BP is attempting a “top kill” solution to stem the gushing flow of oil which is spewing from the seafloor in the Gulf of Mexico.
What’s a “top kill”?
The primary objective of the top kill process is to put heavy kill mud into the well so that it reduces the pressure and then the flow from the well. Once the kill mud is in the well and it’s shut down, then we follow up with cement to plug the leak.
For the top kill procedure BP is designing equipment to pump the highest kill rate it can, irrespective of the flow rate of oil from the well, to force a downward flow of mud into the well. This, combined with the heavy drilling fluid is designed to eventually stop the flow. This has never been attempted at these depths. This is very complex – and involves several complex procedures coming together.
How will it be done?
BP has the Q4000 vessel at the surface which has a crane for lifting heavy equipment and is a central part of the surface equipment for this procedure. It also has a number of other vessels: the HOS Centerline, with Halliburton pumping equipment; the HOS Strongline; and the BJ Services Blue Dolphin and Halliburton Stim Star IV pumping boats.
A total of 50,000 barrels of mud will be on location to kill the well – far more than necessary, but BP says it wants to be prepared for anything. Pumping capacity on location is more than 30,000 hydraulic horsepower.
The mud will be pumped down the 6-5/8 inch drill pipe (pipe is connected to the Q4000), then through 3-inch hoses, which go through the manifold on the seafloor. Then the mud moves through another set of 3-inch hoses attached to the Deepwater Horizon BOP choke and kill lines.
With the manifold, BP can also pump the ‘junk shot’ if necessary to stop too much of the kill mud going out through the top of the BOP rather than going down into the well to stop the flow. By switching valves in the subsea manifold, the company can inject the ‘bridging material’ (the junk), which will prevent such losses and enable the top kill to continue.
BP says it has been been testing the junk shot on-shore, looking at different configurations of what might restrict the flow out of the Deepwater Horizon riser and what types of materials would help shut it off. Materials in a junk shot can include well-known items such as pieces of tires, golf balls, and pieces of rope.
BP says most of the equipment is on site and preparations for this operation are underway.
