They found a few issues that needed to be dealt with. First, pristine graphene is hard to disperse in water, so it is unsuitable for water-based muds. Graphene oxide (GO) turned out to be much more soluble in fresh water, but tended to coagulate in saltwater, the basis for many muds.
The solution was to "esterify" GO flakes with alcohol. "It's a simple, one-step reaction," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. "Graphene oxide functionalized with alcohol works much better because it doesn't precipitate in the presence of salts. There's nothing exotic about it."
In a series of standard American Petroleum Institute tests, the team found the best mix of functionalized GO to be a combination of large flakes and powdered GO for reinforcement. A mud with 2 percent functionalized GO formed a filter cake an average of 22 micrometers wide -- substantially smaller than the 278-micrometer cake formed by traditional muds. GO blocked pores many times smaller than the flakes' original diameter by folding.
Aside from making the filter cake much thinner, which would give a drill bit more room to turn, the Rice mud contained less than half as many suspended solids; this would also make drilling more efficient as well as more environmentally friendly. Tour and Andreas Lttge, a Rice professor of Earth science and chemistry, reported last year that GO is reduced to graphite, the material found in pencil lead and a natural mineral, by common bacteria.
"The most exciting aspect is the ability to modify the GO nanoparticle with a variety of functionalities," said James Friedheim, corporate director of fluids research and development at M-I SWAC
|Contact: David Ruth|