"are gas shows above the target generally indicating a higher...

"are gas shows above the target generally indicating a higher chance of a better gas charge in the lower target? i.e is the process one where gas is generated in the source rock, then migrates over time into a deeper reservoir? can someone shed light on this slightly technical question?"

Glass half empty or half full

Hydrocarbons above your zone of interest may indicate that the seal for you zone of interest has leaked. So mybe the zone of interest is now full of water.

OR

The zone of interest may be full and occasional earth movements momentarily breach the seal and allow a puff of hydrocarbon through which accululates at a higher level.

Which is correct?

Obviously some hydrocarbon is evidence that there are hydrocarbons on the basin. In the gulf coast this is a total 'no brainer'.