Research on Operation Optimization of Fluid Sampling in Wireline Formation Testing with Finite Volume Method

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

By considering the sensitivity parameters such as reservoir heterogeneity, probe suction area, mud-filtrate invasion depth during the drilling, in this article authors has used the method if finite volume
to construct a simulation analysis. With the aid of the developed simulations, one may not only desing but also calculate the
formation ofthe fluid sampling operations and also calculating the content of the hydrocarbon and pressure fo the flowing. Additionally, authors have exhibited the performance and influecen in the process of Wireline Formation examination.
it is highlighted that the introduced technology may stand as as a powerful and useful technique for measurement of the fluid sampling with consideration of the function of optimizing fluid sampling measures.
Also predicting indicators of this study, for instance hydrocarbon content and breakthrough time during the sampling may be improved significantly. Contents of this study may also be useful in geological exploration and oilfield technological developments.
In general this work is well-written and well-organised and provides a step by step procedure for the future readers. However present reviewers feels following comments should be considered correctly before final judgement of the paper
1) In Eq. (1)-(3), definition of x,y,x',y' should be provided
2) Why two different values are assumed for Figures (1) and (2)
3) A proper reference should be given for Eq. (8). Otherwise a step by step development of this equation is needed
4) In Eq. (11)-(17) there are some parameters which are not introduced. Define them
5) Have authors performed a mesh convergence is theor study?
6) What is the general conclusion from Table (5)? More discussions are needed here
7) Enrich the literature review on the subject by considering more works such as [Remote Sensing, 2022, 14(9), 2103. doi: 10.3390/rs14092103], [Physics of Fluids, 2024, 36(4), 045147, 10.1063/5.0203411], [Smart Grid, 2022, 13(3), 1691-1708, 10.1109/TSG.2022.3140212],
[Measurement, 2024, 114999, DOI : 10.1016/j.measurement.2024.114999]

Author Response

Dear Reviewer,

Thank you very much for your high recognition of our article, it is our honor. We also greatly appreciate your review comments, which have been very helpful to our research. We have made improvements. The details are as follows:

Comments 1: In Eq. (1)-(3), definition of x, y, x' should be provided

Response 1: Thank you for reviewing. The additions have been made. Please review the revised article: Lines 140-142.
Comments 2: Why two different values are assumed for Figures (1) and (2)
Response 2: Thank you for reviewing. This section is primarily to demonstrate the application effect of the variable step-size grid division method described in this paper. Specifically, it shows the formation of different grid models through the control of a variable parameter. That is, when ΔD=0, a longitudinal fixed-step grid model is produced, and when ΔD≠0, a longitudinal variable-step grid model division method is used. Based on your suggestion, we have also made additional content updates. Please review the revised article: Lines 166-168.

Comments 3: A proper reference should be given for Eq. (8). Otherwise a step by step development of this equation is needed

Response 3: Thank you for the reminder, and I apologize for my oversight. In the process of reservoir numerical simulation, this equation is primarily obtained through the combined transformation of the mass equations for the oil phase and water phase, resulting in a discrete equation. Since this is a relatively common approach, it was not repeated in the paper. Based on your suggestion, we have added the reference source for this method. Please review the revised article: Line 216 and Reference [19].
Comments 4: In Eq. (11)-(17) there are some parameters which are not introduced. Define them

Response 4: Thank you for reviewing. The additions have been made. Please review the revised article： Lines 263-266.
Comments 5: Have authors performed a mesh convergence is theory study?
Response 5: Thank you for reviewing. In the process of solving numerical simulation equations, the smaller the grid cells and the greater the number, the higher the probability of non-convergence. Firstly, this paper provides a variable step-size grid division method, which has a certain optimization effect on maintaining the convergence of the equation-solving process. More importantly, if non-convergence occurs during the equation-solving process, the convergence can be optimized by reducing the iteration time step, although this will result in reduced solving efficiency. Therefore, the exploration of grid convergence was not studied as a separate technical point. Of course, the study of equation-solving convergence has significant research value, and we hope to address it as a separate research point in future studies. Finally, based on your suggestion, we have added supplementary explanations about convergence. Please review the revised article: Lines 238-241.

Comments 6: What is the general conclusion from Table (5)? More discussions are needed here.

Response 6: Thank you for reviewing. The additions have been made. Please review the revised article： Lines 497-501.

Comments 7: Enrich the literature review on the subject by considering more works

Response 7: Thank you for recommending the excellent research paper. We have read it in detail and found many of the technologies to be very advanced, providing important inspiration for our ongoing research work. We also hope to draw on the relevant technical ideas in our subsequent research efforts.

Lastly, we would like to express our sincere gratitude once again for your review and your high recognition of our article. It is our honor.

Reviewer 2 Report

Comments and Suggestions for Authors

Review report:

For the operation optimization of fluid sampling in Wireline Formation Testing during

drilling process, this paper proposes a numerical simulation technique based on the finite volume

method which takes into account factors such as probe type, mud invasion and formation

characteristics. Through this method, calculation of key indicators such as hydrocarbon purity and

flow pressure can be achieved during fluid sampling. It plays an important role in production

capacity evaluation, fluid property analysis and other tasks related to oil and gas exploration and

development, while also possessing great innovation and research value.

Firstly, a variable step-size radial grid division technique that integrates parameters such as

wellbore radius and probe suction area information can be used not only to describe underground

fluid seepage characteristics, but also has the advantages of reducing the total number of grids and

improving computational speed.

More importantly, a numerical simulation model for Wireline Formation Testing fluid

sampling is constructed based on the Finite Volume method, which can take into account

information such as formation permeability, sampling probe type, and fluid sampling rate. By

combining incomplete LU decomposition and SBiCG solution technology, key production

indicators such as formation pressure and fluid saturation, hydrocarbon purity and flow pressure

under different conditions can be quickly solved.

This provides important technical support for optimizing the design, tracking, and adjustment

of sampling operations, effectively improving work efficiency and reducing production costs.

Furthermore, this demonstrates the value of numerical simulation technology in field operations.

Therefore, this paper is acceptable and publishable.

Best regards.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Dear Reviewer,

Thank you very much for your high recognition of our article, we would like to express our sincere gratitude for your review. It is our honor. Some phrasing errors have been corrected. Please review the revised article: Lines 48, 50, 52, 189, 503 and 505.

Lastly, we would like to express our sincere gratitude once again for your review and your high recognition of our article.

Reviewer 3 Report

Comments and Suggestions for Authors

The paper deals with a very significant topic, which has great industrial impact. The introduction is clear, the numerical simulations are described in details, the presented results are sound and clearly important from industrial perspective.

However, overall the text feels a bit "ambiguous" - in that sense, that the FVM method is described in great details, which makes the reader perceive it as the main topic of the article, and then there are different applications of the numerical simulations, which feel as another main topic.

Please try to:

1. Be more specific what exactly your FVM method brings new when compared to many FVM codes already available and why it is crucial for WFT.

2. Focus more on one topic and make it clear you want to present a new FVM method for WFT simulations or if you want to present the practical applications of the method.

(Just to make it clear - I am not asking for major revisions. The results are already there and they look good. )

Comments on the Quality of English Language

The quality of English is fine. I only noticed a few minor things:

Line 48: "was studied by numerical simulation" - plural (simulations) might fit there better. Or was really only a single numerical simulation used to study the optimization method?

Line 50: There is "mothed" instead of "method".

Line 52: Please correct / reformulate the sentence "Implemented the inversion process of rock physical parameters", it does not seem to be complete.

Line 187: "automatically satisfying the discretization with conservatively." seems to be an incomplete sentence. Please correct / reformulate.

Lines 490 and 492: Formulation "time has been advanced" would be better formulated as "time has been improved".

Author Response

Dear Reviewer,

Thank you very much for your high recognition of our article, it is our honor. We also admire your meticulous attitude towards scientific research, which has helped us identify some detailed issues. Following your suggestions, we have completed the revisions to the article. The details are as follows:

Comments 1: Line 48: "was studied by numerical simulation" - plural (simulations) might fit there better. Or was really only a single numerical simulation used to study the optimization method?
Response 1: Thank you for reviewing. The modifications have been made. Please review the revised article: Line 48.
Comments 2: Line 50: There is "mothed" instead of "method".

Response 2: Thank you for reviewing. The modifications have been made. Please review the revised article: Line 50.
Comments 3: Line 52: Please correct / reformulate the sentence "Implemented the inversion process of rock physical parameters", it does not seem to be complete.

Response 4: Thank you for reviewing. The modifications have been made. Please review the revised article: Line 52.

Comments 4: Line 187: "automatically satisfying the discretization with conservatively." seems to be an incomplete sentence. Please correct / reformulate.

Response 4: Thank you for reviewing. The modifications have been made. Please review the revised article: Line 189.
Comments 5: Lines 490 and 492: Formulation "time has been advanced" would be better formulated as "time has been improved".

Response 5: Thank you for reviewing. The modifications have been made. Please review the revised article: Lines 503 and 505.

Comments 6: Be more specific what exactly your FVM method brings new when compared to many FVM codes already available and why it is crucial for WFT.

Response 6: Firstly, fluid sampling during WFT plays a crucial role in the analysis of reservoir fluid properties and reservoir characterization. The calculation and analysis of hydrocarbon purity and flow pressure are two important indicators for optimizing operational procedures. Numerical simulation techniques can comprehensively consider reservoir properties, fluid characteristics, probe features, and the flow characteristics of underground fluids (not limited to FVM), thereby enabling the calculation of hydrocarbon content and flow pressure, which holds significant scientific value.

At present, in the process of oil and gas field exploration and development, compared to the existing FVM often used for reservoir-scale numerical simulations, there is less research specifically focused on the calculation of hydrocarbon content and flow pressure during fluid sampling in WFT. Therefore, based on the research content described in this article, we understand that the focus of this study includes: 1) Incorporating the probe’s suction area as an influencing factor into the numerical simulation equations formed by the FVM; 2) Specifically targeting the fluid sampling operation process, this study can comprehensively consider factors such as probe type, reservoir properties around the well, and sampling speed, to construct and research a targeted numerical simulation model and calculation method, rather than numerical simulation techniques for the entire reservoir area. Please review the revised article: Lines 226-229, and Eq. (8), Eq. (23). We are truly grateful for your suggestions and assistance.

Comments 7:  Focus more on one topic and make it clear you want to present a new FVM method for WFT simulations or if you want to present the practical applications of the method.

Response 7: Thank you very much. Overall, the theme of our research is focused on the fluid sampling process during WFT. We have studied a variable step-size grid model division method and combined it with the FVM for numerical simulation. This led to the development of a numerical simulation seepage model for the fluid sampling process, as well as methods for calculating hydrocarbon purity and flow pressure. Consequently, it is possible to analyze the hydrocarbon content, breakthrough time, and flow pressure of the sampled fluid under different probe models, operation speeds, and reservoir permeability conditions. Additionally, through several case studies, we have gained deeper insights, which can help and provide references for optimizing the actual operation process. Thank you again for your suggestions. We also hope our description is clear, and we look forward to more technical discussions and exchanges in the professional field in the future. Once again, thank you for your review work, which has provided important guidance for our research.

Lastly, we would like to express our sincere gratitude once again for your review and your high recognition of our article. It is our honor. Your recognition is the greatest motivation for us to persistently tackle scientific and technological challenges.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Revised version is satisfactory and may be accepted in its current form