- © The Mineralogical Society Of America
A petroleum reservoir consists of a zone with hydrocarbons that may potentially be produced and used as an energy resource. The hydrocarbons may have liquid (oil) properties, gas properties or the reservoir may consist of an oil zone with a gas cap on top. Often a water-rich zone is found beneath the hydrocarbon zone. The petroleum reservoir fluids found in the hydrocarbon zone may be divided into
Natural gas mixtures
Gas condensate mixtures
Black oil (or “ordinary” oils)
The various fluid types can be distinguished by the content of heavy hydrocarbons and by the phase behavior (number of phases, phase compositions and phase properties). Table 1⇓ shows examples of each type of fluid composition. A natural gas mixture only contains trace amounts of components heavier than C6 while at the other end of the fluid scale, a heavy oil is dominated by components heavier than C6. The properties of heavy oil may in fact be influenced by components as heavy as C200.
The phase behavior of petroleum reservoir fluids is often referred to as PVT properties where P stands for pressure, V for volume (or more correctly molar volume) and T for temperature. Because production takes a petroleum reservoir fluid through significant changes in pressure and temperature, it is of great practical interest to know the volumetric changes occurring as a result of changed T and P conditions. It is also of interest to know how the total volume will split between gas and liquid as a function of T and P and how changes in T and P will affect the densities and …