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View Diary: BP Top Kill Diary # 7 as of 10 pm MDT appx (374 comments)

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  •  There's a very good reason ... (0+ / 0-)

    First of all - Top Kill and Junk Shots are related procedures.

    If they had tried a Junk Shot with the well going at full pressure, they could have risked creating a Hydraulic Shock when the leaks were "plugged." That could have torn off the blow-off-preventer, as a worst case.

    Doing the initial Top Kill helped reduce the pressure in the well, reducing the eventual hydraulic shock that followed a junk shot.

    They did an initial junk shot with larger objects, and then they have done new junk shots, while continuing the Top Kill effort.

    An important distinction: Stopping Top Kill refers to halting the advance of the mud column down the well, not abandoning the procedure. They are Killing the Well from the Top Down, by advancing a mud column into the well, hoping to get a column of mud that counteracts the upwards pressure of the hydrocarbons wanting to escape.

    But in order to prevent the mud column coming back up, they are pumping - which explains the venting out of the leaks and the open riser.

    So keep these things in perspective:

    1. Top Kill - to advance a mud column down the well. When that is stopped, the mud column advance halts, until the next stage.
    1. Junk Shots - to shoot objects into the blow-out-preventer, in order to try to jam shut the leaks in it. You don't want to close it off suddenly, which is why they begin with larger objects, that permit flow through them.
    1. Then they advance the mud column again, using the counterpressure that has increased, because they have reduced the leakage.
    1. Another junk shot, stopping up the leaks even more, allowing a greater build-up of counterpressure, letting them advance the mud column again.

    They have to do this in stages, and with caution, in order to avoid opening up greater leaks, ripping off the damaged riser (which is restricting flow), or worst-case: losing the blow-out-preventer (BOP).

    "If you don't use your majorities, you lose your majorities."

    by SteinL on Sat May 29, 2010 at 07:37:05 AM PDT

    [ Parent ]

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