gdy 105 million jv origin energy, page-33

Very interesting, from the annual report:

"Why do the wells need to be so large? Why is an 8½” well in the granite necessary? We have already shown that our hydraulic stimulation treatments can create very large heat exchangers/reservoirs, with the reservoir developed from Habanero 1 having dimensions of some 3 km by 1.5 km (this is the largest developed reservoir in the world). The injection and production testing already carried out has been assessed by Dr Ralph Weidler, our principal reservoir consultant from Q-con. His modelling has shown that we should expect:

• A very low temperature decline of about 40°C in the geothermal brine over the first 50 years of operation;

• A volume of hot fluids in the bottom fracture zone of 11 million cubic metres

• A very low impedance, i.e. a very low resistance to high flow rates through the fracture zone.


The larger reservoir dimensions and lower impedance allows us to place injection and production wells at larger separations and flow at higher rates without significant temperature drawdown over time. It is the ability of the reservoir to produce at high flow rates that
requires large diameter wells."


Impedance (and corresponding flow rates) is a critical factor that has caused geothermal projects to fail in the past (Ortahaza in Hungary is an example). The huge flow rates displayed by GDY are absolutely critical to low-cost geothermal production.