Functionalized graphene oxide plays part in next-generation oil-well drilling fluids

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 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 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.

Story Source:

The above story is reprinted from materials provided by Rice University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Dmitry V. Kosynkin, Gabriel Ceriotti, Kurt C. Wilson, Jay R. Lomeda, Jason T. Scorsone, Arvind D. Patel, James E. Friedheim, James M. Tour. Graphene Oxide as a High-Performance Fluid-Loss-Control Additive in Water-Based Drilling Fluids. ACS Applied Materials & Interfaces, 2011; : 111213103240001 DOI: 10.1021/am2012799

Light-sensing receptor plays role in temperature sensation: study

A light-sensing receptor that's packed inside the eye's photoreceptor cells has an altogether surprising role in cells elsewhere in the body, Johns Hopkins scientists have discovered. Using fruit flies, they showed that this protein, called rhodopsin, also is critical for sensing temperature.

A report on the work appears March 11 in Science.

“For decades, this well-known molecule — one of the most-studied sensory receptors — was thought to function exclusively in the eye as a light receptor, but now we have found that fly larvae and possibly other organisms use it to distinguish between slight temperature differences,” says Craig Montell, Ph.D., a professor of biological chemistry and member of the Center for Sensory Biology in the Institute for Basic Biomedical Sciences. “And it makes you wonder about what was the more ancient role for rhodopsin — was it used originally for light or temperature detection?”

The Hopkins team identified rhodopsin while investigating the process that results in the activation of a temperature-sensor protein known as a TRPA1, one of many so-called “trip” channels abundant on sensory cells that receive communication from the outside world. Montell discovered earlier that TRPA1 enables fly larvae to detect tiny changes in the range of temperature that’s optimal for their survival. However, unlike TRP channels that function in avoiding hot and cold temperatures, TRPA1 was not directly turned on by changes in temperature in the comfortable temperature range, which extends from 18 to 24 degrees centigrade (equivalent to about 64 to 75 degrees Fahrenheit).

The team set out to determine what receptor responds to the temperature in order to set off the signaling cascade that results in TRPA1 activation.

A reasonable place to start looking for likely suspects, Montell said, was the large family of G-protein coupled receptors, because they are cell-surface molecules known to activate TRP channels. Still, the researchers were faced with more than a hundred possible gene candidates, each coding for a different G-protein coupled receptor in flies: If it was a GPCR, then which one?

“There were no precedents for a GPCR functioning in thermosensation, leaving us wonder where to start,” Montell says. “We considered rhodopsin, even though it was thought to be required exclusively for light reception, because some of the other proteins that we showed previously to function in thermosensation were required in photoreceptor cells.”

Using larvae missing the gene that codes for rhodopsin, the team conducted a series of tests to compare their behaviors with normal (wild-type) animals. The researchers released about 75 larvae on a plate with two temperature zones; half of the plate was kept at their favorite temperature of 18 degrees C, and the other at an alternative temperature, ranging from 14 to 32 degrees C. After 10 minutes, the researchers counted the number of larvae that had crawled to the 18-degree side, and the number on the side with the alternative temperature. They discovered that in contrast to the wild-type larvae, which preferred 18 degrees over any other temperature, the larvae lacking rhodopsin couldn’t discriminate temperatures in comfortable range, just like the larvae lacking TRPA1. However, the rhodopsin mutant larvae were able to choose 18 degrees over temperatures that were too hot or cold.

“The genetics and the behavior show that rhodopsin is required for thermosensation,” Montell says. “Larvae that contain mutations disrupting rhodopsin are profoundly defective in their ability to sense temperatures, but only in the comfortable range. The simplest interpretation of these results is that rhodopsin is activated by temperature and this in turn, activates TRPA1. However, we cannot exclude that there is an additional accessory protein required for rhodopsin to act as a thermosensor.”

This rhodopsin which functioned in “feeling” temperature was required in a new type of thermosensory neuron in the body wall of fruit fly larvae as well as in neurons in the head region of the animals.

Montell says this new thermosensing role for rhodopsin has absolutely nothing to do with light. Wild-type fly larvae kept in a dark box were able to choose the preferred 18 degrees centigrade over 24 degrees C.

The indirect activation of the TRPA1 channel via a signaling cascade that requires rhodopsin most likely represents “a quality of life issue” for the larvae, Montell muses. It allows to them to give up avoiding temperatures that are slightly less preferred than 18 degrees and to adapt if they can’t find their favorite temperature in their thermal landscape. Direct activation of TRP channels by noxious temperatures is more about survival.

Provided by Johns Hopkins University (news : web)