Trapped Pressure during Well Control

All,

We have had a situation where the BHP changed significantly during well killing

The operational steps are as following

• Drilling with 1.72 sg Mud weight at 3300 m, where influx was suspected
• Shut in the well and measured SIDPP and SICP , where SIDPP was 630 and SICP was 840 psi.
• Based on the above SIDPP, a KMW of 1.85 sg was prepared, and well killing was started through driller's method.
• After 1st circulation once the influx was out [ It was confirmed as water, due to reduced chlorides level], the SIDPP and SICP both were same at 950 psi. There was however no reason for this rise in SIDPP.
• The initial KMW of 1.85 was pumped, after which the SIDPP was 590 psi and SICP 660 psi. This meant a new KMW of 2.05 sg
• We then successfully managed to kill the well with 2.05 sg, but during the killing we found that the string is stuck.

Since we have circulation possible,this is a probable case of differential, but the question is the well balanced at 2.05 sg, how can it be a differential ?

Also, is it possible that the 950 psi shown when the influx was outs was actually the trapped pressure that forced us to increase the MW?

Does anyone has experience with trapped pressure with well control and what is your technical understanding on this case? 

10 Answer(s)

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