Numerical Simulation Investigation on Fracture Propagation of Fracturing for Crossing Coal Seam Roof

Round 1

Reviewer 1 Report

In my opinion it suffers from:

1.-A clear nomenclature of all the terms used.

2.- In section 2 the bibliography they use as a base is missing.

3.-In formulas 5 and 6 the difference between CI and C1 is not understood.

4.-They do not explain what the variables that appear in equations 5, 6, 7 and 8 are.

5.- In formula 8, which is K_k², is it permeability or toughness?

6.-In formula 12 they use dx in the denominator without saying what it represents, but it is also not a differential dx as we all know it, I imagine it is an increment and they should use Dx.

7.-In figure 1 they use dx and dy in a discrete environment should be Dx and Dy

8.- What is the difference between the C of equation 14 and the C of equation 2?

9.- How do you ensure the convergence of the Newton-Raphson method for this case?

10.-Figure 3 cannot be understood without explaining the nomenclature.

11.- In reference 7 the year is missing.

12.-I can't find two articles of interest for your research

-K. Li et all “Three-Dimensional Propagation Simulation and Parameter” Hindawi Mathematical Problems in Engineering, Volume 2019, Article ID 3164817, 11 pages

-Zhong Qi Yue, Hong Tian “Generalized Kelvin solution based boundary element method for crack problems in multilayered solids”, Engineering Analysis with Boundary Elements 26 (2002) 691–705

I think the job requires rewriting it again.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Considering the vertical fracture toughness and loss inhomogeneity between layers, the mathematical model of horizontal well fracturing in roof of coal seam is established, and the favorable geological conditions of fracturing through roof are studied. But this study did not present and justify any novelty and significance of this work compared with current state of knowledge, and lack of the research background as well as significance. The simulation result is not well analyzed, either. Therefore, this paper needs to have a major revision before publication.

1.      The first two sentences of the introduction need to be modified. What is the relationship between "coalbed methane resources" and coal seam mining? There seems to be no direct logical relationship between the two.

2.      There are many formulas in the article, but the meanings of specific symbols need to be explained so that readers can read them easily.

3.      In results and analysis, The calibration of model parameters does not distinguish overburden, roof and coal seam. The parameters of the three rock strata are consistent in modeling. How to reflect the differences of different rock strata?

4.      In results and analysis, What is the reason for choosing the viscosity of fracturing fluid of 10 mPa? Is this realistic?

5.      What is the osmotic pressure during the simulation? On what basis?

6.      Is it reasonable to use 13-12-13MPa in 3.1.1 to represent "high-low-high" in-situ stress and 11-12-11MPa in 3.1.2 to represent "low-high-low" in-situ stress? And is the subsequent stress combination reasonable? These stresses do not seem to differ greatly.

7.      In section 3.1.2, the basic mechanical parameters and in-situ stress of overburden and coal seam are the same. Why is it easier for cracks to propagate in coal seam?

8.      In Section 3.1.2, do not use results at the simulation scale to suggest working parameters at the engineering scale.

9.      The introduction of this manuscript is not complete enough for mining-induced rock fracture propagation. Therefore, the introduction needs to be supplemented, e.g., (ⅰ) Fracture behaviour of microwave-heated granite under indentation: Experimental and numerical investigation. Engineering Fracture Mechanics, 2022, 269, 108535 (ⅱ) Numerical simulation of water-silt inrush hazard of fault rock: A three-phase flow model. Rock Mechanics and Rock engineering, 2022, DOI: 10.1007/s00603-022-02878-9. (ⅲ) Solid grain migration on hydraulic properties of fault rocks in underground mining tunnel: Radial seepage experiments and verification of permeability prediction. Tunnelling and Underground Space Technology, 2022, 126, 104525.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

It has improved enough for publication

Reviewer 2 Report

The authors have addressed my comments very well. The paper can be accepted now.