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).
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