[elpadre]

just wondering - why do they have to go so deep to tap into the line??

[rarestia]

I’m guessing it has something to do with the angle at which they’re drilling. They can’t drill something at an angle too acute, or they’ll risk a collapse of the tunnel. Whereas if they drill straight down and gradually angle it toward the old well, the tunnel can withstand greater pressures from the sea floor.

Mind you, I’m not a professional, just an observation.

[Donald Rumsfeld Fan]

just wondering - why do they have to go so deep to tap into the line??

Good question. I am hoping some one with drilling expertise will explain the mechanics of this operation.

Also ...exactly how do they tap into the existing drill hole and plug it.

Deep water drilling with all that high pressure to deal with must be a tricky undertaking.

[rwh]

The new well needs to be able to control pressure on the new well it drilled and control pressure on the well it is tapping into.

While drilling a well they control pressure on by using what they call mud. To control the pressure the weight of the mud needs to meet or exceed the pressure of the well at the depth they are drilling. The formula is quite easy- Depth in feet x pounds per gallon of fluid x .052. This will give you the force in psi that the column of fluid is exerting at a certain depth. At 18,000 ft that mud weight is going to have a lower ppg than at 18,000 ft.

Also, when they tap into the well they are going to be losing mud to the well they are taping into and are going to need to have the ability to replace the mud at a rate as high as the other well is going to be taking on that mud. If the other well takes on the mud at a higher rate then the new well will lose pressure control of the new well they drilled.

[Smokin' Joe]

In order to control both wells (the relief well and the uncontrolled well, they have to be able to introduce heavyweight drilling fluid at a depth which will provide enough pressure to stop flow from the reservoir.

The extra depth gives a taller fluid column in the relief well, and that translates into more pressure against the producing formation to hold the oil in the formation. If they tried to intersect at too shallow a depth they would encounter a significant risk of having two uncontrolled wells and another disaster.

In addition, the rock layers deeper are often more conducive to directional steering, enabling the directional drillers to do a more precise job.