ABSTRACT
As we saw in Chapter 12, petroleum reservoir fluids can exist in the reservoir and on the surface either in a single-or in two-phase conditions. The primary variables dictating the state of the reservoir fluids being system pressure, system temperature, fluid composition, and the chemistry of the components. For example, reservoir fluid exists as a single phase outside the phase envelope or outside the area bounded by the bubble-and dew-point curves. The boundary of the phase envelope of a reservoir fluid defines the conditions for the vapor or gas phase and the liquid phase to exist in equilibrium. Furthermore, as pressure and temperature conditions change, the quantities, compositions, and properties of the equilibrium vapor and liquid phases vary at different points within the phase envelope.
