Gas vs OilGoaweigh, you're smack on with gas displacing the oil down dip because gas is more buoyant...something analogous (in reverse) to mercury displacing water from a bathtub. The expelled oil is dispersed updip from the spill point of the structure/strat trap displacing water until it is trapped somewhere else higher up or to the surface (oil sands). Of course gas may not be available or in sufficient quantity to displace all the oil, so you may wind up with a gas cap on an oil
leg. I've attached another source rock presentation (Thomas, 2014) that leads me to think that if you were to find gas anywhere along the Pnal to east coast of Trinidad turbidite fairway it would be in the Carapal Ridge to Royston prospect area. This is based on Thomas's maps of source richness (HI) and maturity (Ro).
It's curious that one way of producing overpressure in a reservoir (there are 4 or 5) is to generate oil or gas. The conversion of kerogen to oil or gas involves a volume increase which generates pressure which causes the hydrocarbon to eventually be expelled forcibly from its source and ultimately injected into a trap if one exists. Gas more so than oil. I've collected a number of pressure gradient readings in the fairway and it would appear than from mud weights and actual measured pressures the highest pressures are in the BW-5 well-Cascadura-BW-7well area, perhaps confirming a higher possibility of gas.
As for Chinook, the 'adjacent' BW 7X well had free oil in the mud. Chinook is 200? M away and 50? M updip from the 7X. If there is no rapid facies change or fault separation and hundreds of feet of reservoir as at 7X, I see no reason for there not to be oil in Chinook...albeit with a possible gas cap.
Bear in mind the Karamat/Herrera sands at Chinook are expected to be deeper by 1500'? so expect reduced porosity, maybe in the mid to high teens. However the "severe tectonics" mentioned at 7X if still present at Chinook could help with permeability.
Royston on the other hand is in the 10,000' depth range meaning somewhat reduced porosity which could be mitigated by overpressure and fracturing. It is said to exhibit 700' of "gas effect". In petrophysics-speak this is normally seen in the logs as "neutron-density crossover", a very reliable indicator of gas.
I'm optimistic but this geology and Overpressure can be tough.