Freegas

Free gas is a term used in multiple disciplines. In physics and thermodynamics, the free gas (often called an ideal gas) describes a collection of non-interacting particles confined to a volume. The model assumes negligible intermolecular forces except for elastic collisions. It yields the ideal gas equation PV = NkT and predictions such as a linear dependence of internal energy on temperature. Real gases approximate a free gas at high temperature or low density, but deviations occur at high pressure or low temperature.

In petroleum engineering, free gas refers to natural gas that exists as a separate gaseous phase within the pore spaces of a rock, as opposed to gas that is dissolved in the crude oil (solution gas) or gas contained in a cap above the oil (gas cap). The quantity of free gas affects reservoir performance, expansion, recovery techniques, and pressure maintenance. Phase behavior models distinguish free gas and dissolved gas to forecast production.

In energy policy and common usage, the phrase free gas may appear in discussions of subsidies or public distribution, where natural gas is provided at zero or negligible cost to end users under government programs. This non-technical usage is context-dependent and not a standardized technical term.

History and related concepts: The ideal-gas model traces to the work of Boltzmann, van der Waals, and others in the 19th and early 20th centuries, and its success helped underpin kinetic theory and thermodynamics. In reservoir engineering, free gas is contrasted with dissolved gas and gas cap phenomena to model fluid behavior in rocks.