POLLUTION caused by extracting oil from wells that are close to running dry could be all but eliminated by some ingenious fluid mechanics.
As an oil well empties, the crude oil extracted from it is increasingly laden with water, often producing a watery gunk that is about nine parts water to one part crude. Much of this oil is in the form of minute droplets that are held in suspension.
To separate this oil, it is necessary to add a chemical cocktail of emulsion breakers and 鈥渇locculants鈥�. This disrupts the surface forces on the droplets that maintain the emulsion, allowing them to combine into larger blobs which float to the surface. The cocktail of chemicals remains in the waste water, and can contaminate groundwater, or seawater if the well is offshore, when it is disposed of.
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Now experiments by mechanical engineer Boyd Greene of Nu-Corp in Byhalia, Mississippi, show that it is possible to disrupt the emulsion by setting the oil drops spinning. This loosens the water鈥檚 grip on the oil, so it can be extracted without chemicals.
Greene passes the emulsion into a chamber where it experiences steady 鈥渓aminar鈥� flow: that is, flow with no turbulence. In laminar flow, fluid moves faster the further it is from the wall of the chamber, as if it were made up of a series of concentric layers slipping over one another. This means that fluid on one side of each droplet is always moving faster than on the other, so it experiences a turning force that sets it spinning.
In lab tests on Greene鈥檚 system, at Mississippi State University in Starkville, more than 99 per cent of the oil from a water/oil mixture was recovered. Trials of a scaled-up system will begin at an oil well later this year. If the trials are a success, the system will be welcomed by both environmentalists and the oil industry. Greene says he is already in talks with the oil companies.
Neil Oakey, an engineer at BP in London, who specialising in oil recovery from near-depleted wells, says that if the results scale up, the technology will be an important development. 鈥淚f it works it will save money and increase the oil recovered. But most importantly, it will provide clean water for disposal or reinjection,鈥� he says.
