Nanotechnology Helping to Recover More Oil

QDOTS imagesCAKXSY1K 8(Nanowerk News) When petroleum companies abandon an oil  well, more than half the reservoir’s oil is usually left behind as too difficult  to recover. Now, however, much of the residual oil can be recovered with the  help of nanoparticles and a simple law of physics.
Oil to be recovered is confined in tiny pores within rock, often  sandstone. Often the natural pressure in a reservoir is so high that the oil  flows upwards when drilling reaches the rocks containing the oil.
Less oil without water
In order to maintain the pressure within a reservoir, oil  companies have learned to displace the produced oil by injecting water. This  water forces out the oil located in areas near the injection point. The actual  injection point may be hundreds or even thousands of metres away from the  production well.
Eventually, however, water injection loses its effect. Once the  oil from all the easily reached pores has been recovered, water begins emerging  from the production well instead of oil, at which point the petroleum engineers  have had little choice but to shut down the well.
The petroleum industry and research community have been working  for decades on various solutions to increase recovery rates. One group of  researchers at the Centre for Integrated Petroleum Research (CIPR) in Bergen,  collaborating with researchers in China, has developed a new method for  recovering more oil from wells – and not just more, far more.
The Chinese scientists had already succeeded in recovering a  sensational 15 per cent of the residual oil in their test reservoir when they  formed a collaboration with the CIPR researchers to find out what had actually  taken place down in the reservoir. Now the Norwegian partner in the  collaboration has succeeded in recovering up to 50 per cent of the oil remaining  in North Sea rock samples.
Nanoscale traffic jams
Water in an oil reservoir flows much like the water in a river,  accelerating in narrow stretches and slowing where the path widens.
When water is pumped into a reservoir, the pressure difference  forces the water away from the injection well and towards the production well  through the tiny rock pores. These pores are all interconnected by very narrow  tunnel-like passages, and the water accelerates as it squeezes its way through  these.
The new method is based on infusing the injection water with  particles that are considerably smaller than the tunnel diameters. When the  particle-enhanced water reaches a tunnel opening, it will accelerate faster than  the particles, leaving the particles behind to accumulate and plug the tunnel  entrance, ultimately sealing the tunnel.
This forces the following water to take other paths through the  rock’s pores and passages – and in some of these there is oil, which is forced  out with the water flow. The result is more oil extracted from the production  well and higher profits for the petroleum companies.
The density gradient between particles and water slows the particles’ movement through the winding passages within the rock
Left:  The density gradient between particles and water slows the particles’ movement  through the winding passages within the rock. The particles accumulate and  consolidate at bottleneck points to block the rock pores. The pressure builds in  adjacent pores, forcing out the oil (shown in green). Right: Once the oil is  freed, the surrounding pressure drops. The blockages gradually dissolve and the  polymer particles commence flowing with the water. (Illustration: CIPR)
Elastic nanoparticles
The particles that are used are typically 100 nanometres in  diameter, or 100 times smaller than the 10-micron-wide tunnels.
The Bergen and Beijing researchers have tested a variety of  particle sizes and types to find those best suited for plugging the rock pores,  which turned out to be elastic nanoparticles made of polymer threads that  retract into coils. The particles are made from commercial polyacrylamide such  as that used in water treatment plants. Nanoparticles in solid form such as  silica were less effective.
China first with field studies
The idea for this method of oil recovery came from the two  Chinese researchers Bo Peng and Ming yuan Li who completed their doctorates in  Bergen 10 and 20 years ago, respectively. The University of Bergen and China  University of Petroleum in Beijing have been cooperating for over a decade on  petroleum research, and this laid the foundation for collaboration on  understanding and refining the particle method.
Field studies in China not only yielded more oil, but also  demonstrated that the nanoparticles indeed formed plugs that subsequently  dissolved during the water injection process. Nanoparticles were found in the  production well 500 metres away.
“The Chinese were the first to use these particles in field  studies,” says Arne Skauge, Director of CIPR. “The studies showed that they  work, but there were still many unanswered questions about how and why. At CIPR  we began to categorise the particles’ size, variation in size, and structure.”
At first it was not known if the particles could be used in  seawater, since the Chinese had done their trials with river water and onshore  oilfields. Trials in Bergen using rock samples from the North Sea showed that  the nanoparticles also work in seawater and help to recover an average of 20?30  per cent, and up to 50 per cent, more residual oil.
Centre of Excellence of great benefit to  society
The Centre for Integrated Petroleum Research (CIPR) is the only  institution for petroleum research under the Centres of Excellence (SFF) scheme.  CIPR is now supplementing its expertise on oil reservoirs with nanotechnology  know-how in seeking ways to recover residual oil.
Success could have far-reaching impacts. The state-owned  petroleum company, Statoil, is seeking to increase current recovery rates, which  range from under 50 per cent, to roughly 60 per cent.
“We hope this new method can help to raise recovery rates to  60?65 per cent,” says Mr Skauge.
Looking to field test
Now the Bergen researchers want to test out the method  large-scale.
“We’d like to try it in the North Sea and are in contact with  Statoil, but we are certainly not the only ones hoping for a chance. We are  competing with many promising methods for raising recovery rates,” explains Mr  Skauge. “That is why we may well test the method onshore in other regions, such  as the Middle East. Several actors from there have contacted us after reading  our published papers.”
Still questions unanswered
In the meantime the researchers will be learning as much as they  can about particles and pores.
“We are working hard to understand why the particles work well  in some rock types and more marginally in others,” says Kristine Spildo, project  manager at CIPR. “This is critical for determining which North Sea fields are  best suited to the method.”
Source: By Claude R. Olsen/Else Lie, Research Council of  Norway

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