On Countdown last night, Keith Olberman reported that the relief well is 40 feet away from the well that’s blown out, and it’s expected to take several more weeks to reach it. I thought I’d clarify this, since it may be a little confusing as to why it is going to take several weeks to drill 40 feet.
Per USA Today the relief well is aimed for a point 18,000 feet deep. From the somewhat nonspecific language of the news article, I’m assuming that the 18,000 feet is the subsea1. This means that the actual drill string for the well will likely be significantly longer than 18,000 feet, since it’s being drilled directionally and is thus not the shortest possible distance from the point they’re aiming for.
My knowledge mostly relates to how wells are drilled on land, but as far as I know, the principle is the same for offshore drilling. Basically, the actually drill bit is at the end of the drill string, which stretches the length from the rig floor to wherever the bit happens to be at the time. The drill string is effectively a long, long pipe through which the bit can be powered and drilling fluid (mud) can be circulated.
Drill string is, as you can imagine, not just one insanely long pipe. It’s made out of joint after joint after joint of pipe. This pipe normally comes in lengths between 30 and 45 feet. So basically, when you’re drilling you start with, say, a 45 foot length of pipe. You drill down 45 feet until that pipe is basically at the floor of the rig, then you add another 45 foot length of pipe, then drill down more. And so on. And so on.
The sectional nature of drill pipe is important in this case because as drill string is pulled from the hole, you also have to break it off a section at a time and stack the pipe on the racks. This process can be done fairly efficiently for what it is, but that doesn’t quite get around the fact that when you have to pull an 18,000+ foot drill string out of a hole 45 (or whatever) feet at a time, it’s not exactly a speedy process.
And that is, in fact, what’s having to be done, at pretty regular intervals. As close as the relief well is, they really don’t want to miss the Macondo’s2 pipe, and they’re effectively attempting to locate something a bit smaller than a dinner plate. Directional surveys do have error attached to them, so they don’t have a precise enough location on the well they’re trying to hit to just drill blindly.
So basically what is happening at this point is that the relief well is drilling a little bit (maybe a foot or so, I don’t know for certain) and then they’re pulling up the entire (18,000+ foot) drill string so they can put a magnetic tool down the wellbore to check the location of the Macondo’s pipe. Then they pull up the magnetic tool, put all 18,000+ feet of the drill string back down and drill a little more.
I think “excruciating” is a fair way to describe this process. But with the care that’s taken, there will hopefully be a very good chance of hitting the blown out well on the first try, which is the really important thing. Playing fast and loose is certainly part of what caused this issue; hopefully some care and precision will get the Macondo killed finally.
Also, I’ll add that around the time the relief wells started drilling, we had a company meeting. I didn’t end up attending, but my husband did and reported what had been said. It was mostly one of the VPs passing on information about the disaster. One of the things he said is that THE best directional drilling engineer in the business is at the helm of the relief well. So here’s hoping.
ETA: I found this video released by BP3 explaining (with animations) the drilling process for the relief wells. The narration isn’t exactly scintillating, but I think the animation can really help you visualize the process. I’ll admit, the thing I found most interesting was the enormous range in casing sizes that they’ve had to set. Casing gets set in layers; I’ve never seen this many layers, but then again I’ve never worked on a well at a depth of more than 10,000 feet.
Note: In the video, they refer to “MD.” That stands for “measured depth,” which is the length drilled. Measured Depth is normally not the same as Subsea Depth, since it’s really a measure of wellbore length rather than a quantification of depth below sea level. In this case, they mention a 13,000 foot measured depth, which may seem a little confusing. They’re talking about 13,000 feet drilled and not counting the additional footage that it takes just to get from the drilling platform at the ocean surface to the ocean floor, which is approximately 5,000 feet.
1 – Depth below sea level as measured in a line perpendicular to the surface of the sea.
2 – The proper name of our favorite underwater oil “volcano.”
3 – I consider this video propaganda-free, since it’s a good representation of the drilling process and at no point does the boring narrator compare directional drilling to “a graceful dive into the Earth’s hallowed seas of rock” or some shit like that.