Ann: Exploration Update, page-122

Sure,
As they are drilling an 81/2" hole through rocks nearly 5km underground, they circulate mud to wash the chips up to surface, these are inspected to see what lithology they are (sand or shale for instance). The gas readings are also measured from the mud. The way they gather further data on the rocks is by measuring the density, sonic and resistivity of the sediments, either whilst drilling or by running a set of tools down the hole by wireline later. In the case of a sandstone, if it has gas in it, there is still some water in the pore spaces, say 20-40%, but saline water is conductive, so low resistivity. If a sand is high resistivity it could have gas in it, or fresh water, which is less likely at depth. They use the water salinity in the nearest well to remove the water salinity effects and calculate the amount of gas in the pores in the rock.
Industry understanding is that using the water salinity from SE-1, the electric log responses calculated gas in SE-2&3, when they flowed them, they contained mainly water. The calculations were wrong because the water was much fresher (lower salinity) in these two wells. This is not normal to get such a variation, but not unknown. The inference is that one or more of the faults between SE-1 and SE-2&3 must be sealing and 2&3 are accessing a separate acquifer. The presence of faults that have good sealing characteristics is a feature of the Kingia in the Perth Basin, and just makes it more complicated, but also more interesting, as then structures that you might not drill elsewhere in the world might work here.
Sorry for the ramble, its a very stimulating basin to explore in....