1. Depletion-Drive (Solution-Gas Drive) Reservoirs
When pressure drops below Pb then gas evolves the flows with oil.
GOR increases above Rsi.
Eventually, GOR can peak, then decline as oil rate drops faster.
GOR > Rsi (typical behavior)
2. Water-Drive Reservoirs
Pressure may stay near bubble point longer.
Less gas liberation.
GOR may remain close to Rsi or even below Rsi if gas is trapped or segregated.
OR Rsi or GOR < Rsi
3. Gas-Cap Drive Reservoirs
If gas cap is produced → very high GOR.
If only oil zone is produced then GOR may increase moderately.
GOR can be much higher than Rsi depending on coning or breakthrough.
GOR > Rsi (if gas cap coning occurs)
4. Heavy Oil Reservoirs
Low Rsi to begin with.
Gas mobility is low.
GOR can remain low or increase slowly.
GOR may stay Rsi for long time
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