As Coast Guard admiral Thad Allen has explained, sustained pressure readings above 8,000 pounds per square inch (psi) would show that the wellbore is more or less intact, while pressures of 6,000 psi or less would mean there could be major problems:
We are looking for somewhere between 8,000 and 9,000 PSI inside the capping stack, which would indicate to us that the hydrocarbons are being forced up and the wellbores are being able to withstand that pressure. And that is good news.
If we are down around in the 4,000 to 5,000, 6,000 range that could potentially tell us that the hydrocarbons are being diverted someplace else, and we would have to try and assess the implications of that. And as you might imagine, there are gradations as you go up from 4,000 or 5,000 PSI up to 8,000 or 9,000. …
We will at some point try to get to 8,000 or 9,000 and sustain that for some period of time, and these will be done basically, as I said — if we have a very low pressure reading, we will try and need (ph) at least six hours of those readings to try to ensure that that is the reading. If it’s a little higher, we want to go for 24 hours. And if it’s up at 8,000 or 9,000, we would like to go 48 hours just to make sure it can sustain those pressures for that amount of time.
The former director of Sandia National Laboratories says the pressure readings so far have been ambiguous.
As the Washington Post points out:
The initial pressure readings are in an ambiguous range, and officials will have to make a difficult judgment call on whether to keep the well shut in or reopen it, according to Tom Hunter, retired director of the Sandia National Laboratories and a member of the federal government’s scientific team overseeing the test.
“If it were a lot higher, it would be an easier decision to make,” Hunter said.
Hunter, who witnessed the test from BP’s war room in Houston, told The Washington Post that the pressure rose to about 6,700 psi and appeared likely to level out “closer to 7,000.” He said one possibility is that the reservoir has lost pressure as it has depleted itself the past three months.
“It’s just premature to tell. We just don’t know whether something is leaking or not,” Hunter said.
We will need to wait another 24 hours or so – and engineers will have to continue monitoring sonar and visual images (both help determine if any oil is leaking from the seafloor), and seismic data (to determine if there are any new leaks below the seafloor) – before engineers can determine how stable the well is.