Well Integrity Technical Section

Good afternoon folks,

I am looking for a pointer as to where I can find a wall thickness loss percentage or mm per year figure for casing / tubing? I have seen a figure being cast about (my head is telling me that it is something like 0.2 mm / year and it was in an API booklet) and although it may not be the best figure to look at, the wells that I have been looking at have very little to no information to work with and this may give me a starting point.

I have seen one, but for the life of me I cannot find it when I need to reference it and I am hoping that someone out there can help me!

Thanks,

Stuart
-------------------------------------------
Stuart Wardlaw
Well Engineer
Expro North Sea Ltd.
-------------------------------------------

Stuart,

I can't add much to Matteo's comments.  There are many ways to calculate expected corrosion rates.  Their prediction accuracy is very dependent on the well materials, fluid types, fluid velocities, and much more.

If you want more specific advice you will have to provide a more specific question and describe the well condition with more detail (type of material, depths, fluid types (especially CO2 & H2S), artificial lift, length of time, flow rate, etc).

-------------------------------------------
Dan Gibson
Completion / Well Integrity Advisor
Gibson Petroleum Consultants
FulshearTX
-------------------------------------------

Gentleman,

 

Thanks for the input so far to this discussion, on reflection I should have thought a little more about my actual question before sending it out on a Friday night. I agree with all the comments so far that to look at one well and with little to no information, to say that it will have 'X' % or 'X' mm loss per year is entering very dangerous territory. What I am looking for is a reference that is contained within a document and I am positive that it is in an API spec (although it may have been in an Oil & Gas UK / Norwegian / etc. document).

Thanks,

Stuart

-------------------------------------------
Stuart Wardlaw
Well Engineer
Expro North Sea Ltd.
Stonehaven
-------------------------------------------

Hi Stuart,

Metal loss will depend on the corrosivity of the environment and on the ability of the flow to remove "rust" and replenish any reactive substances (such as oxygen).
Injectors are normally a big issue because you're pumping fluids that have been exposed to air: brine can easily eat up to 2 mm/year if poorly controlled. Even fresh water may lead to corrosion rates anywhere in the 0.05-0.5 mm/year range, depending on flow rate, oxygen and chloride content, and hardness.
If you're producing reservoir fluids and the casing is not water-wet (e.g. if your BSW is less than ~10%), then you may as well neglect metal loss. If you have a water film and acidic, salty reservoir brine (with, say CO2 and H2S), you may have substantial metal loss, in the mm/year range.
You can get orders of magnitude from literature, estimate metal loss using semi-empirical correlations (such as Norsok M-506 CO2 corrosion rate calculation model), or use complex chemical equilibrium calculations. In reality there are a lot of passivating and dynamic factors that are hard to account for when you're starting from basic principles.
Probably the best would be to analyse actual monitoring data and then figure out what the causes are and how to improve control if performance is not acceptable.

By the way: casing corrosion logs may be slightly tricked by coating or cement, and cross-physics comparison (say between ultrasonic and electro-magnetic) is always fraught with errors. So you have to take into account the accuracy of your measurements as well.

Best regards,
Matteo

-------------------------------------------
Matteo Loizzo
Wellbore integrity consultant
Berlin
-------------------------------------------