Page 123 - Geology and Geochemistry of Oil and Gas

CLASSIFICATION OF CRUDE OILS 95
TABLE 5.4

Frequency of occurrence (% of total samples analyzed) of various crude oil types (after Botneva, 1987)
Chemical type % Chemical type %
I 39.7 VI 6.1
II 16.4 VII 7.4
III 12.4 VIII 6.8
IV 3.6 IX 1.5
V 6.1

TABLE 5.5
Content of various hydrocarbons in 200–4301C boiling fraction (after Petrov, 1984)
Hydrocarbons Content in oils of different types (%)

A 1 A 2 B 1 B 2
Alkanes 15–60 (25–50) 10–30 (15–25) 5–30 (10–25) 4–40 (6–10)
n-Alkanes 5–25 (8–12) 0.5–5 (1–3) 0.5 Not found
Isoprenoids 0.05–6 (0.5–3) 1–6 (1.5–3) 0.5–6 (0.2–2) Not found
Cycloalkanes 15045 (25–40) 20–60 (35–55) 20–70 (35–55) 20–70 (50–65)
Arenes 10–70 (20–40) 15–70 (20–40) 20–80 (20–45) 25–80 (25–50)
Note: Most commonly encountered values are in parentheses.

Problems associated with the petroleum forecasting may not be solved, unless the
genetic uniformity/nonuniformity of the crude oils in a given field and region is
determined.
In order to subdivide the crude oils into genetic types, the criteria for the iden-
tification of genetic types have been developed. The genetic indicators in crude oils
are associated with the organic matter composition of the source rocks. There is
some disagreement among petroleum geologists as to what these genetic parameters
are. According to one school of thought, there are just a few genetic types of crude
oils. These types are the same in all petroleum provinces worldwide and are defined
by the facies-genetic type of organic matter (sapropelic, humic and their combina-
tions) and by the degree of oxidation or metamorphism of the organic matter. The
other approach is that the crude oil genetic type is defined by the specific charac-
teristics of the composition of parent organic matter and the chloroform-extractable
bitumen that are specific for each source rock within each petroleum basin. It was
found that changes in the biomass composition occurred in the Phanerozoic:
(1) the number of taxons increased;
(2) the diversity of forms grew, as well as the replacement of some forms by the
others; and
(3) changes occurred in the biochemical composition of organisms (changes were
caused by the evolution of the living matter in Phanerozoic, as well as by the