Gas Cavern Conundrum
So in a recent HAZOP it was decided to add a second layer of pressure protection on the wellbores connecting the salt caverns to the wellheads. On the first (and only thus far) well we ran plugs removed the wellhead, added a hangar and new production string inside the wellbore casing which was already cemented in place (for roughly 40 years now). A cement job was done to cement the new tubing/production string.
When the wellhead was finally in place we found that the 2500m of annulus cement was not holding pressure. Seemed like a bad cement job. The curious thing is that we were seeing higher pressure buildup in the new tubing hangar (communicating with th ecemented annullus) than was in the cavern. we were seeing slow buildups to 5000psi with only 4000 psi in the production string.
My personal opinion was a hydraulic multiplier effect inside the cement - but no way to prove it obviously. Bond logs do not show anything out of the ordinary (but I'm a surface guy so I wouldn't know what to look at.
Anybody here ever see a similiar phenomena? Anyone have any ideas how the hanger could buildup more pressure than what is in the cavern? Thanks in advance. Note: I am not the responsible engineer in this case, just a casual observer doing work on the surface facilities.