Numerical Study on Transient Annular Pressure Caused by Hydration Heat during Well Cementing

Round 1

Reviewer 1 Report

The manuscript deals with the modelling of annulus pressure resulting from the hydration of well cementing.  In the current form, it only presents results without providing explanations of what are being simulated and presented in the paper.  This is a major shortcoming from the academic point of view.  I would therefore suggest declining the paper.  I have listed some of the questions that the authors may wish to consider for their future submissions:

 

Section 3.1. A justification on how coefficients alpha 1 and 2 should be provided.

 

Figure 3. Definition of time zero should be i.e. when the cement is in contact with water or setting.  Related to this, why does the simulated value plotted in the vertical axis not start from point zero?

 

Section 3.2. To justify the results presented in this section, basic information on what is being simulated such as geometry, dimensions, material properties, parameters used in the simulation etc should be provided and explained.

 

Section 4 and 4.1.  The initial condition of the simulation should be provided and explained.  Was the cement being assumed to be present over the entire depth instead of being ‘pumped’?  If so, the authors should provide comments on to what extent this would affect the accuracy of the results. 

 

Figure 6.  Thickness and other dimensions of casing, formation and wellbore should be provided and explained.

 

Section 4.2.  As before, the definition of time zero should be provided.

 

Section 4.3. A clarity on the level of lateral/radial confinement should be provided, and location of the monitored pressure.  Without this information, the simulated pressure cannot be justified.

 

Line 277.  The Authors stated that the annular pressure of 7MPa may threaten the wellbore integrity. The authors do need to justify this statement as this is very small compared to the mechanical properties of ordinary steel commonly used for wellbore casing.

 

Sections 4.4-4.6.  As before, what are being simulated and presented here?  Basic information such as location of monitoring, boundary conditions, simulation parameters should be provided and explained.

Author Response

Dear Reviewer and Editor,

Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Numerical study on transient annular pressure caused by hydration heat during well cementing” (ID: applsci-1566588). We appreciate very much for giving us an opportunity to revise our manuscript. Those comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion and new additions are marked in red in the paper. The point to point responds to the comments are listed in the following file.

Author Response File: Author Response.docx

Reviewer 2 Report

Specific comments to be addressed by authors to improve discussion of the results are - 

L38 - Please present data on thermal expansion of cement/concrete mixtures under such conditions from literature .

L55 - Please mention the typical size of the annulus

L56 - When does the cement hydration occur? What is the duration between mixing cement slurry and when the well head is shut in? 

L66 - What class of cement is utilized here? How does your model scale for class H cements, where the aluminate content is low?

L79 - What is the justification behind using this model? The form of the equations seen here is similar to Parrot-Killoh model. How similar or different is this from the Parrot-Killoh and the modified Parrot-Killoh model and other hydration kinetics models?

L196 - What is the justification behind choosing these specific temperatures? At first glance this appears arbitrary. Please add clarification.

Fig. 3 - Typically heat flow curves are plotted as time dependent curves More specifically d(alpha)/dt versus time. This is a little hard to follow. What is the purpose of plotting the curve this way? Can't the same experimental vs modeling plot be done with change in time?

Fig. 3 and 4 - At what age does alpha reach 0.8 or 0.9? Is the modeling calculated for infinite time?

Table 2 - Is this the density of cement or cement slurry?

L242 - I would also consider showing calculations for temperature rise at all depths.

Fig. 8 - What is the implication of this? If there are temperature differentials at different depths, what would be the effect of differential shrinkage? Can the differential shrinkage be calculated from this as a next step? I would discuss implications.

Author Response

Dear Reviewer and Editor,

Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Numerical study on transient annular pressure caused by hydration heat during well cementing” (ID: applsci-1566588). We appreciate very much for giving us an opportunity to revise our manuscript. Those comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion and new additions are marked in red in the paper. The point to point responds to the comments are listed in the following file.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript entitled " Numerical study on transient annular pressure caused by hydration heat during well cementing” developed a kinetics model for cement hydration under different curing temperatures, a transient temperature prediction model during well cementing considering the interactions between temperature and cement hydration, and a prediction model of annular pressure considering the change of cement temperature and the change of annulus volume.

The authors should address the following technical comments before any further process.

Technical comments:

• The similarity index shows 31% similarity. The authors should work to reduce this percentage.
• The word "established" was repeated several times in the abstract. I think the technical writing of this manuscript should be improved.
• Line 45: Does it mean no previous studies were conducted? The literature review should be expanded to include more relevant references and the authors should highlight how their study is providing a different approach or adding significantly to what has been done.
• Lines 70-71: The terms in equation 1 should be defined in lines 70-71.
• Line 84: I think you mean "Equation (3)", not "Equations (4)".
• Line 92: Is this sentence correct? The number of equations?
• Lines 98-100: More clarifications should be provided on how to determine these parameters. It will be better to provide this diagram and show how to determine m and K. The same note is in lines 111-112.
• Line 186: I think you mean equation (24), not equation (30).
• Line 204: This reviewer did not see Figure 2. The authors should correct the order of the figures.
• Line 208: Is it "calculated results" or "calculation results"? I think it will be better to change the caption of this figure to be "a comparison between the calculated and experimental results. Moreover, the axes titles should be defined to be more readable.
• Line 246: The numbers of figures in the text are not matching with the number of figures. The authors must correct this error.
• Did the developed model consider the type of the surrounded soil? I think the type of soil will affect the value of pressure.

Author Response

Dear Reviewer and Editor,

Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Numerical study on transient annular pressure caused by hydration heat during well cementing” (ID: applsci-1566588). We appreciate very much for giving us an opportunity to revise our manuscript. Those comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion and new additions are marked in red in the paper. The point to point responds to the comments are listed in the following file.

Author Response File: Author Response.docx

Reviewer 4 Report

The authors presented a novel approach to model annular pressure due to cementing. The mathematical models seem rigid, and could be useful to improve the safety of drilling operations. I also appreciate author efforts to put nice high-resolution figures. However, I found that this manuscript needs an extensive editing of English language and style. Please react to my comments below.

• Line 12, grammatical error: “series of threats”
• Line 13, consider change “seldom” to “rarely”
• Line 15, grammatical error: “curing temperatures”
• Line 16-17, consider change “On based of these, ” to “Based on these assumptions, ”
• Line 18, remove “on”
• Line 21, consider change to “and then a decrease,” or “, and then decreases,”
• Line 23, change it to “the geothermal gradient, the cement hydration heat, and the wellbore diameter.” or “geothermal gradient, cement hydration heat, and wellbore diameter.”
• Line 32, capitalize “Mines”
• Line 37, grammatical error: “two reasons”
• Line 43, change to “Wojtanowicz [9] and Rong [10]”
• Line 56, change “researchers” to “studies”
• Line 62, grammatical error: “are drawn”
• Line 38-39, I am not sure if the sentence “Currently, researches about annular pressure caused by gas migration are conducted by numerical researchers.” is significance to be put on introduction. You may want to remove it, or you can add some references after word researchers.
• Line 37, change comma to and: “ thermal expansion in annulus and gas …”
• Line 41, grammatical error: “is the main reason”
• Line 46-47, change to “researchers” to “research”
• Line 77, change to “by the ratio between transient …”
• Line 85, grammatical error: “models”
• Line 145, I don’t get what you mean by “finite differential”, please consider change it to “partial differential” or “finite difference”
• In Fig. 2, could you explain why at cement hydration degree >60, the experimental rate deviates from the initial decline rate.  
• In Fig 3, please explain big discrepancies between experimental data and the model, especially at cement hydration degree>20.
• Line 210, grammatical error: “show”
• Line 222, grammatical error: “are based on”
• Line 301, grammatical error: “, and loses”
• Line 311, grammatical error: “are drawn”
• Line 321, grammatical error: “and then decreases” 
• Line 322, consider change to “and then a decrease,” or “, and then decreases,”
• Line 324, change it to “the geothermal gradient, the cement hydration heat, and the wellbore diameter.” or “geothermal gradient, cement hydration heat, and wellbore diameter.”
• Line 332, remove “Please add: ”
• Please remove line 337-342: “The appendix is an optional… ”. This paragraph is an instruction on the template.
• Line 366-367, add the SI unit of heat.

 

 

Author Response

Dear Reviewer and Editor,

Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Numerical study on transient annular pressure caused by hydration heat during well cementing” (ID: applsci-1566588). We appreciate very much for giving us an opportunity to revise our manuscript. Those comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion and new additions are marked in red in the paper. The point to point responds to the comments are listed in the following file.

Sincerely

 

Author Response File: Author Response.docx