[QUOTE=billslugg;43604]Is it true that the reason they wanted to put the top plug at 3000’ below mud level rather than 300’ was that they wanted to remove the valuable drilling mud? If so, they would just have to replace it when they came back to put the well into production, right? So why remove it in the first place?[/QUOTE]
I believe they planned to set the second barrier cement plug at +/- 8300 ft. Why? I’m not 100% sure but I’ll venture a guess.
By displacing with Sw from 8300 ft to the top of the BOP, we maintain at least a BHP overbalance and never induce an influx. Furthermore, The heavy Spacer would be just above the BOP and as long as we close the Annular quickly, the heavy fluids should remain in place without contaminating the SW below the Annular. We perform the Negative test, and if any BOP issue exists we immediately can restore the overbalance on the well. This would only be a secondary or back-up consideration in the event of BOP failure, a back-up plan.
If failure of the negative test was established, the immediate action would be to re-establish the overbalance by closing the Kill line Failsafe valve and pressuring up the well to the overbalance value.
The next step would be to consider bullheading the hydrocarbon influx back into the formation. Then, displacing the Sw with 14 ppg mud. Meanwhile, with the Annular still closed, the riser could be displaced to 14 ppg mud, which would have to be pumped from the boat to the vessel.
Bottom line, although the displacement takes place 3000 ft below the seabed, there is always an overbalance on the well preventing hydrocarbons entering in the event of a failed cement job. The negative test is the first opportunity to test whether or not the well is capable of flowing…or, whether the cement has failed to seal the well. Personally, I don’t see a problem with it as long as we perform the negative test correctly. This was not done.