Here's a detailed article from the Economist explaining the huge uncertainties and problems with carbon storage and capture. Some key points:
In 2005 the Intergovernmental Panel on Climate Change, a group of scientists that advises the United Nations on global warming, came up with a range of $14-91 for each tonne of emissions avoided through CCS. Last year, the IEA suggested that the price for the first big plants would be $40-90. McKinsey, a consultancy, has arrived at an estimate of €60-90, or $75-115.
Either way, that is more than the price of emissions in the European Union: about €10 a tonne. America does not have a carbon price at all yet. A bill defeated last year in the Senate would have yielded a carbon price as low as $30 in 2020, according to an official analysis. So CCS might not be financially worthwhile for years to come....
Omar Abbosh, of Accenture, a consultancy, says that carbon trading as practised in the EU and contemplated in America does not give enough certainty about future carbon prices to justify an investment in a CCS plant. Mr Paelinck of Alstom agrees: no board would risk spending €1 billion on one, he says, without generous subsidies.The article indicates that the cost of individual CCS plants could be anything from $1 billion to $1.8 billion US dollars. (And that might be based on the fact that the USA apparently has a pre-built system of pipelines in their oil areas that could be used for transported the CO2. I assume Australia does not have anywhere near as extensive a system.)
And will it even work long term? Even small leaks would be a problem:
Carbon dioxide forms an acid when it dissolves in water. This acid can react with minerals to form carbonates, locking away the carbon in a relatively inert state. But it can also eat through the man-made seals or geological strata intended to keep it in place. A leakage rate of just 1% a year, Greenpeace points out, would lead to 63% of the carbon dioxide stored in any given reservoir being released within 100 years, almost entirely undoing the supposed environmental benefit.That CCS is being promoted so heavily seems simply to be a triumph of an industry's self preservation instinct over common sense.