Kate Mackenzie The relief well drilling timeline, explained

The relief wells being drilled to intercept the gushing Macondo well are expected to be the real way to fix the problem. Dates of July and now August have been given as estimated times for their completion, but confusingly, BP and the Deepwater Horizon Unified Command are not using the same language to describe the progress.

BP said on Monday the first Gulf relief well is at 15,936 feet, and Deepwater Horizon command said on Tuesday that it’s at 10,677 feet. Reports that the well was within a mere 200 feet of its target didn’t help.

So how much further until the relief well is completed? Someone asked Thad Allen yesterday, and this is what they were told:

Q: Hello, Admiral. Thanks for taking my question. You keep saying that the driller ship three is down to about 10,000 feet and it’s closing in on for an intercept. But BP said early on that the well had been drilled down to 18,000 feet. Does it not have to go down all the way to 18,000 feet to do the intercept?

ADMIRAL ALLEN: It does not. I believe they’re going to try and intercept somewhere around between 16,700 and 17,000 feet. We will confirm that for you and put out a statement tomorrow. They don’t have to go clear to the reservoir, which is at 18,000 feet, and what they’re going to do is they’re going to close in and very slowly close to that point where they will then drill through the wellbore casing, and if they need to, drill through the pipe itself. But you are right; they’ll be slightly above the level of the reservoir.

Was that responsive?

Er, not really. In fact, this and some of the other questions around containment show that the communications to the public about exactly what’s going on are not being handled very clearly between BP and JIC, despite all the tweeting, videos, and fancy share buttons.

What we managed to ascertain on Tuesday, which Allen apparently did not, was that two different types of numbers are being thrown around. The 10,667 feet Allen is referring to is the depth from the ocean floor. The 15,936 feet BP is talking about is the *total* depth — that is, they are including the water depth of close to 5,000 feet.

So, as of Monday morning UK time, the first relief well had reached approximately 16,000 feet of a total depth (including water) of its total target depth of 18,000 feet.

However the total depth required is actually more than 18,000 feet, because the well will then begin to drill at an angle, as BP spokesman Robert Wine told us by email:

The relief wells are coming in from the side, starting about half a mile away on the seabed. They drill down and then turn towards the leaking well closer to the reservoir level. So their overall length will be longer than 18,000ft.

[This incidentally also explains the '200 feet' story; that was an estimate of the horizontal distance from the well bore itself, rather than the distance from actually intercepting the well.]

Click through on this image for more detail:

Wine also explained the process that will be under way soon:

The first well from the DD3 [Development Driller III, the first relief well-drilling rig to commence work in early May] is 200ft laterally (sideways) from the well. It will “range in” using electro-magentic sensors – detects the presence of the steel casing – drill a bit closer, sense, drill, sense, etc getting closer each time. The intention is to draw close to the leaking well, and run alongside for a length. This will give best chance of ‘flooding’ the surrounding stratum, the annulus and the well bore with mud, then cementing it.

He added that the drilling progress will slow down as it nears the target depth, because of this need for more frequent calibration.

The other question that seems to be constantly confused is when BP actually expects to kill the well (in a process similar to the ‘top kill’ – that is pumping drilling mud into the well), as opposed to just intercepting it.

August, says Wine, is indeed when the kill itself is expected to take place.

As we’ve written before, reaching the precise target with a relief well can be very tricky; but BP is clearly  confident that it will achieve success if it’s giving a timeframe for completing both the interception and the kill.

Related links:

Relief wells: Getting the interception right - FT Energy Source
‘There could be something in the wellbore that can be problematic’ - FT Energy Source