July 02, 1991

Article at Reuters

Microbes help boost oil output, revive old wells

Bass Strait, off the south coast of mainland Australia, where bacteria help extract more oil from seemingly exhausted wells.

By Wilson da Silva

SYDNEY – Companies spend millions of dollars exploring for oil and when a well is “exhausted” 70 per cent of the crude often remains in the ground.

But Australian scientists say a new technique is being tested that prompts microbes living deep in oil reservoirs to strip crude from the surrounding walls of porous rock, making the trapped oil extractable.

At tests conducted in the small Alton field in Queensland the technique lifted output some 40 per cent. Over a 350-day period production rose to 4,995 barrels a month from 2,885. The Biological Oil Stimulation (BOS) process was developed at the University of Canberra. It works by modifying the outside skin of bacteria in a reservoir, making them attach themselves to oil globules trapped in rock pores.

The expanded, heavier oil globules fall from the pores and merge with other oil droplets, which are then carried away with the free-flowing oil stream already being pumped to the surface.

“It’s a bit like oil in a sponge. When you squeeze it there’s always oil left in it,” microbiologist Alan Sheehy told Reuters. “We use the bacteria to expand the volume of the oil droplet. This reduces the force required to pump the oil out.”

“In the laboratory and in field trials, we’ve been able to get a lot of the residual oil back,” Sheehy said from Melbourne.

Lincoln Paterson of Australia’s Commonwealth Scientific and Industrial Research Organisation, whose geomechanics division has studied enhanced oil recovery, said that on average only 30 per cent of crude is extracted from the world’s wells.

“All of the world’s easy oil is gone,” he said. “After drilling, a lot of oil is left behind trapped in the pores of reservoir rock,” he said from Melbourne.

Scientists estimate 10,000,000,000,000,000,000 barrels of oil could be recovered with enhancement techniques.

In some oil fields, such as Bass Strait off the south coast of mainland Australia, recovery is as high as 50 per cent, while in many fields in the United States it is as low as 15 per cent.

Oil, at depth and under great pressure, normally clings to surrounding rock. Drilling aims to extract the free-flowing oil. After some 15 per cent of reserves are extracted, wells produce gas and water as these lighter elements seep into the reservoir.

By the time 30 per cent is drawn, most output is water, making the well uneconomical and forcing an end to operations. In the past five years, more than 100,000 wells in the U.S. have been abandoned due to falling output, industry publications say.

Many methods have been tried to dislodge the remaining oil – flooding reservoirs with water, steam or gaseous hydrocarbons like ethane, pushes the oil towards pumping equipment.

Apart from stripping oil from pores, BOS can help cut out the amount of water. Bacteria can be altered to emulsify the oil and water, a mixture which then blocks off the lighter water and gas from passing through the oil and into the well shaft.

The technique has been licensed to Live Oil Services Pty Ltd, a Melbourne company that in the 1980s spent 17 million dollars (13 million U.S.) to make its Vortoil oil/water separating technology a world leader.

Director Noel Carrol said the company had spent 5.5 million dollars (4.2 million U.S.) developing BOS technology, and in two months will field trial it at large North Sea oil platforms producing 40,000 to 60,000 barrels per day.

“It’s still experimental, it has not been tried on wells producing more than 1,200 fluid barrels per day...But we’re very confident. I’ve been told by an oil company executive that this could hold the key to a quarter of the world’s oil supply.”

The problem with conventional enhanced oil recovery (EOR) technologies is that many rely on high-priced chemical agents or require on-site pumping of their dislodging material. The BOS technique costs less than A$1 (US$0.76) per extra barrel that is extracted using the process.

Conventional EOR methods are applied only when potential gains are great.

Adelaide-based Santos operates Australia’s only EOR project in the Tirrawarra field of the Cooper Basin of central Australia.

Santos engineer Glen Johnson said the company produced an extra 3.5 million barrels of oil over four years by flushing ethane into reservoirs. The process has added 18 million barrels to the field’s estimated recoverable reserves, he said.