By Louis A. Bloomfield, Ph.D.
Professor Physics, University of Virginia
The ongoing oil spill in the Gulf of Mexico is primarily a physics problem and, as such, should be susceptible to a physics solution. But two of the simplest physics solutions — sealing the top of the well with the blowout preventer’s hydraulic valves and pumping dense liquid drilling mud down the well hole (the “top kill”) — were both tried and failed for technical reasons. Propelled upward by a pressure in excess of 108 pascals (about 1, 000 atmospheres) at the bottom of the 18,000-foot well hole, the oil has resisted efforts to stop its flow from the top. All hopes have now turned to the relief wells, which won’t be ready for the “bottom kill” (pumping dense drilling mud up the leaking well hole) for at least another month. Bad weather or bad luck could further prolong the spill.
My suggestion is to focus not on the top of the well, but on the bottom of the well. I propose to stop the flow of oil by filling the well hole from the bottom up with dense, streamlined objects that are capable of descending into the uprushing stream of oil by gravity alone. An object that has a downward terminal velocity in the oil that is greater than the oil’s upward flow velocity will gradually descend to the bottom of the well. If those objects are dropped one after the next into the top of the well, the well will slowly fill up with them. They may hover in the oil initially, levitated by upward drag forces, but they’ll eventually collapse into a dense heap that is several miles deep. When they do, they will form the coarse equivalent of a “packed powder,” and the oil will have to traverse all the nooks and crannies in that powder to reach to top of the well. Given the viscous drag forces acting on the oil as it flows through the “powder,” the oil’s flow will be extremely slow.
Assuming the most pessimistic estimates for the leak rate (60,000 barrels per day) and the narrowest diameter of the casing near the bottom of the well hole (7 in or 17.8 cm), the upward velocity of the oil is likely to average at most 4.5 m/s (about 15 ft/s). Assuming that upward flow velocity, streamlined iron objects or rods less than 2 or 3 cm (about 1 in) in diameter should be able to make it to the bottom of the well. Objects made of lead or still denser metals should easily reach the bottom of the well.
The bottom of the well is porous rock rather than a vast underground cavern, so the objects will accumulate after descending through the oil. Eventually, several million kilograms of objects will fill the well hole and reduce the oil flow to a trickle, in spite of the roughly 1000 atm pressure drop between the bottom and top of the well. It may be helpful to include deformable objects, ones that can form particularly narrow channels for the oil or even true seals within the heap. It may also be valuable to include sharp, hardened steel or tungsten carbide objects that can grip the metal casings of the well hole and help prevent the oil from lifting the heap upward.