Replies

For starters, they have the survey data from the original wellbore: that gives the position of the wellbore within a few inches at most relative to the position of the relief well wellhead. From there, survey tools are used to measure the azimuth and angle of the drill string along the relief wellbore as it is drilled, which enables the directional drillers to steer the relief wellbore toward the existing and uncontrolled wellbore.

There are a couple of technologies out there, one which uses pads which push the lower part of the drill string over in the intended (target) direction, the other uses a mud motor, which is bent a specific number of degrees (usually 2 or less) and which uses the flow of drilling mud through the mud motor to rotate the drill bit. Both technologies permit the wellbore to be steered by knowing which way the tools are aimed, that determined by MWD (measurement while drilling) survey tools contained in the drill string--the data relayed to the surface by a pulser in the drill string and pressure transducers at the surface which pick up the pulses which are decoded by the MWD computers to give the information as to azimuth and inclination of the tools.

The series of surveys show the progress of the wellbore, and with a specific target, it is a matter of working out the math and steering the drill bit to the target.

Believe it or not, that is a bit simplified, and good directional drillers will compensate for variations in tool response which come with variations in geology.

On all the wells I have worked, we get the best results when the MWD, Directional Drillers, Geologists and engineers work together as a team. I'm sure BP has the best available people they know for the job, people with experience in the area.

As far as tapping into the existing wellbore, if they can hit the casing, they can mill into it, cutting a hole in the casing. From there, it is a matter of having heavy enough mud (drilling fluid) in the wellbore to provide pressure to control the relief well, and to be able to introduce that mud into the other wellbore to control the 'wild' well also. Once controlled, then they can 'set' a plug in both the cased wellbore and the open (relief) well and let the heavy drilling fluid hold it and the produced fluid in place.

In the event the problem might be a flaw in the cement job, then the formation fluid will be channeling up the outside of the casing, and remediation may be more tricky, but will involve basically the same process: introducing heavy drilling fluid to control the well, and then setting a cement plug to maintain that control and remediate the cement job by filling the channel. The latter would be a more difficult situation.

The weight of the drilling fluid should be sufficient to hold the oil in the currently producing well long enough for the cement plug to harden, and once the wellhead situation is remediated, the well could be produced by drilling out the cement plug, or simply plugged and abandoned in favor of drilling new wellbores with even more substantial safety precautions.

Now that the characteristics of the area are better known, the hazards can be better dealt with.