Definition - What does Gas Drive mean?
Gas Drive is a mechanism of pressure depletion that forms free gas in oil reservoirs which had no free gas initially. This mechanism is applied when the pressure drops below the bubble point. When the reservoirs deplete, the pressure drops below the bubble point and gas comes out of the solution to create a gas cap on the top. This cap is then pushed down on the liquid which helps in maintaining the pressure. These reservoirs are used as the benchmark for comparing other producing mechanisms.
Petropedia explains Gas Drive
Gas Drive, also known as depletion drive and solution gas drive, occurs only when natural gas is present in the cap below oil. Based on the discovery pressure, the drive reservoir can initially be either saturated or unsaturated. In the saturated reservoirs, reservoir pressure is found at the bubble point. When oil is produced, pressure falls and the bubbles of the solution gas are formed in the reservoir and this liberation of the solution gas provokes oil to shrink. In the unsaturated reservoirs, the reservoir pressure is more than bubble point of oil. There is no free gas in the reservoir as long as the pressure remains greater than the bubble point. Reservoir drive energy is offered only by limited expansion of water, soil and rock.