Salt formation cementing questions from readers
We received some public enquiries about salt formation cementing. I thought that it would be helpful to post my answers here and allow further discussion in the comments section.
These are the two questions came through our website:
1. What is the response of salt vs good bond cement on the log?
2. Can salt around the casing resemble or seem like a good cement bond?
Here is a quick summary or the answer:
The Cement Bond Log tool measures how ‘bonded’ the casing is… This is called attenuation, which means, in simple terms, whether the casing is free to vibrate or not. Is it allowing sound propagation, i.e., resonance?
There are some things to consider when dealing with salt formations:
1. They are difficult to cement because fluids and cement can dissolve them (the larger the hole the lower, the cement bond quality).
2. Salt formations are plastic.
3. Salt formations have a high density (2.0 to 3.0 sg).
Salt formations like evaporites can act as fast formations, lowering CBL amplitude and bringing VDL signals sooner than casing arrivals.
So, in salt formation cementing, the CBL would appear to indicate good cement. But the VDL will show either fast formations, (where there is cement in between casing and formation), or free-pipe-like if the salt formation (due to its low heterogeneity — heterogeneity is what causes the VDL to be irregular) has direct contact with the casing (due to salt movement/plastic behaviour).
Please feel free to provide, or request more information below.
Dear Mr. Diaz,
Could you interpret some CBL/VDL logs if I send you those files?
thank you
Jahromi, thanks for your comment.
In principle yes, however please next time submit your question using the form in https://better-cementing-for-all.org.
All well specific information, such as well and formations names must be removed.
Good article about the CBL readings in salt formation. Is there any special considerations for the cement slurry in salt formation? How much NaCl would you use in cement slurry and can you replace the NaCl onto KCl?
The concentration is at least 18% NaCl BWOW (up to 30%). The idea of the salt content is to prevent dissolution of the salt formation. If there is fast salt creep sometimes is recommended low NaCl concentration < 18% to promote early compressive strength development. (<15% Nacl is an accelerator). Kcl can be used up to 5% for the same purpose of Nacl in addtion to prevent shale swelling. Additionally, if in the same well section there is a combination of salt and non-salt formation is was found recommended to use low NacL concentration (<18%) or Kcl up 2 -5%. The main reason is that high Nacl concentration up 30% is good for the cement in front of the salt formation but detrimental for the cement in front of the non-salt formation.
Thanks, so, the KCl can be used instead of NaCl to prevent dissolution of the salt formation? I read one article where it is recomended upto 3% of KCl instead of NaCl.
Yes, Oleg. It is possible and in some cases recommended, as I mentioned. I will also be cheaper alternative.