Cushion gas is the portion of gas that is permanently retained within an underground natural gas storage reservoir to maintain sufficient pressure for the facility to operate effectively. In subsurface storage systems, such as depleted oil and gas reservoirs, aquifers, or salt caverns, gas is injected during periods of low demand and withdrawn during periods of high demand. However, not all injected gas is recoverable. Cushion gas remains in place throughout the operational life of the storage facility and is essential for providing the pressure support needed to enable the cyclical injection and withdrawal of the working (or active) gas.
Cushion gas establishes the base pressure of the reservoir, ensuring that deliverability rates (the rate at which gas can be withdrawn) remain commercially viable. Without adequate cushion gas, reservoir pressure would decline to levels that impair flow performance, making withdrawal inefficient or even technically infeasible. The volume of cushion gas required depends on reservoir characteristics such as porosity, permeability, and structural integrity, as well as the type of storage formation. Although cushion gas represents a significant initial capital investment, because it is not intended to be withdrawn under normal operations, it is a basic functional of the gas storage system and is typically maintained for the entire operational lifespan of the facility.
