The seal certainly is a key factor. The Noonkabah top seal looks to be quite thick which is good. Don't know much about its composition though. By what they say, this type of seal has been found to be good in some other wells in the Canning Basin, but there has only been a total of 250 o&g wells drilled since starting in 1920's.
Vaguely recall that BRU cited Rafael Shallow formation had some similarities to Ungani West or Far West, where they recovered some oil and even installed a spur line.
Looking at the 3D cross section you posted, you will notice that the reservoir-containing block is uplifted with respect to the block on the left side of the fault and the green layer of the Poole Reservoir butts up against the Noonkabah top seal on the left side of the fault - meaning that there is a good chance of a competent seal there. But this is only one cross section so cannot tell if this follows for the rest of the area of closure shown in the plan view but at least no other fault lines are shown in plan. Cannot say the same for the lower and apparently smaller Grant Reservoir. Light green shows their expectation as to the extent of the reservoir I presume.
Some posting here seem to think oil & gas exploration is deterministic, which it definitely isn't. Geologists and geophysicists do the best they can with interpreting minimal information.
