Thursday, December 29, 2011

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

Researchers measure nanometer scale temperature

 Atomic force microscope cantilever tips with integrated heaters are widely used to characterize polymer films in electronics and optical devices, pharmaceuticals, paints, and coatings. These heated tips are also used in research labs to explore new ideas in nanolithography and data storage, and to study fundamentals of nanometer-scale heat flow. Until now, however, no one has used a heated nano-tip for electronic measurements.

"We have developed a new kind of electro-thermal nanoprobe," according to William King, a College of Engineering Bliss Professor in the Department of Mechanical Science and Engineering at Illinois. "Our electro-thermal nanoprobe can independently control voltage and temperature at a nanometer-scale point contact. It can also measure the temperature-dependent voltage at a nanometer-scale point contact."

"Our goal is to perform electro-thermal measurements at the nanometer scale," according to Patrick Fletcher, first author of the paper, "Thermoelectric voltage at a nanometer-scale heated tip point contact," published in the journal Nanotechnology. "Our electro-thermal nanoprobe can be used to measure the nanometer-scale properties of materials such as semiconductors, thermoelectrics, and ferroelectrics."

The electro-thermal probes are different than thermal nanoprobes typically used in King's group and elsewhere. They have three electrical paths to the cantilever tip. Two of the paths carry heating current, while the third allows the nanometer-scale electrical measurement. The two electrical paths are separated by a diode junction fabricated into the tip. While the cantilever design is complex, the probes can be used in any atomic force microscope.

In addition to Fletcher, co-authors of the paper include Byeonghee Lee, and William King. The research was performed in the Nanoengineering laboratory as well as the Micro and Nanotechnology Laboratory and the Materials Research Laboratory at Illinois.

Story Source:

The above story is reprinted from materials provided by University of Illinois College of Engineering.

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

Journal Reference:

Patrick C Fletcher, Byeonghee Lee, William P King. Thermoelectric voltage at a nanometer-scale heated tip point contact. Nanotechnology, 2012; 23 (3): 035401 DOI: 10.1088/0957-4484/23/3/035401

Shearing triggers odd behavior in microscopic particles

 Microscopic spheres form strings in surprising alignments when suspended in a viscous fluid and sheared between two plates -- a finding that will affect the way scientists think about the properties of such wide-ranging substances as shampoo and futuristic computer chips.

A team of scientists at Cornell University and the University of Chicago have imaged this behavior and have explained the forces causing it for the first time. Its findings appear in the Dec. 19-23 early edition of the Proceedings of the National Academy of Sciences.

"The experimental breakthrough revealed that these string structures were perpendicular to the shear instead of parallel to it, contrary to what many in the field were expecting," said Aaron Dinner, associate professor in chemistry at UChicago and a study co-author.

The experiment was led by Itai Cohen, associate professor of physics at Cornell, who custom-built a device that would enable him simultaneously to exert shearing forces on suspended colloids (the spheres) and image the resulting motion at 100 frames per second with a confocal microscope. Imaging speed was critical to the experiment because the string-like structures appear only at certain shear rates.

"This issue of strings has been pretty controversial. I'm not sure that we've solved all the controversies associated with them, but at least we've made a step forward," Cohen said.

Shearing forces affect the dynamic behavior of paint, shampoo and other viscous household products, but an understanding of these and related phenomena at the microscopic level has largely eluded a detailed scientific understanding until the last decade, Dinner noted.

Futuristically speaking, these forces potentially could be harnessed to produce microscopic patterns on computer chips or biosensors via special paints that flow easily when layered in one direction, but becomes hard when layered in another direction.

Cohen's objective was more scientifically immediate: to devise an experiment that would overcome the technical difficulties associated with measuring the mechanical properties of the colloidal strings while also imaging their formation. "The holy grail is to be able to understand how the structure leads to the mechanical properties and then to be able to control the mechanical properties by influencing the structure," Cohen explained.

Cohen, PhD'01, received his doctorate in physics at UChicago, as did lead author Xiang Cheng, PhD'09, a postdoctoral associate at Cornell who assembled the team; and co-author Xinliang Xu, PhD'07, a postdoctoral scholar at UChicago. The study co-authors also included Stuart Rice, the Frank P. Hixon Distinguished Service Professor Emeritus in Chemistry at UChicago and a 1999 recipient of the National Medal of Science.

As members of UChicago's Materials Research Science and Engineering Center, Rice and Dinner are part of a larger effort to determine how materials behave under the influence of various dynamic forces. Some of their physics colleagues analyze forces operating on macroscopic scales, while chemists such as Rice and Dinner attempt to assess how those findings might apply to microscopic phenomena.

Rice and his UChicago co-authors used computer simulations to develop a precise explanation for the string-like colloidal structures that formed in the Cornell experiment. "The previous simulations all left out the consequences of the flow created in the supporting fluid as the particles move, the so-called hydrodynamic forces," Rice said.

"A very large fraction of the work in the field neglects hydrodynamic forces because it's hard. You try and get away with what you can," Rice noted with amusement. "But in this case it turns out that the inclusion of those forces is the crucial element."

The simulations allowed the UChicago team to control various experimental parameters to assess their relative importance. "You can play God," Rice said. "The important finding is the overwhelming role of the lubrication forces and the anti-intuitive result that they create."

The lubrication force comes into play when two colloids come together to behave much like macroscopic ball bearings soaking in a reservoir of goopy fluid.

"Pulling them apart would be working against the fluid and so it would be very hard," Dinner said. "So actually, when you get a collision in these colloidal systems, those lubrication forces hold them together much longer, and that actually allows for some of the unique dynamics that give rise to the structure. That was specifically what the simulations showed."

Xu, the UChicago postdoctoral scholar, adapted a mathematical formula developed by John Brady at the California Institute of Technology to simplify the simulations, which ran for days and weeks at a time. "Every time you rearrange the particles, the interactions are different," Rice said. "If you were to calculate that directly, it would be extremely tedious."

But Xu's adapation of Brady's formula enabled him to generate a table of hydrodynamic interactions that listed each particle configuration. Xu found that he could accurately simplify the simulation by focusing on just two of the experiment's seven layers of colloids.

The simulations and the experiment showed that even after three centuries of study, the field of hydrodynamics continues to yield surprising discoveries. "We are still discovering novel behavior that is fundamentally determined by the hydrodynamics," Rice noted.

Story Source:

The above story is reprinted from materials provided by University of Chicago. The original article was written by Steve Koppes.

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