PetrobrasComputer simulations must be run before testing solutions to extract more oil from rocks in oil fieldsPetrobras
The objective of the research of physicist Caetano Miranda, professor in the Department of Mechanics and Materials Physics in the Institute of Physics of the University of São Paulo (IF-USP), is to employ nanoscience to increase the productivity of oil wells, extracting oil from underwater and land reservoirs that are not recovered using traditional methods. The researcher’s main idea, which uses computational modeling to simulate the inside of oil wells on a micro- and nanometric scale, is to use nanoparticles of oxides, such as silica, impregnated with surfactants — substances used by oil companies when exploiting reserves — to extract the oil adhering to the rocks in the reservoirs. Today, only 35% of the oil contained in wells is extracted, on average. The objective of the new technique is to double this percentage.
In order to understand how the silica nanoparticles will affect oil extraction, one must understand that neither oil nor gas are stored in pockets or large caverns undersea or underground. Oil and gas accumulate in empty spaces of porous, sedimentary rocks, like water in a soaking-wet sponge. When a well is drilled, part of the oil flows naturally due to the pressure difference, which is higher in the reservoir and lower on the surface. “During this first extraction phase, about 5% to 15% of the hydrocarbons stored in the deposit are removed. This percentage depends on certain factors, such as the type of rock in the reservoir and characteristics of the oil, such as its viscosity,” explains Miranda.
When well production drops, oil companies inject water, carbon dioxide (CO2) and nitrogen into the well to displace the oil still present in the reservoir. These fluids are introduced into the wells at a point a certain distance from the production site and act in a purely mechanical way, pushing the oil towards the drill hole. In this secondary oil recovery phase, up to 35% of the total volume can be extracted from most wells worldwide.
After this point, if oil company studies show it to be worthwhile economically, they continue to extract oil from the reservoir, injecting surfactants into the well in order to displace the remaining crude. “A surfactant is a product similar to soap that changes the interfaces between oil, rock and salt water, the three components of the system. It reduces the interface tension between these components in the reservoirs and changes the viscosity of the oil, making it flow more easily,” explains Miranda. There are, however, two problems with this substance. The first is its high cost. The oil company needs to use large quantities of surfactant, which requires complex transportation logistics because most wells are located in remote locations. The second problem is that surfactants do not tolerate high salinity levels and high temperatures well. They precipitate under these conditions, sticking to the surface of the rock. When this happens, they do not affect the viscosity of the residual oil, and thus do not help in its extraction.
The computational modeling research carried out by Miranda focuses precisely on the selection of the best material to act as a surfactant. The researcher studies nanoparticles capable of facilitating the extraction of the oil and gas retained in nano- and micropores in rocks while attempting to understand the behavior of these nanostructures. “We do not know what happens with oil or natural gas when they are confined in nanopores. We do not even know the percentage of oil and gas retained in them,” says Miranda.
The use of nanoscience in the oil industry, according to the USP professor, began in 2008 due to a request from the Society of Petroleum Engineers (SPE) and it has now become a subfield of a wider interdisciplinary field called nanogeoscience. It studies the phenomena that occur on the nanometric scale in geological materials and attempts to understand the effects of nanostructured or nanoconfined systems on larger scales. According to the researcher, in 2008 silica nanoparticles were already being used commercially in other fields, such as biomedicine and catalysis, in synthesizing new materials. “The question was to learn how these nanostructures behave under the extreme conditions of the reservoirs, where temperatures can reach 400oC and the pressure can exceed 200 atmospheres (atm). We need to know if we can modify the interaction between the oil, rock, and salt water,” he explains. “Our studies indicate that the silica nanoparticles could potentially be used to extract the oil.”
Another challenge was to make silica nanoparticles effective as a surfactant. “Based on molecular simulations, we tried to discover what would be the best product to add to the nanostructure, since there are many on the market. The silica nanoparticle, by itself, changes the interface between the oil, rock and salt water, but with the addition of a surfactant the effect is even greater,” says Miranda. “We want to understand why it alters the wettability of the oil.” Wettability is the capacity of a liquid to maintain contact with a solid surface when the two are placed together. “We resorted to computer simulation because of the cost-benefit ratio. Carrying out tests of surfactants in reservoirs would be too costly and take too long.” If a surfactant works with silica nanoparticles, its quantity and cost would be much less than that if the surfactant were used alone.
Another aspect of the research is to study nanostructures that could be employed to “illuminate” the oil fields, extracting more information from the reservoirs, such as details on the porosity of the rocks, the fluids in them, their chemical composition and the environmental temperature and pressure. This information is essential to the decisions made by the production engineering team. The use of nanoparticles, according to Miranda, could enhance the response of magnetic resonance studies carried out during drilling: the technique is used to map deposits. In order to do this, nanoparticles would be injected into the well together with water, serving as contrast agents. “In general, our studies seek better understanding, on a molecular scale, of the mechanisms and phenomena that occur in oil wells. We want to have an atomistic view of the process and determine the consequences on larger scales,” he affirms.
Computer code
Three PhD dissertations, four master’s theses and more than a dozen articles have been produced during the last eight years as part of Caetano Miranda’s research. His work is related to a four-year project financed by FAPESP and coordinated by physicist Alex Antonelli, of the Gleb Wataghin Physics Institute at the University of Campinas (Unicamp). “The objective of our project is to study a variety of condensed matter properties using computational modeling. Miranda uses the same tools that we use and, for this reason, we can share both computers and computer code,” affirms Antonelli. “In principle, we can understand on the computer — which acts like a virtual laboratory — the processes we already know and possibly improve them at a lower cost, without having to test a new idea in practice.”
Support from oil companies
Miranda also receives funding from Petrobras, in addition to that from FAPESP. His research falls under the government-owned company’s Thematic Networks program, established in 2006 and carried out in partnership with Brazilian research universities and institutions. “Professor Miranda’s work is part of the Advanced Oil Recovery Thematic Network,” says petroleum engineer Lua Selene Almeida, of the Petrobras Research Center (CENPES). “It is a very advanced, cutting-edge study. He is helping us model physical phenomena that occur in oil wells on a scale very different from that studied in our laboratories,” says the researcher.
Another source of funding is the Advanced Energy Consortium (AEC), an international consortium of oil industry companies, including the British-Dutch Shell, British Petroleum (BP), the Norwegian Statoil, the Spanish Repsol, the French Total and the Brazilian Petrobras, focused on financing nanoscience applied to the oil industry. The project supported by AEC included researchers from the University of Texas at Austin, an important research center in the oil and gas industry. “While our group was doing computer simulations, they carried out experiments,” says Miranda, pointing out that laboratory tests and experiments, stages that precede silica nanoparticle experiments in oil fields, will also be done in the near future at IF-USP.
“Computational simulations are much cheaper and must less risky than laboratory experiments,” says chemist Flávia Cassiola, a Brazilian researcher at Shell International Production and Exploration in Houston, Texas. “The oil industry is very interested in improving methods, contributing more details on reservoir characteristics for the simulation. Shell has several groups working on computational simulations in its technology and innovation centers and Professor Miranda is our expert on the subject. His work has helped us develop and enhance our advanced oil and natural gas recovery methods,” says Cassiola.
Project
Computational modeling of condensed matter: a multi-scale approach (nº 2010/16970-0); Grant Mechanism Thematic Project; Principal Investigator Alex Antonelli (IFGW-Unicamp); Investment R$ 356,196.00 and US$225,400.00.
