The largest carbon burial experiment in the world began in earnest on Thursday when the drilling of a 2100-metre well began in the Otway Basin, on the coast of southern Australia. The project promised the most comprehensive monitoring for leaks to date.

If all goes well, researchers from the Canberra-based Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) will start injecting carbon dioxide into the new well in July. They will start by extracting CO2 from a nearby natural geological reservoir and compressing it into a "supercritical fluid" – a gas-liquid hybrid. This will be injected via the new well into a sandstone reservoir (this animated graphic demonstrates the process).

The reservoir is shaped liked an upside-down saucer that is partially-filled with methane gas, and covered by a series of impermeable rock layers. Over the following six to nine months, 100,000 tonnes of supercritical CO2 will be injected.

“We plan to demonstrate that the CO2 will move into the reservoir as predicted,” says Kevin Dodds of CO2CRC and CSIRO Petroleum in Perth. The Otway Basin Pilot Project will also be the most intensely monitored carbon burial project so far in the hopes of demonstrating that CO2 can be safely and securely kept underground.

Green light
“We’re not going to [use carbon burial] unless my Dad and yours believe that it’s going to work," says geologist of Susan Hovorka, at the University of Texas at Austin, US. "We need to lay our cards face up, and let the public know what is going on down there. Otway should be a good opportunity to do this.“ Hovorka leads a team running the Frio Brine carbon burial experiment in Texas, and was a member of the team that reviewed the Otway Basin Project for the International Energy Agency.

Carbon burial – or geosequestration – is one of several techniques being developed to reduce the amount of CO2 released into the atmosphere when coal, oil, or gas are burned (see also $25 million prize for greenhouse gas removal). The gas, which causes global warming, would be captured from power plants and then stored underground.

The idea received a significant legal boost on 10 February when an international law came into force allowing the greenhouse gas to be buried beneath the sea floor (see Green light for carbon burial).

Flushing out
Currently, there are several commercial carbon burial projects around the world. The biggest, in the North Sea’s Sleipner gas field, stores one million tons of CO2 each year in an underground sandstone formation.

Sliepner saves Norwegian oil company Statoil carbon taxes, and cuts Norway’s annual output of greenhouse gases. But the aim of most commercial projects is to use CO2 to push out more oil, rather than to find a way of reducing greenhouse gas emissions, and monitoring for leakage is minimal.

In contrast, the Otway Basin experiment involves intensive monitoring of levels of CO2 in soil, water and air. The project includes adding tracers to the injected CO2 to enable researchers to identify whether the detected gas is from vegetation, natural underground sources or from the CO2 store, says David Etheridge, an atmospheric scientist at CSIRO in Aspendale near Melbourne, Australia.

Clean fresh air
The location of the Otway Basin Project is an advantage because air measurements can be made while prevailing winds bring clean air from the Southern Ocean, uncontaminated by industrial or natural sources of CO2.

“There is no CO2 source out there. It’s a lot different to what you have in Texas with CO2 sources all around from off-shore oil and drilling, shipping and cities,” says Hovorka.

Carbon burial is mostly needed for coal-fired power stations, which account for about a quarter of global CO2 emissions, but obstacles beyond remain to be overcome. These include reducing the cost of the technologies that capture CO2 from power stations, and testing a variety of geological sites for their suitability for carbon burial.

Peter Cook, CO2CRC chief executive, adds: “We need a policy and pricing environment that will encourage people to use the technology.”