89
Reservoirs and Reservoir Fluids
oil to crude oil (Figure 4.3), because of the complexities of the maturation process (Speight, 2007),
and should be represented as such in any models. In fact, analytical methods such as fractionation
and high-performance liquid chromatography (HPLC) have shown conclusively that the asphaltene
fraction is a mix of unknown (at best speculative) molecular types (Figure 4.4) (Speight, 1994, 2001,
2002; Speight and Long, 1996).
In spite of this, average parameters and average properties continue to be used for derivation of
predictive models when the behavioral characteristics for any average structure for such a complex
mixture cannot in any way be truly representative of the behavior of the different constituents. Thus,
it is not surprising that many models for heavy oil behavior are of little value in terms of predictive
capability of heavy oil behavior and the models generally flounder on the rocky shores of asphaltene
science (Andersen and Speight, 1999).
4.5.2 FrACtIonAtIon
Fractionation of heavy oil into components other than the asphaltene fraction (Figure 4.1) has also
been of interest in following recovery procedures. By careful selection of a characterization scheme
Deasphalting liquid
Molecular weight
n-C 5
n-C 7
Relative polarity
FIGURE 4.2 Representation of the asphaltene fraction as a collection of species of different molecular
weight and polarity.
Polarity
Mol. wt.
Mol. wt.
Mol. wt.
Polarity
Polarity
(a)
(b)
(c)
FIGURE 4.3 Asphaltene constituents (a, b, and c) from different crude oils vary in the relationship between
molecular weight and polarity depending on the relative amounts of the precursors and the maturation process
parameters (see Figure 4.2 for comparison).
Reservoirs and Reservoir Fluids
oil to crude oil (Figure 4.3), because of the complexities of the maturation process (Speight, 2007),
and should be represented as such in any models. In fact, analytical methods such as fractionation
and high-performance liquid chromatography (HPLC) have shown conclusively that the asphaltene
fraction is a mix of unknown (at best speculative) molecular types (Figure 4.4) (Speight, 1994, 2001,
2002; Speight and Long, 1996).
In spite of this, average parameters and average properties continue to be used for derivation of
predictive models when the behavioral characteristics for any average structure for such a complex
mixture cannot in any way be truly representative of the behavior of the different constituents. Thus,
it is not surprising that many models for heavy oil behavior are of little value in terms of predictive
capability of heavy oil behavior and the models generally flounder on the rocky shores of asphaltene
science (Andersen and Speight, 1999).
4.5.2 FrACtIonAtIon
Fractionation of heavy oil into components other than the asphaltene fraction (Figure 4.1) has also
been of interest in following recovery procedures. By careful selection of a characterization scheme
Deasphalting liquid
Molecular weight
n-C 5
n-C 7
Relative polarity
FIGURE 4.2 Representation of the asphaltene fraction as a collection of species of different molecular
weight and polarity.
Polarity
Mol. wt.
Mol. wt.
Mol. wt.
Polarity
Polarity
(a)
(b)
(c)
FIGURE 4.3 Asphaltene constituents (a, b, and c) from different crude oils vary in the relationship between
molecular weight and polarity depending on the relative amounts of the precursors and the maturation process
parameters (see Figure 4.2 for comparison).