Experimental Study on Improvement Mechanism of Electric Heating-Assisted Cyclic Steam Stimulation of Horizontal Well

Round 1

Reviewer 1 Report

What is the novelty of the paper?

The manuscript is not well structure.

The experimental setup, measurement techniques are not well presented.

The scientific soundness of the paper is very low.

An actual photo of the experimental setup is to be added.

How the temperature profile of fig 3 is realized? how many thermocouples are used ? what are their locations?

What is the interest of the presented mathematical model ? (since the work is experimental)

An experimental uncertainty study is to be performed.

The conclusion is to be rewritten.

The English level is relatively low.

Author Response

Dear Editors and Reviewers,

    Thank you very much for your helpful comments and suggestions. According to your comments of reviewers and editor, we have carefully and meticulously revised the manuscript (applsci-1973066), and responded, point by point to the comments mentioned the page, and line numbers. The revised parts are marked in red to highlight, the amendments and deleted contents are marked with strikethrough to highlight deleted sections. "Revision, changes marked" see the attachment

Reviewer #1:

[Comment 1]: What is the novelty of the paper?

[Reply 1]: Thank you for your careful review. In order to illustrate novelty and target of our study, previous studies have been summarized and cited in the manuscript. Comparisons between our study and previous investigations were also conducted in the “introduction” section. The novelty of the paper: (1) On the basis of considering co-heating of electric heating and steam, a mathematical model of reservoir heating assisted by electric heating for Cyclic-Steam-Stimulation of horizontal Wells is established in stages. (2) The accuracy of the analytical formula is verified successfully by experiments and mathematical model fitting. (3) Through several groups of macroscopic model experiments and typical well group prediction, the enhance oil recovery mechanism and potential of electric heating assisted horizontal well Cyclic-Steam-Stimulation at each stage is comprehensively revealed

[Comment 2]: The manuscript is not well structure.

[Reply 2]: Thanks for your valuable comment. We have adjusted the structure of the article according to your comments and suggestions.

[Changes]: Please see Lines 22~36 on Page 9, Line 19~33 on Page 10 in the "Revision, changes marked".

[Comment 3]: The experimental setup, measurement techniques are not well presented.

[Reply 3]: Thanks for your valuable suggestion. A detailed introduction of corresponding experimental equipment and measurement technology have been added to the section of “Experimental equipment and parameters” in the revised manuscript.

[Changes]: Please see Line 29~38 on Page 6, Line 1-32 on Page 7 in the "Revision, changes marked".

[Comment 4]: The scientific soundness of the paper is very low.

[Reply 4]: Thank you for your careful review. In this paper, a mathematical model of electric heating assisted horizontal well Cyclic-Steam-Stimulation is presented according to the mathematical model of conventional horizontal well Cyclic-Steam-Stimulation put forward by predecessors. Then, the accuracy of the proposed mathematical model is verified by fitting the wellbore temperature field obtained from the laboratory test of electric heating assisted horizontal well Cyclic-Steam-Stimulation with the calculation results of the mathematical model. Meanwhile, several groups of conventional horizontal well Cyclic-Steam-Stimulation and electric heating assisted horizontal well Cyclic-Steam-Stimulation experiments were carried out, and the prediction and recovery factor of typical well groups were compared, revealing the key mechanism and potential of electric heating for enhance oil recovery. Article has a relatively rigorous scientific rationality, but because of the irrationality of previous articles structure, the logic of this paper is not clear enough, causing you to question the scientific rationality. The manuscript has been revised according to your comments and suggestions. I hope the revised manuscript will present you with better scientific logic and rationality.

[Comment 5]: An actual photo of the experimental setup is to be added.

[Reply 5]: Thanks for your valuable suggestion. The physical photo of the experimental setup has been added to the section of “Experimental equipment and parameters” in the revised manuscript.

[Changes]: Please see Line 1~7 on Page 8 in the "Revision, changes marked".

[Comment 6] How the temperature profile of fig 3 is realized? how many thermocouples are used? what are their locations?

[Reply 6]: Thank you for your careful review. For the electric heating assisted horizontal well Cyclic-Steam-Stimulation experiments, we used a relatively advanced multi-point measuring thermocouple Omega, with five temperature sensors evenly distributed on each thermocouple. 6 thermocouples with 30 sensors are uniformly deployed from the center to the inner wall inside the model. Because the cylindrical model is completely centrosymmetric, the temperature profile of the model can be measured effectively. And then, temperature profile is output by monitoring computer, electric heating data acquisition software. The introduction of thermocouple has been added to the section of “Experimental equipment and parameters” in the revised manuscript.

[Changes]: Please see Line 1~32 on Page 7 in the "Revision, changes marked".

[Comment 7]: What is the interest of the presented mathematical model? (Since the work is experimental)

[Reply 7]: Thank you for your careful review. Experiment is a very important part of this paper, but this paper is not only about the experimental content. This paper aims to establish the reservoir heating mathematical model of electric heating assisted horizontal well Cyclic-Steam-Stimulation on the basis of the conventional horizontal well mathematical model proposed by predecessors, and then verify the accuracy of the proposed mathematical model through the experimental part. It provides a reliable theoretical formula model for the study of electric heating assisted Cyclic-Steam-Stimulation in horizontal wells. It is the interest of the presented mathematical model.

[Comment 8]: An experimental uncertainty study is to be performed.

[Reply 8]: Wellbore heat loss, thermal conductivity of horizontal well wall, and the difference between the model and the actual formation are all experimental uncertainties. Firstly, the thermal compensation insulation sleeve has reduced the wellbore heat loss to a minimum. Secondly, since the heating resistance is placed outside the horizontal well pipe in the model, the influence range of wellbore thermal conductivity is almost negligible. Finally, the main body of the experimental model is a proportional model corresponding to the actual formation. The verification of the mathematical model of Cyclic-Steam-Stimulation in horizontal Wells assisted by electric heating and the study of the key mechanism are fully satisfied. Therefore, the influence of experimental uncertainty on the research content of the paper is in the negligible range. The experimental uncertainty study has been added to the section of “Physical simulation experiments for E-CSS of horizontal well” in the revised manuscript.

[Changes]: Please see Line 8~20 on Page 9 in the "Revision, changes marked".

[Comment 9]: The conclusion is to be rewritten.

[Reply 9]: Thanks for your valuable suggestion. The conclusion of the article has been revised and rewritten.

[Changes]: Please see Line 11~30 on Page 17 in the "Revision, changes marked".

[Comment 10]: The English level is relatively low.

[Reply 10]: Thanks for your valuable comment. The English of the article has been revised and polished accordingly.

[Changes]: Please see Page 1-18 in the "Revision, changes marked".

Author Response File: Author Response.docx

Reviewer 2 Report

In this article the authors resolve the issues of high porous medium flow resistance, low oil production rate, high oil decline rate, and low oil recovery factor for Cyclic-Steam-Stimulation (CSS) of horizontal wells in heavy oil reservoirs, the CSS method assisted by electric heating (E-CSS) of horizontal wells was proposed in this study. Combining the heat from electric heating and steam during E-CSS, the analytical model of formation temperature rise was established for the three phases of electric-assisted CSS (i.e., injection, soaking, production), and physical experiments were carried out to compare the performance of conventional CSS and E-CSS. The experimental results were used to validate the analytical model and reveal the key electric heating mechanism on the horizontal CSS performance.

I recommended for publication after minor revision.

My observations are:

1. Remove the reference blocks from the introduction section. Write the importance of each paper of the researcher instead of blocks. The introduction section will more informative.

2. In the exponential integral function (see after Eq. (1)), the function exp(t)/t has a singularity at t=0. How you will justify mathematically and physically?

3.  Add commas and dots in the appropriate places after every mathematical equation.

4. Figure 2 must be high quality.

Author Response

Dear Editors and Reviewers,

    Thank you very much for your helpful comments and suggestions. According to your comments of reviewers and editor, we have carefully and meticulously revised the manuscript (applsci-1973066), and responded, point by point to the comments mentioned the page, and line numbers. The revised parts are marked in red to highlight, the amendments and deleted contents are marked with strikethrough to highlight deleted sections. 

Reviewer #2:

In this article the authors resolve the issues of high porous medium flow resistance, low oil production rate, high oil decline rate, and low oil recovery factor for Cyclic-Steam-Stimulation (CSS) of horizontal wells in heavy oil reservoirs, the CSS method assisted by electric heating (E-CSS) of horizontal wells was proposed in this study. Combining the heat from electric heating and steam during E-CSS, the analytical model of formation temperature rise was established for the three phases of electric-assisted CSS (i.e., injection, soaking, production), and physical experiments were carried out to compare the performance of conventional CSS and E-CSS. The experimental results were used to validate the analytical model and reveal the key electric heating mechanism on the horizontal CSS performance.

I recommended for publication after minor revision.

My observations are:

[Comment 1]: Remove the reference blocks from the introduction section. Write the importance of each paper of the researcher instead of blocks. The introduction section will more informative.

[Reply 1]: Thank you for your constructive suggestion. The “introduction” section has been revised according to your suggestion.

[Changes]: Please see Line 8~21, 32~46 on Page 2 in the "Revision, changes marked".

[Comment 2]: In the exponential integral function (see after Eq. (1)), the function exp(t)/t has a singularity at t=0. How you will justify mathematically and physically?

[Reply 2]: Thanks for your careful review. In the mathematical sense, when t =0，-r²/4aλt = -∞, at this point, exponential integral function Ei(-r²/4aλt) = 0， so T= T_i . It physically means that the reservoir temperature without heating is equal to the initial reservoir temperature.

[Comment 3]: Add commas and dots in the appropriate places after every mathematical equation.

[Reply 3]: Thanks for your valuable suggestion. For the equation listed individually, I strictly follow the journal format requirements. And equation in the literal line has been revised according to your suggestion.

[Changes]: Please see Page 4~6, Page 12~13 in the "Revision, changes marked".

[Comment 4]: Figure 2 must be high quality.

[Reply 4]: Thanks for your valuable suggestion. Figure 2 has been revised to ensure its high quality.

[Changes]: Please see Line 1~7, on Page 8 in the "Revision, changes marked".

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Accept as it is