Experimental Study on the Effect of Fractures on the Irreducible and Movable Water in Water-Bearing Tight Sandstone Gas Reservoirs
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this manuscript entitled " Experimental Study on the Effect of Fractured on the Irreducible and Movable Water in Water-Bearing Tight Sandstone Gas Reservoirs”, I think it's better to discuss about below questions. Therefore, I suggest a revision for the manuscript before publication.
- the authors should complete the following sentence, as it is in the abstract: “To analyze the gas-water flow mechanisms in pre-fracturing and post-18 fracturing reservoir conditions.”
- “The experiments demonstrate that pore structures are significantly modified through hydraulic fracturing.” Why? Please try to explain its main mechanisms.
- “pressure gradients by 90%.”, it is a very high value and strongly can affect the production. The authors should carefully mention the results and analyze them for the real cases of petroleum industry.
- In the begin of introduction section, where the challenges are considered, it is recommended to mention corrosion due to the water presence. For this purpose, the next work can be used: https://www.ijcce.ac.ir/article_252008.html
- the procedure of conduction of gas drive experiments should be added in details.
- “Each similarity parameter requires an in-depth analysis of its physical 161 mechanisms in engineering conditions”, the authors mean probably the “reservoir conditions”.
- In table 3, it is better to demonstrate the changes as percentage.
- “In general, there is a linear relationship between the flow resistance and the water saturation in gas-water phase seepage.”, as presented in the results, there is no linear relationship. In addition, R2 should be added to better follow this relationship.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsReview
Journal: Processes (ISSN 2227-9717)
Manuscript ID: processes-3641105
Type: Article
Title: Experimental Study on the Effect of Fractured on the Irreducible and Movable Water in Water-Bearing Tight Sandstone Gas Reservoirs
Section: Energy Systems
General comments
The article presents an experimental study of the transformation of irreducible water into mobile water in tight sandstone gas reservoirs following hydraulic fracturing. Authors use advanced techniques such as NMR, Micro-CT and triaxial in-situ flow system to analyze changes in pore structure and their impact on fluid mobility. This research is timely, given the increasing reliance on hydraulic fracturing in unconventional gas fields. The information presented in the paper fills a critical gap in understanding the mechanisms of water production after fracturing.
Critical comments
- The article emphasizes the short-term, 3 to 6 month increase in water production after fracking and ignores long-term behavior.
This raises questions:
- Do pore structures return to their pre-fracking state over time?
- How does long-term production affect irreducible water remobilization?
These omissions are critical for field applications, where regional operators must predict whether spikes in water production are temporary or permanent. Since the time scope of the study seems truncated, it is necessary to address these issues in a dozen sentences based on the authors' previous research and knowledge.
- The study is based on only three reservoir classes H1, H2, H3 from a single Dongsheng Gas Field. While Authors justify this by comparing similarities between reservoir and open pit cores, the sample size is statistically somewhat insufficient to generalize the results to heterogeneous tight sandstone reservoirs. Additionally, differences in mineralogy, cementation or stress history common in such formations are overlooked. Without broader sampling, claimed percentages, such as 12.4-19.2% pore coalescence, may be context-specific rather than universal.
It is necessary to address this state of affairs in a dozen sentences and somehow justify, from the authors' point of view, the validity of the generalization adopted on the basis of such a set of studies.
- Scaling from the laboratory scale to the field scale is based on similarity criteria (Tab. 1), with no critical limitations to such scaling. For example, can a 10 cm³ core really replicate fracture networks covering 100-150 m under real in situ conditions? The assumption that dimensionless groups perfectly replicate reservoir dynamics is questionable given, for example, the complexity of stress-dependent permeability in compact sands.
Therefore, please at least comment in a dozen sentences on this simplification (or post a scaling error sensitivity analysis).
- Authors identified two changes in pore structure: diameter enlargement and isolated pore connectivity, but unfortunately did not explain the dominant mechanism or its geomechanical factors. Further questions arise that need to be answered in the text of the article:
- Does shear failure have a greater effect than proppant deposition?
- Are these processes uniform across different reservoir classes?
Micro-CT images (Fig. 6) are only qualitative.
Could Authors provide at least 1-2 quantitative indicators, e.g., changes in pore-to-throat ratio and/or coordination number distributions, which would reinforce the message.
Please add a dozen sentences answering these 2 questions and, if possible, an example of a quantitative indicator supporting the theses.
- The study focuses on water mobility, but ignores gas-water interactions. Hence, further questions arise:
- How does gas slip (Klinkenberg effect) change the threshold pressure in fractured and matrix zones?
- Are the relative permeability curves (Fig. 11) affected by fracturing fluids or clay swelling?
These factors, which are crucial in tight gas reservoirs containing water, are simplified or ignored. Since the role of the gas phase in displacing irreducible water needs to be at least hinted at, I would ask you to complete the article with at least a dozen sentences on this issue.
Decision: the article can be published only after correcting / completing the defects indicated in points 1-5.
The perceived editorial faults are indicated in *.pdf.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe work was improved after revision. I recommend it for publication.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Editors and Authors,
I have no further criticisms after the amendments.
The article can be published.
Yours faithfully.
