As it has become more difficult to find new reservoirs for oil and gas production, the petroleum industry has shifted focus to researching ways to extract more hydrocarbons out of reservoirs already in production. At NTNU, research is underway to investigate the potential of using nanofluids as a new agent for enhanced oil recovery (EOR).
What are nanofluids?
Nanofluids are composed of nanoparticles suspended in fluids. A nanoparticle is 1 to 100 nm in size. For comparison, a human hair is 80,000 to 100,000 nm in diameter. NTNU’s Nano-EOR petroleum group focuses on using silica nanoparticles because they are cheap to produce, can be easily modified to enhance desirable properties, and have a low capital cost for installation.
The researchers suspend the nanoparticles in saltwater at concentrations ranging from 0.01 to 1 weight percent. They also do research with metal oxide nanoparticles suspended in saltwater.
Why use nanofluids for EOR?
Most of the oil reservoirs in the North Sea use seawater to help produce oil. Seawater is injected into the reservoir and helps push the oil to the production wells. However, after the water reaches the production well (water break-through), additional injected water will mostly follow the water path and not push out more oil. This is mainly due to the differences in viscosity between the water and oil and also the interfacial tension between the oil and water phases.
In other words, oil is “thick” (viscous) and does not flow very well, but water is “thin” (less viscous) and flows easily through the reservoir. Also, some oil remains bound to the rock in the reservoir or trapped in hard-to-reach pore channels. Seawater injection is an effective method for increasing oil production, but additional methods need to be developed and applied in order to get more of the oil out of the reservoir.
Adding nanoparticles to the injected seawater can help scrub the remaining oil out of the reservoir. In lab tests at NTNU, special silica (sand) nanoparticles have increased oil recovery when added to seawater that is injected into oil-saturated sandstone blocks. These blocks are like miniature petroleum reservoirs and, combined with other experiments, they help the researches understand how the nanoparticles interact with the rock and oil.
How can nanofluids increase oil recovery?
There are many different mechanisms that the nanoparticles can use to enhance oil recovery including the following:
- Nanoparticles can increase the viscosity of the seawater to help push it through oil zones.
- Nanoparticles can lower the interfacial tension between the oil and seawater so oil that was lodged in tiny pore throats can be released into the water highways.
- Nanoparticles can create a wedge-film that strips the oil droplets off the rock surface.
- Nanoparticles and nano-gels can be used to selectively plug water paths, forcing the water to flow through oil–filled paths.
NTNU’s Nano-EOR petroleum group
NTNU’s Nano-EOR petroleum group currently consists of professor Ole Torsæter, PhD candidates Katie Aurand and Shidong Li and four MSc students.
This blog entry was written by PhD Candidate Katie Aurand, NTNU
– The Department of Petroleum Engineering & Applied Geophysics