I should have added: a second reason could be reduction of permeability (to zero) in parts of the Nullara such that fluids can't flow between the two locations. If so, we're talking about a separate accumulation at SB from that at Pt Torment. If this is the case, SB could be a gas cap over oil (and maybe water). they never reached the bottom of Nullara so we don't know what's there, frustratingly.