How a giant 'jelly doughnut' could get the good oil

The world is not running out of oil, according to Montana State University microbiologist Prof Bill Costerton -- it's just too difficult to get the vast amounts of oil that remain in the ground after oilfields expire.

Costerton, speaking at the ASM 2002 conference in Melbourne this week, said oil drillers merely skimmed off the easily accessible oil, typically leaving behind as much as 70 per cent of the original reserves.

He said that at least as much oil remained potentially accessible in depleted oilfields around the world as has been consumed during the 20th century -- the problem was how to get it to the surface.

Costerton, an expert on microbial biofilms -- the slimy goo that coats bacteria-infested surfaces -- told the conference about a simple but potentially revolutionary technique could literally squeeze huge amounts of oil out of old oilfields, and lead to much more efficient exploitation of new reserves.

"The first 15 per cent of the oil from a typical oilfield comes out under gas pressure, and then when the pressure starts to fall off, it's common practice to inject water to force more oil to the surface," he said.

"You inject water at a particular point into oil-bearing porous rocks, hoping to force it sideways so it can be tapped by wells drilled around the periphery. But often, the wells only bring up the same water that was pumped into the ground, or a water-oil emulsion."

The challenge is to corral the oil with back-pressure, to prevent it being pushed beyond the network of drill holes surrounding the injection site.

Injecting water creates more problems, said Costerton -- bacteria in the flooded oil-bearing rock strata produce hydrogen sulphide gas, which turns light sweet crude into foul-smelling 'sour' crude.

Drillers have had limited success instilling localised 'plugs' of polyuronic acid, an expensive polymer.

Budget solution

Costerton, who heads the Centre for Biofilm Engineering at Montana State University, went looking for a cheaper solution -- using naturally occurring bacteria to plug the rock pores with their sugar-like secretions, to form a giant 'plastic bag' that would prevent both oil and water escaping.

The bacteria form extensive colonies that consist of about 15 per cent by weight of bacterial cells, and 85 per cent 'slime' -- the combination forms a biofilm.

The first experiments did not go well -- the bacteria formed a localised impermeable biofilm extending only a few centimetres from the injection site. So it was back to the drawing board, and Costerton literally found a sweet solution.

It involved starving the bacteria, which caused them to divide repeatedly until there was hardly room to accommodate their own genetic blueprints -- from an original size of around one micron, the rod-shaped bacteria end up at about a third of their original size and 1/200th of their original volume. At this size, the cells enter a dormant state.

The shrunken, dormant cells are then injected with water into the oil-bearing rock, where their tiny size allows them to disperse easily through fine pores and fractures in the permeable strata.

"We've been able to get them out to a radius of several kilometres. Then we inject a 'chaser' -- a few truckloads of molasses to provide an energy source," Costerton said.

As the molasses chaser spreads out, it catches up with the bacteria and they grow and begin reproducing vigorously, and begin producing huge amounts of slime that create what Costerton described as "a giant jelly doughnut" around the injection site.

The seal is extremely effective. Costerton and the Montana group have coined a new name for a unit of impermeability called a CAFF -- "Tighter than a Crab's Arse at 40 Fathoms".

"We don't know how much more oil we can get out this way, but we estimate between 10 and 20 per cent -- more than was extracted the first time around. If the film develops in the vicinity of a well, we can reshape the hole in the donut by digesting it away with bleach."

"It's still experimental, but we've treated an old oilfield in Montana, and there's a good plug in place, because the pressure has gone up around five CAFFs -- from 4200psi to around 5600psi. Any higher than that and you begin fracturing the rock, which you don't want.

Application

"We think we can go back into old, depleted oilfields in Oklahoma and Texas and with minimal new investment, pump out a whole bunch of extra oil," he said.

The bacterial biofilm technique can also be used to establish an underground 'curtain' to confine leachates from old mining sites - gold mines, for example can contaminate aquifers with deadly cyanide. "For these bacteria, cyanide is like jelly beans -- they use the nitrogen as an energy source."

The Montana group has also solved the problem of water 'souring' oil. "It's an awful problem, because the hydrogen sulphide is extremely corrosive and eats holes in oil pipelines, so oil companies won't accept it."

"If you inject nitrite into the water, you can completely stop the reaction that produces hydrogen sulphide, so it produces inert nitrogen gas."

Costerton said his team had been talking with BHP Billiton about using the process for its oilfields. He said the oilfields of Bass Strait, now nearing the end of their economic life, were an obvious Australian candidate for the biofilm treatment.