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3.4. Evidence for the observed thermal
effects in other studies of petroleum fluids
In line with the definition of asphaltenes as true chemical
species (cf. Introduction) and attribution of the observed thermal
effects to phase transitions, involving asphaltenes, we concluded
that the specific pour point behaviour of Fig. 1 may be a wide-
spread phenomenon, inherent to various asphaltene-containing pe-
troleum fluids, irrespective of their individual composition, geologi-
cal or geographical origin.
Confirmations of this conclusion have been found by an exten-
sive literature analysis (presently limited to Russian-language
publications), including field laboratory reports, reference books,
technological recommendations, etc.
Some of the relevant data are presented in Fig. 5. The three
curves at the top are reproduced from [23] and show the dependen-
cies of T
pour
on the pre-treatment temperatures of three crude oils
from: 1) the Zhetibaj reservoir in Kazakhstan (filled triangles); 2)
the Koturtepe reservoir in Turkmenistan (open circles); 3) the
Kara-Chukhur reservoir in Azerbaijan (open squares).
Filled circles in Fig. 5 show the dependence on T
pt
of the pour
point of a residual fuel oil (reproduced from [24]). In spite of a low
resolution of the data sets in Fig. 5 (10–15°C increments of T
pt
),
there is an apparent similarity of these results with our data of
Fig.1. This similarity is not only qualitative (an increase of the
pour point in pre-heated fluids), but also quantitative with respect
to the specific temperatures T
pt
, providing the largest pour points
(35–41°C in Fig. 3, as compared to 36–38°C in our studies).
It should be noted, that in the original publications [23, 24]
the existence of the discussed thermal effects have not been recog-
nised. The experimental results, reproduced in Fig. 5, obviously
have been presented by the authors just as some “excess informa-
tion” and the anomalous pour point behaviour have not been dis-
cussed, or even referred to, in the respective texts.
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