What killed top-kill?
DOI: 10.1063/1.3582231
What killed top-kill? Global news coverage of the blown-out BP-operated Macondo well documented several efforts to stem the roughly 8 million liters per day of crude oil that gushed into the Gulf of Mexico from April to July 2010. One notable failure was the “top-kill” method to plug the well by pumping a dense slurry of drilling mud into it—reportedly, much of the mud was swept out by the spewing oil. A recent study by scientists at Lawrence Livermore National Laboratory and Washington University in St. Louis points to fluid shearing as the chief culprit in top-kill’s failure. Turbulent eddies, caused by the velocity differences between the counterstreaming mud and oil, likely sheared the mud, breaking it up into packets of fluid whose settling velocities were an order of magnitude smaller than the upward velocity. In laboratory experiments, the researchers confirmed their theory and demonstrated a possible solution, adding a viscoelastic polymer to an aqueous cornstarch mixture to represent the drilling mud. As the images show, the control fluid (left, in green) suffered turbulent breakup, but the polymer-laced fluid (center) descended as a coherent slug or, at lower flow rates (right), as stringy, connected globules. The researchers calculate that a polymer-doped slug of drilling mud at the Macondo well would have descended with a terminal velocity of roughly 7 m/s, nearly double the estimated 3.7 m/s ascent of escaping oil. (
