Source Rock Evaluation and Hydrocarbon Expulsion Characteristics of Effective Source Rocks in the Fushan Depression, Beibuwan Basin, China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

See in the attachment

Comments for author File: Comments.docx

Author Response

I am immensely grateful for your insightful suggestions. Regarding the mean value algorithm presented in Table 2, I have taken your advice into account. In this iteration, the study area has been delineated into four distinct regions. This approach allows for a more nuanced comparison with the previous study's stratigraphic segmentation, particularly in highlighting the differences between the two sub-concavities, akin to the precipitation and depositional centers.The distinction between these centers and their implications for the subsequent discussion on casein types has been further clarified. In light of the reviewers' comments, I have conferred with my co-authors and decided to prepose the description of the mean value analysis. This is followed by an evaluation of the planar dispersion from point to point, which enhances the logical progression of the article.

Additionally, I have made adjustments to Table 2 to better facilitate the reader's understanding and to ensure that the presentation aligns with the narrative flow of our research.

Thank you once again for your valuable input and we have specific answers to your suggestions

Comments 1: Clarify if you are reporting Leco TOC measurements of RockEval TOC measurements.

response 1: In the realm of Section 3.2, entitled "Laboratory Methods," I acknowledge that the original content was somewhat deficient. Consequently, I have enriched this section by incorporating additional analytical techniques. Specifically, I have included the experimental protocols and instrumental setups for pyrolysis and Rock-Eval Total Organic Carbon (TOC) analysis, as you previously suggested. Furthermore, I have supplemented the text with electron micrographs, which are pivotal for enhancing the comprehensiveness and visual substantiation of my manuscript. These additions are designed to bolster the methodological rigor and the overall integrity of the research presented.

Comments 2: The values used in Figure 5 to classify SR intervals that contain Type II2 or Type III kerogen as Good, Medium, or Poor are incorrect because they apply only to SRs that contain Type II1 kerogen.

response 2: Thank you for your prompt reminder. Upon reviewing the cited literature (Dembicki Jr., 2009, AAPG Bulletin, 93, pp. 341-355), it is evident from Data Table 2 that the Liushagang Formation within the Fushan Depression contains type II1 casein. Consequently, samples of type II1 casein were selected for the mapping exercise.

Comments 3: In Figure 9, you project the VR trendlines to a value of 0.1% at the surface.  The correct value to use is 0.2% at the surface.  In addition, you use VR = 0.5% as the thermal maturity when SRs begin to generate petroleum.  The standard value is VR = 0.6%.  Making these changes will cause the onset of oil generation in several intervals to be moderately deeper than what you have concluded.  This also requires that you change the contour lines shown in Figure 10.

Response 3: The Fushan Depression within the Beibuwan Basin is characterized by elevated sulfur content, which results in a reduced vitrinite reflectance (Ro) threshold for hydrocarbon generation. Consequently, the onset of hydrocarbon generation occurs at a lower temperature, and the threshold for hydrocarbon expulsion is also low. The thermal maturity index is calibrated at 0.5. These findings are consistent with the data provided by PetroChina Hainan Fushan Oilfield Exploration and Development Co.Regarding the figures, I have revised Figure 9 (now Figure 8) in accordance with your feedback. Unnecessary lines have been eliminated, and the horizontal axis has been adjusted to enhance the clarity of the Ro data pattern. Additionally, Figure 10 (now Figure 9) and all associated planar diagrams have been enlarged to facilitate a more rapid and comprehensive data interpretation for the readers.

Comments 4: Show the uncertainty (at the 1δ value) of VR measurements for representative SR samples.

Response 4: Thank you for your insightful suggestions. The standard deviation ranges and corresponding values have been incorporated into Table 2. Additionally, the reflectance values (Ro) have been included in both Table 2 and Table 3. These enhancements will bolster the reliability and clarity of the data presented in the article.

Comments 5: If PetroMod software provides these results, show the volumes or mass of oil and natural gas that your HC charge model estimates were generated by each SR interval -- not simply the mass of oil.  This is especially important if any SR intervals entered the wet gas window around interest.

Response 5: I couldn't concur more with your perspective. However, it's imperative to note that this assessment must be integrated with inclusions analysis. Solely relying on software simulation is insufficient for determining the volume or mass of hydrocarbons extracted from each stratigraphic interval within the study area. This is because the simulation is inherently one-dimensional, and it does not facilitate calculations that extend beyond this scope. Nevertheless, we have tailored our results to meet the production requirements of our partner, PetroChina Hainan Fushan Oilfield Exploration and Development Co., Ltd. This approach has led to a significant advancement in our understanding of the Liushagang Formation within the Fushan Depression and the broader Beibu Gulf Basin.

 

Reviewer 2 Report

Comments and Suggestions for Authors

The current research on the source rocks of the Liushagang Formation within the Fushan Depression of the Beibuwan Basin in China is notably underdeveloped. Prior investigations into the spatial distribution and hydrocarbon expulsion properties of these source rocks have been somewhat ambiguous, thereby impeding a comprehensive understanding of the resource potential and the delineation of prospective resource zones. In this study, the source rocks of the Liushagang Formation have been meticulously stratified and subjected to a thorough evaluation, culminating in the development of a Hydrocarbon Expulsion Model for the Liushagang Formation in the Fushan Depression. The sample selection presented herein is considered to be reasonably sound, and the experimental conditions have been chosen with consideration of the geological context, thereby conferring practical geological relevance. However, it is suggested that the manuscript undergoes minor revisions prior to publication. For a detailed critique, please refer to the annex. The principal feedback is as follows:

（1）      Geological Characteristics of Source Rocks: In this section, the inclusion of a stratigraphic thickness statistics table for the seven source rock intervals within the Liushagang Formation is recommended. Such a table would enhance the reader's comprehension of the principal attributes of these strata. While the "Isopach Map of Source Rock Thickness in the Liushagang Formation, Fushan Depression," effectively illustrates the stratigraphic variability across the entire basin, it does not facilitate the rapid acquisition of specific numerical data.

（2）      In the section titled ' Hydrocarbon generation and expulsion conceptual model ' the employment of formulae and the significance of symbols are elucidated with precision. It is recommended that the substantiation of the perspective be augmented by enhancing the citation of pertinent antecedent literature.

（3）      For Figures 9 and 12, please ensure alignment with the layout conventions of other illustrations within the manuscript. Adjusting the size may entail redistributing the panels (e.g., A, B, C, etc.) across multiple pages to maintain coherence and clarity within the visual presentation.

（4）      During the source rock assessment, there is a redundancy in the characterization of various strata. While this does not compromise the overall clarity, it is advisable to review and refine the descriptions for enhanced precision and conciseness.

（5）      I am particularly intrigued by the sixth section of the article, which delves into the 'Organic Composition of Source Rocks.' The concepts presented in this section are notably innovative. The hydrocarbon potential of these organic-rich lacustrine shales is primarily contingent upon the depositional environment and the current burial depth of the sediments, which are discussed in meticulous detail. The article posits that the hydrocarbon source rocks in other continental basins could be explored further, employing this novel framework for discussion.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Thank you for your acknowledgment of my submission. Upon careful consideration of your insightful suggestions, I have implemented the following revisions to enhance the manuscript:

Comments 1: Geological Characteristics of Source Rocks: In this section, the inclusion of a stratigraphic thickness statistics table for the seven source rock intervals within the Liushagang Formation is recommended. Such a table would enhance the reader's comprehension of the principal attributes of these strata. While the "Isopach Map of Source Rock Thickness in the Liushagang Formation, Fushan Depression," effectively illustrates the stratigraphic variability across the entire basin, it does not facilitate the rapid acquisition of specific numerical data.

Response 1: In the segment dedicated to the geological assessment of hydrocarbon source rocks, I have refined the subsequent paragraphs for enhanced clarity. Additionally, the tables have been meticulously revised to incorporate supplementary data, thereby significantly enhancing the reader's comprehension and accessibility to the pertinent information.

Comments 2: In the section titled ' Hydrocarbon generation and expulsion conceptual model ' the employment of formulae and the significance of symbols are elucidated with precision. It is recommended that the substantiation of the perspective be augmented by enhancing the citation of pertinent antecedent literature.

Response 2: In the context of this study's experimental approach, I have conducted Total Organic Carbon (TOC) analysis, pyrolytic decomposition, and Rock-Eval (Ro) measurements in accordance with established experimental and analytical protocols. These procedures have been supplemented by the incorporation of recent literature references that provide additional insights into the subject matters. Such as Rock-Eval pyrolysis should be used due to its limitation and impacts of kerogen and mineralogical compositions of organic-rich rocks (Hunt, 1991; Hazra et al., 2017, 2019; Karayigit et al., 2021; Vu et al., 2013; Yang and Horsfield, 2020)."

Comments 3:  For Figures 9 and 12, please ensure alignment with the layout conventions of other illustrations within the manuscript. Adjusting the size may entail redistributing the panels (e.g., A, B, C, etc.) across multiple pages to maintain coherence and clarity within the visual presentation.

Response 3: The figures have been revised accordingly: Figure 9 has been updated to correspond with Figure 8, and Figure 12 has been adjusted to align with Figure 13, as per the specifications outlined in the article.

Comments 3: During the source rock assessment, there is a redundancy in the characterization of various strata. While this does not compromise the overall clarity, it is advisable to review and refine the descriptions for enhanced precision and conciseness.

Response 4: For the stratigraphic nomenclature and other geological terminologies have been comprehensively revised and scrutinized. I am immensely grateful for your insightful suggestions, which have significantly contributed to enhancing the caliber of my manuscript.

Comments 5: I am particularly intrigued by the sixth section of the article, which delves into the 'Organic Composition of Source Rocks.' The concepts presented in this section are notably innovative. The hydrocarbon potential of these organic-rich lacustrine shales is primarily contingent upon the depositional environment and the current burial depth of the sediments, which are discussed in meticulous detail. The article posits that the hydrocarbon source rocks in other continental basins could be explored further, employing this novel framework for discussion.

Response 5: The hydrocarbon-generating potential of organic-rich lacustrine shales is contingent upon the depositional settings and the present burial depth of the strata. Further exploration of this topic will be undertaken within the context of the Liushagang Formation in the Fushan Depression, where I have incorporated electron micrographic analyses. It is my intention to delve deeper into these observations in forthcoming research endeavors.

Reviewer 3 Report

Comments and Suggestions for Authors

The title must be corrected: Evaluation, not Evaluaition.

In the abstract   …hydrocarbon sequestration peaks at Ro = 0.8%.... (What does it mean sequestration in the context of thermal maturity?)

In the introduction: It would be nice to add volume of oil (bbl) in addition to tons, and reserves of natural gas is missing 3 in m³.

Line 58 – fat oil (What the authors intend to express?)

Figure 1 –The color representing “uplift” must be brown in the legend, according to the map.

Figure 3 – contour line in the legend is not referring to any variable.

Tables 1, 2, 3, and 13– complete the units Depth (m), TOC (%), S1 and S2 (mg HC/g rock), S1 + S2 (mg HC/g rocha).

Line 205 – please explain what coefficient of restitution stands for.

Line 257 – At the present, the subsidence center remains constant. It is an obvious statement, is there any specific point to make it?

Line 282 -  …planar distribution map…  What is the idea intending to transmit with planar?

Figures 5 and 8 – It is necessary to add the reference of the author who firstly suggested these graphs.

Figure 9 – hydrocarbon expulsion threshold is not clear in the figure.

 

Coments:

I am not indicate to revise the calculations presented in the manuscript, so I recommend to the editors request the revision of an expert on this subject.

Source rock thickness is frequently referred in text as having 500 m or more. I suggest the inclusion of a concise explanation of the method to interpret that. For a reader it seems more the color of the rock rather than the TOC content and S2 that was used a criteria to determine the thickness of the source rock interval.

The numbers in maps are too small. Please use bigger numbers.

Figures must be centered between margins, following the paragraphs.

Units used in the text must be completed, for example, in line 465, 430 mg HC/g rock.

In figure 13 it is necessary to explain why authors used two different units to express “mean expulsion ratio”, mg/g and mg/g/100m? Also, the units must be completed as commented above.

To clarify the understanding I suggest to refine the explanation about accumulation factor, it is not clear what it means. Is it the amount of petroleum able to be trapped?

I suggest also to the author to comment a little bit more about the classification of the organic matter. Who published this OM classification types II₁ and II₂, or it is a new classification?

Comments on the Quality of English Language

The paper needs a minor revision of the English language. Most of the potential problems I detected are related to words not in accordance with the English jargon for geochemistry, and that I commented above.

Author Response

I extend my sincerest gratitude for your insightful suggestions and comments. Your feedback has been meticulously reviewed and incorporated into our manuscript on a point-by-point basis.

Regarding the oversight in the title, I appreciate your prompt notification. Rest assured, the title has been amended according to your specifications.

In response to your inquiry about the Reflectance of Vitrinite (Ro), it currently stands at 0.8%, which is the maximum efficiency of 97.7% of this study

With respect to the unit of production, I am grateful for your reminder. The report provided by our partner, PetroChina Hainan Fushan Oilfield Exploration and Development Co., which substantiates our claims. They prefer to use volume to represent reserves.

In the interest of precision, the term 'fat oil' has been replaced with 'abundant hydrocarbon resources' to convey the intended meaning more formally.

For the graphical revisions, the following adjustments have been made:

• The color of the 'bulge' in Figure 1 has been altered to brown.
• The outline line has been omitted from the legend of Figure 3.
• Units have been appended to the headers of Tables 1-3 to ensure clarity.

The coefficient of recovery mentioned in the text refers to the hydrocarbon potential recovery factor.

In the discussion of the sedimentation centers, we have demonstrated that throughout the geological history, neither the sedimentation nor the depositional centers have ever shifted from their positions within the Huangtong Sag and the Bailian Sag.

The phrase in Line 282, which was deemed inappropriate, has been expunged from the manuscript.

For the sourcing of geological plates, the following citations have been added:

• Figure 5 (after Dembicki Jr., 2009)
• Figure 8 (after Peters, 1986)

Additionally, modifications have been implemented in Figure 9 to highlight the Ro data. I have also included the mean values for Ro in both Table 2 and Table 3 for comprehensiveness.

For the ‘Source rock thickness is frequently referred in text as having 500 m or more’ that appears in the description of Fig. 4, as a supplement, and in order to let the readers better understand the whole article, I put this part of the content in the later.

 

Comments 1: The numbers in maps are too small. Please use bigger numbers.

Response 1: We have rearranged the three figures and enlarged each one partially to make it easier for the reader to access the digital information more quickly.

Comments 2: Figures must be centered between margins, following the paragraphs.

Response 2: We centred and reformatted the figure so that it was more in line with the journal's rules.

Comments 3: In figure 13 it is necessary to explain why authors used two different units to express “mean expulsion ratio”, mg/g and mg/g/100m? Also, the units must be completed as commented above.

Response 3: Figure 13 has been corrected to show the hydrocarbon-expulsion ratio and the hydrocarbon expulsion rate. Thank you for correcting the error.

Comments 4: To clarify the understanding I suggest to refine the explanation about accumulation factor, it is not clear what it means. Is it the amount of petroleum able to be trapped?

Response 4: Here is the transport and accumulation coefficient of hydrocarbonsmigration and accumulation coefficient, which has been modified in the table.

Comments 5: I suggest also to the author to comment a little bit more about the classification of the organic matter. Who published this OM classification types II₁ and II₂, or it is a new classification?

Response 5: References have been made in the text (after Peters, 1986).In this case it refers to the cheese root type (Petroleun Formation and Occurrence B.P. Tissot D.H. Welten 1984)

Comments 6: on the Quality of English Language:The paper needs a minor revision of the English language. Most of the potential problems I detected are related to words not in accordance with the English jargon for geochemistry, and that I commented above.

Response 6: Thank you for your careful and patient overall guidance. You have made revisions and checks on this part, including deleting content, using units, revising the formatting of reference articles, replacing vocabulary and adding references,

Thank you for your suggestion, your help is very important to us, has been changed according to your request!

Reviewer 4 Report

Comments and Suggestions for Authors

The MS, titled “Source Rock Evaluation and Hydrocarbon Expulsion Characteristics of Effective Source Rocks in Fushan Depression, Beibuwan Basin, China",  reports the hydrocarbon generation potential of lacustrine source rocks. The organisation and applied methods are proper for the aim of the study; nevertheless, some parts are still needing revisions, as follows:

a) The authors made discussions about the %Ro values, but it is not mentioned that these values are based on measured %Ro values or calculated %Ro values using Tmax according to Jarvies’ method.

b) If the %Ro is based on measured %Ro values, please add the data about the used microscope, the standard material for reflectance measurements, and the maceral classification.

c) Please add the model and type of used Rock-Eval pyrolysis equipment and followed the methodology in this study.

d) Although the maceral compositions and plotting data from the HI-Tmax diagram are in agreement, the lack of microphotographs of identified macerals in the samples is decreasing the soundness of the study. Since this data is important for supporting the assumption of the authors, please provide selected microphotographs of the identified macerals in the samples.

e) Section 4 should be discussed after Section 5 or within Section 7 using Rock-Eval pyrolysis and %Ro values.

f) Please make more visible contours and numbers in Figures 4, 6, and 7.

 

I added several notes and corrections to the revised MS. Please check them out. Overall, I suggest a moderate version and would like to check the revised MS.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English of MS is more and less good; nevertheless, small grammar and typo corrections are still needing

Author Response

We extend our sincere gratitude for the insightful feedback you have provided. Upon thorough examination of the document 'peer-review-39548127.v1.pdf' that you so kindly submitted, we have meticulously addressed each of the editorial remarks. The revisions encompass a spectrum of amendments, including:

1. The elimination of superfluous content to enhance clarity and conciseness in Abstrat.
2. The standardization of units for consistency and accuracy throughout the text. delete all "0" and leave blank in Table 2.
3. The rectification of the citation format to adhere to the established academic standards, like control scape problem in the entire MS and References are cited after Figures 4 and 7 (formerly Figures 5 and 8).
4. The substitution of terminology to ensure precision and alignment with geological nomenclature. I accepted all the replacements such as liptinite macerals.
5. The supplementation of the reference list with pertinent literature to bolster the scholarly foundation of the work. (Hunt, 1991; Hazra et al., 2017, 2019; Karayigit et al., 2021; Vu et al., 2013; Yang and Horsfield, 2020).

We have also made changes to your suggestions.

Comments 1: The authors made discussions about the %Ro values, but it is not mentioned that these values are based on measured %Ro values or calculated %Ro values using Tmax according to Jarvies’ method.

Response 1: We provide an additional description in 3.2 Laboratory methods.

Comments 2: If the %Ro is based on measured %Ro values, please add the data about the used microscope, the standard material for reflectance measurements, and the maceral classification.

Response 2: We provide an additional description in 3.2 Laboratory methods. In the latest Tables 2 and 3, the data for Ro and the corresponding SD and N have been supplemented.

Comments 3: Please add the model and type of used Rock-Eval pyrolysis equipment and followed the methodology in this study.

Response 3: Added to 3.2 Laboratory methods as requested.

Comments 4: Although the maceral compositions and plotting data from the HI-Tmax diagram are in agreement, the lack of microphotographs of identified macerals in the samples is decreasing the soundness of the study. Since this data is important for supporting the assumption of the authors, please provide selected microphotographs of the identified macerals in the samples.

Response 4: We provide microphotographs of identified macerals in the samples (Figure 12). I couldn't agree more that providing microphotographs can be more scientific. To enhance the precision of microcomponent identification and classification, the present study employs microscopic examination of the microcomponents within the casein root. While the translucency may not be as pronounced compared to whole-rock microcomponents, the method offers enhanced precision in delineating component boundaries.This approach ensures that the obtained data are more reliable. However, the transparency of the photographs necessitates the use of specific techniques to discern inertinite macerals in the E2L1 formation of the Huangtong Sag. These observations corroborate the hypothesis that, despite a higher total organic carbon (TOC) content, the formation may not possess the requisite conditions for hydrocarbon generation.

Comments 5: Section 4 should be discussed after Section 5 or within Section 7 using Rock-Eval pyrolysis and %Ro values.

Response 5: In accordance with your recommendation, Geological characteristics of source rock have been relocated to section 5. Additionally, the Rock-Eval pyrolysis (Ro) data have been incorporated into Tables 2 and 3, and the coloration of the mudstone has been specified in Table 3. This arrangement is designed to enhance the reader's comprehension and facilitate

Comments 6: Please make more visible contours and numbers in Figures 4, 6, and 7.

Response 6: We have rearranged the three figures and enlarged each one partially to make it easier for the reader to access the digital information more quickly.

We are confident that these revisions will significantly elevate the quality and credibility of the manuscript.

We are confident that these revisions will significantly elevate the quality and credibility of the manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I appreciate that you valued my feedback and made most of the changes that I recommended.  But you did not respond to an important technical issue I previously mentioned that you need to address before this paper can be accepted for publication.  Specifically, how did you determine the amount of each kind of maceral present in the rock samples shown in Table 2 (data summarized in Figure 11)?  Did an organic petrographer perform a visual kerogen analysis (VKA) on each of these samples?   Or did you use Rock-Eval HI values to estimate the amount of each kind of maceral present (after making assumptions about the HI value of the sapropel, exinite, and vitrinite end members)?

Here is why it is important to clarify what you did.  Assume a source rock sample has an HI value = 400.  That sample might be a 50:50 physical mixture of oil-prone sapropel (HI = 600) and gas-prone vitrinite (HI = 200).  Alternatively, it might contain only oil+gas-prone organic matter with HI = 400 that originally was oil-prone organic matter that later was partially oxidized or partially degraded by microbes.  (I think you used HI values to estimate the amount of oil-prone and gas-prone macerals in these samples.)  In the first case, only the oil-prone organic matter in the kerogen will generate petroleum (=crude oil) at Ro = 0.8.  In the second case, all the kerogen will generate crude oil plus natural gas at that level of thermal maturity.   

You also need to modify Figure 8 and then briefly comment on a few issues.  The x-axis on this figure should be logarithmic (ranging from 0.1 to 1.0) – not arithmetic because Ro increases linearly with depth on a logarithmic scale.  Then add a line on each of the sub-figures that passes through Ro = 0.2 at the surface and appropriate Ro values measured on the rock samples selected from wells located in each area.  Then you need to explain the following results:

(1)    Huangtong Sag:  Why do Ro values range so widely (from 0.5 to 0.9+) on samples collected from the E2L2X interval from 3700-3900 m?  Also, the green data points form a linear array with depth – but why do they project to Ro = 0.2 at a depth of ~1000 m?

(2)    Bailian Sag:   Why does the slope of the line through the Ro values measured on samples collected from the E2L2X interval change so dramatically at a depth of ~3700 m?

(3)    Southern Slope Zone:  Why do the Ro values form two linear arrays - -  one which projects to Ro  = 0.2 at the surface, and a second one that projects to a higher Ro value at the surface?

A minor technical comment is that on Line 1646 and Line 1658 you describe burial at the Yong 7 well and the Lian 23 well as “continuous”.  But you also state that at these locations there were three periods of uplift.  The burial was not continuous if uplift also occurred.

Also correct the following errors:

(1)    Line 941, change Silicon  (Si ) --  which makes no sense - -  to the RockEval parameter S1: i.e., distillable HCs

(2)    Lines 941-942:  You describe the Hawk RockEval parameters Sulfur (S) and Sulfur as Pyrolyzable (Ss).  Does the Hawk analysis measure sulfur?  And do you mean pyrolyzable kerogen (S2) instead of pyrolyzable sulfur (Ss)?

(3)    Lines 944-945:    You describe the liberated hydrocarbons as S and Ss.   Do you mean S1 and S2?

(4)    Line 946:  You describe the CO2 yield as S2.  Do you mean S3?

(5)    Line 1225 (Caption of Figure 4):  E2L1X samples should be labelled (f) – not (d).  And E2L1S samples should be labelled (g) – not (e).

(6)    Line 1275:  Mention that these source rocks generate oil at Ro = 0.5 because they contain Type II-S kerogen (which is how you responded to my comment).

(7)    Table 2:  Reverse the column labels Std. Dev. and N.    

Author Response

I extend my sincerest gratitude for the meticulous review of my manuscript and for the insightful suggestions that are instrumental in enhancing the caliber of my submission. For your reference, I have meticulously revised and highlighted the sections you recommended for alteration. Below is a detailed account of your esteemed feedback and my corresponding responses:

Comments 1: I appreciate that you valued my feedback and made most of the changes that I recommended.  But you did not respond to an important technical issue I previously mentioned that you need to address before this paper can be accepted for publication.  Specifically, how did you determine the amount of each kind of maceral present in the rock samples shown in Table 2 (data summarized in Figure 11)?  Did an organic petrographer perform a visual kerogen analysis (VKA) on each of these samples?   Or did you use Rock-Eval HI values to estimate the amount of each kind of maceral present (after making assumptions about the HI value of the sapropel, exinite, and vitrinite end members)?Here is why it is important to clarify what you did.  Assume a source rock sample has an HI value = 400.  That sample might be a 50:50 physical mixture of oil-prone sapropel (HI = 600) and gas-prone vitrinite (HI = 200).  Alternatively, it might contain only oil+gas-prone organic matter with HI = 400 that originally was oil-prone organic matter that later was partially oxidized or partially degraded by microbes.  (I think you used HI values to estimate the amount of oil-prone and gas-prone macerals in these samples.)  In the first case, only the oil-prone organic matter in the kerogen will generate petroleum (=crude oil) at Ro = 0.8.  In the second case, all the kerogen will generate crude oil plus natural gas at that level of thermal maturity.   

Response 1: In addressing the question of “how to determine the amount of each kind of maceral present in the rock samples shown in Table 2 (data summarized in Figure 11) ”，the primary approach is through the method you previously referenced: an organic petrographer conducts a visual kerogen analysis (VKA) on each sample. This technique is favored for its precision in identifying and quantifying maceral constituents. Additionally, I have provided Figure 12, which illustrates the Microscopic identification of kerogen macerals and types of Liushagang Formation in Fushan Depression. The decision to focus on kerogen microscopic components for microscopic examination, as opposed to whole-rock components, stems from the superior classification capabilities of the former. This approach ensures a more precise delineation of maceral components, thereby enhancing the reliability of the identification outcomes. Furthermore, the Hydrogen Index (HI) is considered in the classification process, with its specific values accessible from the vertical axis of Figure 7. Your reminder to incorporate the HI index is indeed crucial, and in conjunction with your suggestions, this classification aligns with the second scenario: “all the kerogen will generate crude oil plus natural gas at that level of thermal maturity.”

Comments 2: You also need to modify Figure 8 and then briefly comment on a few issues.  The x-axis on this figure should be logarithmic (ranging from 0.1 to 1.0) – not arithmetic because Ro increases linearly with depth on a logarithmic scale.  Then add a line on each of the sub-figures that passes through Ro = 0.2 at the surface and appropriate Ro values measured on the rock samples selected from wells located in each area.  Then you need to explain the following results:

(1)    Huangtong Sag:  Why do Ro values range so widely (from 0.5 to 0.9+) on samples collected from the E2L2X interval from 3700-3900 m?  Also, the green data points form a linear array with depth – but why do they project to Ro = 0.2 at a depth of ~1000 m?

(2)    Bailian Sag:   Why does the slope of the line through the Ro values measured on samples collected from the E2L2X interval change so dramatically at a depth of ~3700 m?

(3)    Southern Slope Zone:  Why do the Ro values form two linear arrays - -  one which projects to Ro  = 0.2 at the surface, and a second one that projects to a higher Ro value at the surface?

Response 2: We have revised Figure 8 in accordance with your recommendations, reverting the x-axis to logarithmic scaling and restoring the range to 0.1-1.0. Concerning your suggestion to include a trend line, we conducted a thorough review of the pertinent literature. It has been observed that experts typically refrain from adding extraneous lines to facilitate clearer data interpretation for the readers. Therefore, we have chosen not to incorporate such a line. We seek your understanding in this regard."

For the interpretation of the results:

(1)    Huangtong Sag: The reflectance of vitrinite (Ro) within the E2L2X hydrocarbon source rock stratum is observed to exhibit a broad distribution ranging from 0.5 to 0.9+. This variability is attributed to the influence of igneous intrusions, which result in anomalous Ro values in this particular area.

(2)    Bailian Sag: In addition to the maturity anomaly observed at the igneous intrusion site, which results in a broad distribution of the vitrinite reflectance (Ro) values within the E2L2X stratigraphic section, the scarcity of well distribution in the eastern region also limits the availability of measured values necessary for a comprehensive regional characterization. Consequently, I have combined the analogue values with the measured ones to illustrate a continuous variation in Ro. After consultation with my co-author, we have decided to retain the analogue values for this section. We trust this approach will be understood and deemed appropriate.

(3)    Southern Slope Zone: In the southern sector of the Fushan depression, the Hongguang and Meitai regions are situated respectively to the east and west of the southern slope belt. Regrettably, the paucity of empirical data has necessitated the utilization of simulated values on two occasions, resulting in the formation of two linear arrays. However, the amalgamation of these two blocks is inconsequential to the ultimate conclusions drawn from the overarching discourse.

Comments 3: A minor technical comment is that on Line 1646 and Line 1658 you describe burial at the Yong 7 well and the Lian 23 well as “continuous”.  But you also state that at these locations there were three periods of uplift.  The burial was not continuous if uplift also occurred.

Response 3: In the interest of precision, I have removed the term 'continuous' from my statement, acknowledging my oversight in its application. I appreciate your prompt to correct this matter.

Comments 4: Also correct the following errors:

(1)    Line 941, change Silicon  (Si ) --  which makes no sense - -  to the RockEval parameter S1: i.e., distillable HCs

(2)    Lines 941-942:  You describe the Hawk RockEval parameters Sulfur (S) and Sulfur as Pyrolyzable (Ss).  Does the Hawk analysis measure sulfur?  And do you mean pyrolyzable kerogen (S2) instead of pyrolyzable sulfur (Ss)?

(3)    Lines 944-945:    You describe the liberated hydrocarbons as S and Ss.   Do you mean S1 and S2?

(4)    Line 946:  You describe the CO2 yield as S2.  Do you mean S3?

(5)    Line 1225 (Caption of Figure 4):  E2L1X samples should be labelled (f) – not (d).  And E2L1S samples should be labelled (g) – not (e).

(6)    Line 1275:  Mention that these source rocks generate oil at Ro = 0.5 because they contain Type II-S kerogen (which is how you responded to my comment).

(7)    Table 2:  Reverse the column labels Std. Dev. and N.   

Response 4: I extend my sincere gratitude for the constructive feedback you have provided. Upon reviewing my initial submission, I acknowledge the oversights in the application of terminological precision and the resultant inaccuracies. I have taken your comments to heart and have meticulously revised the document to address the specific points raised.

(1)    The symbol "Si" has been rigorously replaced with "S₁" to maintain consistency with geological nomenclature.

(2)    The phrase "Have changed it" has been corrected to "S₂" for clarity and adherence to the established abbreviations.

(3)    The verb tense inconsistencies have been harmonized to "S₁ and S₂" to ensure uniformity throughout the text.

(4)    The lowercase "Ss" has been elevated to "S₃" to align with the established abbreviation protocol.

(5)    The caption of Figure 4 has undergone a necessary revision from the erroneous "(d) E₂L_1X source rocks (e) E₂L_1S source rocks" to the accurate "(f) E₂L_1X source rocks; (g) E₂L_1S source rocks," reflecting the correct stratigraphic units.

(6)    In light of your query regarding the hydrocarbon temperature and maturity in the Fushan Depression, I have revisited and reaffirmed the conclusions reached in collaboration with PetroChina Hainan Fushan Oilfield Exploration and Development Co., Ltd. The agreement on the thermal maturity index of 0.5 is a point of consensus and is highly valued.

(7)    Lastly, in accordance with your directive, the column labels "Std. Dev." and "N" have been appropriately reversed to reflect the correct order.

I appreciate your diligence in reviewing my work and your commitment to upholding the highest standards of geological discourse. Your attention to detail has been instrumental in enhancing the quality of my submission.

 

Thank you once again for your valuable input.