Characteristics of Reservoir Boundary Ranging with While-Drilling Impulse Sound Source

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors address the interesting subject of acoustic boundary ranging while drilling.

They investigate the possibility to restrict the directivity of a small source with a small reflector, and apply the arrangement in a 2D While-drilling near-wellbore reservoir boundary model.

The paper has some weaknesses, and my opinion is that it cannot be published as presented.

1. one can achieve directional sound radiation by combination of simple sources (monopole, dipole, etc.) or by a larger surface, e.g. a reflector. However, when using a larger surface, its "aperture size" must be comparable to the wavelength. In the paper the authors mention focusing, which usually means that the source targets distances inside the farfield distance. (< a^2/lambda, where a is the aperture radius).  The dimensions investigated here is too small for this, the source is planned used for reflectors/scatterers in the farfield. The directinal gain seems to be limited as inn Figure 7 it seems as the level backwards is approximately 60% of that forwards. In Figure 
The reflector is also muchs maller than than the wavelength (approx 188mm @8kHz) in all dimensions.

This should be discussed in the paper, maybe as a design challenge, and then compare the results with what one could be expect to find from a radiating source (e.g. a piston) with the same size as the "opening radius".

2. The authors should describe the methods and the results in more detail. Some examples:
- line 136, sound pressure level 265dB. What is the reference for the dB scale?
- line 153, Depth of the reflector is A, but in eq.(1) A is used as the amplitude of the source.
- what is the definition sound pressure peak value (max in waveform, max envelope,) ? Where is the pressure evaluated ?
- What is Caliber in section 2.2 and fig.5 ? Is it the reflector opening?
- In fig.6 it would have been easier to compare the two curves if peak level where plotted in dB.
- in Fig 7 it would also be easier to compare the curves if the levels were in dB. Preferably normalized to the axis level.
- in Fig. 7 what is the axis levels, what is 1*10^7?

- in Fig.4 and 5 the pressure level is in the range 10^5, while in Fig.6 it is in the range 10^7. 

- What are the dimensions of the receivers in the COMSOL model? How is the received signal evaluated (e.g. integral of pressure over the source)?

It is difficult for me to understand why it is necessary to verify that COMSOL, a well proven software, works well. It is compared to a reference method, the real-axis integration method (which there is no reference to). Furthermore the COMSOL model is sect.3 is 2D, while the verification is performed for a 3D case. If this verification was put in sect.2 where the COMSOL model is 3D it would fit in better.
The agreement between the two is quite good. There are some extra bumps in the Comsol model, approx 1.5ms after the main pulse.

The ranging methods used are well described (Fig.12-13, Eq.(4-9)), but there is no description of how arrival times are determined ("first break", maximum envelope, zero crossings, or other.
And how are the signals from the Formation-Reservoir interface echo identified/all other signals removed, as indicated in Fig.15.

In Fig 15. Why does the formation reflected wave almost simultaneously at all receivers?

 

 

Author Response

Dear Reviewer,

Thank you very much for taking the valuable time to conduct a thorough review of this manuscript and for providing constructive comments and suggestions. Your comments have accurately identified the deficiencies in the research framework and content presentation of this paper, which are of great guiding significance for improving the academic quality and rigor of the manuscript. We have carefully studied and analyzed all your comments item by item, and made corresponding revisions and supplements to address each issue. We hereby present our detailed responses and revisions as follows:

 

Comments 1:[ One can achieve directional sound radiation by combination of simple sources (monopole, dipole, etc.) or by a larger surface, e.g. a reflector. However, when using a larger surface, its "aperture size" must be comparable to the wavelength. In the paper the authors mention focusing, which usually means that the source targets distances inside the farfield distance. (< a^2/lambda, where a is the aperture radius).  The dimensions investigated here is too small for this, the source is planned used for reflectors/scatterers in the farfield. The directinal gain seems to be limited as inn Figure 7 it seems as the level backwards is approximately 60% of that forwards. In Figure

The reflector is also muchs maller than than the wavelength (approx 188mm @8kHz) in all dimensions.

This should be discussed in the paper, maybe as a design challenge, and then compare the results with what one could be expect to find from a radiating source (e.g. a piston) with the same size as the "opening radius".]

 

Response 1:Thank you for pointing this out. There is a certain ambiguity in the wording of the original text, which may have caused your confusion. Section 2.1 of the paper introduces two types of energy bunching devices: the ellipsoidal type and the rotational paraboloid type. Specifically, the ellipsoidal energy bunching device converges acoustic waves to a single point, whereas the rotational paraboloid energy-bunching device adopted in this paper collimates acoustic waves into a beam of parallel waves rather than focusing them on a specific point. The term (energy focusing) used in the original description is somewhat ambiguous; it has now been revised to (energy bunching) to accurately characterize the performance of the rotational paraboloid energy bunching device in collimating acoustic waves into a parallel beam.

The purpose of introducing the energy bunching device in our research is to address the drawback of the impulse sound source (which is essentially a monopole source) lacking azimuthal directivity, and providing gain for the impulse sound source is not the primary objective. In addition, the acoustic waves excited by the impulse sound source employed in this paper are broadband signals ranging from 0 to 100 kHz, with its excitation dominant frequency set at 8 kHz, rather than a single-frequency signal operating at 8 kHz.

 

Comments 2:[ The authors should describe the methods and the results in more detail. Some examples:

- line 136, sound pressure level 265dB. What is the reference for the dB scale?

- line 153, Depth of the reflector is A, but in eq.(1) A is used as the amplitude of the source.

- what is the definition sound pressure peak value (max in waveform, max envelope,) ? Where is the pressure evaluated ?

- What is Caliber in section 2.2 and fig.5 ? Is it the reflector opening?

- In fig.6 it would have been easier to compare the two curves if peak level where plotted in dB.

- in Fig 7 it would also be easier to compare the curves if the levels were in dB. Preferably normalized to the axis level.

- in Fig. 7 what is the axis levels, what is 1*10^7?

- in Fig.4 and 5 the pressure level is in the range 10^5, while in Fig.6 it is in the range 10^7.

- What are the dimensions of the receivers in the COMSOL model? How is the received signal evaluated (e.g. integral of pressure over the source)?]

 

Response 2:Thank you for pointing this out. We agree with this comment.

1. The sound pressure level (SPL) used in the paper is calculated based on the reference sound pressure of acoustic waves in water; we have supplemented this explanation in the paper, see Lines 149–150.
2. We have revised the duplicated variable name herein to B, see Line 190.
3. The peak sound pressure in this section refers to the maximum value of the received waveform; we have provided a clarification on this in the paper, see Lines 185–187.
4. The term "Caliber" herein refers to the aperture radius; we have revised the label description in the figure, see Figure 5 in Line 200.
5. We have converted the sound pressure in the figures to sound pressure level (SPL) and redrawn the figures, see Figures 7 and 8 in Lines 227 and 242.
6. We have added units to the figure, see Figure 8 in Line 242.
7. This inconsistency in the simulation results arises because we adopted a newly established model when plotting these figures, where the material parameters of the new model are inconsistent with those of the previous model. We have corrected the error, re-performed the calculations, and revised the original figure, see Figure 7 in Line 227.
8. We employed the domain point probe in COMSOL as the acoustic wave receiver and investigated the total sound pressure received by it; we have provided a clarification on this in the paper, see Lines 296–298.

 

 

Comments 3:[ It is difficult for me to understand why it is necessary to verify that COMSOL, a well proven software, works well. It is compared to a reference method, the real-axis integration method (which there is no reference to). Furthermore the COMSOL model is sect.3 is 2D, while the verification is performed for a 3D case. If this verification was put in sect.2 where the COMSOL model is 3D it would fit in better.

The agreement between the two is quite good. There are some extra bumps in the Comsol model, approx 1.5ms after the main pulse.]

 

Response 3:Thank you for pointing this out. We agree with this comment. Since this study has not yet been verified by physical experiments, we are concerned that the use of COMSOL simulation alone cannot provide sufficient persuasiveness. Therefore, we adopted the real-axis integration method for verification, and supplemented the root mean square error (RMSE) to quantitatively analyze the consistency of the calculation results of these two methods. In accordance with your comments, we have moved this section to Section 2.1, see Lines 159–180.

 

 

Comments 4:[ The ranging methods used are well described (Fig.12-13, Eq.(4-9)), but there is no description of how arrival times are determined ("first break", maximum envelope, zero crossings, or other.

And how are the signals from the Formation-Reservoir interface echo identified/all other signals removed, as indicated in Fig.15.]

 

Response 4:Thank you for pointing this out. We agree with this comment. This study adopted the method of first simulating the full wave trains of the complete model and the model with the oil-bearing reservoir removed separately, then subtracting the two waveforms to eliminate all interference signals. For the determination of wave arrival time, we used the method of extracting the peak value of the acoustic wave envelope. Supplementary explanations of these methods have been provided in Section 3.2, Lines 347–356 of the manuscript.

 

 

Comments 5:[ In Fig 15. Why does the formation reflected wave almost simultaneously at all receivers?]

 

Response 5:Thank you for pointing this out. This is because the P-wave and S-wave velocities in the formation material parameters used herein are relatively high, and the distance between the reservoir boundary and the drill collar as well as the distance between each receiving point are relatively short, which leads to the received reflected wave waveforms appearing to arrive almost simultaneously in the figure. However, the distance can be calculated with relatively high accuracy by extracting the arrival time of the reflected waves and applying the ranging formula provided in this paper.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

The manuscript addresses an important problem in reservoir boundary ranging using an impulse sound source while drilling. However, in its current form it requires major revision, as the introduction needs strengthening, several statements lack adequate references, the numerical modelling is insufficiently documented, and parts of the results require deeper analysis and discussion.

 

Page 1, lines 34–36
Several general statements are made regarding unconventional reservoirs and exploration challenges. These statements should be supported by appropriate and up-to-date references.

Page 1, lines 38–39

“Although China's unconventional oil and gas reservoirs have huge reserves, the drilling and production technologies and equipment lag behind the world's leading level.”
This is a strong and potentially controversial claim. The authors should either support it with solid references or rephrase it in a more neutral and evidence-based manner.

Page 1–2, lines 41–44
Please add references to support the statements regarding rotary steerable and geosteering technologies.

Page 2, lines 53–56
The description of logging-while-drilling measurements (resistivity, gamma ray, neutron porosity, density, acoustic velocity) is useful, but each method should be supported by at least one appropriate reference.

Page 2, lines 60–62, 64–67, and 68–76
These paragraphs contain important background information but are mostly descriptive. Please ensure that key claims are properly referenced and that the novelty of the current study is clearly distinguished from existing work.

Page 2, lines 80–82
The limitations of monopole, dipole, and multipole detection technologies are briefly mentioned. This is an important point. I recommend expanding this discussion by:

Explaining why azimuthal directivity, resolution, or detection distance are limited

Supporting the discussion with relevant references
This would significantly strengthen the motivation of the study.

Section 2 (general comment)
I recommend adding a dedicated subsection describing the COMSOL Multiphysics setup, including: The specific modules and physics interfaces used, The solver type (e.g., direct/iterative, time-domain settings), Meshing strategy and mesh sensitivity considerations, Boundary conditions and any numerical assumptions
This information is essential for reproducibility.

Page 9, line 256
The statement that the two curves show “a high degree of overlap” is qualitative. I recommend adding a quantitative statistical comparison, such as: RMS error, or, Correlation coefficient, or Similarity index. This would strengthen the model validation.

Page 9, lines 269–270
There is a formatting issue with duplicated table naming (e.g., “Table Table 1”). Please carefully check and correct all table and figure labels throughout the manuscript.

Figure 10
Is the observed trend consistent for other source frequencies? If so, this should be clearly stated in the text. If not, a brief discussion explaining the frequency dependence would be helpful.

Section 3.5: Ranging Effect Under Condition of Actual Formation Parameters
This section represents the closest part of the manuscript to a real case study, yet it is relatively short. I recommend: Adding figures or maps showing the study areas, providing more geological context and explanation, clearly explaining why these formations were selected, expanding this section would significantly improve the practical relevance of the paper.

 

I recommend revising the conclusions to: Clearly summarise the main findings, explicitly state the key contributions, discuss limitations and future research directions. Instead of listing detailed numerical values and percentages in the conclusions, these could be: Moved to a Discussion section (recommended), or briefly summarised without excessive numerical detail.

 

Author Response

Dear Reviewer,

Thank you very much for taking the valuable time to conduct a thorough review of this manuscript and for providing constructive comments and suggestions. Your comments have accurately identified the deficiencies in the research framework and content presentation of this paper, which are of great guiding significance for improving the academic quality and rigor of the manuscript. We have carefully studied and analyzed all your comments item by item, and made corresponding revisions and supplements to address each issue. We hereby present our detailed responses and revisions as follows:

 

 

Comments 1:[ Page 1, lines 34–36 Several general statements are made regarding unconventional reservoirs and exploration challenges. These statements should be supported by appropriate and up-to-date references.]

 

Response 1:Thank you for pointing this out. We agree with this comment. We have added relevant references to support this argument and highlighted the revised content for easy identification; the updated text is located in Lines 34–36 on Page 1.

 

 

Comments 2:[ Page 1, lines 38–39 “Although China's unconventional oil and gas reservoirs have huge reserves, the drilling and production technologies and equipment lag behind the world's leading level.”

This is a strong and potentially controversial claim. The authors should either support it with solid references or rephrase it in a more neutral and evidence-based manner.]

 

Response 2:Thank you for pointing this out. We agree with this comment. We have revised the expression here and added relevant references to support it; the revised content has been highlighted for easy identification, and it is located in Lines 38–40 on Page 1.

 

 

Comments 3:[ Page 1–2, lines 41–44 Please add references to support the statements regarding rotary steerable and geosteering technologies.]

 

Response 3:Thank you for pointing this out. We agree with this comment. We have added relevant references to support this argument and highlighted the revised content; the updated text is located at Page 1–2, Lines 41–44.

 

 

Comments 4:[ Page 2, lines 53–56 The description of logging-while-drilling measurements (resistivity, gamma ray, neutron porosity, density, acoustic velocity) is useful, but each method should be supported by at least one appropriate reference.]

 

Response 4:Thank you for pointing this out. We agree with this comment. We have added relevant references to support this argument and highlighted the revised content; the updated text is located at Page 2, Lines54–57.

 

 

Comments 5:[ Page 2, lines 60–62, 64–67, and 68–76 These paragraphs contain important background information but are mostly descriptive. Please ensure that key claims are properly referenced and that the novelty of the current study is clearly distinguished from existing work.]

 

Response 5:Thank you for pointing this out. We agree with this comment. We have added relevant references to support this argument and highlighted the revised content; the updated text is located at Page 2, Lines61–74.

 

 

 

Comments 6:[ Page 2, lines 80–82 The limitations of monopole, dipole, and multipole detection technologies are briefly mentioned. This is an important point. I recommend expanding this discussion by:

Explaining why azimuthal directivity, resolution, or detection distance are limited

Supporting the discussion with relevant references

This would significantly strengthen the motivation of the study.]

 

Response 6:Thank you for pointing this out. We agree with this comment. We have provided a detailed elaboration as requested, added relevant references, and highlighted the revised content; the updated text is located at Page 2, Lines 81–90.

 

 

Comments 7:[ Section 2 (general comment)

I recommend adding a dedicated subsection describing the COMSOL Multiphysics setup, including: The specific modules and physics interfaces used, The solver type (e.g., direct/iterative, time-domain settings), Meshing strategy and mesh sensitivity considerations, Boundary conditions and any numerical assumptions

This information is essential for reproducibility.]

 

Response 7:Thank you for pointing this out. We agree with this comment. We have supplemented the content on the basis of Section 3.1 of the original manuscript, adding COMSOL simulation settings such as model configurations, physics interfaces and mesh generation. Relevant references have also been incorporated, and the revised parts have been highlighted; the updated content is located at Page 9–10, Lines 265–284 and 296–326.

 

 

Comments 8:[ Page 9, line 256 The statement that the two curves show “a high degree of overlap” is qualitative. I recommend adding a quantitative statistical comparison, such as: RMS error, or, Correlation coefficient, or Similarity index. This would strengthen the model validation.]

 

Response 8:Thank you for pointing this out. We agree with this comment. We have introduced the root mean square error (RMSE) in the manuscript to quantitatively analyze the consistency between the real-axis integration method and COMSOL simulation results; the revised content has been highlighted, and it is located at Page 5, Lines 173–175.

 

 

Comments 9:[ Page 9, lines 269–270 There is a formatting issue with duplicated table naming (e.g., “Table Table 1”). Please carefully check and correct all table and figure labels throughout the manuscript.]

 

Response 9:Thank you for pointing this out. We agree with this comment. We have checked the entire manuscript, corrected the identified errors, and highlighted the revised content; the updated part is located at Page 10, Line 299.

 

 

Comments 10:[ Figure 10 Is the observed trend consistent for other source frequencies? If so, this should be clearly stated in the text. If not, a brief discussion explaining the frequency dependence would be helpful.]

 

Response 10:Thank you for pointing this out. Due to the page limit of the manuscript, when investigating the influence of various parameters on the relative ranging error, this study was conducted with the excitation dominant frequency fixed at 8 kHz, and in-depth research on the trends under other dominant frequencies has not been carried out (see Figures 10, 11, 14, etc.). Therefore, we have not made revisions to the manuscript in response to this comment, and we apologize for any inconvenience caused. We will conduct in-depth research on other dominant frequencies in future work.

 

Comments 11:[ Section 3.5: Ranging Effect Under Condition of Actual Formation Parameters

This section represents the closest part of the manuscript to a real case study, yet it is relatively short. I recommend: Adding figures or maps showing the study areas, providing more geological context and explanation, clearly explaining why these formations were selected, expanding this section would significantly improve the practical relevance of the paper.]

 

Response 11:Thank you for pointing this out. We agree with this comment. We have consulted relevant literature, drawn a simplified map of China's petroleum resource distribution (Figure 15) for this part of the text, provided a brief description of the map, and added relevant references. The revised content has been highlighted, and the updated section is located at Page 15, Lines 454–460.

 

 

Comments 12:[ I recommend revising the conclusions to: Clearly summarise the main findings, explicitly state the key contributions, discuss limitations and future research directions. Instead of listing detailed numerical values and percentages in the conclusions, these could be: Moved to a Discussion section (recommended), or briefly summarised without excessive numerical detail.]

 

Response 12:Thank you for pointing this out. We agree with this comment. We have revised the conclusion section of the manuscript and removed the original extensive numerical descriptions to make the conclusions more concise. Meanwhile, we have discussed the limitations of this study as well as future research directions. The revised content has been highlighted, and the updated sections are located at Page 17, Lines 496–501, 506–510 and 515–522.

Reviewer 3 Report

Comments and Suggestions for Authors

Subsoil use is a field with a wide range of challenges. These relate to geology, production, forecasting, and many other issues. Oil and gas production involves extracting raw materials from the Earth's interior. Oil- or gas-saturated rocks represent a complex structure composed of various media (solid, aqueous, and gas). Rock forecasting is crucial for industry development. Analysis of rock structure during drilling is essential. Existing methods for determining reservoir boundaries need to be improved and new ones developed. The various sensors with various operating methods are used in subsoil use. Sensors are one of the main tools for positioning, condition tracking, and monitoring of objects. At the same time, the digitalization of subsoil use currently requires the creation of numerical analogs of system elements, including sensors, not only for analyzing their operation but also for the subsequent transition to digital shadows and twins. The authors provide a basis for numerical modeling of a specific type of sensor, both to assess the impact of its geometry on functionality and to model technological processes. This is an important topic, relevant for the development of not only subsoil use but also sensors. However, the current form of the article does not allow for an assessment of its contribution to the development of scientific fields due to the publication's structure and the lack of a comprehensive conceptual and mathematical formulation of the problems, as well as a research plan.

 

Comments and recommendations:

1. The review does not address the industry's problems in terms of sensors and numerical modeling of sensor operation, as well as their use for reservoir boundary determination. The problem is unclear. It is also unclear what research has already been conducted on this topic. The contribution of the current work to the development of the industry is not disclosed. The role of this work in subsurface management, sensors, and modeling is currently not addressed in the introduction.
2. The article lacks a section with a comprehensive research statement. Materials, methods, and models are described briefly, their descriptions scattered throughout the sections. Without a problem statement, it is impossible to fully assess the contribution of the solution to the scientific problem. This needs to be addressed. Provide a clear statement of all research stages and a plan for the computational experiments. Models and properties of materials should also be fully disclosed. The joint modeling of different environments is also required described and characterized.
3. A conceptual and mathematical formulation is required for all computational experiments. What are the conditions at the interfaces of the environments considered? Is the influence of the system's degree of discretization on the numerical solution of the problem analyzed? What are the limitations of a two-dimensional problem formulation? The two-dimensional formulation of the problem does not take into account the spatial configuration of either the sensor or the environment. Depending on the formulation, is a semi-infinite medium or a medium with a specified thickness modeled. But in this case, spatial geometry cannot be taken into account.
4. The specifics of the numerical modeling are also not disclosed. What elements are used to model the study object and the environments? How are they characterized in terms of computational mechanics? What is the description of the numerical model and its limitations?

Author Response

Dear Reviewer,

Thank you very much for taking the valuable time to conduct a thorough review of this manuscript and for providing constructive comments and suggestions. Your comments have accurately identified the deficiencies in the research framework and content presentation of this paper, which are of great guiding significance for improving the academic quality and rigor of the manuscript. We have carefully studied and analyzed all your comments item by item, and made corresponding revisions and supplements to address each issue. We hereby present our detailed responses and revisions as follows:

 

Comments 1:[ The review does not address the industry's problems in terms of sensors and numerical modeling of sensor operation, as well as their use for reservoir boundary determination. The problem is unclear. It is also unclear what research has already been conducted on this topic. The contribution of the current work to the development of the industry is not disclosed. The role of this work in subsurface management, sensors, and modeling is currently not addressed in the introduction.]

 

Response 1:Thank you for pointing this out. We agree with this comment. We have revised the introduction section, adding descriptions of the key measurement parameters of logging while drilling (LWD), the limitations of sound sources such as monopoles and dipoles, as well as the advantages of the impulse sound source adopted in this paper, and supplemented relevant references to support these contents. Meanwhile, we have briefly elaborated on the contributions of this study to the development of impulse sound source technology. The revised content has been highlighted, and the updated parts are located in the introduction section on Pages 1–3.

 

 

Comments 2:[ The article lacks a section with a comprehensive research statement. Materials, methods, and models are described briefly, their descriptions scattered throughout the sections. Without a problem statement, it is impossible to fully assess the contribution of the solution to the scientific problem. This needs to be addressed. Provide a clear statement of all research stages and a plan for the computational experiments. Models and properties of materials should also be fully disclosed. The joint modeling of different environments is also required described and characterized.]

 

Response 2:Thank you for pointing this out. We agree with this comment. We have supplemented the content on the basis of Section 3.1 of the original manuscript, analyzed the advantages and disadvantages of simulations under different dimensions, supplemented specific model parameter configurations, the adopted physics interfaces, and multiphysics coupling settings, analyzed the requirements for mesh sizing, provided mesh sizing and other COMSOL-related parameters, and added relevant references to ensure the reproducibility of the research results of this study. The revised content has been highlighted, and the updated sections are located at Page 9–10, Lines 265–284 and 296–326.

 

 

Comments 3:[ A conceptual and mathematical formulation is required for all computational experiments. What are the conditions at the interfaces of the environments considered? Is the influence of the system's degree of discretization on the numerical solution of the problem analyzed? What are the limitations of a two-dimensional problem formulation? The two-dimensional formulation of the problem does not take into account the spatial configuration of either the sensor or the environment. Depending on the formulation, is a semi-infinite medium or a medium with a specified thickness modeled. But in this case, spatial geometry cannot be taken into account.]

 

Response 3:Thank you for pointing this out. We agree with this comment. Consistent with our response to the second comment above, we have discussed the boundary conditions of the model, the factors affecting the solution accuracy of the finite element discretization method, as well as the limitations of the 2D model simulation in Section 3.1, and clarified the nature of the infinite formation and that the results of the 2D model simulation cannot fully reflect the geometric characteristics of the actual spatial structure. The revised content has been highlighted on Pages 9–10.

 

 

Comments 4:[ The specifics of the numerical modeling are also not disclosed. What elements are used to model the study object and the environments? How are they characterized in terms of computational mechanics? What is the description of the numerical model and its limitations?]

 

Response 4:Thank you for pointing this out. We agree with this comment. This study adopts the transient pressure acoustics equation to characterize the propagation characteristics of acoustic waves in the medium, defines the material properties of drill collars and formations using the isotropic linear elastic model, and achieves the numerical solution of the model by combining the finite element discretization method. As for the specific details of numerical modeling, consistent with our responses to the 2nd and 3rd comments above, we have provided supplementary explanations in Section 3.1 on Pages 9–10, and the revised content has been highlighted.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I think the text after revision is easier to read and can be re-examin for the reader. 

However, it is difficult for me to understand that "energy bunching" is the correct explanation for the elevated pressure level. The device is much smaller than the wavelength. The results in figure 7 shows elevated pressure on the source's axis (approx 6dB). While in figure 8 one can see that the device also transmit higher level in the backward direction than without the reflector, approx -3dB compared to forward direction. In other words, the radiated power is higher with the reflector arrangement than without. But it is still almost omnidirectional. 

I am not familiar with "energy bunching" but if it indicates that energy is directed in a specific directions, I cannot see that the results in the paper support that energy bunching take place.

 

If the authors had inspected the acoustic field inside the reflecting device  I would expect they would see a field similar to that inside a loudspeaker enclosure at low frequency, or maybe a resonant effect in the depth direction of the "reflector cavity". 

Fig. 16: When it comes to the processing of the signal it would be of interest to know the difference in gain between full-wave train and the reflected waveform diagrams. The reader could get an impression of the challenge to identify the signal of interest in practise, to me it seems as the full-wave signal dominates at several depths.
 

Author Response

Dear Reviewer,

We sincerely appreciate your taking the time out of your busy schedule to review our manuscript once again and for providing highly insightful second-round revision suggestions. Your valuable comments have accurately pinpointed the key remaining issues in this paper, offering crucial guidance for us to further refine the research content and enhance the overall quality of the manuscript.

In response to all the points raised in your current review, we have carefully studied and analyzed each comment one by one, and made corresponding revisions and supplements to address every single issue. The detailed explanations of the revisions are provided below.

 

 

Comments 1:[ However, it is difficult for me to understand that "energy bunching" is the correct explanation for the elevated pressure level. The device is much smaller than the wavelength. The results in figure 7 shows elevated pressure on the source's axis (approx 6dB). While in figure 8 one can see that the device also transmit higher level in the backward direction than without the reflector, approx -3dB compared to forward direction. In other words, the radiated power is higher with the reflector arrangement than without. But it is still almost omnidirectional.

I am not familiar with "energy bunching" but if it indicates that energy is directed in a specific directions, I cannot see that the results in the paper support that energy bunching take place.

If the authors had inspected the acoustic field inside the reflecting device  I would expect they would see a field similar to that inside a loudspeaker enclosure at low frequency, or maybe a resonant effect in the depth direction of the "reflector cavity".]

 

Response 1:Thank you for pointing this out. Since the acoustic waves excited by the impulse sound source are broadband signals, they always contain multiple frequency components. Therefore, no matter how we adjust the dimensions of the energy-bunching device, there will always be frequency components whose wavelengths are larger than the dimensions of the device. In addition, the drill collar is subjected to high pressure, impact and vibration during downhole operation. To ensure the mechanical strength of the drill collar, in-depth research is still required for the design of the shape and dimensions of the energy-bunching device.

We investigated the acoustic field pressure variation diagrams at different moments during the sound wave propagation process and found that although the acoustic waves exhibit the characteristics of plane waves inside the energy-bunching device, they do radiate spherical waves outside the device. This may account for the gain generated in the direction opposite to the opening direction of the energy-bunching device, which is indeed an issue we did not consider in our research. For the impulse sound source, installing the energy-bunching device can indeed produce a certain gain in the sound pressure level in the direction of the device’s opening. As shown in Figure 8, when the opening direction of the energy-bunching device is set at 0°, there is still a gain in the range of 300° to 60°, albeit with a limited gain amplitude. Compared with the case without the energy-bunching device in Figure 7, this gain can still provide some assistance for the research on reservoir boundary ranging in this paper.

Although the characteristics of plane waves and spherical waves of the energy-bunching device were mentioned in previous studies conducted in our laboratory, they were not discussed in depth. Your opinions play an important guiding role in our research and point out the deficiencies in our current work. We will adjust our subsequent research directions based on your suggestions. Specifically, we will carry out physical experiments on the energy-bunching device and continue to improve its shape and dimensions. Meanwhile, we will conduct research on other different sound source combinations (such as dipoles and multipoles), hoping to solve the problems currently encountered.

 

 

Comments 2:[ Fig. 16: When it comes to the processing of the signal it would be of interest to know the difference in gain between full-wave train and the reflected waveform diagrams. The reader could get an impression of the challenge to identify the signal of interest in practise, to me it seems as the full-wave signal dominates at several depths.]

 

Response 2:Thank you for pointing this out. We agree with this comment. We have supplemented the description of the gain difference between the full-wave train and the reflected waveform in Figure 16 within the manuscript. There exists a significant difference in sound pressure level between the received direct-mode wave and the reflected wave. If not processed accordingly, the reflected wave will be submerged in the direct-mode wave and thus indistinguishable. All the revised parts in the manuscript have been highlighted, with the specific location at Page 16, Lines 476–481.

 

 

Once again, we sincerely appreciate your careful review of this manuscript and your valuable comments. Should you have any further questions or suggestions, please do not hesitate to contact us at any time. We wish you all the best in your work!

Sincerely,

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for submitting the revised version of the manuscript.  All my comments have addressed satisfactorily, and the manuscript has improved significantly. I am happy to recommend acceptance of the paper.

I only note a few minor typographical errors that should be corrected before final publication:

Page 5, line 172

Page 10, line 299

Page 12, line 401

Page 15, line 457

Aside from these minor issues, I have no further comments.

Regards,

 

Author Response

Dear Reviewer,

We sincerely appreciate your taking the time out of your busy schedule to review our manuscript once again and for providing highly insightful second-round revision suggestions. Your valuable comments have accurately pinpointed the key remaining issues in this paper, offering crucial guidance for us to further refine the research content and enhance the overall quality of the manuscript.

In response to all the points raised in your current review, we have carefully studied and analyzed each comment one by one, and made corresponding revisions and supplements to address every single issue. The detailed explanations of the revisions are provided below.

 

 

Comments 1:[ I only note a few minor typographical errors that should be corrected before final publication:

Page 5, line 172

Page 10, line 299

Page 12, line 401

Page 15, line 457]

 

Response 1:Thank you for pointing this out. We agree with this comment. We have corrected all the errors identified in the manuscript, and all the revised content has been highlighted for easy reference. The specific revision locations are as follows: Page 5, Line 172; Page 10, Line 299; Page 12, Line 401; Page 15, Lines 456 and 469.

 

 

Once again, we sincerely appreciate your careful review of this manuscript and your valuable comments. Should you have any further questions or suggestions, please do not hesitate to contact us at any time. We wish you all the best in your work!

Sincerely,

 

Reviewer 3 Report

Comments and Suggestions for Authors

Subsoil use is a field with a wide range of challenges. These relate to geology, production, forecasting, and many other issues. Oil and gas production involves extracting raw materials from the Earth's interior. Oil- or gas-saturated rocks represent a complex structure composed of various media (solid, aqueous, and gas). Rock forecasting is crucial for industry development. Analysis of rock structure during drilling is essential. Existing methods for determining reservoir boundaries need to be improved and new ones developed. The various sensors with various operating methods are used in subsoil use. Sensors are one of the main tools for positioning, condition tracking, and monitoring of objects. At the same time, the digitalization of subsoil use currently requires the creation of numerical analogs of system elements, including sensors, not only for analyzing their operation but also for the subsequent transition to digital shadows and twins. The authors provide a basis for numerical modeling of a specific type of sensor, both to assess the impact of its geometry on functionality and to model technological processes. This is an important topic, relevant for the development of not only subsoil use but also sensors.

There are reference errors (Error! Reference source not found.) to literary sources in the article, for example, lines 172 and 299. Please check the document.

Author Response

Dear Reviewer,

We sincerely appreciate your taking the time out of your busy schedule to review our manuscript once again and for providing highly insightful second-round revision suggestions. Your valuable comments have accurately pinpointed the key remaining issues in this paper, offering crucial guidance for us to further refine the research content and enhance the overall quality of the manuscript.

In response to all the points raised in your current review, we have carefully studied and analyzed each comment one by one, and made corresponding revisions and supplements to address every single issue. The detailed explanations of the revisions are provided below.

 

 

Comments 1:[ There are reference errors (Error! Reference source not found.) to literary sources in the article, for example, lines 172 and 299. Please check the document.]

 

Response 1:Thank you for pointing this out. We agree with this comment. We have corrected all the errors identified in the manuscript, and all the revised content has been highlighted for easy reference. The specific revision locations are as follows: Page 5, Line 172; Page 10, Line 299; Page 12, Line 401; Page 15, Lines 456 and 469.

 

 

Once again, we sincerely appreciate your careful review of this manuscript and your valuable comments. Should you have any further questions or suggestions, please do not hesitate to contact us at any time. We wish you all the best in your work!

Sincerely,