Research on the Effect of Shale Core Mechanical Behavior on Casing Deformation
Round 1
Reviewer 1 Report
Dear Authors,
a potentially interesting manuscript, but with significant gaps to be considered a complete article.
It will indicate the most important issues for improvement in my opinion.
1. Better discussion in the context of what has been done in this field (so far), I recommend here the analysis and discussion of issues present in the literature, especially in the LF-NMR connection:
- insight into compounds signatures in low field 1H NMR
- low field 1H NMR characterization of mesoporous silica MCM-41 and SBA-15
- identification of proton populations,
- overcoming the barriers of nanoporous porosity.
- petrophysical evaluation of the Lower Permian formation as a potential reservoir (here in the context of T2lm changes along with pressure and significance for permeability)
2. Description of possible methods of quality verification of the proposed method. Here, the minimum requirement is to describe (and discuss the importance of) further steps to verify the method based on research, complementary measurements, e.g. using phantoms or other LF-NMR techniques and approaches.
Some suggestions:
Analyzing the issues listed in point 1, the following topics arise for clarification and discussion:
- lack of TE echo time and other LF-NMR parameters for many nanopore systems, TE too long is insufficient to measure T2 from all protons filling the pores, here a form of calibration to the standard proton content, e.g. H2O is recommended, then calibration porosity recorded by T2 versus e.g. mass-volume porosity allows to assess the correctness of measurements. Additionally, what about the proton signal from the probe (what about coil ringing?) and the protons that are chemically bound to clay and organic matter, shouldn't that be subtracted before the ILT transform? It seems that for the analysis of e.g. ILT a differential signal should be taken?
- the authors do not take into account the effect of diffusion on the distribution of PSD by T2, below 10 nm it should be noticeable.
- PSD or PTD distribution graphs suggest that pores with nanometric diameters are under-measured. we precisely determine the scope of our PSD in the nanometer range,
- what is the SNR for the TE used, how much was the accumulation, what did the raw signal look like, for full saturation and the highest pressure.
- in the literature there are correlations between LF-NMR parameters and, for example, organic and clay matter
- the division into types of porosity in LF-NMR (correct) allows for a better assessment of changes occurring under pressure, e.g. the observed increase in T2lm with increasing pressure suggests the need to correct the permeability measured in laboratory conditions. It also shows the dependence of these changes on the content of clay matter.
These and other topics should be discussed in the context of the given literature issues, point 1.
Finally, it should be more precisely stated what the practical meaning of the results is, currently the manuscript is more like a measurement report.
Author Response
Thank you very much for giving us the opportunity to revise our manuscript entitled “The research of the effect of shale core mechanical behavior on casing deformation” (Manuscript ID: Processes-2063130). Thanks for your reasonable advice. As reviewer suggested, we have revised in the paper (see the revised paper).
Detailed Response to Reviewers:
Reviewer #1:
- Better discussion in the context of what has been done in this field (so far), I recommend here the analysis and discussion of issues present in the literature, especially in the LF-NMR connection:
- insight into compounds signatures in low field 1H NMR
- low field 1H NMR characterization of mesoporous silica MCM-41 and SBA-15
- identification of proton populations,
- overcoming the barriers of nanoporous porosity.
- petrophysical evaluation of the Lower Permian formation as a potential reservoir (here in the context of T2lm changes along with pressure and significance for permeability)
Response: Thank you for your valuable question. Nuclear magnetic resonance (NMR) is a physical phenomenon that the spin nucleus (such as proton) system in the strong magnetic field environment absorbs the energy of the matched RF field imposed by the outside (the energy is the same as the energy difference of the spin nucleus system). The macroscopic magnetization vector formed by magnetization of the sample in a strong magnetic field is deflected after being subjected to a vertically applied RF field. The deflected magnetization vector causes the change of magnetic flux in the process of restoring to equilibrium, resulting in the nuclear magnetic resonance signal in the coil. Not all the spin motions of atomic nuclei can produce nuclear magnetic resonance. Different atomic nuclei produce different nuclear magnetic resonance effects according to the number of neutrons and protons in the atomic nucleus. If the number of protons and neutrons in the nucleus is even, the spin of this nucleus does not produce nuclear magnetism. We call this nucleus a nonmagnetic nucleus. On the contrary, we call the nucleus whose spin motion can produce nuclear magnetism magnetic nucleus. It is found that 1H, 13C, 19F, 15N, 23Na, 31P are magnetic nuclei.
As a source rock, shale is mainly composed of quartz feldspar clay minerals, and its organic matter is mainly kerogen. Its clay minerals and cheese basically contain C and H elements, and the characteristics of its shale are considered in the actual measurement process. The C element and H element in shale clay and organic matter are evaluated as a system and the medium in pores as a whole system. To explore the pore changes under different stresses. However, under different stress states, the lithology of the core itself does not change, but only the stress changes with different pores, and the occurrence state of different pore fluids changes with the change of pores, so as to judge the change process of pore structure.
- Description of possible methods of quality verification of the proposed method. Here, the minimum requirement is to describe (and discuss the importance of) further steps to verify the method based on research, complementary measurements, e.g. using phantoms or other LF-NMR techniques and approaches.
Response: Thank you for the recognition of our work. In this work, the causes, mechanisms and process of casing deformation caused by shale reservoir slip are analyzed. Through a large number of literature research and technical exchanges between experts and scholars, the conventional approach is to assume that shale is a homogeneous, isotropic and brittle material, and simulate the casing deformation process based on the finite element method. Based on NMR technology and true triaxial test device, the mechanical properties, porosity, permeability, micro porosity, and micro fracture morphology of shale core are tested. The tests results are used to to provide data and test methods for establishing shale reservoir model. So that the simulation of casing deformation caused by fracturing formation slip in water of shale reservoir is more accurate.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper is focused on the effect of shale core mechanical behavioron on casing deformation. I suggest the following major revisions before next review:
(1) Figure 6: there is a red line below MPa in the y axis. Please revise it.
(2) Same problems with comment 1 in x axis for Figures 12 and 13.
(3) Line 198: gas permeability usually use apparent permeability. It is OK that if this paper does not show the mechanism of apparent permeability. But it should be given a brief introduction with the following references:
On the flow regime model for fast estimation of tight sandstone gas apparent permeability in high-pressure reservoirs
A model for gas transport in dual-porosity shale rocks with fractal structures
(4) Simulation: what is the inputs for this model? Did you do any validation of the simulation result against experiment?
(5) Figure 20a: it is suggested to plot the relationship between the peak and the pressure, and explain why.
(6) Figure 21: please provide more explanations of different stages on signal changing.
Author Response
Thank you very much for giving us the opportunity to revise our manuscript entitled “The research of the effect of shale core mechanical behavior on casing deformation” (Manuscript ID: Processes-2063130). Thanks for your reasonable advice. As reviewer suggested, we have revised in the paper (see the revised paper).
Detailed Response to Reviewers:
Reviewer #2:
(1)Figure 6: there is a red line below MPa in the y axis. Please revise it
(2) Same problems with comment 1 in x axis for Figures 12 and 13.
Response: All revisions are highlighted in red in the manuscript
- Line 198: gas permeability usually use apparent permeability. It is OK that if this paper does not show the mechanism of apparent permeability. But it should be given a brief introduction with the following references
Response: Thank you for your kindly reminder.For this part, we have added 2 additional references.
- Simulation: what is the inputs for this model? Did you do any validation of the simulation result against experiment?
Response: we have added the table of input parameters of finite element model. The finite element model was validated according to the experiment results. The simulation result of model was verified by the vacation of the casing inner diameter under the external load.
- Figure 20a: it is suggested to plot the relationship between the peak and the pressure, and explain why.
Response: Thank you for your question. Inthis figure, we think that the relationship between total signal value and pressure is correct, and it is a good method to judge the critical yield value, while the NMR peak value can not fully reflect the overall pore structure
- Figure 21: please provide more explanations of different stages on signal changing.
Response: Thank you for your question. As a source rock, shale is mainly composed of quartz feldspar clay minerals, and its organic matter is mainly kerogen. Its clay minerals and cheese basically contain C and H elements, and the characteristics of its shale are considered in the actual measurement process. The C element and H element in shale clay and organic matter are evaluated as a system and the medium in pores as a whole system. To explore the pore changes under different stresses. However, under different stress states, the lithology of the core itself does not change, but only the stress changes with different pores, and the occurrence state of different pore fluids changes with the change of pores, so as to judge the change process of pore structure.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you for the explanations, but they do not answer my doubts. I have formulated the points to be clarified, which I think are important, but perhaps too general.
Now specifically.
Figure 18. a. Are we seeing here an evident increase in porosity after destruction and the formation of porosity with much smaller pore diameters than originally? Is it physical or geological? How to explain it? In addition, we see a significant increase in the size of the total porosity ? The porosity is proportional to the integral of the T2 curve, which is the area under the curve. Of course the "blue" signal around 10s is an ILT artifact. For bulk water we have about 3s, if it were rock crevices, then the signal should be mx. up to 3 sec.
Here it is worth seeing the literature on LF-NMR, e.g. "nuclear magnetic resonance and computed microtomography confronted with narrow channel and fracture porosity" or others.
For figure 18.b. we have the opposite situation. It would be good to show how the porosity value changes, and how T2lm, corresponding to the average pore diameter, changes.
n addition, it would be nice to see these changes for the differential distribution of T2, which corresponds only to the fluid that entered and exited the rock matrix (mentioned issue with LF-NMR, overcoming the barriers of nanoporous porosity). The authors rightly wrote that the NMR signal can and does (provided we have a suitable short echo time -TE) from various protons, apart from fluid in pores, also from organic matter, as well as from protons in physically or chemically bound clays.
Significant changes in T2 distributions depending on the composition and amount of clay and organic matter are shown in the literature.
Hence, the transition from T2 to PSD should be very careful, attentive and conscious
The authors do not provide the parameters of NMR measurements, echo time, number of echoes, B0 field, SNR ? These parameters should be minimally present to assess the quality of the T2 analysis.
For shales, it was shown that for PSD (pore size distribution) of the order of 2nm, it is important that TE is not greater than 60 µs to record the signal from all pores.
These are important issues that should be clarified, the discussion also does not take into account issues and literature related to LF-NMR and shales, which is especially important for short TEs. This would increase the value of the manuscript.
In order not to delay the publication process, I give a "minor", however, I suggest the correction of these, in my opinion, significant inaccuracies.
All the best for the new year
Author Response
Thank you for the recognition of our work. Please see the detailed comments in the word file. Happy new year!
Author Response File: Author Response.docx
Reviewer 2 Report
Good to go
Author Response
Thank you for the recognition of our work. Happy new year!
