TIME Magazine 7.7.2008The Cooper Basin is one of several basins nestled under the superstructure of the Great Artesian Basin. The Eromanga Basin lays above, the Warburton Basin beneath the Cooper Basin. Formed during the Permian period the Cooper Basin has become Australia's richest onshore source of oil and natural gas. Gas is supplied via pipeline from Moomba to Sydney and Adelaide.
During Permian times the Gondwanan plate travelled in a southward direction. Today's Cooper Basin was an intra-cratonic downwarp in a polar region. The climate was harsh and the flora stunted. There might have been a few thousand square kilometres of peatlands supporting ferns and mosses. Surrounding highlands were covered under a Permian ice sheet. When the ice melted masses of sediments were spilled into the lowlands (1). They covered the peat vegetation faster than it could decay. The sediments kept growing until early Triassic times. And they grew so thick that their pressure created enough heat to transform all that peat stuff into coal, oil and gas - trapped in porous sediments sealed underneath by granite.
The look of the basin is dictated by its hydrology (see Cooper Creek, Coongie Lakes and Rivers of the Great Artesian Basin), its climate and the lay of the land which is essentially flat.
It drains an area of 296 000 km² (114 000 miles²) as the Thomson-Barcoo-Cooper catchment and is part of the internal Lake Eyre drainage basin (2). The Barcoo becomes Cooper Creek just north of Windorah. Apart from unreliable local falls the basin's water supply originates in the north. Located in Australia's arid zone with summer temperatures frequently exceeding 40ºC in the shade (104ºF) and night frost during winter, flora and fauna of the basin are highly specialized around diverse landforms.
There are dune fields (see also Simpson Desert), gibber plains (see also Sturts Stony Desert), floodplains and wetlands. The gradient of the basin is extremely low at 17cm (6.7in) to the kilometre (10.77in to the mile) in its middle reaches. Influx from the north lets water quickly spill over the shallow channels and spread over wide areas where it lingers almost motionless like a giant lake. High temperatures evaporate the water quickly into shrinking waterholes and the numerous salt lakes of the basin.
The wetlands of Coongie Lakes are listed under the RAMSAR convention as important oases surrounded by desert.
Apart from its ‘dirty' hydrocarbons the basin has the potential to become a practically inexhaustible source of ‘clean' geothermal energy. This is naturally produced by radioactive decay in a 1000 square kilometer slab of granite, ten kilometers deep. It contains the world's largest and hottest heat reservoir in non-volcanic rock: the South Australian Heat Flow Anomaly. That heat remains well insulated under kilometer-thick sedimentary units which are poor heat conductors.
To utilise the heat two boreholes have to be drilled five kilometers down into the earth (16 400ft). They are 20-odd centimeters in diameter and a kilometer or so apart. Under high pressure cold water is pumped down the first borehole- the injection well - to the granite base, where the temperature exceeds 250ºC (482ºF). The pressurised water opens the natural cracks in the rock and connects with the second borehole, the production well. Through it, superheated steam and water surges back to the surface and against a heat exchange. This contains a medium with low boiling point, like liquid butane. It vaporises into steam. Steam spins turbines which produce electricity. Cooled down, the butane goes back into the heat exchange, while the cooled water goes down the first borehole again.
To be commercially viable the circulation speed of the water has to be just right. It must be better than a trickle. Yet, the flow must not be too fast and cool the rock before its heat can be replenished by conduction from its underground surroundings.
To see what it looks like at the base between the two wells engineers add a dye to the injection well. Pressed through those cracks at the bottom the colour will ‘smear out' and leave a pale guess about optimal circulation speed.
The energy stored in one cubic kilometer of hot granite is estimated to equal that of 40 million barrels of oil (5). Hot rock spots have been identified in every Australian state - enough potential energy never to worry again.
However, the startup costs are huge for Engineered Geothermal Systems (EGS), and the location often remote. $200 million might be needed to set up a plant from scratch to commercial vialbility. Added to that are the costs in transmission assets. For Geodynamics, a prominent player in the field, the closest connection point to the national grid is 500km away. But once running thermal energy would not only be the cleanest, but eventually also the cheapest energy source.
Innamincka (population between 12 and 15 plus 50 000 transient tourist per year) and the little settlement on the Moomba gas fields will be the first in Australia to receive energy from hot rocks (3). This was to happen near the end of 2009. But some chemical reaction caused a crack in the steel casing in one of the wells.
Back to research - and maybe a delay of two years.
Some 99% of the Earth's mass is hotter than 1000ºC (1832ºF). Theoretically, it could meet global energy needs for many thousand years (4).
Iceland has become the first country to derive 100% of its electricity from clean geothermal (‘hydrothermal') sources. Luckily, cold Iceland gets hot just a few hundred meters below surface.
In November 2009, the two leading players out of 61 applicants received $153 million in governmental development grants under the Renewable Energy Demonstration Program (REDP). They are Petratherm working on a 30-megawatt plant; and Geodynamics with a multi-well project under construction.
Sources:
1) http://www.pir.sa.gov.au/geothermal
3) Sydney Morning Herald 30.May 2008/20.Aug.2008/3.Dec.2008/7-8 Nov 2009/21-22 Nov.2009
see also:
http://info.anu.edu.au/mac/Newsletters_and_Journals/ANU_Reporter/_pdf/vol_28_no_06/hotrock.html
and New Scientist 19.7.2008 (‘Who Needs Coal When You Can Have Deep Heat?')
4) Issue 10 ‘Deutschland' 3/2006
5) TIME Magazine 7.7.2008