Graphene holds potential for diverse applications, including battery materials, electrodes, high-speed electronics, water filtration, and solar energy harvesting. We've discussed most of those applications in earlier blog posts, and not a day passes without some progress in one of those directions hitting the world headlines. Little media attention, however, has been paid to a young and exciting application of graphene – oil exploration.
Most of the world's growing energy demand is fulfilled from some form of fossil fuel, like coal and oil. It is well known that oil exploration and the energy sector are big business, but also potentially damaging to the environment. Oil spills and uncontrolled oil well explosions form just a part of the risk involved in oil exploration. Another cause for concern is the efficiency of extraction, and potential losses, or leaks of oil into the environment. Graphene is being explored for its use in various stages of the exploration and extraction process.
Much of the research on graphene for oil has come out of the lab of Prof. James Tour at Rice University. In their early work (published in 2012), the group first showed that adding platelets of graphene oxide to a common water-based drilling fluid decreased the losses of the fluid to the surrounding rock, as compared to a standard mixture of clays and polymers used in the drilling industry today.
Image: Graphene platelet plugging a nanopore (from ACS Applied Materials and Interfaces 4, 222 (2012))
These fluids are pumped downhole as part of the process to keep drill bits clean and remove cuttings. With traditional clay-enhanced fluids, 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. The thinner graphene layer budged much more easily than the the layer which would remain after a traditional clay-enhanced liquid was used. A drilling fluid with 2 percent functionalized graphene oxide formed a filter cake an average of 22 micrometers wide — substantially smaller than the 278-micrometer cake formed by traditional drilling fluids. GO blocked pores many times smaller than the flakes’ original diameter by folding.
Graphene can also be put to use for well logging. Well logging techniques provide data on the geological properties of reservoirs of interest to the oil and gas exploration industry. A commonly used logging technique uses wirelines to provide information about an oil or gas well. Wirelines are long wires with sensors attached to them, which are lowered into an exploration hole to provide information about the hole and its contents. An extension of wireline logging is logging-while-drilling, which relies on sensors at the end of the drill itself. Both methods utilize oil-based fluids for drilling and lubrication. Oil-based fluids, however, are not very good conductors of electricity, which is where graphene enters the scene. The group of Tour developed a solution that contains magnetic graphene nanoribbons (MGNRs). The MGNRs form part of a conductive coating in oil-based drilling fluids, improving the reliability of the information that is sent back up the hole by the sensors. Furthermore, the magnetic properties of the ribbons could also be exploited for using the ribbons themselves as advanced sensors. The Tour group filed a patent for this application.
Finally, since graphene nanoribbons can be made small enough to pass into tiny crevices of the rock which holds precious oil, some envision little graphene-based robots creeping through rocks, sending wireless data which contains information on oil location and concentration.