Preliminary Study on the Phenomenon and Mechanism of Granite Core Discing in Laboratory Drilling Test
Round 1
Reviewer 1 Report
Better figures/graphs required.
Necessity in detailing quantitatively the information present in the results and conclusions.
Author Response
We have revised the manuscript according to the comments and suggestions of reviewers.
Reviewer 2 Report
The manuscript by Tang et al. experimentally examined the core discing under low pressure and supported their observations through FEM analysis. Overall the paper is well presented, there are a few grammatical/spelling errors, which needs to be corrected.
Author Response
We have revised the manuscript according to the comments and suggestions of reviewers.
Reviewer 3 Report
Reviewer’s introduction
Investigations into the failure mode of core discs under high stress and low confining stress have been conducted, and the characteristics of the morphology and surface fractal dimension have been used to identify the failure modes of core discs. This study looks at the failure mode of granite core discs using both experimental and numerical analysis. According to experimental findings, core discing occurs at high drilling rates >15mm/min and no lateral stress. The interaction between the drill bit and the rock has been studied using Ansys. The research indicates that when tensile stress is applied, the stress concentration results in core discing. Furthermore, it has been established that the penetration rate affects core discing the most.
The article is well-written, presented and discussed. Following minor revision, the manuscript should be considered for publication.
Reviewer’s comments
1. Lines 14-15 and Line 66: Under low confining pressure (0 MPa)? The sentence should read as follows: under no confining pressure.
2. Line 44: Wang et al. [18].
3. What about other drilling factors such as weight on bit (WOB), bit type and condition (new or used), drilling fluid, torque, drilling speed, rock type? Do they have influence on core discing phenomenon?
4. Does the depth of the core disc vary depending on the rate of drilling?
5. Figs. 7- 9:
- Fig. 7: Caption should read as: Monitored bit drilling pressure along complete core length at various drilling rates.
- Fig. 8: Caption should read as: Monitored bit drilling torque along complete core length at various drilling rates.
- Fig. 9: Caption should read as: Monitored bit specific energy along complete core length at various drilling rates.
- It is recommended to add the following comment: It is noted that the variations features of drilling pressure, torque, and specific energy began at one-third (e.g., 30 mm) of core length when implementing high drilling rates (e.g., >15 mm/min.)
- The resolutions of Figs. 7- 9 are quite low.
- It suggested that Figs. 7-9 should be combined into a single (e.g., Fig. 7) with caption reads as: Monitored bit drilling pressure (left), torque (middle), and specific energy (right) along complete granite core length at various drilling rates.
6. Line 156: the superscript of the unit mJ/mm3
7. The same recommendation for Figs. 10-12:
- Integrate them in one graph (e.g., Fig. 8) with caption reads: A shaded 95 % confidence interval of bit drilling pressure (left), torque (middle), and specific energy (right) at varied drilling rates.
- Place the correlation coefficients between brackets or under each line equation.
8. Lines 185-186: test 3, test 4 and test 5 are shown in Fig. 14 b, c and d respectively.
9. Fig. 14a depicts the test 1 and test 2 (at low penetration rates <15mm/min.).
10. Line 217 and 219: is it a steep or a step?
11. Lines 272-273: “Normal displacement constraints were imposed on the back surfaces perpendicular to the drilling direction”. What about the model's base boundary conditions?
12. In the model, how did you simulate a water supply/port?
13. The drilling conditions used in numerical modelling are listed in Table 4. How are these values determined?
14. Line 321: add also: “and high drilling rates”.
Author Response
- Lines 14-15 and Line 66: Under low confining pressure (0 MPa)? The sentence should read as follows: under no confining pressure.
We have revised it.
- Line 44: Wang et al. [18].
We have revised it.
- What about other drilling factors such as weight on bit (WOB), bit type and condition (new or used), drilling fluid, torque, drilling speed, rock type? Do they have influence on core discing phenomenon?
In the manuscript, only the drilling rate and confining pressure were discussed preliminarily, and the weight on bit (WOB), bit type and condition (new or used), drilling fluid, torque, drilling speed, rock type and other factors were strictly controlled in the laboratory test. The above factors may affect the core cake formation, but no further discussion will be made in this paper.
- Does the depth of the core disc vary depending on the rate of drilling?
Based on the existing laboratory test phenomenon, no obvious correlation has been found temporarily.
- Figs. 7- 9:
- Fig. 7: Caption should read as: Monitored bit drilling pressure along complete core length at various drilling rates.
- Fig. 8: Caption should read as: Monitored bit drilling torque along complete core length at various drilling rates.
- Fig. 9: Caption should read as: Monitored bit specific energy along complete core length at various drilling rates.
- It is recommended to add the following comment: It is noted that the variations features of drilling pressure, torque, and specific energy began at one-third (e.g., 30 mm) of core length when implementing high drilling rates (e.g., >15 mm/min.)
- The resolutions of Figs. 7- 9 are quite low.
- It suggested that Figs. 7-9 should be combined into a single (e.g., Fig. 7) with caption reads as: Monitored bit drilling pressure (left), torque (middle), and specific energy (right) along complete granite core length at various drilling rates.
We have revised it. We combined Figs. 7-9 into a single.
- Line 156: the superscript of the unit mJ/mm3
We have revised it.
- The same recommendation for Figs. 10-12:
- Integrate them in one graph (e.g., Fig. 8) with caption reads: A shaded 95 % confidence interval of bit drilling pressure (left), torque (middle), and specific energy (right) at varied drilling rates.
- Place the correlation coefficients between brackets or under each line equation.
We have revised it.
- Lines 185-186: test 3, test 4 and test 5 are shown in Fig. 14 b, c and d respectively.
We have revised it.
- Fig. 14a depicts the test 1 and test 2 (at low penetration rates <15mm/min.).
We have revised it.
- Line 217 and 219: is it a steep or a step?
It is step. Because it looks like a step of stair.
- Lines 272-273: “Normal displacement constraints were imposed on the back surfaces perpendicular to the drilling direction”. What about the model's base boundary conditions?
This statement has been revised.The top, bottom, left and right surfaces of the model was fixed.
- In the model, how did you simulate a water supply/port?
The model simulates the drill bit rotating at high speed, so the port is not considered. The WOB uniformly acts on the annular area at the hole bottom.
- The drilling conditions used in numerical modelling are listed in Table 4. How are these values determined?
The values in Table 4 are from the measured values of indoor drilling tests.
- Line 321: add also: “and high drilling rates”.
We have revised it.
