Pressure-Volume-Temperature analysis is a vital component in subsurface engineering and any description of reservoir or reservoir fluids will require PVT analysis. Generally, the purpose of conducting PVT analysis on fluid samples is to characterize the fluid and understand its various properties such as Viscosity, bubble point pressure, solution gas oil ratio etc. These tests that are conducted in the laboratory come at great costs and are often omitted by E&P companies to economize the project.
These oil & gas properties are nevertheless required for engineering calculations, model creation and predicting forecasts on the reservoir. To simplify the characterization, industry soon came up with empirical correlations that were generated from dataset that included PVT analysis of fluids from a wide range of reservoirs, location & type. These generalized correlations with their operating window became the new standard for calculating PVT properties of oil, condensate, gas & water.
PVT correlations can be broadly categorized in two domains, Black oil correlations & Compositional PVT or Equation of State. For this MiLog, lets discuss standard widely used black Oil correlations. Standard correlations are used to calculate fluid properties on wide range of pressures & temperatures such as reservoir conditions. Following are some of the common correlations that were developed based on pvt analysis from specific locality therefore most applicable in the same locality:
1. Vasquez and Beggs
2. Glaso et al - North Sea Reservoirs
3. Al-Marhoun et al - Saudi Arabian Oils
4. Petrosky and Farshad - Gulf of Mexico
5. Standing Correlations - California Oil
6. Hanafy et al - Egyptian Oil
Full equations of these correlations are available with great explanation at Fekete manuals, found here.
PVT module of our novel frac simulator FEDS also uses correlations to characterize fluid for simulation purposes, just like almost all modelling & simulation software available for petroleum/reservoir engineering. However note that FEDS uses a compositional PVT module based on Equation of State rather than simplifying it through Black oil correlations. Following is a screenshot of PVT module in FEDS.
A special mention here is Rankine temperature scale which is widely used in almost all correlations mentioned above. Rankine scale has a special connection with the oil & gas industry. I think a separate MiLog is warranted on this topic to elaborate further.
