BP Spill: Fingers Crossed

Flow stopped, but what about well integrity?

Part of the problem, apparently, is that the well pressure has not reached the 8 - 9,000 psi level that it was hoped it would reach, but instead it is reported to have fallen slightly shy of 7,000 psi. While this is below the expectation, it is higher than the 6,000 psi that Admiral Allen had set as the target below which they would assume a loss in integrity, and restart the flow of oil to the surface vessels.

To try and add a little context to this, at the beginning of the leak, the pressure of the oil and gas in the rock at the bottom of the well was measured at 11,900 psi. When the oil and gas fill the well that fluid column has a certain weight that balances some of the rock pressure, and the difference should be the pressure at the top of the column (which is where the BOP and stack sit). That gives the 8 – 9,000 psi range.

If the well pressure at the BOP is measured, however, at just shy of 7,000 psi then there are two possibilities. The first is that there has been so much flow of fluid out of the well that the driving pressure of the fluid in the rock has fallen by the 1,500 psi or so that brings the pressures down to those seen.

While that is a possibility, it may be unlikely because, at the time that the Top Kill was tried and as the Admiral noted just the other day, the well pressure could not be raised above 6,000 psi as they pumped in mud, even though at one stage they stopped the flow of oil out of the well.

What this could indicate is that there is a possibility of crossflow at the bottom of the well. What this means that the oil and gas that are flowing out of the reservoir into the bottom of the well, are, under the pressure in the well, now flowing into a higher reservoir of rock, now that they can't get out of the well. Depending on where that re-injection flow is, this may, or may not, suggest that the casing has lost integrity. This is a topic that has been covered in the comments at The Oil Drum, where fdoleza has noted: