Transmitted electron microscope photomicrograph of
bacteria in an Australian coal seam methane
reservoir.
Image by CSIRO

One of the world’s largest carbon geosequestration projects is about to swing into action off the coast of the Pilbara.

It has been set up as part of the Gorgon liquefied natural gas project on Barrow Island off the West Australian coast, run by energy giant Chevron, in a bid to reduce greenhouse emissions.

By injecting CO₂ into a safe underground reservoir, the project’s carbon dioxide emissions can be reduced by 40 per cent, Chevron Energy Technology president Mark Puckett told the Australian Petroleum Production & Exploration Association’s annual conference in Perth last week.

He said the Gorgon joint venture did canvass several other greenhouse gas abatement options, including communal forestry, revegetation programs, support for renewable industries and the supply of CO₂ as a feedstock for other industries.

But after looking at all the options, they found that injecting CO₂ into underground reservoirs would actually reduce the project’s emissions rather than just offset them.

Chevron looked at several saline reservoirs and depleted oil and gas fields on and offshore between Exmouth and the Burrup Peninsula before concluding that the deep-seated Dupuy Formation reservoir beneath Barrow Island was the best location.

The Dupuy is a massive sand body about 2,300m below the surface. That depth will keep the injected CO₂ in a supercritical phase, retaining the density of a liquid as well as the properties of a gas, so that it fills the maximum available pore space, according to Mr Puckett.

The structure of the Dupuy also provides predictable migration pathways and it contains several less permeable interleaved siltstone layers that will impede migration of the CO₂ plume.

In addition, the Dupuy sand is overlain by a major seal and there are numerous other impervious seals between that and the surface.

The company says the formation can be accessed onshore and close to the proposed LNG plant site where CO₂ will be stripped from the gas stream.

The Gorgon project will involve injecting about 120 million tonnes of CO₂ over 40 years with close monitoring of the subsurface pressure regimes and the movement of the CO₂ plume.

The injected CO₂ will come into contact with sub-surface water and dissolve in it until the water is saturated with carbon dioxide, Chevron says.

Some of the CO₂ will also be trapped by surface tension imposed by the individual mineral grains in the rock.

A certain amount of water remains bound to the mineral grains by surface tension. Some of the injected CO₂ will dissolve in this residual water and there will also be small droplets of supercritical CO₂ trapped within the pore spaces by the surface tension between the formation water and the CO₂.

Although Chevron said it was confident about the safety and environmental aspects of the planned geosequestration project on Barrow, modelling and data gathering will continue.

The company expects front-end engineering design for the Gorgon gas project to be completed in 2009 with a final investment decision to follow soon after.

In other science innovations announced at the conference, the CSIRO said its scientists were investigating whether injecting coal seams with certain kinds of bacteria and carbon dioxide could produce commercially viable quantities of methane gas.

Speaking at the APPEA Conference, CSIRO's Dr Mohinudeen Faiz said research performed in the Sydney Basin showed that microbial activity could significantly increase the levels of methane in coal seam 'sweet spots'.

"We are discovering ways to culture micro-organisms that produce methane and pin point the nutrients and environmental conditions that encourage their activity," Dr Faiz said.

"Once we can establish the type of environment that encourages growth of the microbes, we plan to stimulate the natural micro-organisms by injecting nutrients that the organisms thrive on, into coal reservoirs."