Ideally, laboratory measured PVT data should be utilized. Many times, laboratory data is not available and correlations must be used instead. This post will discuss PVT properties and correlations that can be used to estimate them. It is difficult to say which correlation should be used when. This is because most of the correlations were developed with regional crude samples. The best correlation is the one that matches your data.
Many investigators have used PVT laboratory test results, and field data, to develop generalized correlations for estimating properties of reservoir fluids. The main properties which are determined from empirical correlations are the bubble point, gas solubility, volume, density, compressibility, and viscosity. The correlations typically match the employed experimental data with an average deviation of less than a few percent. It is not unusual, however, to observe deviations with an order of magnitude higher when applied to other fluids.
- Bubble Point Pressure (Pb):
The bubble point pressure, also known as the saturation pressure, is the pressure, at some reference temperature, that the first bubble of gas is liberated from the liquid phase. The reference temperature is usually the reservoir temperature, but any temperature can be used. Note that the bubble point pressure is a function of temperature and changing the reference temperature will change the bubble point pressure.
Statistical analysis of correlations:
Al-Shammasi, in his SPE paper “A Review of Bubble point Pressure and Oil Formation Volume Factor Correlations” (SPE-71302-PA, April 2001), compiled a databank of 1,243 data points from the literature. This was supplemented by 133 samples available from a GeoMark Research database (GeoMark Research. 2003. RFD base (Reservoir Fluid Database)), bringing the total number of data points to 1,376. These data were then used to rank the bubble point pressure correlations. The following Table summarizes the ranges of data used for bubble point pressure, temperature, oil FVF, Solution GOR, oil gravity, and gas specific gravity.