Effect of Contact Area on Deflection Flow Behavior in a Bifurcated Fracture
Round 1
Reviewer 1 Report (Previous Reviewer 1)
The authors have addressed most of my remarks and improved critical parts of the manuscript. There are still typographic errors present (for example line 137 "he" -> "the" that should be corrected before publishing the paper either by the authors or the publishing department. I personally would not be happy with the limited amount of information about the numerical model (right now not even the employed code is mentioned) but given the scope of the paper I leave this up to the editors/authors to decide wether this should be enhanced.
Author Response
The authors have addressed most of my remarks and improved critical parts of the manuscript. There are still typographic errors present (for example line 137 "he" -> "the" that should be corrected before publishing the paper either by the authors or the publishing department. I personally would not be happy with the limited amount of information about the numerical model (right now not even the employed code is mentioned) but given the scope of the paper I leave this up to the editors/authors to decide wether this should be enhanced.
Answer: Thanks to the reviewer for the approval. We modified 'he' as "the" in line 137. We also examined the other typographic errors in the article.
For the information about the numerical model, we added the contents in lines 117-119: We used the stable flow analysis module of COMSOL software, set up the corresponding water inlet, outlet, and boundary conditions, and analyzed the corresponding water velocity changes at the exits under the condition of fixed inflow flow.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (New Reviewer)
The analysis of the permeability component under the influence of external force is based with the different closure of the Bifurcated fracture. The paper has a unique research perspective, and it reveals the causes and law of deflection flow.
After some modifications this paper can be accepted.
1.In Fig.2, Identify exactly the ‘Contact area’ and ‘Cross-section’. This is very important.
2.In Fig.7, Please explain the meaning of the numbers in Fig.7.
3.In Fig.9, Please explain the meaning of the numbers in Fig.9.
4.In Fig.11, Why are the slopes of the lines all the same? What is the physical background and significance?
Author Response
The analysis of the permeability component under the influence of external force is based with the different closure of the Bifurcated fracture. The paper has a unique research perspective, and it reveals the causes and law of deflection flow.
After some modifications this paper can be accepted.
1In Fig.2, Identify exactly the ‘Contact area’ and ‘Cross-section’. This is very important.
Answer：We have changed the Fig, 2. The contact area refers to the size of the contact surface generated by the contact between fracture surfaces, and the cross-section length refers to the length of the contact area perpendicular to the direction of fluid flow. And we added the sentences in lines 113-115.
2.In Fig.7, Please explain the meaning of the numbers in Fig.7.
Answer: The numbers in Fig. 7 shows the difference in outlet velocity of bifurcated fracture under different contact area. When the cross-section does not change, the deflection behavior of the fracture does not change even if the contact area increases. When the cross-section increases, the velocity difference of the fracture also increases, indicating that the cross-section of the fracture is an important factor affecting the deflection flow behavior. We have added this sentence in line 215.
3.In Fig.9, Please explain the meaning of the numbers in Fig.9.
Answer: Fig. 7 proves that the cross-section is an important factor affecting the deflection flow behavior. The numbers of Fig. 9 are also the difference of velocity, which proves that the cr0ss-section is the reason that affects the deflection flow behavior in fracture. In Fig. 9, the change of contact area is reflected the cross-section. When the length of the cross-section increases, the difference value of the fracture become larger, and the deflection behavior of the fracture becomes more obvious, indicating that the cross-section is the factor affecting the change of deflection flow behavior. We have added this sentence in lines 250-253.
4.In Fig.11, Why are the slopes of the lines all the same? What is the physical background and significance?
Answer: Fig. 11 shows the relationship between the velocity difference and the contact cross-section It is found that the velocity difference increases linearly with the increase of the cross-section, and the slope is the same. This is because the increased contact cross-section area of one channel reduces its own circulation channel and increases the flow rate of the other channel. This indicates that the relationship between the fracture cross-section and the velocity difference is regular in the study of rectangular contact deflection flow. The main reason of velocity difference is the fracture contact cross-section. It is possible to predict the velocity difference after the cross-section continues to change according to the corresponding relationship, which can provide theoretical guidance for the deflection of water on the pipe or the migration of resources such as oil and gas. We have added this sentence in lines 272-275.
In addition, we have checked the English language and style, and the paper has been polished by the professional language service agency. So please check and trust the accuracy of our language.
Reviewer 3 Report (New Reviewer)
The deflection flow effect is an important discovery for describing fluid flow in bifurcated fractures. This has certain theoretical significance for the flow control of groundwater and bifurcation pipelines. Please address the comments below:
1. How to control the angle in the experiment and the asymmetry of the angle will affect the experimental results.
2. How to control the shunt of flow in the case of one outlet.
3. Why only one contact area is considered? there are many contact areas in the fractures.
4. The difference between the pressure data of bifurcated fracture is small (Fig 3), please explain.
5. In line 39. “a rock is” should changed to “rocks are”.
6. In line 47. “the” should delete.
7. In line 104. The “have” should change to “has”.
8. In line 191. The “contact” should change to “contract”.
Author Response
The deflection flow effect is an important discovery for describing fluid flow in bifurcated fractures. This has certain theoretical significance for the flow control of groundwater and bifurcation pipelines. Please address the comments below:
1How to control the angle in the experiment and the asymmetry of the angle will affect the experimental results.
Answer: In the preparation of rock samples, the instrument can be used to cut the fracture angle into the same, and the experimental angle can not be exactly the same. And the technological error will not affect the experiment.
2How to control the shunt of flow in the case of one outlet.
Answer: We set up a shunt pipe at the outlet. After passing through the channel, the fluid enters the intersecting fracture as shunts at the fracture intersection, and flows out along the shunt pipe. Bonding the middle part of rock with intersecting fractures and shunt pipe through epoxy resin can effectively prevent the fluid flowing out the intersecting fracture channel mixing, and will not affect the experimental results.
3Why only one contact area is considered? there are many contact areas in the fractures.
Answer: The contact area and cross-section length can be controlled quantitatively in order to find out the results better. Meanwhile, the study of fracture contact with one contact area considered will be simple for analyzing the deflection flow behavior. In later studies we will discuss the influence of biased flow in multi-contact zones.
4The difference between the pressure data of bifurcated fracture is small (Fig 3), please explain.
Answer: We also found that a similar contact area can cause a large flow difference. This makes us wonder whether the length of the fracture contact area will also have an impact on the experimental results. Therefore, we use numerical simulation to consider the effect of cross-section length of contact area on deflection fluid behavior.
5In line 39. “a rock is” should changed to “rocks are”.
Answer: We have changed the “a rock is” to “rocks are”.
6In line 47. “the” should delete.
Answer: We have deleted the “the”.
7In line 104. The “have” should change to “has”.
Answer: We have changed the “have” to “has”.
8In line 191. The “contact” should change to “contract”.
Answer: We think the ‘contact’ is the right word.
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Please see the attached PDF with my comments.
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
Some suggestions are as follows,
1. In the experiments, as for the samples with bifurcation fractures, how to describe the fracture surface? JRC?
2. Also, in the experiments, how to solve the water sealing, which is very important for measuring the pressure and flow velocity.
3. The rectangle in the samples should be shown, how to realize the sample arrangement？please give the real samples with the rectangle.
4. As for the no.2 figure in Fig.5, the cure in the low pressure is different from others, why?
5. As for Fig.5, the curve of QA and QB for Pc=1 and Pc=6 is very close, why is different from others with Pc=2,3,4,5? And the curve is very same for the Pc=5 and Pc=5, how to explain it.
6. As for Fig.8, the difference cannot be shown for different rectangle area, how to explain it?
7. As for Fig.9 and 10, we find the value in outlet A and B is very similar for the last three conditions, why?
8. Please give some clear pictures.
9. Please give some tables to describe the representative values of some key sections.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The suggestions have not been paid more attentions and have not revised yet.
