A Novel Numerical Method for Geothermal Reservoirs Embedded with Fracture Networks and Parameter Optimization for Power Generation
Round 1
Reviewer 1 Report
1. when above boiling point，the fluid includes watet and steam, does the model consider the phase transition? This should be elabrated.
2. There should be a comparation of the proposed model and existing model, or the advantage and limits of the model should be pointed out.
Author Response
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Reviewer 2 Report
This is a manuscript presenting a method to reduce the computational time for the simulation of fractures and wellbores in geothermal reservoirs. The presentation is overall clear. My comments are as follows:
-line 174 replace "embarrassment" with "difficulty"
-line 190 relpace "verify" with "assess"
-make a Table and include the information presented in lines 198-201.
-In Fig. 3 include the name of the x-axis variable and its units.
-Fig. 4 is too small. The numbers and axes are not legible/visible
-line 452 (Fig. 9) replace "flow rate" with "velocity". What velocity is depicted in these diagrams?
-Fig. 10 Whose temperature is depicted in the figure?
I have included specific suggestions
Author Response
Thanks a lot for your time reviewing our paper and helping us improve this work! We appreciate it very much! Please see the attachment for detailed review comment responses.
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Reviewer 3 Report
The manuscript entitled “A novel numerical method for geothermal reservoirs embedded with fracture networks and parameter optimization for power generation” is relevant to the scope of the magazine.
The cited references cover to a satisfactory degree the scientific field of the presented work. 14 out of 43 references are written within the last 5 years.
The mathematical background of the proposed method is robustly presented and supports the novelty of the approach as described by the authors. The basic concern is that in the simplification concept, where the fractures are regarded as zero-thickness surfaces, one of the fundamental properties of the fractures (the aperture)- which gives fractures a 3d entity - is not directly taken into account. From a computational point of view, it is a very smart approach and has been persuasively validated by the runs in the simple cubic models. In any case, simplifications that favor computational performance always are susceptible to a risk of declining significantly from the physical context of the simulated system.
A few questions arise also about the practical value of the method in real reservoirs. The authors have tested the proposed method in a granite reservoir where fractures “are uniformly distributed in the study domain”. This is not usually the case. Fracture reservoirs are heterogenous to highly heterogenous and very demanding statistical work is required to prepare a DFN model that resembles in a satisfactory way reservoir conditions. Is the method applicable to such types of reservoirs? Can the model work on layered DFN models? For example, in carbonate fracture reservoirs fractures may vary significantly at different stratigraphic levels.
The optimization method proposed by the authors is of great practical value and can be very helpful (with the limitations described above) in well design.
The quality of figures and tables is of high quality and minor changes are required (see attached file).
More comments and notes for the improvement of the manuscript can be found in the attached file.
The use of English is very satisfactory and only in a few cases the syntax is confusing.
To conclude, the presented manuscript is of high value and the proposed method can be a very useful tool for well design and production optimization of geothermal fields. The limitations of the method are «consistent” with the constraints that arise when we try to simulate complex physical systems. In this context, it is recommended to accept for publication the present manuscript, with minor corrections.
Comments for author File: 
Comments.pdf
Very few corrections, see attached file.
Author Response
Thanks a lot for your time reviewing our paper and helping us improve this work! We appreciate it very much! Please see the attachment for detailed review comment responses.
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Reviewer 4 Report
*Please consider that same as the operational condition, the reservoir characteristics will affect the heat extraction performance. For a better sensitivity analysis, these parameters should be considered too. See the following works:
#Thermo-hydro-mechanical modeling of an enhanced geothermal system in a fractured reservoir using carbon dioxide as heat transmission fluid-A sensitivity investigation.
#Simulations and global sensitivity analysis of the thermo-hydraulic-mechanical processes in a fractured geothermal reservoir.
*In the previous studies the well placement in the fractured reservoirs is examined in detail and the production efficiency is discussed. It should be noted that beside the well placement, the heat loss alongside the injection and production wellbores is an important factor which should be considered. Please see the following studies:
#Impact of Well Placement in the Fractured Geothermal Reservoirs Based on Available Discrete Fractured System.
#Hydro-Thermal Modeling for Geothermal Energy Extraction from Soultz-sous-Forêts, France.
*Line 164: Please put a reference for the water viscousity. Other thermodynamic properties is a function of the temperature too (specific heat capacity, thermal conductivity, density...). Please mention the way which you treat these parameters.
*You need a model validation with the experimental data or an analytical solution. In the above papers, you will find an example.
*Line 218: Which program? Please cite it.
*The data in Table 1 is a reasonable range, but please use references.
*I did not see the boundary conditions for the mechanical behavior. Also, the initial values for the vertical and horizontal stresses.
*Please use a reference for the Table 3.
*Line 383: Please use a better header.
No comments!
Author Response
Thanks a lot for your time reviewing our paper and helping us improve this work! We appreciate it very much! Please see the attachment for detailed review comment responses.
Author Response File: Author Response.docx
