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Graphene’s
star is rising as a material that could become essential to efficient,
environmentally sound oil production. Rice University researchers are
taking advantage of graphene’s outstanding strength, light weight and
solubility to enhance fluids used to drill oil wells.
The
Rice University lab of chemist James Tour and scientists at M-I SWACO, a
Texas-based supplier of drilling fluids and subsidiary of oil-services
provider Schlumberger, have produced functionalized graphene oxide to
alleviate the clogging of oil-producing pores in newly drilled wells.
The
patented technique took a step closer to commercialization with the
publication of new research this month in the American Chemical Society
journal Applied Materials and Interfaces. Graphene is a one-atom-thick
sheet of carbon that won its discoverers a Nobel Prize last year.
Rice’s relationship with M-I SWACO
began more than two years ago when the company funded the lab’s
follow-up to research that produced the first graphene additives for
drilling fluids known as muds. These fluids are pumped downhole as part
of the process to keep drill bits clean and remove cuttings. With
traditional clay-enhanced muds, differential pressure forms a layer on
the wellbore called a filter cake, which both keeps the oil from flowing
out and drilling fluids from invading the tiny, oil-producing pores.
When
the drill bit is removed and drilling fluid displaced, the formation
oil forces remnants of the filter cake out of the pores as the well
begins to produce. But sometimes the clay won’t budge, and the well’s
productivity is reduced.
The
Tour Group discovered that microscopic, pliable flakes of graphene can
form a thinner, lighter filter cake. When they encounter a pore, the
flakes fold in upon themselves and look something like starfish sucked
into a hole. But when well pressure is relieved, the flakes are pushed
back out by the oil.
All
that was known two years ago. Since then, Tour and a research team led
by Dmitry Kosynkin, a former Rice postdoctoral associate and now a
petroleum engineer at Saudi Aramco, have been fine-tuning the materials.
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% functionalized GO
formed a filter cake an average of 22 µm wide—substantially smaller than
the 278-µm 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 Lüttge, 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 SWACO and a co-author of the
research. “Therefore we can ‘dial in’ our application by picking the
right organic chemistry that will suit the purpose. The trick is just
choosing the right chemistry for the right purpose.”
“There’s
still a lot to be worked out,” Tour said. “We’re looking at the
rheological properties, the changes in viscosity under shear. In other
words, we want to know how viscous this becomes as it goes through a
drill head, because that also has implications for efficiency.”
Muds
may help graphene live up to its commercial promise, Tour said.
“Everybody thinks of graphene in electronics or in composites, but this
would be a use for large amounts of graphene, and it could happen soon,”
he said.
Friedheim
agreed. “With the team we currently have assembled, Jim Tour’s group
and some development scientists at M-I SWACO, I am confident that we are
close to both technical and commercial success.”
Other
authors of the paper are Rice graduate student Gabriel Ceriotti, former
Rice research associates Kurt Wilson and Jay Lomeda, and M-I SWACO
researchers Jason Scorsone and Arvind Patel.
Graphene Oxide as a High-Performance Fluid-Loss-Control Additive in Water-Based Drilling Fluids
