BP on May 26th provided an update on developments in the response to the MC252 oil well incident in the Gulf of Mexico.
Subsea efforts continue to focus on progressing options to stop the flow of oil from the well through interventions via the blow out preventer (BOP), and to collect the flow of oil from the leak points. These efforts are being carried out in conjunction with industry experts and governmental authorities.
A series of diagnostic tests are currently underway on the Deepwater Horizon’s failed BOP to improve understanding of the status and configuration of the BOP and determine whether a ‘top kill’ procedure can be successfully executed. These tests involve pumping drilling fluids into the BOP to measure pressures and validate flow paths. When complete, a decision will be made on the execution of the top kill procedure itself.
This top kill procedure has not been carried out offshore at 5,000 feet water depth before, and its success cannot be assured. It is expected that the entire procedure could take up to two days, and it cannot be predicted how long it will take for the operation to prove successful or otherwise. Should it be necessary, plans and equipment are in place to combine the top kill process with the injection under pressure of bridging material into the BOP to prevent or limit upward flow through the BOP.
BP will continue to provide a live video feed from the seabed through the diagnostic testing and top kill, if undertaken. Throughout the diagnostic process and top kill procedure very significant changes in the appearance of the flows at the seabed will be expected. These will not provide a reliable indicator of the overall progress, or success or failure, of the top kill operation as a whole.
Should the top kill not succeed in fully stopping the flow of oil and gas from the well, BP would then intend to move forward to deployment of the LMRP cap containment system.
Deployment of this system will involve first removing the damaged riser from the top of the BOP to leave a cleanly-cut pipe at the top of the BOP’s lower marine riser package (LMRP). The LMRP cap, an engineered containment device with a sealing grommet, would then be connected to a riser from the Discoverer Enterprise drillship and then placed over the existing LMRP with the intention of capturing most of the oil and gas flowing from the well.
The LMRP cap is already on site and it is anticipated that this option will be available for deployment by the end of May.
Additional options also continue to be progressed, including the option of lowering a second blow-out preventer, or a valve, on top of the failed Deepwater Horizon BOP.
Work on the drilling of two relief wells, begun on May 2 and May 16, continues. Each of the wells is estimated to take some three months to complete from the commencement of drilling.
Top kill procedure
Image credit: British Petroleum
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 BP follow up with cement to plug the leak.
For the top kill procedure BP is designing equipment to pump the highest kill rate that they 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.
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. BP 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 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,BP can inject the ‘bridging material’ (the junk), which will prevent such losses and enable the top kill to continue.
BP has 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.
Most of the equipment is on site and preparations continue for this operation
Source: British Petroleum