Coal Seam Gas and The Great Artesian Basin  

Posted by Big Gav in ,

The SMH says "Protecting the water wealth of the Great Artesian Basin is the latest challenge for the coal seam gas industry" - Grappling with science and sceptics.

Beneath the bone-dry surface of inland Australia, west of the Great Dividing Range, a vast body of water is slowly flowing towards the sea.

If the Great Artesian Basin could somehow be sucked up from underground and put in one place, it would form a water cube of 40 kilometres, holding more than 100,000 times as much water as Sydney Harbour.

As it is, the water is squashed between thick layers of sandstone into an interlinked network of aquifers that stretch from Dubbo in NSW, through most of Queensland and parts of the Northern Territory and South Australia. It ''flows'' through pores in the rock at the glacial pace of a few metres per year.

The basin has existed in its current form for millions of years, but one of the biggest tests to its existence will come in the next decade. Beneath the layers of water lie some of the world's most extensive coal seams. Just as the sandstone aquifers contain water, so the coal seams contain methane.

To get the methane to the surface so it can be burned as a fuel, tens of thousands of shafts, most of them only about 10 centimetres wide, will be threaded through the aquifer layers. In most cases, water, sand and chemicals will then be forced down the shafts at high pressure, to fracture the coal seams and get to the gas. Large amounts of underground water will also have to be pumped out. After a few years, the wells will have to be sealed so that no gas or water leaks out, ever.

This will all have to be done without turning the fragile Great Artesian Basin into a continent-sized pin cushion.

It is probably one of the greatest engineering challenges undertaken in Australia, and the companies planning the operation exude confidence that the technical problems can be overcome. About $50 billion in investment, not to mention the long-term integrity of Australia's groundwater, is riding on them being right. Their optimism rests on several decades of collective experience in drilling through and around aquifers, mostly without known adverse effects. For the past five years, an elite corps of hydrologists, geologists and engineers, many of them Australian but with a large international contingent drawn here by the mining boom, has been grappling with the specific problems posed by drilling through the basin without wrecking it and managing the water that will be pumped out.

Philippa Kassianos, the leader of the water studies section at the resources company Santos, estimated this week that its gas drilling project on the eastern edge of the basin would bring 344 billion litres of water to the surface over the next 30 years, about one-tenth of the amount of water needed to restore the health of the Murray-Darling river system.

Most of it would be brackish and unsuitable for agriculture, but the company is planning to build water treatment plants that mean 90 per cent of the water can be sold to farmers or injected back underground. The remaining 34 billion litres of salty brine will stay on the surface in storage ponds until a use can be found for it. The process is not new - Santos has been extracting coal seam gas for 15 years in Queensland - but the scale is unprecedented. ''Santos needs to be as good at handling CSG water as we are at handling gas,'' Kassianos said.

The coal seam gas industry as a whole could extract 300 billion litres per year over the next 25 years, most of it from the Great Artesian Basin, according to federal government estimates. As farmers are grappling to do more with less and adapt to a more stringent licensing system, the water being sucked up from the basin as a by-product of coal seam gas extraction will see the total volume brought to the surface rise by 60 per cent.

Queensland's Department of Environment and Resource Management is the main agency on the spot, and it has issued a flurry of edicts designed to curb some of the more cavalier elements of the gas industry, including a ban on some fracking chemicals and tighter drilling regulations.

It is completing a detailed study of the expected impacts of the new gas fields on the eastern artesian basin, but has already expressed its desire for as much water as possible to be injected back into underground aquifers. ''It's a period of epic growth across the industry,'' said the department's director-general, Jim Reeves. ''We, as a department, are dealing with changes we have not faced before.''

Even before drilling on a large scale is under way, there have been mistakes and some isolated pollution incidents. In 2009, near Dalby, a well operated by the Queensland Gas Company undergoing hydraulic fracturing ''unintentionally provided a route for water in the aquifer'', the company said. Upwards of 100 litres of fracking fluid mingled with underground water, but this was not reported to authorities for 13 months. ''QGC believes the risk to human health or to water supply, or to both, have been negligible,'' the company said.

But the real impact on the basin is likely to come from the cumulative, long-term effects of large-scale drilling and pumping. The National Water Commission says the potential water impacts of the coal seam gas boom are not well understood, but are likely to have adverse effects on other water users.

''Extracting large volumes of low-quality water will impact on connected surface and groundwater systems, some of which may already be fully or over-allocated, including the Great Artesian Basin and Murray-Darling Basin,'' its latest advice on the matter says.

Drilling of the 40,000 planned wells could have a series of consequences, it says. These include changing pressures in underground aquifers so that potable water mingles with unusable water, fouling bores, reduced flows in rivers and land could subside ''over large areas, affecting surface water systems, ecosystems, irrigation and grazing lands.''

The water commission, a government agency, is reluctant to be seen as partisan in the coal seam gas debate, but last month it expressed doubt about the long-term effects of the gas boom.

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