A Microfluidic Experiment on CO2 Injection for Enhanced Oil Recovery in a Shale Oil Reservoir with High Temperature and Pressure
Round 1
Reviewer 1 Report
The results (although very much qualitative) certainly make sense and are interesting. The overall logic is clear and reasonable. The manuscript is however poorly written.
The authors made deep review of modern problems and approaches of enhanced oil recover by huff-n-puff CO2 method. Nevertheless, information about competing and alternative approaches would be suitable for estimation.
229-233 lines postulate a linear expansion rate, but do not take into account the finite dissolution rate. At some point equilibrium will be approached. The lower the concentration gradients, the longer is the time needed to dissolve CO2 due to diffusion. How important is the linearity for conclusion of the paper.
252 Haines jump phenomena: references are needed.
An explanation of the analysis process and calculation of the amount of micro-residual oil after CO2 huff-n-puff in more details would positively influence the ability of readers understand and evaluate the work. I recommend adding it to the methods section.
Additionally, image processing methodology description needs the resolution of microscope and methods of oil-gas pixel classification. These crucial details would help to estimate the quantitative results of residual oil production.
The authors of the paper repeatedly mention the influence of the structure of the porous medium. However, mobilization mechanisms were described only on the scale of pore/channel/throat. Due to the Haines jump phenomena (which is described in the paper) it’s would be nice to estimate the structure of the porous sample.
Figure 15 should be in percentages, but it’s in fractions.
Due to the fact of seepage study by the authors, more details for Figure 11 should be provided. What frequency of image analysis was?
“…but the seepage mechanism research in the process of 60 CO2 huff-n-puff has not been clear with few studies”
Exactly, what studies?
Figures numbers are, most likely, shuffled out of order and referenced improperly starting from the Results section. Figure is 13 mentioned out of order
Brackets in equation (1) do not make much sense
Quite a lot sentences of over-explanation and duplicating of word (lines 63-65, 165, 266-267, 349-350 etc.) Enjoyed reading it. This paper describes the workflow of microscopic visualization experiment of enhanced oil recovery by huff-n-puff method with CO2 as a carrier gas.
The word “realize” is used improperly in many places and it’s not even possible to guess what the authors mean
“law of oil-gas two-phase flow in shale reservoirs”. Which law? There several sentences like that
Overall, the English is really really poor? Far below reasonable for understanding level.
Mandatory major revision. Right now the manuscript is not publishable.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
My suggestions, comments and recommendations are in the following paragraphs.
- The title of the manuscript sounds informative and attractive.
- Abstract. Please be careful in the abstract about the use of abbreviations. Their meaning may seem obvious, but they can cause a lot of confusion. Therefore, please avoid using the abbreviation EOR in the abstract. Could you emphasize the uniqueness of your study more to make the abstract more attractive?
- The introduction, which serves as the theoretical background of the paper, is nicely developed, but lacks depth in my opinion, as it is rather descriptive. Please elaborate on this point. What could be useful is to add a table summarizing the last key results.
- I think the authors should more clearly state the purpose of the paper already in the Introduction. In some places, the purpose of the paper is indicated, but readers should be aware beforehand of what to expect. Please include a brief summary of the following chapters at the end of the Introduction. Please also indicate the novelty of the presented work.
- The methodology of the experiment seems to be nicely designed.
However, there is a lack of information and some details, such as the number of repetitions.
It would be good to check Figure 1, I have doubts that all descriptions are legible (they are too small). Please also emphasize here the uniqueness of the study. In my opinion, the experiment is nicely described.
- Is it possible to develop (based on a literature search) some hypotheses that were tested by the experiment. I think this would be useful to better understand what was expected and what was actually achieved.
- The results are well described and are reasonable. What I really like are the graphics, which are nicely designed and are very informative.
- What I find completely lacking is a section devoted to discussing the results achieved. The results here should be reflected with the international literature and recent findings.
- The ending is good, but I would have expected more about the implications, i.e. how the proposed solution can be helpful. I also think that in this type of study, it would be appropriate to devote some space to the factors influencing the results. Could you elaborate in the summary section on these limitations of the study (regarding methodology, settings, inputs, etc.)?
- The list of references should be expanded to better cover the recent debate.
I would like to thank the authors for their work on the manuscript so far. I think the manuscript will be a good fit for Energy, but some more work is needed. As it stands, the manuscript is not ready for publication and a major revision is needed. I hope the authors will find my comments useful. I am honored to have reviewed the manuscript for this journal.
Best regards,
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
i think now the paper is acceptable
Reviewer 2 Report
Accept in present form
