Freeing underground oil, with water
Although world demand for oil is increasing, some estimates indicate that crude oil output has hit a plateau at 85 million barrels a day and, within a few years, will begin to decline. “We are reaching a capacity as to how much oil we can get out of the ground,” says Civil and Environmental Engineering Assistant Professor Dante Fratta. “But when we pump, we leave about 50 percent of the oil in there.”
Like the greasy post-dinner buildup on a kitchen stove, much of that remaining oil coats the rocks and minerals in an oil field. “In some formations, the oil gets attached to the surface, and it’s difficult to remove,” says Fratta.
With Geology and Geophysics Professor Herbert Wang and Universidad Nacional de Córdoba (Argentina) Assistant Professor Franco Francisca, Fratta is developing an enhanced oil recovery method that uses salt water as a wedge to “scrape” oil away from rough, porous underground surfaces.
Their method, which they are studying in laboratory experiments, exploits the power of a technique called electrowetting.
The phenomenon of electrowetting emerged in the late 1800s, though the actual term wasn’t used until the 1980s and researchers didn’t begin applying electrowetting in MEMS and microfluidic systems until the 1990s. “The idea is to be able to change the surface tension between different surfaces on fluids,” says Fratta. “You can control the contact angle by applying a large electric field.”
By applying this electric field, researchers can change the angle at which a drop of liquid contacts another liquid or solid surface. A smaller contact angle means the drop is spread out; as the contact angle becomes larger, the drop starts to look round, like a bubble. “We have been doing studies in which we can emulate the process of using this electrowetting phenomenon to be able to change the contact angle with respect to different natural surfaces—rocks and minerals,” says Fratta.
Using their electrowetting technique, the researchers would inject a detergent-saltwater mixture into the oil reservoir and then apply a large voltage to sensors placed throughout the oil field. Both the voltage and detergent reduce the surface tension of the water droplets, essentially flattening them and turning them into wedges that can release the oil. “So you have an oil drop, and you force the water to go in between,” says Fratta.
While the researchers have shown that the technique works in the laboratory, their next challenge is figuring how to implement on a scale the size of an oil field.