A fine foam for extracting oil

To capture every drop of hydrocarbons in tiny rock fissures that are highly difficult to access, scientists at Rice University in the United States, with funding from Abu Dhabi institutions, are studying the use of the frothy material, writes Daniel Bardsley.

Although the UAE’s reserves are actually predicted to last decades longer than that, it is still the case that limits on supply will place an ever greater premium on ensuring that every last drop of oil is extracted from oil fields in the Arabian Gulf. Courtesy Adnoc
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No one needs to be told that the Middle East is rich in oil. The region boasts more than half of the world’s proven crude reserves, with Saudi Arabia’s estimated 260 billion barrels accounting for 16 per cent of the world’s stockpile.

The UAE has close to 100 billion barrels in its underground inventory, and the country is among the planet’s top 10 producers of crude oil, pumping close to 3 million barrels of black gold a day.

But nothing lasts for ever. The British oil company BP estimates that the world’s total proven oil reserves of 1.7 trillion barrels would be depleted in 53 years were we to sustain the current rates of extraction.

Although the UAE’s reserves are actually predicted to last decades longer than that, it is still the case that limits on supply will place an ever greater premium on ensuring that every last drop of oil is extracted from oil fields in the Arabian Gulf.

This has focused attention – and UAE research funds – on efforts to extract more oil from individual fields.

When oil is extracted, typically the first 5 to 10 per cent bubbles to the surface through the reservoir’s own pressure, something known as primary recovery.

In the secondary recovery phase, water or gas is injected to increase pressure inside the reserve. That drives a further 30 per cent or so to the surface.

That still leaves behind a vast amount of oil, and often gas, too. What remains can be extremely tricky to get to, with much of it lurking in miniscule fissures in rocks.

It is at this stage that tertiary recovery or enhanced oil recovery (EOR) methods come into play. There are a host of such methods – some use surfactants (substances that reduce a liquid’s surface tension), others use gas or water, or combinations of them.

A team of scientists at Rice University in Texas, funded by several Abu Dhabi organisations, have been looking at something else entirely – foam.

To test it, they made a special mock-up of porous rock that was just a few centimetres across and had large numbers of tiny cracks. Liquids with low viscosity, such as water, rushed through large cracks in the model, leaving most of the oil behind.

By contrast, the foam’s bubbles gave it a much higher viscosity. That meant it flowed much more slowly – and so the foam’s liquid was forced into the tiny crevices that led off from the main cracks.

“Foam is really good at plugging high-permeability zones and diverting fluids to low-permeability zones where most of the oil is likely to remain trapped after the initial stages of the oil recovery process,” said Dr Charles Conn, the senior author of the paper published in the journal Lab on a Chip.

“This ‘mobility’ control is unique to foam because its viscosity – its resistance to flow – is dependent on the rock permeability in such a way that fluids would rather divert around foam-trapped bubbles, even if that means pushing into lower permeability rock. This is good; that’s where the oil is.”

The differences between foam and other potential EOR methods were huge. After four minutes, foam had pushed out three quarters of the oil from a low-permeability region of the structure.

When a combination of oil and gas was used, more than half the oil was left behind. With water alone, only 2 per cent of the oil was recovered.

A beneficial characteristic of foam was the way in which it tended to become drier as it progressed through the model. This made it move more slowly and pushed more of its liquid into tiny pores.

The Rice University study was partly funded by the Abu Dhabi National Oil Company (Adnoc), the Abu Dhabi Company for Onshore Oil Operations (Adco), the Petroleum Institute of the UAE and other UAE-based oil industry organisations.

They all have a keen interest in driving improvements in EOR techniques.

“It is expected that the Gulf region will need to use enhanced oil recovery methods as production levels start to decline,” said Dr Sibani Lisa Biswal, an associate professor at Rice University and a co-author of the paper.

“Our work provides options for when secondary recovery methods begin to decline.”

Indeed, Dr Conn believes that EOR “is the future”. Although foam’s potential has long been known, the oil industry’s commitment to developing EOR methods has over the years fluctuated along with the price of oil.

“Sooner or later, industry will need to get serious about developing the competency and understanding needed to manage EOR projects,” said Dr Conn, adding that oil companies that develop links with academic institutions involved in EOR research, and invest in staff specialised in the field, would “have a huge advantage when these types of operations become more common”.

Although many Arabian Gulf countries are exploring EOR strategies – including the UAE, Bahrain, Kuwait and Oman – there is not a one-size-fits-all solution.

“Every reservoir is different, so the best strategy for one field isn’t necessarily going to work for others,” said Dr Conn.

Appropriately then, Dr Biswal and her fellow researchers are looking at how higher temperatures and pressures influence the effectiveness of foam-based EOR.

Oil industry experts from the Arabian Gulf region, as well as those in other parts of the world, are likely to keep a close eye on the findings of their study.

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