Page 235 - PVT Property Correlations

Selection of PVT Correlations Chapter | 9 205

Correlation Selection Based on Type of Fluid
Several correlations that pertain to specific fluid type were developed for
oils or gases. For example, the correlations of De Ghetto et al. (1995) were
developed for heavy and extraheavy crude oils, and therefore, use of these
correlations is recommended for heavy oils. Use of these correlations outside
their range of applicability usually leads to errors that may be easily
avoided.

Correlation Selection Based on Required PVT Model
(Application)

In some applications, the required PVT model determines the correlations to
use. If the black-oil model is to be used, many correlations are available. If
the modified black-oil (MBO) model is needed for a certain application,
fewer options are available. Although individual PVT properties are avail-
able for some MBO PVT properties, two correlation families are available
for all four MBO PVT properties [solution gas oil ratio (GOR); vaporized
oil gas ratio; oil formation volume factor; and gas formation volume factor].
These correlations and their applications were discussed in Chapter 5, Gas
Condensates, and Chapter 6, Volatile Oil (El-Banbi et al., 2006; Nassar
et al., 2013).

Correlation Selection Based on Data Range and Ranking
One successful practice in selection of PVT correlations based on input data
entails identification of a suitable range for every correlation. Al-Shammasi
(2001) reviewed multiple correlations and compared their performance
against a large database of oil PVT data. Al-Shammasi (2001) performed a
study for bubble point pressure and formation volume factor correlations
only. The study concluded that greater accuracy in prediction from PVT cor-
relations could be achieved if correlation selection is based on API gravity
values input. According to Al-Shammasi’s grouping idea, Glaso (1980) bub-
ble point pressure correlation is most suitable for very heavy oil (API gravity

less than 10 API); Macary and El-Batanoney (1992), for medium API grav-

ity oil (between 10 and 20 API); and Al-Marhoun (1988), for higher quality

oil (20 30 API).
Al-Zahaby et al. (2012) expanded Al-Shammasi’s work and created clus-
ters of input data. For each cluster, they found the best correlation(s) to use
among a reasonable number of oil PVT correlations out of all oil PVT prop-
erties. They also collected the ranges of applicability of the correlations
recommended in their work. Their approach is based on two steps: (1) the
selection of a subset of correlations for every PVT property by use of the
input data and applicability ranges for each correlation and (2) the ranking of