The trouble with crude oil is that it is often very crude鈥攁 sticky,
viscous goo that鈥檚 nothing like the light stuff that flows into your tank on the
filling station forecourt. Turning that goo into something useful is a
billion-dollar nightmare for the oil industry.
But not all crude is the same. Different oilfields have different crudes.
Some are 鈥渟our鈥�: heavy, viscous and packed with toxic contaminants; others are
lighter, 鈥渟weet鈥� crudes. Not surprisingly, oil companies have concentrated on
pumping out the lighter crudes that are cheaper to extract and refine, leaving
the thicker stuff underground. But as new finds of oil dry up, and with most of
the cleanest reserves gone, the oil industry is facing a famine.
The heaviest crudes, which make up over 60 per cent of the world鈥檚 known oil
reserves, are now trapped below the surface, according to Eugene Premuzic of the
US Department of Energy鈥檚 Brookhaven National Laboratory in Upton, New York.
鈥淭hey are difficult and costly to recover by conventional methods. Until now we
have really just been skimming the light crude off the top,鈥� he says. 鈥淏ut that
cannot go on.鈥� The pressure is on to find economical ways to get the heavy stuff
out of the ground and onto the forecourt.
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So oil companies are turning to bacteria for help. Some bugs, they鈥檝e
discovered, can live happily underground and devour even the thickest crude,
breaking it down into something more manageable. Others can munch their way
through contaminants such as sulphur compounds and heavy metals. If researchers
can find the right bacterial cocktail, they might end up turning the oil
industry on its head.
The problem of heavy crudes is particularly acute in Uncle Sam鈥檚 back yard,
where most of them currently aren鈥檛 worth extracting. These are sour crudes,
heavily laced with all sorts of organic contaminants that contain nitrogen,
heavy metals and, perhaps worst of all, sulphur compounds. At the same time,
many large oil companies face the prospect of either bringing these thick crudes
to the surface or going out of business.
鈥淭exaco has significant holdings in heavy and high-sulphur crude oil
reserves,鈥� says Robert Shong, from the company鈥檚 exploration and producing
technology department in Houston, Texas. Texaco鈥檚 crudes in Venezuela, says
Premuzic, 鈥渁re solid at room temperature鈥�.
The new determination to crack the sour crude problem comes just when nobody
wants to buy sulphur-rich fuels any more. Many governments are imposing
swingeing cuts in sulphur emissions to clean up urban smogs and cut acid rain.
In the US, for instance, petrol at the pump contains on average 340 parts per
million of sulphur. In May 1999, President Bill Clinton announced plans for
tougher sulphur emissions standards that will, by around 2006, require a 90 per
cent reduction in sulphur content to a maximum of 30 parts per million. Similar
rules for diesel are expected to follow.
In Europe this year, BP Amoco responded to pressure for low-sulphur fuels by
putting on the market a 鈥済reen鈥� diesel containing less than 50 ppm of
sulphur.
Sulphur is also bad news at the refinery鈥攊t is corrosive and gums up
other refining processes. Conventional methods of stripping sulphur from oil in
the refinery are expensive, a single desulphurisation plant costing $60
million or more to set up. These plants need large amounts of hydrogen, high
temperatures and high pressures to strip the sulphur from the crude, and they
churn out hard-to-handle waste products. Worst of all, they work least well with
the thick crudes for which they are most needed.
Since the oil industry鈥檚 traditional chemistry has failed to deliver the
goods, many companies are now looking to biologists for help. The solution, says
Shong, could lie in microorganisms that can break down heavy crude into lighter,
sweeter fractions and remove contaminants such as sulphur at the oilfield. His
own company is playing for big stakes here. A recent study by Texaco of just
four of its oilfields put the potential gain to the company of a cheap
oilfield-based desulphurisation process at $300 million a year.
In the past decade the US Department of Energy has invested in finding and
patenting such microorganisms. Premuzic has pioneered much of the work, by going
bug prospecting. 鈥淲e have built up a collection of extremophiles bugs that live
in extreme conditions from around the world, and have begun looking at what they
could do,鈥� he says. Some of his best bugs have come from the sulphurous
environments of slag heaps and boiling mud holes in New Zealand and Iceland.
They excrete enzymes that break down complex organic molecules, including
sulphur compounds, just as gastric juices break down a good lunch.
In principle the process is simple enough. 鈥淏ioprocessing oil basically
involves mixing a water-soluble catalyst鈥攖he microorganism鈥攚ith air
and the oil,鈥� says Shong. Most oilfields are awash with water coming up with the
oil. So you just add bugs and stir. As part of the research programme, Abhijeet
Borole and colleagues at the US government鈥檚 Oak Ridge National Laboratory have
developed a novel electro-spray reactor to produce good contact between the oil,
oxygen and microorganisms. Inside the reactor, the enzymes in sulphur-eating
bugs such as Thiobacillus thiooxidans catalyse oxidation processes that
rip sulphur atoms from organic sulphide compounds in the oil, such as
dibenzothiophene (DBT). The sulphides are converted into sulphate salts that
dissolve in water. The water, now containing the bugs sated on sulphur, is
separated from the oil and hey presto: low-sulphur oil ready for the
refinery.
Some of the bugs will eat other contaminants too, including nitrogen
compounds and heavy metals such as nickel, which can poison the catalysts in an
oil refinery. Each bug has its own taste for the perfect meal. Premuzic claims
that to date his team has produced microorganisms that will, in the lab at any
rate, convert large hydrocarbons to lighter molecules, such as alkanes with less
than 20 carbon atoms. They also reduce levels of organic sulphur and nitrogen
compounds by up to 40 per cent and heavy metals by up to 50 per cent. The
resulting 鈥渃rude鈥� is sweeter and lighter than before, much more like the stuff
oil companies prefer to pump to their refineries. 鈥淯p to now we have used single
organisms, but eventually we are likely to use a cocktail of them to optimise
results,鈥� says Premuzic.
They will need to show their versatility. Every oilfield is different, says
Shong. At some, for instance, DBT is the main problem; at others, it is hardly
present. So the cocktail of microorganisms will have to be customised to work
efficiently with the particular mix of pollutants, including different
sulphides, in the field鈥檚 crude oil. This, he points out, is another important
reason for carrying out bioprocessing on the oilfields themselves, before the
crudes from different fields get mixed up.
Treatment at the oilfield offers other benefits, too. Transport is one: it鈥檚
much easier to move crude when it has been cleaned up than in its thick, sour
state. Another is the length of time鈥攑robably days鈥攏eeded for
bioreactions to take place. Refinery operations are normally measured in hours,
as companies rush to maximise output from their expensive equipment, often on a
small site. 鈥淢ost refineries maintain continuous operation and high throughput,
unlike a field operation where, in some cases, oil can be held in a tank for
several days awaiting transportation,鈥� says Shong.
More controversial is the fate of the waste from biological processing. The
bugs will be filtered out of the water for reuse but the waste water, containing
sulphur and organic salts, will have to go somewhere. As Shong says: 鈥淚n a
refinery, this new waste stream becomes an added problem.鈥� However, in the field
the water can be diluted and reinjected into the former oil-bearing rocks below.
鈥淭here are clear economic incentives for doing pre-treatment at the wellhead,鈥�
he says. Environmentalists may take a different view.
Early efforts at biological treatment of crude oil were made as long ago as
the 1940s, but failed to catch on because the bugs ate so much of the
hydrocarbons that they lowered the value of the oil. There were other problems,
too. Soviet engineers developed a method for injecting oil wells with bugs that
generate detergents to clean up crude before it was pumped to the surface. But,
says Premuzic, the bugs required their own food supply鈥攎olasses鈥攖o
be sent down with them. 鈥淭he system actually worked fine so long as you had a
lot of cheap molasses available,鈥� he says. 鈥淭he Russians used waste from sugar
beet. But without a large local supply, it is not economic.鈥�
Premuzic says his new breeds of bacteria are a great improvement. He has
concentrated on coaxing them to live, eat and work in an oily environment by a
process of natural selection. He adds the bacteria鈥攂ugs such as
Sulfolobus acidocaldarius and Acinetobacter calcoaceticus鈥攖o
oil-filled 鈥渃ooking鈥� vessels. The microorganisms that survive the initial
temperatures and pressures go on to repeat the process under more extreme
cooking conditions. The resulting bacteria not only survive these salty, toxic
conditions with temperatures that reach 85 掳C and pressures of up to 2500
pounds per square inch, they happily chomp their way through large hydrocarbons
and sulphur compounds in the oil.
Others are taking the route of genetic modification. Since 1992, researchers
at Energy Biosystems in Houston, Texas, have been cloning and sequencing
desulphurising genes in bacteria such as Rhodococcus rhodocrous. Its
researchers are now engineering the cloned genes to magnify their clean-up
properties and to introduce them into other host organisms. But so far they are
using the technique only to remove sulphur from oil products that have already
passed through the refinery. This is an easier task, says Shong, who has worked
with them. 鈥淭heir bugs work well with DBT. But in crude, DBT is not the only
sulphur compound, and often not even the most important. And for these, with
higher molecular weights than DBT, it doesn鈥檛 work.鈥�
Shong believes the real future for biological desulphurisation is in
processing crude oil. And he believes that the logical final step could be to
put the entire operation underground, where the oilfield itself will become the
reactor tank. 鈥淲e could put a solid support down the well. It might carry a
filter cartridge containing bugs, so that the oil passes through the cartridge,鈥�
he says. 鈥淥r alternatively we could inject the organisms directly into the
ground. They need some air to live, but not much. The amount of air dissolved in
water routinely put into the wells would be enough.鈥�
All this is still high-risk research, admits Shong. 鈥淎 proof of concept of
the process for crude oil is not in hand. Downhole conditions add too many
variables right now. But if we can get the bio-upgrading process to succeed
then the next step is definitely well-bore application. Downhole application is
definitely a goal.鈥� It could also be the first step towards taking all sorts of
refining processes underground. One day, what comes to the surface may look much
more like what comes out of the forecourt pump.
Cleaning up in China
Premuzic鈥檚 team is about to begin turning this crystal-ball gazing into
reality. 鈥淔or the first time our processes are about to be used outside the
lab,鈥� he says. His bugs will be put to work in earnest to improve the recovery
of oil in an oilfield in northern China. The site remains secret because of
delicate negotiations involving both the US and Chinese governments. 鈥淚t is a
sensitive time politically,鈥� he says. But the choice of a Chinese partner is not
as surprising as it seems.
In one of the most ambitious clean-up programmes organised anywhere in the
world China is currently engaged in two massive technological
efforts鈥攕witching from burning coal to using oil and natural gas, and
ridding itself of sulphurous urban smogs. According to UN data, nine of the
world鈥檚 ten most smog-bound cities are in China. Sulphurous acid rain is
reducing crop yields across a third of the most populous country on Earth. So it
has incentive enough to try and get in on the ground floor of a new
technology.
And what goes for China today goes for the world tomorrow. Phil Palmedo, who
licenses Premuzic鈥檚 systems to oil companies, is convinced that there is a
global market for sulphur-eating, oil-loving bugs that can get to grips with the
dregs at the bottom of the dirtiest oil wells. 鈥淭his approach looks beyond the
short term to meet the long-term strategic needs of the US and the world. Oil
reserves once deemed out of practical reach will now be made available for
processing, so that the resulting fuels will burn more cleanly.鈥�