Mechanical Behavior and Optimization of Tubing String with Expansion Joint during Fracturing in HTUHP Wells

Round 1

Reviewer 1 Report

The proposed article is a continuation and development of the results on modeling tubing with compensators, obtained and published by the authors in 2017-2022.

In the introduction, the current state of the problem is sufficiently given and the main results of previous studies are presented.

The main result of the article is a finite element model of a tubing string with compensators in the entire section of the well and an analysis of the results obtained on the basis of this model.

To study the effect of a compensator on the mechanical behavior of a tubing string under various hydraulic fracturing conditions, two types of structures were calculated and compared: a string with a compensator and a string without a compensator.

The presented figures and tables well illustrate the results obtained by the authors.

In conclusion, the main results of the article are presented. In my opinion, the article is of undoubted interest for applications and can be published in prewsent form.

Author Response

• Comment: The proposed article is a continuation and development of the results on modeling tubing with compensators, obtained and published by the authors in 2017-2022. In the introduction, the current state of the problem is sufficiently given and the main results of previous studies are presented. The main result of the article is a finite element model of a tubing string with compensators in the entire section of the well and an analysis of the results obtained on the basis of this model. To study the effect of a compensator on the mechanical behavior of a tubing string under various hydraulic fracturing conditions, two types of structures were calculated and compared: a string with a compensator and a string without a compensator. The presented figures and tables well illustrate the results obtained by the authors. In conclusion, the main results of the article are presented. In my opinion, the article is of undoubted interest for applications and can be published in present form.

Response: Thanks for your high evaluation for our paper and recommendations for publication. We also appreciate your positive and constructive comments regarding our manuscript, and we have made careful modifications on the original manuscript based on major assessment with results from other authors.

Reviewer 2 Report

The article is interesting by considering the volume of work and data obtained. Some recommendations refers to:

• Use some references for the equations 1 to 9. Also, even if the elements are explained at the first part of the article, the ”key” parameters must be explained also here.
• The methodologies used, the devices and softwares must be clearly presented in separate paragraphs (maybe it is better to rearrange the point 3).
• Use some references for points 3.1. and 3.2.
• Some parts from the article with data are not sufficient discussed (eg. Figures 3,4 and Table 1).
• Please use some data in conclusions.

Author Response

Review #2：The article is interesting by considering the volume of work and data obtained. Some recommendations refers to:

• Comment: Use some references for the equations 1 to 9. Also, even if the elements are explained at the first part of the article, the ”key” parameters must be explained also here.

Response: The advice suggested by reviewer is very accurate and reasonable. Therefore, we have revised the title (see the revised paper):

• Comment: The methodologies used, the devices and softwares must be clearly presented in separate paragraphs (maybe it is better to rearrange the point 3).

Response: Thanks for reviewer’s reasonable advice. Therefore, we have revised the title (see the Point 3 in the paper):

• Comment: Use some references for points 3.1. and 3.2.

Response: Thanks for reviewer’s reasonable advice. As reviewer suggested, we have revised the points 3.1. and 3.2 in the paper.

• Comment: Some parts from the article with data are not sufficient discussed (eg. Figures 3,4 and Table 1).

Response: We are very sorry for our negligence of the problem. The advice suggested by reviewer is very accurate and reasonable, therefore, we have revised related contents in the abstract:

“The mechanical property results of 13Cr110 can be characterized from the stress-strain curve in Fig. 3, and the mechanical parameters are listed in Table. 1. According to the curve, it can be seen that this material presents obvious elastic and plastic stages, and when the strain reaches about 6%, the stress of the material reaches the tensile strength σu. Based on the curve in Fig. 3, several key parameters can be extracted in Table. 1, The it can be found that the tested average yield strength σ_y of 13Cr110 is 831.76MPa, average ultimate strength σ_u is 922.46MPa and the average percentage elongation δ is 19.16%. Meanwhile, the test results of material strength at different temperatures can be presented in Fig. 4. It can be seen that the yield strength, tensile strength and elongation of the material decrease obviously with the increase of temperature. The yield strength σ_y of 13Cr110 under different temperatures (50℃, 75 ℃, 100 ℃, 125 ℃ and 150 ℃) are 831.7MPa, 805.8MPa, 786.5MPa, 765.3MPa and 742.7MPa respectively. The ultimate strength σ_u are 922.4MPa, 902.7MPa, 885.6MPa, 865.5MPa and 846.5MPa respectively. The percentage elongation δ are 19.16%, 18.01%, 17.20%, 16.11% and 14.99% respectively. These experimental results considering the strength change because the change in temperature are also extended to modelling the tubing string to obtain an accurate simulation.”

• Comment: Please use some data in conclusions.

Response: Thanks for reviewer’s reasonable advice, we have revised the describe in the paper. (see the conclusion in the revised paper).

Reviewer 3 Report

The paper assesses the evolution of internal forces in a steel tubing induced by the drop of temperature associated with medium flow during hydraulic fracturing. The results of a finite element analysis are presented for models with and without an expansion joint.

 

The paper is relatively clearly written, nevertheless its content resembles more an engineering report or a case study than a research article because its findings are quite specific system analysed and not universal. 

 

The section on the experimental part should be extended. What was the shape of the tensile strength specimens? Was the time of 10 min sufficient to heat the specimens to required temperature in the hot-air furnace? 

 

line 88: has not excited in previous research. - I do not understand this sentence.

line 227: can be seem as -> can be seen as

several places: tubingstring -> tubing string

missing articles on several places: on packer -> on the packer, of tubing -> of the tubing, etc.

Author Response

• Comment: The paper assesses the evolution of internal forces in a steel tubing induced by the drop of temperature associated with medium flow during hydraulic fracturing. The results of a finite element analysis are presented for models with and without an expansion joint. The paper is relatively clearly written, nevertheless its content resembles more an engineering report or a case study than a research article because its findings are quite specific system analysed and not universal..

Response: Thanks for your high evaluation for our paper. Indeed, the mechanical behavior of the tubing string with expansion joint in a HTUHP well has been studied. But, through a detailed study of an example, the influence law of expansion joint on the tubing string and the packer, hidden danger of expansion joint and important parameters of expansion joint are put forward to provide detailed theoretical reference and basis of expansion joint for field application, this case in our work is the carrier of our viewpoint. Meanwhile, our work is aimed at providing a research method and logical process and this approach can be applied as a typical process to tubing safety assessments in other wells.

• Comment: The section on the experimental part should be extended. What was the shape of the tensile strength specimens? Was the time of 10 min sufficient to heat the specimens to required temperature in the hot-air furnace?

Response: The advice suggested by reviewer is very accurate and reasonable. The “3. Experimental” has been rearranged and revised (see the revised paper), and the shape of the tensile strength specimens is presented in the paper. We have done a lot of tests and finite element simulation before, and the results show that when the diameter of the sample is less than 15mm, the time of 10 min is sufficient to heat the specimens to required temperature in the hot-air furnace,

• Comment: line 88: has not excited in previous research. - I do not understand this sentence.

Response: We are very sorry for our negligence of the problem. Considering the reviewer’s suggestion, we have reorganized the described in the Introduction (see the paper).

• Comment: line 227: can be seem as -> can be seen as; several places: tubingstring -> tubing string; missing articles on several places: on packer -> on the packer, of tubing -> of the tubing, etc.

Response: Thanks for reviewer’s reasonable advice. Considering the reviewer’s suggestion, we have revised the grammatical errors (see the paper).

Round 2

Reviewer 3 Report

The authors have addressed all issues pointed out in the previous review report. I consider the paper acceptable for publishing.