equation of state

1. n. [Enhanced Oil Recovery, Well Testing]
An equation that specifies fluid density as a function of pressure and temperature. A large body of scientific literature describes these functions for all kinds of hydrocarbons, and also for complex mixes of various hydrocarbons with other hydrocarbons and with other fluids. Once the components of a reservoir fluid are determined, the known hydrocarbon properties become a valuable tool in making further calculations of well-test results and predictions of future well and reservoir behavior.