sydney investor briefing, page-30

Geojac,

You may possibly have been conflating present well spacings of 500m with the ideas for Hab 4 cluster which is 9.2 km West from Hab 1.

The optimum spacing of future wells within a cluster is a key issue to determine. The present 500m separation was initially taken somewhat abitrarily when little was known of the natural granite fractures, of the high degree of connectivity that we now know does exist, and of the relative ease with which stimulation can effect fluid flows. If such knowledge had been available then a spacing of 1000m would have been chosen. It will be understood that by drilling arrays of wells on a 1 km grid rather than on 0.5 km represents a saving of drilling 75% of wells (1 well per square km instead of 4).

Last week the talk was to aim at the possibility of increasing the spacing still further to two km, i.e. having 9 holes on a 4 km square grid. With the 500m spacing there would have been 64 wells in the same area. Now that is a real saving.

O . X . O

X . O . X 4km on edge

O . X . O

[No, this is not noughts and crosses; it is a square drill hole array with insertion and production wells!]

So what limits the spacing? The issue is whether all or sufficient of the heat can be extracted from the rock in between the wells. It is determined by the nature and number of fracture zones, and the high flow rates that can be induced.
It is only by careful stimulation and testing on the close proximity wells that the optimum can be determined. Of course the granite structure in one location on the tenement may not be indentical to another, so that there are always some unknowns. That is why the Hab 4 cluster is chosen at some distance from Hab 1. The granite structure and heat reservoir may then be interpolated.

Juke