Page 100 - Petrophysics

PETROLEUM CHEMISTRY 73

HEAW. DEGRADED OILS:
AROMATIC ARONAllC
PHALTIC -NAPHTHENIC

INTERMEDIATE

PARAFFINIC 011 PARAFFINIC
-NAPHTnENlC OILS

HTHENIC OILS

N+ISO-ALKANES CYCLO-ALKANES
(PARAFFINS) (NAPHTHRIES)
Figure 2.19. Terna y diagram for classi@ation of crude oils as either paraf$nic,
naphthenic, or aromatic [14/.

Tissot and Welte refined this classification further into six groups by
adding intermediate types of oils using a ternary diagram Pigure 2.19)
[ 141. According to this classification, an oil is considered aromatic if the
total content of aromatics, asphaltenes, and resins is 50% or greater.
Paraffinic oils contain at least 50% of saturated compounds, 40% of
which are paraffins. Likewise, naphthenic oils are those composed
of 50% or more saturated compounds, of which 40% or more are
naphthenes. The gases and low-boiling point fractions of petroleum
contain greater amounts of the low-molecular-weight alkanes. Inter-
mediate boiling fractions contain greater amounts of the cyclic alkanes
and aromatics, where the higher boiling point fractions (> 75OoF-399"C)
are composed predominantly of the naphtheno-aromatics. Hunt presen-
ted the composition of a crude oil, which is classified as naphthenic
according to Figure 2.19, because the oil contains 49% naphthenes and
the total amount of saturated hydrocarbons (paraffins and naphthenes)
is 79% (Table 2.9) 1331.
Also listed in the table are the molecular size ranges (number of carbon
atoms per molecule) of average refinery fractions of this crude oil and the
approximate weight percentages of each fraction that can be obtained
from the naphthenic crude oil described above.
The U.S. Bureau of Mines Research Center at Bartlesville, Oklahoma,
standardized the classification of crude oils by distillation and character-
ized a large number of oils from oilfields around the world. The distillation
of a crude oil from the Oklahoma City oilfield is shown in Table 2.10.
A liter of oil is placed in the flask and the temperature is raised gradually