More than five weeks into the Gulf of Mexico oil spill caused by the explosion and sinking of drilling rig Deepwater Horizon, BP plc mounted its most ambitious attempt yet to stop the flow of oil from the ruptured well.

At about 1 p.m. CDT Wednesday BP began what is called a “top kill,” a procedure in which heavy drilling mud is pumped into the well at a high rate via its choke and kill lines in the hope of overcoming the flow of oil and natural gas so that the well can be capped with cement.

Earlier plans had called for the procedure to begin last Sunday; then it was moved to Tuesday and then Wednesday. BP COO Doug Suttles had said the delays were necessary in order to properly plan the attack on the well. Suttles said previously that the top kill would likely be complete or nearly so by the end of the day Wednesday. However, later estimates by the company said the procedure would take about two days.

Top kills have been successful at stopping wells before but never a mile below the sea surface where the leaking well is.

Success was not assured. BP put the top kill’s chance of success at 60-70%; however, others were less optimistic, placing the odds below 50% (see Daily GPI, May 25). If the measure fails, a “junk shot,” in which a variety of different size and shape objects from golf balls to knotted pieces of rope, etc. would be shot into the well’s failed blowout preventer.

Meanwhile, the drilling of two relief wells continued. The first could take two months or more to complete; the second, which was started later, is a backup to the first. A relief well is seen as the closest measure to a sure thing for stopping the well’s flow.

The spill is the result of a well blowout that occurred a month ago and resulted in the sinking of the BP-contracted Deepwater Horizon, a drilling rig owned by Transocean Ltd., and the death of 11 crew members. (see Daily GPI, May 24; May 18).

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