Why is Whicher Range unsuited to hydraulic fracturing?
The gas in the Whicher Range field is found within a conventional sandstone reservoir (predominantly sand/quartz grains) at a depth of around 4 kilometres below ground. The rock is around 250 million years old. The reservoir, at this depth, still allows the free, natural flow of gas without hydraulic fracturing (fracking).
Natural gas flow occurs from within the rock via the spaces between individual grains or pores; through connecting pathways between pores (this is known as permeability).
The Whicher Range gas reservoir has a clay mineral coating around the sand/quartz grains. This clay mineral swells on contact with water which can be introduced either from drilling or from some fracking fluids. This narrows the pathways for the gas to move through the rock, reducing the permeability of the reservoir and in turn the ability to naturally flow gas.
Previous operators believed that reservoir stimulation or fracking would address the previous low flow rates, but their experience demonstrated that these techniques compounded the problem, by virtue of introducing water based fluids into the clay coated reservoir. This is evident by gas flow rates that were commonly lower after fracking than prior.
Photomicrograph of Whicher Range Sandstone