Productivity Analysis and Evaluation of Fault-Fracture Zones Controlled by Complex Fracture Networks in Tight Reservoirs: A Case Study of Xujiahe Formation
Round 1
Reviewer 1 Report
The manuscript entitled “Productivity Analysis and Evaluation of Fault-fracture Zones Controlled by Complex Fracture Networks in Tight Reservoir A Case Study of Xujiahe Formation” combines the literature discusses the sustainable development of tight gas reservoirs and the production difficulties caused by the uncertain evolution of fractures, introduces the geological conditions and structural characteristics of the Xujiahe Formation, establishes a three-dimensional geological model based on measured and survey data, and performs parameter analysis on the influencing factors of fractures and fracture mesh model. The research logic of the whole manuscript is relatively clear, consistent with the theme of the journal, and can provide certain academic and engineering value. The specific suggestions and opinions are as follows:
(1) The abstract of the manuscript is too lengthy; please simplify it. The background introduction related to the exploration and development of tight sandstone gas in the first part of the abstract may overlap with the content of the introduction, and the "the results show" in the latter part of the abstract should be further summarizedï¼›
(2) Please rewrite the background of Section 2. The original manuscript is written in such a way that the reader feels like it is an introduction of a summary nature, and it is too lengthy. It is strongly recommended to put the background in the introduction and delete itï¼›
(3) Section 4.1 Models: Please check and improve the formulation in line 297ï¼›
(4) The linear relationship between fracture complexity, fracture half length, and net pressure is not strong. Its scatter diagram distribution is relatively discrete, which also reflects the poor fitting effect from R2, and then directly analyzes the parameter relationship with the fitting results. Its rationality needs to be verified; please explainï¼›
(5) In conclusions 2 and 3, please continue to refine the contribution of the conclusion to the actual project, rather than simply describing the research data, including the fluctuation of the ratio of the area between the natural cracks and the main cracks, and the impact of the improvement of crack complexity. And give some suggestions, etc.
The language of the manuscript needs to be improved. Please use more professional vocabulary, and overly long sentences should be further polished to use more academic expressions.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript of Cai et al., "Productivity Analysis and Evaluation of Fault-fracture Zones Controlled by Complex Fracture Networks in Tight Reservoir_A Case Study of Xujiahe Formation," is an article concerning tight reservoir development. The authors present an integrated approach for efficient complex fracture evaluation modeling, SRV/fracture parameter calculation, and productivity analysis methods after fracturing. The paper is very interesting and informative. I recommended it be accepted after minor revision. There are additions/revisions that I feel could improve this paper. A more detailed list of my thoughts follows below.
1. Figure 3 shows the 3D geological model of the Xujiahe formation in Well 1-10. Which methods are you using to characterize the spatial distribution of such rock mechanical properties? Please briefly clarify it.
2. In Section 4 models, some references related to Equations (1) through (4) are missing. Please add these references.
3. In Figure 4, natural fractures are assumed to be perpendicular to hydraulic fractures. Is this fracture pattern consistent with the outcrops or other geological sources? Please supplement the evidence or discussion for this assumption.
4. In Figures 6-9, the unit of Pressure should be MPa rather than Mpa. Please revise them accordingly.
5. The relations of two related parameters in Figs 10-11 are not strong. Please add some discussions about the two relation plots.
6. Are there any available microseismicity data in the study area to validate the fracture network model? Or other databases to validate the robustness of the fracture model？
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript highlights the importance of adopting efficient development technologies in sustainable tight gas reservoir development to optimize the extraction of natural gas resources while minimizing adverse environmental and social impacts. The paper contributes a new systematic evaluation method to investigate the fracture complexity and productivity in fracture-fault zone of tight reservoirs controlled by complex fractures networks by combining the pressure fall-off analysis and differential facture dynamic fitting model and offers good advice on in-situ fracturing measures.
There are some problems, which must be solved before it is considered for publication. If the following problems are well-addressed, this reviewer believes that the essential contribution of this paper are important for integrated technology of fracturing and enhanced oil recovery in tight reservoirs:
(1) Table format should be adjusted according to the template.
(2) Some sentence punctuations needs to be adjusted, such as line 21~24 and line 488-491.
(3) Spaces must be added between numbers and units.
(4) The number of figure is missing. Such as “Results in figure show…”in 431/454,
(5) The format of REFERENCES in 692-695 should be corrected according to template.
(6) CONCLUSIONS needs adjusted, as it’s more of an afterthought. The authors are suggested to highlight important findings and include afterthought oh this work.
Once the above concerns are fully addressed, the manuscript could be accepted for publication in this special journal.
The English should be improved, Such as Line 454~459.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
In this paper, the Authors, show a method to evaluate the gas reservoir volume and fault-fracture zone complexity. The model was developed based on the Xujiahe formation in China, using 3D geological model was developed using seismic results, logging data, and rock mechanics experiments to analyze planar heterogeneity.
The manuscript is interesting, and it is opinion of the reviewer that it can be published after the following revisions.
(1) In the title of the paper, after the word "Reservoir" there is " _ ". It is recommended to insert " : "
(2) the abstract is very long and therefore should be reduced. Only the information necessary to illustrate the content of the research should be included in the abstract; other information can be included in the Introduction section.
(3) In Section 3 the Authors could include a geographic map (e.g., of China) to identify the location of the case study with Malubei-Tongjiang area highlighted in a circle.
(4) In line 278 there are some typos: remove the zero after "2840" (precision here is useless), and add a space after the colon. The correct script is as follows: "... formation (2840-3046m): is mainly ... ". Please carefully reread the entire manuscript and correct similar mistakes.
(5) In Figure 3 the colormap graphical scale is unreadable. Please improve the quality of the image.
(6) It is not clear why in equation 4 there are two lines before and after the curly brackets. If they are two different equations, it is recommended to write it on two lines without using curly brackets.
(7) In the graphs of Figures 6-9 there appear to be green and red lines. Authors should indicate what they denote.
According to what said above, the reviewer’s opinion is that the manuscript can be accepted for publication after the described revisions.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 5 Report
I am privileged to have the chance to assess the high-quality manuscripts submitted for publication. Upon thorough examination of this particular article, I recommend that the authors enhance the quality of their presented photographs and provide more detailed explanations for them to meet the necessary standards for publication in Sustainability journal. Once these revisions are made, I am confident that this article will meet the publication requirements and be a valuable addition to the field of sustainability.
In general, I find the article "Evaluation of Stimulated Reservoir Volume and Fault-Fracture Zone Complexity in Tight Sandstone Gas Reservoirs: A Case Study in the Xujiahe Formation of Northeastern Sichuan Basin" to be a well-written and informative piece of research. The authors provide a detailed analysis of the complex composition of tight sandstone reservoirs, which presents challenges for effective natural gas extraction. The article highlights the importance of natural fracture networks and high-quality reservoirs in controlling gas enrichment in the Xujiahe formation. The authors present a systematic method to evaluate stimulated reservoir volume (SRV) and fault-fracture zone complexity after stimulation, using a 3D geological model developed from seismic results, logging data, and rock mechanics experiments to analyze planar heterogeneity. Overall, this article provides valuable insights into the complex composition of tight sandstone reservoirs and presents a systematic method for evaluating stimulated reservoir volume and fault-fracture zone complexity after stimulation.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 6 Report
This work presents the case of tight gas sandstone reservoirs in terms of productivity analysis starting from fracture evaluation (natural and artificial fractures) and ending up to productivity analysis. The manuscript is generally well-written and well-structured. The results are convincing. However, the manuscript lacks a discussion in introduction and section 2.2. on:
a. the mechanical and hydraulic properties of tight sandstones. The range of sandstone ‘types’ should be presented (cohesionless or unconsolidated sands, weakly cemented and poorly consolidated sandstones, conventional sandstones, tight sandstone reservoirs) and
b. the hydraulic fracturing behaviour under fluid injection of each of these materials. There are quite a few studies in the literature referring to this connection. Please include the appropriate references and establish these relations.
Otherwise, the novelty and contribution of this research does not emerge. On the first read, a question arises as to what makes a difference if there are tight sandstone reservoirs in place and why is this process governed by different processes? The authors should mention the strength, porosity permeability (or hydraulic conductivity) in their discussion.
Here are some detailed comments:
1. L80-82 please provide a reference for those values
2. L84-86 is there a reference about this? Who conducted the simulations? Please provide more details to support the statement.
3. A paragraph should be added in the introduction to include information on the definition of tight sandstones (range of permeability, porosity and strength values) and comparison with conventional sandstones and poorly consolidated sandstones.
4. The associated problems for this application have been nicely presented and objectives are clearly stated.
5. L93: Please spell out SRV please. It appears here for the first time (after the abstract).
6. L92- what do the authors mean by complex fractures? Please compare to conventional reservoirs and weakly cemented reservoirs. Along with comment 3, the authors need to describe unconsolidated sands (or cohesionless sands), poorly consolidated and weakly cemented sandstones (soft sands), conventional sandstones and tight sandstones. There are many experiments conducted in relation to fluid injection to perform hydraulic fracturing in the literature on this range of materials which relate the findings with the hydraulic and mechanical properties. On the weaker end there are many studies utilizing artificially reconstituted specimens using various techniques to generate the cementation which is the bonding material between the particles. The authors need to refer to these findings and also add information on how hydraulic fracturing has been investigated experimentally for tight sandstones. Are there any artificial specimens in this case (can also added in Section 2.2.)?
7. L109 – Do the authors mean linear regression here?
8. Section 2.1 What mathematical method was used in this study and why? It should be mentioned at the end of this section.
9. Section 2.2. Please look at comments 3 and 6 and adjust accordingly.
10. Figure 2: could this be presented in a clearer way? Font size is very small.
11. L286 “The” 3D geological model….
12. Figure 3 legends are two small to read.
13. L359 please correct to: “and the original reservoir, as shown in Figure 5.”
14. L383 Step3. Remove comma and add a fullstop
15. L385 Please correct to: Step 4. Apply….
16. Figures 6-7,9,13 please make font size larger.
17. Conclusion: please comment on the applicability of the findings in other reservoirs.
The paper is well-written.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
accept
accept
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
