Experimental Study and Numerical Simulation of W/O Emulsion in Developing Heavy Oil Reservoirs

Round 1

Reviewer 1 Report

This paper presents interesting results about the W/O emulsion flooding. However, I have some suggestions to the authors, which are as follows:

General Comments:

1) Referencing and citing should be improved. The authors have made many claims in the introduction section, without citing proper references. 

2) Some parts of the methodology section is written like a lab manual. It should be written as research article style. 

3) The authors should clearly present a reason why they selected to inject emulsion, instead of studying the possibility of in-situ generation of emulsion under these conditions. 

Specific Comments:

1) Line 32, The author should state the reason for selecting the used permeability contrast. 

2) Line 52, What is the significance of food medicine and other fields to petroleum engineering. This paper is related to engineering so the readers will also be from engineering, therefore the examples should be related to engineering. 

3) Line 119, What is the motivation of selection of the conditions used in this study? The author should provide any reference or discuss the motivation.. 

4) Line 185, The authors should also provide the reason of this low flow rate used for oil injection, and for water injection. The authors should also discuss about the capillary end effects. Also for coreflood experiments, the authors should present the pressure data along with the recovery factor. 

5) Line 189, Please have some discussion about the objective of 12 hrs of aging. What was the objective of aging here? 

6) Section 2.2.4. More details about the investigation of emulsion flooding. 

7) Line 225, There is only one RPM greater than 7000, so how can we make this claim? "The emulsion is basically stable after 7000 r/min".

8) What is the criteria of stable emulsion for water bleeding rate? Please state clearly in the paper. 

9) More explanation about the physical phenomenon should be presented in section 3.1.1. The authors are just presenting the data without explaining any physical phenomenon. 

10) The numerical simulation section is very brief. The authors shall explain how the lab experimental results were used in the simulation, and also present the relative permeability curve. 

 

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-2012187), and responded, point by point to the comments mentioned on the page, and line numbers. The revised parts are marked in red to highlight, the amendments and deleted contents are marked with gray strike-out font to highlight deleted sections. "Revision, changes marked" see the attachment.

Reviewer #1:

General Comments:

[Comment 1]: Referencing and citing should be improved. The authors have made many claims in the introduction section, without citing proper references.

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

[Changes]: Please see Line 64-93 on Page 2, Line 626-645 on Page 20 in the "Revision, changes marked".

[Comment 2]: Some parts of the methodology section is written like a lab manual. It should be written as research article style.

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

[Changes]: Please see Line 234-252 on Page 6 in the "Revision, changes marked".

[Comment 3]: The authors should clearly present a reason why they selected to inject emulsion, instead of studying the possibility of in-situ generation of emulsion under these conditions.

[Reply 3]: Thank you for your careful review. In-situ self-emulsification requires sufficient formation fluid shear. For the actual formation, because it has a large enough pore volume to meet the conditions required for self-emulsification. For the indoor experiment of core displacement, because the model is a proportional model, the pore volume is reduced by a very large multiple relative to the actual formation, so it can not achieve sufficient fluid shear to form self-emulsification. Therefore, this paper chooses to inject the prepared emulsion to equivalent the effect of self-emulsification. At the same time, it can also simplify the indoor experimental steps, more accurately control the experimental variables, reduce the experimental error, and effectively highlight the profile control effect relative to waterflooding.

Specific Comments:

[Comment 1]: Line 32, The author should state the reason for selecting the used permeability contrast.

[Reply 1]: Thanks for your valuable comment. In the process of mining heterogeneous reservoirs, the permeability of different seepage channels is quite different. There is a permeability contrast, which will cause the displacement fluid to flow only in the high seepage channel and cannot displace the crude oil in the low seepage channel. Therefore, we consider the emulsion plugging ability under different permeability contrast.

[Changes]: Please see Line 50-54 on Page 2 in the "Revision, changes marked".

[Comment 2]: Line 52, What is the significance of food medicine and other fields to petroleum engineering. This paper is related to engineering so the readers will also be from engineering, therefore the examples should be related to engineering.

[Reply 2]: Thanks for your valuable comment. Emulsions in food, medicine and other fields can provide ideas for their application in the oil field, but I think your opinion is also very reasonable, I intend to delete this sentence.

[Changes]: Please see Line 72-73 on Page 2 in the "Revision, changes marked".

[Comment 3]: Line 119, What is the motivation of selection of the conditions used in this study? The author should provide any reference or discuss the motivation.

[Reply 3]: Thanks for your valuable suggestion. Because the actual reservoir temperature is 60 degrees Celsius, stirring speed of 4000 r/min can be equivalent to the shear force in the reservoir formation, and in the stirring time of 60min and water content of 40 %, the preparation of the emulsion and the actual reservoir emulsion particle size similar. So the basic experimental conditions are: stirring speed 4000 r/min, stirring time 60 min, temperature 60 ^oC, and water cut of emulsion set at 40 %.

[Changes]: Please see Line 143-146 on Page 4 in the "Revision, changes marked".

[Comment 4]: Line 185, The authors should also provide the reason of this low flow rate used for oil injection, and for water injection. The authors should also discuss about the capillary end effects. Also for coreflood experiments, the authors should present the pressure data along with the recovery factor.

[Reply 4]: Thank you for your careful review. Saturated oil in the process, with the use of low flow rate injection, can make the saturated front more uniform, driving out most of the water to ensure that the initial oil saturation is greater than 90 %. The capillary end effect has a certain influence on the displacement process, but the injection rate is consistent when the oil is saturated in each group of experiments, so there is the same capillary end effect. In these experiments, it is not a variable and will not affect the comparison between the experimental results of each group. For the double-pipe displacement experiment in this paper, the purpose is to study the profile control of emulsion, so the fractional flow rate is the main characterization parameter, as shown in Figure 18 and Figure 20, and according to Darcy 's law, the change trend of fractional flow rate is the change trend of pressure difference, so it is not necessary to give the data of pressure and flow rate at the same time. On the data of oil recovery, as shown in Figure 19 and Figure 21, this paper has given the relationship curve between oil displacement efficiency and water cut. Oil displacement efficiency is more suitable for characterizing the oil displacement effect of laboratory experiments than oil recovery.

[Comment 5]: Line 189, Please have some discussion about the objective of 12 hrs of aging. What was the objective of aging here?

[Reply 5]: Thank you for your careful review. Because the core is saturated with crude oil under a certain pressure difference, after the saturation is completed, the pressure in the model does not tend to be stable, so it needs to stand for a certain period of time so that the fluid can pass through enough time until the whole model becomes a uniform pressure system, which is the significance of crude oil aging.

[Comment 6]: Section 2.2.4. More details about the investigation of emulsion flooding.

[Reply 6]: Thank you for your valuable comment. We have added a more detailed description in the section of "Investigation of emulsion flooding" of the article according to your comments and suggestions.

[Changes]: Please see Line 269 -296 on Page 7 in the "Revision, changes marked".

[Comment 7]: Line 225, There is only one RPM greater than 7000, so how can we make this claim? "The emulsion is basically stable after 7000 r/min".

[Reply 7]: Thanks for your valuable suggestion. The stability of the emulsion is related to the water bleeding rate of the emulsion. The prepared emulsion is placed in a measuring cylinder, and the temperature required for the experiment is maintained for a certain period of time. The volume of water separated from the emulsion is recorded. General provisions of the experiment, standing for 30 days, the drainage rate of less than 5 %, judged to be relatively stable. From Figure 2, the water bleeding rate varies greatly with stirring speed when it is less than 7000 r/min. When the stirring speed is greater than or equal to 7000 r/min, it is obvious that the water bleeding rate is less than 5 %, so it is judged to be stable after 7000 r/min. Maybe because my description is not clear enough, it leads to your question about this. A clearer description has been added in the corresponding part of the paper.

[Changes]: Please see Line 177-183 on Page 4 in the "Revision, changes marked".

[Comment 8]: What is the criteria of stable emulsion for water bleeding rate? Please state clearly in the paper.

[Reply 8]: Thanks for your valuable comment. The water bleeding rate is equal to the ratio of the volume of the precipitated water to the volume of the emulsion. General experiments that, after 30 days of standing emulsion, if the water bleeding rate is less than 5 %, it is considered to be relatively good stability, and to stand for the same time different emulsions, in which the smaller the water bleeding rate represents the better its stability.

[Changes]: Please see Line 180-183 on Page 4 in the "Revision, changes marked".

[Comment 9]: More explanation about the physical phenomenon should be presented in section 3.1.1. The authors are just presenting the data without explaining any physical phenomenon.

[Reply 9]: Thanks for your valuable suggestion. I showed the photos taken during the experiment in this paper. Figure 2 shows the precipitation of water after the prepared emulsion was allowed to stand for a period of time. It can be seen from the figure that there is water precipitation at the bottom of the measuring cylinder, and the water bleeding rate is equal to the ratio of the volume of water precipitated from the emulsion to the volume of the emulsion itself. Under each experimental condition, the change of water bleeding rate with time was calculated, and then the corresponding curve was made, and then the stability of the emulsion was analyzed.

[Changes]: Please see Line 300-303 on Page 7, Line 304-311 on Page 8 in the "Revision, changes marked".

[Comment 10]: The numerical simulation section is very brief. The authors shall explain how the lab experimental results were used in the simulation, and also present the relative permeability curve.

[Reply 10]: Thanks for your valuable comment. First of all, for the numerical model part, the reservoir parameters used in the numerical model establishment comprehensively consider the optimization results of the emulsion stability study experiment and the model parameters of the core displacement experiment. Then, after the emulsion flooding prediction of the numerical model, the prediction results are matched with the experimental data of core displacement experiment. Therefore, the experiment in this paper is applied to the numerical model by establishing the model and matching the results. The relative permeability curve data of the numerical model has been added to the numerical simulation part in the form of pictures.

[Changes]: Please see Line 572 on Page 18, Line 577-579 on Page 19 in the "Revision, changes marked".

Author Response File: Author Response.docx

Reviewer 2 Report

The authors studied the emulsion system as a heavy oil reservoir. It's a good study. However, in my opinion, some modification is needed.

Major point: The novelty. Please more discuss for me.

Minor points:

The abstract is long. Can summarize its method section.

The introduction is good. However, I think the author can use some more recent studies as well.

Experimental: The authors should mention the trade names for all materials and devices.

How about the time effects on the stability? Did the authors study it? Besides, please mention the time duration of all experiments.

What is the reason for the two materials sections? I think your paper should have one materials section.mix them.

What was the statistical analysis method?

Results:

Use Standard deviation and error bars for all graphs.

 

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-2012187), and responded, point by point to the comments mentioned on the page, and line numbers. The revised parts are marked in red to highlight, the amendments and deleted contents are marked with gray strike-out font to highlight deleted sections. "Revision, changes marked" see the attachment.

Reviewer #2:

[Comment 1]: The novelty. Please more discuss for me.

[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.(1) The stability of emulsion is analyzed by combining several factors, and the influence of each factor on the droplet size of emulsion is studied by visual particle size analysis.(2) On the basis of the analysis of emulsion stability and emulsion particle size distribution, the profile control and plugging capacity of W/O emulsion in heterogeneous reservoirs is studied by double-pipe core displacement experiment.(3) The physical simulation experiment parameters are applied to the numerical model. Through numerical simulation, it is found that when the water content of emulsion flooding is between 40 % and 60 %, the growth rate of water cut slows down, which has a high fitting degree with the physical experiment results.

[Comment 2]: The abstract is long. Can summarize its method section.

[Reply 2]: Thanks for your valuable comment. The abstract of the article has been revised and rewritten.[Changes]: Please see Line 35~47 on Page 1, Line 48~54 on Page 2 in the "Revision, changes marked"

[Comment 3]: The introduction is good. However, I think the author can use some more recent studies as well.

[Reply 3]: Thank you for your constructive suggestion. The "introduction" section has been revised according to your suggestion.

[Changes]: Please see Line 64-93 on Page 2, Line 626-645 on Page 20 in the "Revision, changes marked".

[Comment 4]: Experimental: The authors should mention the trade names for all materials and devices.

[Reply 4]: Thanks for your valuable comment. We have added a more detailed description in the section "Materials and devices" of the article according to your comments and suggestions. Materials and devices for emulsification experiments in "2.1.1 Materials and devices"; emulsion flooding experiment material in "2.2.1 Materials", experimental equipment in "2.2.3 Experimental apparatus". Maybe because my description is not clear enough, it leads to your question about this.

[Changes]: Please see Line 126~133 on Page 3, Line 195~211 on Page 5 in the "Revision, changes marked".

[Comment 5]: How about the time effects on the stability? Did the authors study it? Besides, please mention the time duration of all experiments.

[Reply 5]: Thanks for your valuable comment. In the emulsion stability experiment in this paper, the emulsion was prepared by stirring for 60 min, and then standing for 40 days under the set experimental conditions. The water bleeding rate at multiple time points was recorded in turn, and the relationship curve between water bleeding rate and time was drawn, as shown in Figure 3, Figure 5, Figure 7, Figure 9 and Figure 11. It can be seen from the figure that in the initial stage of the emulsion standing, the water bleeding rate changes greatly as a whole. With the extension of standing time, the change trend of water bleeding rate decreases slowly, until about 30 days, the water bleeding rate tends to be stable, with almost no change. The duration of the experiment has been indicated in the corresponding part of the text according to your requirements.

[Changes]: Please see Line 150~170 on Page 4 in the "Revision, changes marked".

[Comment 6]: What is the reason for the two materials sections? I think your paper should have one materials section. mix them.

[Reply 6]: Thank you for your careful review. We understand what you mean, because there are two experiments in this article. One is the Emulsification experiment and the other is the Emulsion flooding experiment. If I mix them up, it will look messy. Materials and devices for Emulsification experiments at "2.1.1 Materials and devices". Emulsion flooding experiment material in "2.2.1 Materials", experimental equipment in "2.2.3 Experimental apparatus".

[Comment 7]: What was the statistical analysis method?

[Reply 7]: Thank you for your careful review. In this paper, the statistical emulsion droplet size is realized by Image-Pro Plus software. First, photos of the emulsion particle size taken under the microscope are uploaded to the Image-Pro Plus software. Secondly, set the scale length of the picture. Automatic analysis will then be carried out, the "Statistics" section can be the maximum particle size, minimum, average, standard deviation and other data. The "Histogram" part can obtain the particle size distribution histogram.

[Comment 8]: Use Standard deviation and error bars for all graphs.

[Reply 8]: Thank you for your constructive suggestion. The figures have been revised by using standard deviation and error bars according to your suggestion.

[Changes]: Please see Page 13~15 in the "Revision, changes marked".

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors, 

Thank you for your efforts to incorporate the suggested modifications. The paper is acceptable in the current form. 

Author Response

Dear Editors and Reviewers,

Thank you for your careful review and affirmation.

Author Response File: Author Response.docx