer to the Microsoft Word templates. Similarly, Table 5,   Table 6 need to be modified for formatting requirements.

 

Line 189: The experimental simulation in this section should be combined with the Simulation Result Analysis in the next section. This improves readability for readers.

 

Line 436: That's not a very cautious conclusion, and more reservoir conditions are needed to        limit for this conclusion.

 

Line 442: The conclusion needs to summarize the universal law from specific real cases, I       therefore recommend deleting the last given “optimal shut-in time according to the     actual model”.

 

Line 460: References are best listed in the following format:

1.          Author 1, A.B.; Author 2, C.D. Title of the article. Abbreviated Journal Name Year, Volume, page range.

2.          Author 1, A.; Author 2, B. Title of the chapter. In Book Title, 2nd ed.; Editor 1, A., Editor 2, B., Eds.; Publisher: Publisher Location, Country, 2007; Volume 3, pp. 154–196.

3.          Author 1, A.; Author 2, B. Book Title, 3rd ed.; Publisher: Publisher Location, Country, 2008; pp. 154–196.

4.          Author 1, A.B.; Author 2, C. Title of Unpublished Work. Abbreviated Journal Name year, phrase indicating stage of publication (submitted; accepted; in press).

5.          Author 1, A.B. (University, City, State, Country); Author 2, C. (Institute, City, State, Country). Personal communication, 2012.

6.          Author 1, A.B.; Author 2, C.D.; Author 3, E.F. Title of Presentation. In Proceedings of the Name of the Conference, Location of Conference, Country, Date of Conference (Day Month Year).

7.          Author 1, A.B. Title of Thesis. Level of Thesis, Degree-Granting University, Location of University, Date of Completion.

8.          Title of Site. Available online: URL (accessed on Day Month Year).

 

 

It is recommended to have a professional touch up.

Author Response

Dear reviewer：

Thank you for your letter and comments concerning our manuscript entitled “Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs” (ID: sustainability-2486455).

The main corrections of the paper and the responses to the reviewers' comments are as follows, in which the revised content is marked in red, and the newly added content is marked in blue.

1. Comment: Line 12: In this paper, the law of pressure transfer in the shut-in stage after fracturing is studied by numerical simulation. But the content of sustainability is not reflected much in the article, it may be possible to discuss the influence of pressure change on formation stability after shut-in.

Response: In this study, the geological model of the target block was established using the integrated fracturing development software platform, on which the simulation of fracture extension, well shut-in and production was carried out. The changes of reservoir pressure field during shutting in well were analyzed, and the influence law of fracturing fluid volume, shut-in time, reservoir original formation pressure and fracture network complexity on the effect of well shut-in was studied to optimize the shut-in system. The sustainable development goal of this study is reflected in the fact that the integrated model established in this study can realize the efficient and sustainable development of tight oil and gas resources by optimizing the design of several key factors in the development of tight oil and gas.

2. Comment: Line 94: Figure 1 and Figure 2 can be placed in a row.

Response: Figures 1 and 2 have been placed in a row.

3. Comment: Line 121: Please improve the quality of Figure 3 to ensure clarity. Do the same for other similar images.

Response: All images in this study have been checked and adjusted for sharpness.

4. Comment: Line 160: Table 3 needs to be completed in accordance with the three-line table when changing the page. You might refer to the Microsoft Word templates. Similarly, Table 5, Table 6 need to be modified for formatting requirements.

Response: Tables 3, 5 and 6 of this study have been reformatted to ensure that they are not distributed across pages.

5. Comment: Line 189: The experimental simulation in this section should be combined with the Simulation Result Analysis in the next section. This improves readability for readers.

Response: The section on line 189 shows the process of modeling the well shut-in after the completion of the fracturing simulation in this study, and the next section shows the simulation results obtained by examining the influences of each factor on the basis of the established model.

6. Comment: Line 436: That's not a very cautious conclusion, and more reservoir conditions are needed to limit for this conclusion.

Response: The quantitative conclusions obtained in this paper are based on the simulation and optimization of the established model. The optimization results may vary for different models.

7. Comment: Line 442: The conclusion needs to summarize the universal law from specific real cases, I therefore recommend deleting the last given “optimal shut-in time according to the actual model”.

Response: Some of the quantitative conclusions in the conclusion section for the optimization of the specific model have been deleted based on expert recommendations, leaving only the persuasive general laws as the conclusions of this study.

8. Comment: Line 460: References are best listed in the following format.

Response: The format of the references in this study has been modified in accordance with the recommendations of the experts.

 

Special thanks to you for your good comments.

Yours sincerely,

Le Yan

Author Response File: Author Response.pdf

Reviewer 3 Report

 Technically, the article presents a topic related to studying pressure transfer in tight reservoirs to improve the energy efficiency of fracturing fluid. However, there are some issues in the article that could be improved:

1.     While the abstract does not mention any specific novel approaches or techniques, it sets the stage for investigating the integration of fracturing, shut-in, and production processes, which could contribute to the existing body of knowledge. However, more specific details about the novel aspects of the research would be helpful. The abstract could benefit from more clarity and detail on the specific problem being addressed, the methodology used to investigate it, and the implications of the study's findings.

2.      The paper could benefit from a clearer research question or objective to guide the reader toward the main purpose of the study.

3.      Consider the insights and findings from the papers (https://doi.org/10.1016/j.geoen.2023.211716 and https://doi.org/10.3997/2214-4609.202288005) on fluid flow in heterogeneous porous media to enhance the introduction section. By leveraging the comprehensive understanding of flow behavior within porous media presented in that paper, you can improve your study's overall analysis and interpretation about fluid flow and pressure propagation.

4.      Asphaltene particles can cause various challenges during production, such as precipitation, deposition, and plugging of the reservoir. Therefore, it is a good idea to mention the impact of asphaltene particles in the fracture network in the reservoir and the flow conductivity. Look at this paper: https://doi.org/10.1007/s13202-018-0537-1

5.      The Development Characteristics section effectively presents the geological and development characteristics of the M block tight oil reservoir. However, it would be beneficial to include additional details or data to enhance the originality and depth of the information presented.

6.      In the simulation workflow, including unsuitable photos for each step, which are merely screenshots from the software, needs improvement.

7.     Methodology mentions the use of a Petrel software platform for constructing an integrated fracturing, shut-in, and production model. However, it lacks specific details regarding the methodology employed in the study. Providing more information about the specific methods used for the research would improve the paper.

8.     Providing information about the assumptions and limitations of the simulation model would enhance the transparency and reproducibility of the study.

9.     I did not understand the source or origin of the data used in the simulation. It is important to provide information about the data quality and reliability to ensure the validity of the findings. Additionally, the assumptions made during the simulation should be clearly stated, as they can significantly influence the results.

10.  While the conclusions are provided, there is no accompanying discussion or interpretation of the results. It would be beneficial for the authors to explain the underlying mechanisms and provide a more in-depth analysis of the findings. Additionally, including quantitative data or statistical analysis supporting the conclusions would enhance the robustness of the study.

11.  The research would benefit from several considerations. Firstly, comparing the simulation results with field data or case studies would enhance the validation and applicability of the model. Secondly, incorporating economic factors into the analysis, such as the costs and revenue implications of shut-in operations, would provide a more comprehensive assessment. Thirdly, addressing the environmental implications of well shut-in in hydraulic fracturing and exploring potential mitigation measures is important in the context of sustainability. Lastly, discussing the limitations, constraints, and generalizability of the study would ensure that the findings are appropriately interpreted and can be applied to various geological formations and fracturing operations.

 

12.  In terms of writing, the article could benefit from some improvements in clarity, organization, and style. Some of the sentences and paragraphs are pretty long and complex, which could make it difficult for readers to follow the argument. Additionally, the article could benefit from more consistent use of technical terminology and more precise definitions of key concepts.

NA

Author Response

Dear reviewer：

Thank you for your letter and comments concerning our manuscript entitled “Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs” (ID: sustainability-2486455).

The main corrections of the paper and the responses to the reviewers' comments are as follows, in which the revised content is marked in red, and the newly added content is marked in blue.

1. Comment: While the abstract does not mention any specific novel approaches or techniques, it sets the stage for investigating the integration of fracturing, shut-in, and production processes, which could contribute to the existing body of knowledge. However, more specific details about the novel aspects of the research would be helpful. The abstract could benefit from more clarity and detail on the specific problem being addressed, the methodology used to investigate it, and the implications of the study's findings.

Response: Aiming at the current problem of low recovery rate of tight oil and gas and the insufficiency of existing technology, this study establishes an integrated model of fracturing, shut-in and production in tight reservoirs, and investigates the pressure transfer law of tight reservoir during shutting in well, and the results of the study are of great significance for the efficient development of tight oil and gas.

2. Comment: The paper could benefit from a clearer research question or objective to guide the reader toward the main purpose of the study.

Response: Revisions have been made based on expert recommendations to further clarify the main research objectives of this study.

3. Comment: Consider the insights and findings from the papers (https://doi.org/10.1016/j.geoen.2023.211716 and https://doi.org/10.3997/2214-4609.202288005) on fluid flow in heterogeneous porous media to enhance the introduction section. By leveraging the comprehensive understanding of flow behavior within porous media presented in that paper, you can improve your study's overall analysis and interpretation about fluid flow and pressure propagation.

Response: An in-depth study of fluid flow and pressure propagation in heterogeneous porous media has been carried out based on expert opinion and further enriched the references of this paper.

4. Comment: Asphaltene particles can cause various challenges during production, such as precipitation, deposition, and plugging of the reservoir. Therefore, it is a good idea to mention the impact of asphaltene particles in the fracture network in the reservoir and the flow conductivity. Look at this paper: https://doi.org/10.1007/s13202-018-0537-1.

Response: The effect of asphaltene particles on reservoir fracture networks and conductivity has been considered in this paper based on expert recommendations and further enriched with references to this paper.

5. Comment: The Development Characteristics section effectively presents the geological and development characteristics of the M block tight oil reservoir. However, it would be beneficial to include additional details or data to enhance the originality and depth of the information presented.

Response: Since the main purpose of this paper is to study the pressure transfer law during shutting in well of tight reservoirs, only the porosity and permeability characteristics of the target reservoirs are described in the geologic modeling, and a simple theoretical geologic model of the target block is established.

6. Comment: In the simulation workflow, including unsuitable photos for each step, which are merely screenshots from the software, needs improvement.

Response: The numerical simulation in this paper is realized by using the integrated fracturing, shut-in and production model established by Petrel integrated software platform. The numerical simulation workflow demonstrates the process of building the integrated model using this software platform, and therefore screenshots of the software are shown.

7. Comment: Methodology mentions the use of a Petrel software platform for constructing an integrated fracturing, shut-in, and production model. However, it lacks specific details regarding the methodology employed in the study. Providing more information about the specific methods used for the research would improve the paper.

Response: In Section 3, this paper explains the implementation process of geological modeling, fracturing modeling, well shut-in and production modeling, respectively, and elaborates on the process from single modeling to integrated model building.

8. Comment: Providing information about the assumptions and limitations of the simulation model would enhance the transparency and reproducibility of the study.

Response: Since the main purpose of this paper is to study the pressure transfer law in the process of shut-in wells in tight reservoirs, only the porosity and permeability characteristics of the target reservoir are described in the geologic modeling, and it is assumed that the geologic model of the target block is a simple theoretical model. On this basis, the fracturing process is simulated according to the pumping schedule provided in this paper, and the pressure transfer law of the reservoir during the well shut-in period is investigated by changing the parameters such as the well shut-in time and the amount of retained fluid in the reservoir after the end of fracturing.

9. Comment: I did not understand the source or origin of the data used in the simulation. It is important to provide information about the data quality and reliability to ensure the validity of the findings. Additionally, the assumptions made during the simulation should be clearly stated, as they can significantly influence the results.

Response: In this paper, the tight oil reservoir in block M is taken as the research object, and all the data used in the numerical simulation are the real data of this target block. Only in the geological modeling, it is assumed that the reservoir is a homogeneous tight reservoir, and the changes of reservoir porosity and permeability are not considered.

10. Comment: While the conclusions are provided, there is no accompanying discussion or interpretation of the results. It would be beneficial for the authors to explain the underlying mechanisms and provide a more in-depth analysis of the findings. Additionally, including quantitative data or statistical analysis supporting the conclusions would enhance the robustness of the study.

Response: The discussion of the numerical simulation results in this paper focuses on the simulation results following each of the influencing factors. Firstly, the change of reservoir matrix pore pressure is analyzed according to the color chart, then the change of bottom hole pressure is described, and finally the change of production after shutting in the well is discussed. The conclusion chapter is the generalized conclusions and patterns obtained by combining multiple factors.

11. Comment: The research would benefit from several considerations. Firstly, comparing the simulation results with field data or case studies would enhance the validation and applicability of the model. Secondly, incorporating economic factors into the analysis, such as the costs and revenue implications of shut-in operations, would provide a more comprehensive assessment. Thirdly, addressing the environmental implications of well shut-in in hydraulic fracturing and exploring potential mitigation measures is important in the context of sustainability. Lastly, discussing the limitations, constraints, and generalizability of the study would ensure that the findings are appropriately interpreted and can be applied to various geological formations and fracturing operations.

Response: In this paper, numerical simulation will be combined with the actual data of the oil field according to the expert recommendations, and the economic factors can be taken into consideration on the basis of maximizing the production, so as to realize the modeling of multiple types of reservoirs.

12. Comment: In terms of writing, the article could benefit from some improvements in clarity, organization, and style. Some of the sentences and paragraphs are pretty long and complex, which could make it difficult for readers to follow the argument. Additionally, the article could benefit from more consistent use of technical terminology and more precise definitions of key concepts.

Response: This paper has been checked for terminology and paragraphing throughout the text in accordance with expert recommendations, and the presence of lengthy and complex sentences has been reduced to ensure that readers can easily understand the arguments in this paper.

 

Special thanks to you for your good comments.

Yours sincerely,

Le Yan

Author Response File: Author Response.pdf

Reviewer 4 Report

1. Overview and general recommendation:

I enjoyed reviewing the manuscript of “Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs”. Tight oil and gas serve as an alternative for conventional oil and gas. Horizontal wells and multi-stage fracturing are the key technologies for tight oil recovery and a reasonable shut-in system can enhance production. However, previous studies mainly focused on the separate design of fracturing and well shut-in.

In contrast, the authors of this study investigated the pressure transfer during the shut-in process in a tight oil reservoir by employing an integrated fracturing, shut-in and production model. They evaluated the effect of fracturing fluid volume, shut-in time, reservoir original formation pressure, and fracture network complexity on the performance of well shut-in, and they found an optimal value for each parameter.

Overall, the paper is well written. There are just a few things that still need to be addressed. Therefore, I recommend that minor revision is warranted. Detailed comments are listed below.

2. Detailed comments:

(1) Page 2, Line 84. Please define “C₁ reservoir”.

(2) Page 3, Lines 114-115. Insert “and” before “geological”. Also, “needs” after “construction” should be “need”.

(3) Page 4, Line 128. I understand you are taking the value from the average permeability of this reservoir, but why is the permeability in X and Y directions 10 times the one in Z direction?

(4) Page 5, Lines 134-135. What about the width?

(5) Page 6, Line 147. I know Kr stands for relative permeability and I suppose w and o refer to water and oil, but you may need to add a legend to clarify.

(6) Page 14, Line 257. It would be better if you could use the same color for Retention/total fluid volume =90% in both Figure 14 and Figure 15.

(7) Page 24, Lines 419-420. You just repeated this in the following sentence, so delete it.

 

Author Response

Dear reviewer：

Thank you for your letter and comments concerning our manuscript entitled “Numerical Simulation Study of Pressure Transfer Based on the Integration of Fracturing, Shut-in and Production in Tight Reservoirs” (ID: sustainability-2486455).

The main corrections of the paper and the responses to the reviewers' comments are as follows, in which the revised content is marked in red, and the newly added content is marked in blue.

1. Comment: Page 2, Line 84. Please define “C₁ reservoir”.

Response: The C₁ reservoir is a tight reservoir where the target wells are located, and the physical characteristics of the target reservoir are described in Section 2.1 of this paper.

2. Comment: Page 3, Lines 114-115. Insert “and” before “geological”. Also, “needs” after “construction” should be “need”.

Response: Grammatical errors in this article have been corrected based on expert recommendations.

3. Comment: Page 4, Line 128. I understand you are taking the value from the average permeability of this reservoir, but why is the permeability in X and Y directions 10 times the one in Z direction?

Response: When we perform numerical simulations, we usually consider the permeability in the Z direction to be much smaller than the permeability in the X and Y directions, so a multiplicative reduction based on the permeability in the X and Y directions is considered to be the permeability in the Z direction.

4. Comment: Page 5, Lines 134-135. What about the width?

Response: This is a description of the target well. The target well is a horizontal well with a depth of 4281 m and a horizontal section length of 2237 m. Figure 6 shows the well in the reservoir.

5. Comment: Page 6, Line 147. I know Kr stands for relative permeability and I suppose w and o refer to water and oil, but you may need to add a legend to clarify.

Response: In Figure 7 Kr represents relative permeability, W represents water, O represents oil, and Kro and Krw are terms common to the industry.

6. Comment: Page 14, Line 257. It would be better if you could use the same color for Retention/total fluid volume =90% in both Figure 14 and Figure 15.

Response: The line colors in Figure 15 have been revised based on expert comments to ensure consistency with the line colors in Figure 14.

7. Comment: Page 24, Lines 419-420. You just repeated this in the following sentence, so delete it.

Response: Duplicate sentences have been deleted based on expert recommendations.

 

Special thanks to you for your good comments.

Yours sincerely,

Le Yan

Round 2

Reviewer 1 Report

Accept as is.

Reviewer 2 Report

The structure of the article is relatively complete, but the language of the article is suggested to be polished and resubmitted.

Your article is complete after the first revision, but I suggest that the authors make some changes to the wording in several places.

 

Line 26: This sentence is ambiguous. According to the previous content, the amount of retained fluid increases will lead to many of the results mentioned below, but this causality is not reflected in the text. So this sentence needs to be revised. The same problem occurs in line 431.

Reviewer 3 Report

IT is OK to be published.