Research on Critical Liquid-Carrying Model in Wellbore and Laboratory Experimental Verification

Round 1

Reviewer 1 Report

In this paper, the authors  established a new model of liquid film reversal based on Newton’s law of internal friction and gas-liquid two-phase force balance, with critical reverse point obtained using minimum gas-liquid interface shear force method. In this model, influences of the pipe angle on the liquid film thickness was considered, as well as the friction coefficient of the gas-liquid interface was refined based on the experimental data. Compared with the previous model, model in this work performs better considering its prediction discrepancy with experiment data less than 10%, which shows the model can be used to calculate the critical liquid-carrying flow rate of gas wells. Outcome of this work provides better understanding of liquid loading mechanism. The following corrections should be done before further processing;

1- Abstract section should be rewritten more scientifically by presenting results in more detail. It is really non-informative in the present form

2- The following references are recommended to cite in section 1

• Experimental investigation and mathematical modeling of gas diffusivity by carbon dioxide and methane kinetic adsorption
• A new wellbore fluid load diagnosing model based on the energy conservation law.
• Thermodynamic effects of cycling carbon dioxide injectivity in shale reservoirs
• Calculating Model of Frictional Pressure Drop for Gas Well During Foam Drainage.
• Experimental and modeling study of onset of liquid accumulation.
• Mathematical modeling of injectivity damage with oil droplets in the waste produced water re-injection of the linear flow

3- Literature review is really poor and should be compared to the novelty of your work one by one. For example, say ...et al... did this and we present this. why is different and what are the novelties. It is not acceptable to say just the novel points without any comparison.

4- Change section 2 as Governing equations

5- Limitations of the work should be added and discussed.

Author Response

In this paper, the authors established a new model of liquid film reversal based on Newton’s law of internal friction and gas-liquid two-phase force balance, with critical reverse point obtained using minimum gas-liquid interface shear force method. In this model, influences of the pipe angle on the liquid film thickness was considered, as well as the friction coefficient of the gas-liquid interface was refined based on the experimental data. Compared with the previous model, model in this work performs better considering its prediction discrepancy with experiment data less than 10%, which shows the model can be used to calculate the critical liquid-carrying flow rate of gas wells. Outcome of this work provides better understanding of liquid loading mechanism. The following corrections should be done before further processing:

Comment 1: Abstract section should be rewritten more scientifically by presenting results in more detail. It is really non-informative in the present form.

Response 1: Following the reviewer’s suggestion, the abstract has been revised and detailed research results are presented.

Comment 2: The following references are recommended to cite in section 1

• Experimental investigation and mathematical modeling of gas diffusivity by carbon dioxide and methane kinetic adsorption.
• A new wellbore fluid load diagnosing model based on the energy conservation law.
• Thermodynamic effects of cycling carbon dioxide injectivity in shale reservoirs.
• Calculating Model of Frictional Pressure Drop for Gas Well During Foam Drainage.
• Experimental and modeling study of onset of liquid accumulation.
• Mathematical modeling of injectivity damage with oil droplets in the waste produced water re-injection of the linear flow.

Response 2: Following the reviewer’s suggestion, in section 1 of the manuscript, we have added references to the research methods or results of the above articles.

Comment 3: Literature review is really poor and should be compared to the novelty of your work one by one. For example, say ...et al... did this and we present this. why is different and what are the novelties. It is not acceptable to say just the novel points without any comparison.

Response 3: Sorry to bring you a bad reading experience, The introduction of the manuscript has been modified accordingly, and the comparison between this work and other studies has been added.

Comment 4: Change section 2 as Governing equations.

Response 4: Following the reviewer’s suggestion, the title of the second part of the manuscript was changed to Governing equations.

Comment 5: Limitations of the work should be added and discussed.

Response 5: At the end of the paper, the authors added the analysis of the limitations of this work and pointed out the direction of further research.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

I read carefully your very interesting manuscript under the title “Research on critical liquid-carrying model in wellbore and laboratory experimental verification”. The liquid loading in gas wells can cause serious problems in well production, and the prediction of the liquid loading on certain well required an accurate model. Although today there are few models developed by different authors, their accuracy significantly depends on well condition as well as other specific parameters like well trajectory, well construction, etc. With this comprehensive research authors tried developing a new model, validate it and compare it with other models and results obtained by different authors. Regarding your work, I have two general comments:

• although your work is well structured, in my opinion missing very important part related to the difference between your model and model developed by other authors especially in the theoretical part of your work;
• some terms like superficial liquid velocity, superficial gas velocity, critical liquid-carrying gas velocity, , should be explained more in detail. This is very important especially for readers who are not so familiar with oil and gas production technology, as well as with specific problems in gas production and liquid loading.

Also, I have few suggestions for improving the quality of your manuscript as follows:    

• lines 2-3: lower or upper case letter;
• line 32: “gas cannot carry out only the formation water.” or liquid?
• line 33: please replace [2,3,4,] with [2-4];
• line 90: Upper case letter in the title;
• lines 118-119: you have the same title for x- and y- axis, please check!
• line 195: Is Belforid18 author name or company name?
• lines 237-238: please separate value and unit of measurement for pipe diameter;
• line 244: in petroleum engineering, we use 0 degrees for vertical well and 90 degrees for horizontal well;
• line 287: please separate value and unit of measurement for pipe diameter;
• line 315: in table 1. you have gas-to-liquid-ratio in m³/m³, and in your text on page 8. your defined liquid-to-gas ratio as the ratio of superficial liquid velocity and superficial gas velocity; Can you explain that?
• line 328: „:“?

Best regards,

Reviewer

Author Response

I read carefully your very interesting manuscript under the title “Research on critical liquid-carrying model in wellbore and laboratory experimental verification”. The liquid loading in gas wells can cause serious problems in well production, and the prediction of the liquid loading on certain well required an accurate model. Although today there are few models developed by different authors, their accuracy significantly depends on well condition as well as other specific parameters like well trajectory, well construction, etc. With this comprehensive research authors tried developing a new model, validate it and compare it with other models and results obtained by different authors. Regarding your work, I have two general comments.

Comment 1: although your work is well structured, in my opinion missing very important part related to the difference between your model and model developed by other authors especially in the theoretical part of your work.

Response 1: The basic idea of theoretical research is to combine Newton's internal friction law and balance equation to derive. The difference from the existing model is that this work incorporates the wellbore inclination angle parameter, so that the model can be applied to more conditions. And through the experimental results, a correction was made to the interface friction coefficient, and finally a new prediction model was obtained. With the help of numerous field wellbore data, the prediction effect of the new model and the existing models has also been compared, and the comparison results show that the prediction effect of the model proposed in this work is better than others.

Comment 2: some terms like superficial liquid velocity, superficial gas velocity, critical liquid-carrying gas velocity, should be explained more in detail. This is very important especially for readers who are not so familiar with oil and gas production technology, as well as with specific problems in gas production and liquid loading.

Response 2: Following the reviewer’s suggestion, definitions and explanations of some terms have been added to the corresponding positions in the text, such as lines 53-55, lines 116-117, etc.

Comment 3: lines 2-3: lower or upper case letter

Response 3: Following the reviewer’s suggestion, the case letters of article titles have been unified.

Comment 4: line 32: “gas cannot carry out only the formation water.” or liquid?

Response 4: Under this condition, gas can not carry the liquid out of the formation. The water in the formation written by the author is not accurate enough, so it has been corrected.

Comment 5: line 33: please replace [2,3,4,] with [2-4]

Response 5: Following the reviewer’s suggestion, the citation format of references in the main text has been corrected.

Comment 6: line 90: Upper case letter in the title

Response 6: Thank you for your reminder, the first letter of the title has been unified into upper case.

Comment 7: lines 118-119: you have the same title for x- and y- axis, please check!

Response 7: Sorry to bring you a bad reading experience, the title of y- axis in Figure 1 has been corrected.

Comment 8: line 195: Is Belforid18 author name or company name?

Response 8: The reference 18 cited here is authored by Belforid. Due to a writing error, the reference number lacks ‘[ ]’ and has been corrected.

Comment 9: lines 237-238: please separate value and unit of measurement for pipe diameter

Response 9: Following the reviewer’s suggestion, it has been standardized and written. The authors have separated the value and the unit of measurement.

Comment 10: line 244: in petroleum engineering, we use 0 degrees for vertical well and 90 degrees for horizontal well.

Response 10: Thank you for your suggestion. The vertical well is represented by 0°. Figure 4 and the corresponding text part have been corrected.

Comment 11: line 287: please separate value and unit of measurement for pipe diameter

Response 11: Following the reviewer’s suggestion, it has been standardized and written. The authors have separated the value and the unit of measurement.

Comment 12: line 315: in table 1. you have gas-to-liquid-ratio in m3/m3, and in your text on page 8. your defined liquid-to-gas ratio as the ratio of superficial liquid velocity and superficial gas velocity; Can you explain that?

Response 12: Sorry to bring you a bad reading experience. In fact, the two in this article mean the same meaning. The gas-liquid ratio is defined as the ratio of the gas superficial velocity to the liquid superficial velocity. The unit in the table 1 is written as m³/m³, which means the ratio calculated from the gas-liquid flow rate. The expression method is more convenient in experimental research. Under the same pipe diameter, the ratio of gas-liquid flow is equal to the ratio of superficial velocity, because the superficial velocity represents the converted velocity of the single-phase fluid flowing through the entire pipe diameter. In order to avoid similar disputes, the author removed the unit of gas-liquid ratio in the table and presented it in the form of ratio.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear authors,

I read revised version of your manuscript, and I am fully satisfied with improvements you made.

Best regards,

reviewer