hewi

Petratherm's exploration model offers a unique, lower-cost strategy to developing geothermal power, yet the Heat Exchanger Within Insulator (HEWI) system concerns me.

There seems to be a likelihood that the overlying sediments, not being radiogenic themselves, will deplete their heat resevoirs significantly faster than granite heat resevoirs.
A granite resevoir, with heat-bearing rock all around it, will have a higher contained number of joules than a sedimentary resevoir that receives it's energy primarily from only beneath it. When depleted, the granite resevoir can regenerate a portion of the heat extracted.
Can the same be said for the heat extracted from overlying sediments? These 'insulators' may take much more time to re-establish their contained heat, during which time supplementary sites must be developed to offset the non-performers.

If Geothermal is to be viable, reserves need an economic lifespan. It will be interesting to see the rate of depletion from PTRs first producing well compared to GDYs HAB1-HAB3 system. Certainly PTR will have lower capex, but will it have sustainabilty.
If there is precedent of the HEWI model not experiencing accelerated depletion, could someone post details please.

Paralana is anticipated to have an attractive final-depth tempetrature (200.C at 3.6km), but is HEWI an appropriate way to exploit the potential of the site?

If an appropriate economic life cannot be introduced, then Geothermal energy production may remain a fringe industry for longer than is environmentally acceptable. It certainly needs to reduce costing from here. Carbon trading will be a massive advantage, but so too will be the ability to operate a single site for longer than the competing GEO companies.

It may not be a major concern. Firstly, HEWI may work very successfully in the Paralana rocks, and if HEWI ever proved to be less efficient, the model could be reconfigured, or abandoned for a more conventional system.

Higher risk, higher return, eh?!