Characterization of the Petrophysical Properties of the Timahdit Oil Shale Layers in Morocco

Round 1

Reviewer 1 Report

Please see a file attached

Comments for author File: Comments.pdf

Author Response

We have added more references for the description of the optical scanning technique (Popov et al. 1983; Popov et al. 1985; Popov et al. 1999; Popov et al. 2016)

For the TCS method :

Since the measurement error is less than or equal to 2% for thermal conductivity (Popov et al. 1999; Rosener, 2007; Samaouali 2011; El Rhaffari 2016), the calculated thermal diffusivity error is between 0.6 to 3.0 * 10-6 m2 s-1 (Popov et al. 2016).

For the UMT method :

Pulse velocity measurements are affected by different factors. They are well described in BS 1881: Part 203, where concrete moisture content and temperature are two key factors.

For Mercury Porosimetry :

Measurements are performed on an AutoPore II 922O Micromeritics Porosimeter with an accuracy of +- 1%.

Table 2 presents the results obtained for the thermal (thermal conductivity and diffusivity) and acoustic properties (P, S wave propagation velocities and velocity ratio) for different layers of oil shales M, X and Y, for which the mean velocity values, uncertainties and mean deviations were calculated by Excel software.

The value of the mean velocity P is (1733±33) m.s-1 for the M layer, (1364± 20) m.s-1 for the X layer and (986±13) m.s-1 for the Y layer. The mean velocity S is of the order of (918±29) m.s-1 for layer M, (788± 20) m.s-1 for layer X and (653±6) m.s-1 for layer Y. We found that the velocity ratio is (1.89±0.10) m.s-1 for layer M, (1.73±0.05) m.s-1 for layer X and (1.51±0.03) m.s-1 for layer Y.

The thermal conductivity value for averaging the M layer is (0.84±0.08) W.m-1 K-1, for the X layer (0.82±0.08) W.m-1 K-1 and for the Y layer (0.82±0.08) W.m-1 K-1. The mean thermal diffusivity is (0.41±0.04) m2.s-1 for layer M, (0.45±0.04) m2.s-1 for layer X and (0.46±0.04) m2.s-1 for layer Y.

Table 3 shows the values obtained for the mercury porosity and the acoustic velocity ratio. For layer M, we found a porosity of (10.29±0.1) %, for layer X a porosity of (11.94±0.1) % and for layer Y a porosity of (13.83%±0.1) %.

We thank you for this important question which clarifies our results and interpretations. Indeed, in the article that you have specified, we noticed on the one hand that the authors worked on deposits in different regions including Utah, Colorado and Wyoming, so in our case, it is only the Timahdit area deposit. On the other hand, the authors carried out measurements of thermal conductivity for a wide range of temperatures (between 30°C and 300°C), whereas we worked in the ambient temperature range (around 25°C). This clearly shows the difference in experimental conditions, which is proof of the contradictions in the results.

Yes, indeed, these are rocks characterized by thermal and acoustic anisotropies. This approach is still under theoretical development at the Thermodynamics - Energy laboratory at the Faculty of Sciences in Rabat, using a model of the thermal and acoustic transport anisotropy.

Given the brittleness of the bituminous rocks in the Timahdit region and the cutting conditions which require very precise shape parameters, it was very difficult to acquire many samples.

We changed the legend to : Thermal Conductivity Scanner (TCS)

Yes, indeed, this machine can only measure thermal conductivity profiles, but it does not allow the measurement of thermal diffusivity. The latter was concluded by a theoretical calculation of the machine software.

We have added the units of dimension to the equations in lines 230-232

Yes, indeed, this high-precision method, which uses an optical scanner, was developed by Professor Yuri Popov (National Academy of Geological Prospecting in Moscow) as a new method applied in Earth science and thermal physics. We have corrected this in the manuscript.

Several corrections have been made in the manuscript, with more details on the correlations established. The scientific data are currently presented in a formal way and with detailed scientific interpretation.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript “Characterization of the petrophysical properties of 2 the Timahdit oil shale layers in Morocco” addresses a paramount concern about oil shale that could be used in the decision making process of exploration activities. I found this article interesting for a broad scientific audience and consider that the manuscript has a real potential to be published in Geosciences. Having said that I feel this manuscript needs to address few important concerns (as suggested below) that may prove useful:

1. The last sentence in the Abstract is extremely long and hard to follow. Author should break it into 2-3 simple sentences to clearly convey the idea.
2. The pixel resolution of Figure 2 is extremely poor and impossible to read the names of geographic regions in and around the study area. Author should improve its resolution.
3. The pixel resolution of Figure 3 is not of publication quality. Author should improve its resolution.
4. Manuscript contains redundant information such as "A comparison of the two speeds showed that longitudinal waves P are generally faster than transverse waves S". In this respect, the equations 1 and 2 and following discussing of why P-wave travels faster than S-wave is redundant too. P-wave always travel faster than S-wave in any media and it is a verified fact in seismology that exists for more than 100 years. Putting such details in the manuscript does not add any new scientific information and therefore, such details should be omitted.
5. Variables are missing from the text while explaining UTM method for measuring compressional wave velocity (below equation 2) and Mercury injection porosity (below equation 3). Author should insure the completeness of their text throughout the manuscript.
6. In line 189, the "MO" should be corrected to OM content for organic matter.
7. In lines 197, 201, and 211, what does thermal and D properties mean? Author should list the parameter names consistently. It seems that thermal implies thermal conductivity, but it should be written explicitly.
8. In Figure 5, author should mark the position of M, X, and Y layers for the clarity of the readers.
9. Please correct the legend in Figure 6 from Prosite to Porosity.
10. The result and discussion sections describe seismic velocities and their ratio as the proxy to organic matter content, which is based on the observed variation in 3 different layers of the oil shale. However, such conclusion is short sighted. Even though P and S wave velocities are observed to decrease with increasing organic content of the layers, it is not wise to associate the variation in seismic velocities to just the organic content. Seismic velocities are complex function of bulk properties of rock and porosity is one of them. It is possible that the observed variation in velocity in different layers is perhaps related to their porosity as well instead of just of their organic content. This is further supported from porosity variation shown in Table 3 and Figure 6. Author should clearly describe why ratio of P and S wave velocities is preferred over porosity to predict organic content. Why can't the porosity be used to predict the organic content?

Author Response

1.

We have rectified the sentence correctly 

2.

Figure 2 has been replaced by a new figure with a good resolution.

3.

Pixel resolution of Figure 3 is much improved

4.

Redundancies and all unnecessary information have been omitted from the manuscript.

5.

Yes we have revised all the missing variables in the text, the new version is well presented.

6.

It is very well rectified

7.

The corrections requested for the thermal parameters have been carried out correctly.

8.

The positions of the different layers have been clearly marked in Figure 5.

9.

We have corrected the legend prosity by porosity

10.

The results in Figure 6 show that for layers M, X and Y, the velocity ratio Vp/Vs decreases as the organic matter increases. The correlation between porosity and organic matter indicates that as porosity values increase in the wheel, it is clear that organic matter increases as well. This is well rectified in the manuscript

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

REVIEW 2

1. In the previous review the reviewer addressed a following question to the authors: “Table 2: No information on values ± 0.08, ±0.04, ±33, etc. is given. What do these values mean? There is the same question for Table 3.”

The authors ignored this reviewer’s question. No explanation is given here again in the revised manuscript. What do these data mean – uncertainties, mean deviations, maybe something else?

1. Lines 204-210: The information here is a formal repetition of the data shown in Table 2 without any additional information. The text given in lines 204-210 should be removed.

Figures 5 and 6: There are too many errors and carelessnesses. Please read and correct: “Variation the porosity and velocity ratio of organic matter in concentrations the organic matter” (this text should be removed at all!), “repport speeds”, “Figure 6. variations in porosity and …”, not necessary two zeroes on Porosity and Organic matter axes should be removed, symbols % should not be used twice for every of Porosity and Organic matter axes, “Organic matter, %” should be instead of “Organic Matter (%)”, “velocities, m/s” should be instead of “the speeds .10³ (m/s)”, text “Variation of the speeds Vp,Vs and the ratio Vp/Vs as a function of the

Organic Matter for the layers of the butiminous shales” should be removed from the upper part of Figure 5, etc.

1. Line 250: Number of the inequality should be given.
2. Lines 204-207: “m×s^-1” instead of “m.s^-1” should be used.
3. The authors should use a term “velocity” instead of “speed” through the paper.

• It should be mentioned in the paper that the research results are in serious contradictions with the data published previously (e.g. (1) Rajeshwar, K., Dubow, J., Rosenvold, R. [1980] Dependence of thermal conductivity on organic content for Green River oil shales. Industrial & Engineering Chemistry Product Research and Development. 19, 629-632. (2) Popov E., Popov Y., Romushkevich R., Spasennykh M., Kozlova E. 2019. Detailed profiling organic carbon content of oil shales with thermal core logging technique Sixth EAGE Shale Workshop. 28 April - 1 May 2019, Bordeaux, France. https://doi.org/10.3997/2214-4609.201900305, et al.) where a close correlation between oil shale thermal conductivity and TOC was demonstrated. This recommendation was done by the reviewer in the previous review but the authors ignored that completely.

• The authors write in their cover letter: “Yes, indeed, this machine can only measure thermal conductivity profiles, but it does not allow the measurement of thermal diffusivity. The latter was concluded by a theoretical calculation of the machine software.” It is incorrect! The optical scanner measures simultaneously both thermal conductivity and thermal diffusivity directly. No “theoretical calculation of the machine software” is necessary!!! What does it mean “theoretical calculation of the machine software”. It is very strange that the authors of the experimental research do not understand principles of the measurements.

• Equation (eq.1) should be removed as (1) it concerns only thermal conductivity measurement principle, (2) it is not quite correct, (3) it does not describe thermal diffusivity measurements, and (4) it is not critically important in this paper.

Author Response

Report to Review 1

1. The values ± 0.08, ±0.04, ±33, etc. on table 2 and table 3 are the absolute uncertainties and mean deviations, were had calculated by Excel.
2. The text given in lines 204-210 have been removed, we have changed this in the article.
3. All requested changes were made in Figure 5 and Figure 6
4. Number of the inequality have been given (eq. 7)
5. m×s-1” instead of “m.s-1” have been used
6. We have used term “velocity” instead of “speed” through the paper
7. we mentioned in the manuscript that the contradiction with the results is essentially related to experimental conditions (please see lines 211-214)
8. Yes, you are right, The optical scanner measures simultaneously both thermal conductivity and thermal diffusivity directly…
9. The equation has been deleted

Author Response File: Author Response.docx