Well Integrity Technical Section

Hello - Gents,

2 questions
1 ) We are investigating the maximum allowable pressure in the annulus, since high pressure tend to crack the cement.
For that I would need the Young Modulus for cement class G, and for Pozzo cement .
Anyone having an idea about that or littérature references, I would highly appreciate,

2) In the past, we have been also looking at the issues related to performing systematic annular test on the cement.
I understood from the UK HSE, that there are some published work proving that cement is not affected, which I do not beleive, because cement do not accept traction and because you will reach downhole higher pressure than the frac gradient. Anyway, if you have some littérature on that to share that would be highly appreciated.

Thank you very much

Nicolas Bonnier

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Nicolas Bonnier
Drilling and Completion
Geostock
Rueil Malmaison Cedex
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Nicolas,

I am not sure I understand your question and was hoping a cementing 'guru' would help you out.

I will answer your question as best I can and maybe give you some ideas to chase.

First, I have evaluated hundreds of wells for MAASP and never worried about cement cracking, Instead the focus has been on the primary containment system to burst or collapse; the pipe.  Burst and collapse are relatively well understood phenomena and tend to govern the MAASP of the well in each annuli.  There may also be other limits such as packer or hanger loads which impose additional limits.  Loss of the primary containment system is the biggest concern and must be avoided.

Second, I am familiar with cement properties and have been involved in some cement testing over my career.  However, I am not an expert in this area.  Trying to predict mechanical properties of annular cement along the entire well length  must be a tremendous challenge.  For your prediction you will need;

a) to understand clean cement properties under different confining pressures and temps (i.e. depths)
b) to understand contaminated cement properties under different confining pressures and temp
c) to understand the annular cement configuration (channelling, unevenness, patchiness, etc)
d) understand the formation stiffness for each formation along the well
e) to understand the effect of centralized and eccentric  casing with various cement thickness
f) to understand the effect of centralizers on the mechanical stiffness of the system
g) to understand the filtercake that remains on the formation and it's thickness and effective elasticity
h) to understand the mud film that remains on the casing and it's effective elasticity
i) etc

From my experience cement jobs rarely go as well as hoped and cement coverage and strength is rarely uniform.   You would need a detailed cement evaluation log for each well to create a map of cement and cement properties, along the well length, and then assess how that map is loaded by pressure at each depth. That is a daunting challenge.

Third, Why are you worried about cement cracking?  Is this for a gas storage project or similar application where gas migration in the annulus might be an issue?  I would be more concerned about channeling and micro-annuli which can exist in any well  and require attention.   This requires a real focus on the cement job and key success factors (centalization, casing rotation while cementing, spacer design, etc).  If additional assurance is required look at a swell packer or OH packer that can isolate the annulus with a non-cement alternative.

Fourth, cement can be designed and pumped with small fibers that improve the tensile strength of the cement.  There are other additives that can improve the elasticity.  Talk to your supplier about the design of high elasticity/fracture resistant cement and see what they have to offer.  There will be some small scale lab tests that demonstrate improved performance.  I don't believe they have developed tools to predict the performance of this type of cement downhole for the wide range of installed conditions.

Fifth,  I am unsure how you would perform a 'systematic annular test ' on the cement.  The leak rates you are talking about from cracking are very low and would require test designs on the order of 1 gal/day of injection or less.  And I am not sure how you could test the cement depending on the well configuration.  An open shoe would test the formation not the cement.  And a closed shoe will have a mixture of cement capped with sagged mud. And only test the cement down to the shoe where leak off would occur  You cannot possibly test the cement 'cracking' along the well length.   The industry has looked at annulus pressure build-up as the measure of effectiveness.  Calculating cement 'permeability' and assessing the micro-annuli and capillary flow paths through the cement is routinely done by Operators.

I hope this discussion helps. Please do not hesitate to ask any follow up or clarifying questions.

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Dan Gibson
The Well Doctor
Completion / Well Integrity Advisor
Gibson Petroleum Consultants
FulshearTX
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