Will carbon dioxide storage pollute the Great Artesian Basin?

A coterie of Queensland rural, regional and agricultural organisations are calling for a ban on underground carbon dioxide storage near the Great Artesian basin.

They fear plans by a wholly owned subsidiary of Glencore Mining, known as the Carbon Transport and Storage Corporation (CTSco), to pump carbon dioxide (CO₂) underground near the Great Artesian Basin (GAB) could contaminate domestic and pastoral community water supplies.

Numerous mining companies are looking at ways to capture carbon released by the mining process or created by third party manufacturers, to store it under ground on a profit-making basis.

The Senate has begun an enquiry into the CTSco proposal with submissions closing on May 2.

Carbon dioxide (CO₂) is pumped into water all the time – just ask Coca Cola or Pepsi. The risks from carbon dioxide are frequently mitigated – it’s the by-product from internal combustion engines and only kills and injures people who breathe it in, in confined spaces.

CO₂ which has already been released into the atmosphere, where it is known as a greenhouse gas, heats up the Earth, and left unchecked will change the planet’s environment.

Carbon capture and storage (CCS) is thought to be one of the critical steps towards carbon reduction in the atmosphere.

The CSIRO, Australia’s national science agency, says “it is widely recognised that a broad portfolio of emissions reduction and carbon management solutions is required to reduce and remove CO₂ from the system to meet future emission targets.

“Several decades of experience with geological storage projects across the world have shown that CO₂ can be stored securely in the right setting with very low risk of leakage.”

“Captured CO₂ can be compressed, transported to a well, and injected into deep underground reservoirs. These are either depleted hydrocarbon reservoirs or saline reservoirs with a porous rock such as sandstone.

“These microscopic pores hold the CO₂ securely. The reservoirs are capped with an impermeable layer of rock that stops the CO₂ from moving upwards. CO₂ can be stored in these vast reservoirs for thousands to millions of years.”

The CSIRO posted a paper 2 weeks ago which says “The agreement of observation and model gives confidence that the migration trapping mechanisms for saline aquifer storage are sufficiently understood for planning and risk management of large-scale storage.

Dr Matthias Raab is head of the CO2CRC in Victoria, which describes itself as “a world leader in carbon capture, utilisation and storage research.”

Its Otway International Test Centre near Port Campbell in western Victoria has been operating since 2003. It’s subsurface research laboratories comprise the Buttress well (which produces carbon dioxide that was held in the reservoir for millions of years) and 7 CO₂ injection and monitoring wells about 1.5km deep, for CO₂ storage and monitoring.

Carbon dioxide storage: essential says Academy of Science

Raab says he has “the highest degree of confidence” that CO₂ won’t leak into the water aquifers if the right reservoirs are chosen.

“The sealing rocks above the selected storage reservoirs are thick and impenetrable.”

Raab says injecting CO₂ underground is subject to stringent environmental safeguards in Australia and worldwide.

He says as the supercritical carbon dioxide is injected into a subsurface reservoir and goes into solution with the ambient brine filling the pore spaces. The denser solution sinks into safe long-term storage in the lower part of the reservoir.

The CO2CRC is sometimes criticised because it receives funding from Federal Government grants and the oil and gas industry. But Raab points out that it has produced “hundreds of peer-reviewed papers” in collaboration with Australia’s research organisations, including the CSIRO, Geoscience Australia, Curtin University, and The University of Melbourne.

Raab supports CSTco approach to CCS.

“CTSCo proposes to inject CO₂ into a very deep, compartmentalised, brackish subsection of the GAB, which contains only non-potable water and is not connected to any potable water aquifers in the GAB,” he told Cosmos.

“The CSIRO, the University of Queensland, and others have thoroughly investigated this and ruled out any concerns that this injection will contaminate any freshwater in the GAB.”

“This is an important opportunity,” says Raab. “Getting this right would allow Australia to take a leadership role in emission reductions at scale.”

The claims about the water being non-potable are disputed by landholders.

Dr Samintha Perera is a senior lecturer in Geotechnical Engineering at the University of Melbourne, and an expert on carbon dioxide capture. She is also a member of Standard Australia Rock and Soil Testing Committee. Perera is not connected to the CO2CRC.

She tells Cosmos there are 43 carbon storage projects in operation across the globe, including 4 large-scale projects: 2 in Sleipner and Snøhvit in Norway; Salah (Algeria), and Weyburn-Midale (Canada) “which have safely stored over a million metric tonne of CO₂ per annum.”

She says there are around 18 CCS projects at various stages of progress in Australia.

“The Gorgon CCS project operates commercially on Australia’s northwest coast. Although the unexpected water intrusion into the geological reservoir has reduced its planned storage capacity, it has safely stored over 9 million metric tonnes of CO₂ since 2019.”

CO₂ can be safely trapped in underground geological reservoirs through several trapping mechanisms, including structural trapping (CO₂ is trapped below a caprock, which is an impermeable, confining layer overlying the reservoir rocks), capillary trapping (CO₂  becomes immobile through the capillary action and is trapped in the underground rock pores), dissolution trapping (CO₂ becomes dissolute in the pore fluid), mineral trapping (CO₂ interacts with rock minerals and forms stable carbonate minerals) and adsorption (CO₂ is adsorbed into some rock mass, such as coal.)

In some circumstances it is possible that CO₂ might travel between layers underground, as shown in this research in 2020, which revealed “unpredicted, rapid plume elongation has been observed at subsurface CO₂ storage projects worldwide.”

The researchers found that at several industrial-scale storage sites around the world, carbon dioxide migrated laterally away from the injection well much quicker than anticipated and followed pathways that were not predicted by models.

“It is crucial that these models can predict the migration and demonstrate safe storage to owners and policy makers,” the researchers say in the helpful “plain language summary.”

“In this work, we show that one source of the discrepancy is the omission of the impacts of small-scale rock heterogeneities in these models. We … show that centimetre-scale heterogeneities in the rock structure, for example, small mudstone layers in sandstone, can cause rapid migration at larger, metre-kilometre scales.

“These heterogeneities are ubiquitous in nature and provide an explanation for the behaviour seen at storage sites worldwide.”

Perera pointed out this research to Cosmos because it demonstrates that each geological reservoir needs a proper scientific investigation before any large-scale CO₂ injection, to mitigate the risk.

“This is happening in the Otway Basin Project, CO2CRC Otway Project, which is one of the world’s most comprehensive monitoring and verification programs for CO₂ storage.

“The safety of the CO₂ storage process can be confirmed if a low permeable caprock (seal) with required structural integrity exists, where CO₂ storage becomes more stable over time due to the actions of other trapping mechanisms.

“[It] is highly site-specific. Depending on the site, the caprock can be assessed using multiple methods, including seismic surveys, exploration wells, wireline log data, stratigraphic and sedimentological analyses, well tests and laboratory scale testing.“

Perera explains to Cosmos how a gas might shift from an impermeable zone to an aquifer.

“It depends on how its density compares with substances around it.

“Importantly, geological reservoirs preferable for the CO₂ storage process should be located over 800m deep. At such depths, CO₂ converts to its super-critical phase_, which has high density and low viscosity compared to gas CO₂.

“In the supercritical state the distinction between the liquid and the gas phase has disappeared and the fluid can no longer be liquefied by raising the pressure nor can gas be formed on increasing the temperature.

“Due to this density contrast, shortly after the injection, CO₂ can flow upward as a buoyancy-driven flow, changing the phase from super-critical to gas.

“This journey further accelerates the upward migration of CO₂, probably up to 100s of meters, potentially leaking to the freshwater aquifers.”

This is a hypothetical explanation, but CTSCo is not planning to inject carbon dioxide into any regions near potable water aquifers.