Prediction of Overpressure Zones in Marine Sediments Using Rock-Physics and Other Approaches

Round 1

Reviewer 1 Report

The paper discusses the problem of localizing zones of high pore pressure in the subbotom sediments (first tens meters under the seafloor). The paper presents the results of the overpressure zones prediction using a set of methods including empirical ones, and the approach based on the rock-physics modeling that features soft-sand model of unconsolidated media effective properties. The following minor comments should be considered:

1. Fig. 8b, why the poisson ratio present a huge variation between different methods? What is the cause of it. suggest authors to further elaborate.

2. What is the cause of the deviation observed in Fig. 9? The authos should be clear about it and make possible guesses if no definite answer is present.

3. The findings can be well correlated with the hydrate-bearing sediments exploitation, which presents in 0-100 meters below seafloor, where overpressure zones are sometimes possible. The folloing refs can be related in the introduction or discussion section where geohazards related to the drilling of NGH reservoir (clayey-sandy medium) can be a big problem. CJChE 27 (9), 2026-2036,  doi.org/10.1016/j.cej.2022.135368, etc.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors presented the results of the overpressure zone prediction by using a set of methods including the empirical one, and the approach based on rock-physics modeling that features soft-sand model of unconsolidated media effective properties.

My general comments are given below,

1)      The introduction needs to be reformulated to highlight the new/novel aspects, and it should be logically organized.

2)      The manuscript is in lack of a detailed introduction or discussion on the state of art regarding those research background and previous results.

3)      The authors proposed a heuristic combination of the Hertz-Mindlin method and the Hashin-Shtrikman bounds. What is really new in this work remains unclear, according to my reading.

4)      A great amount of contents are given to introduce the geological background. Should it be reduced appropriately?

5)      Please specify the rock physics model and those formulas used in the article.

6)      Please give the detailed modeling process of the rock physical model. It is not clear to me.

7)      For the geological/physical parameters mentioned and the data in the plots, please give the sources or explain how do you obtain/compute them.

8)      A conclusion is at least needed at the end to summarize the main results of this study, as well as the corresponding achievements and remained issues.

9)      The descriptions regarding Figures 9 and 10 are problematic. Should the critical extra load and total vertical stress overlap or not? I am confused here.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The paper discuses an important problem in offshore drilling. The presented calculations give a reliable results but show that there are no “really dangerous” overpressure zones in the studied area and a typical blowout prevention system can deal with them easily. The work is carefully edited.  I recommend this work to be published after minor revision.  Please consider the following questions/suggestions listed below:

1)     In the Introduction section please provide an explanation/theory why or how these overpressure zones were formed. Perhaps the knowledge on the origin of such formations could be here helpful.

2)     Improve the quality of Figure 3 - captions are illegible.

3)     All abbreviations and symbols should be explained (line 287) in the text. Is an internal friction coefficient (line 390) and the shear modulus the same (line 501)? The symbol µ stands for both.

4)     Please consider if it would not be beneficial for readers to add an attachment with exact formulas and algorithm of calculations /transformations. Perhaps a graphical flowchart of calculation for both methods would make it easier for readers to follow the progress of calculations.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I am satisfied with the revised manuscript.