No concerns about the geology, tight sands are a new field here...

No concerns about the geology, tight sands are a new field here in Australia and there is little historical performance data.
The key to establishing reserves is average reservoir pressure.
Either shut in the well for a certain amount of time based on pressure, permeability/porosity, fracture length, drainage area until you get an average pressure reading or estimate it using an established equation.

Likely to have gotten back calculation that shows a shut in time that will give reserves after 15 April and prior to the proposed options extension date

I would expect they might get the options extended on this basis... dealing with a lot of unknowns in exploratory earth physics after all