25th International Meeting on Organic Geochemistry IMOG 2011

P-290
On the problem of preservation of hydrocarbons (HC) and
organic matter (OM) at high pressures (HP) and temperatures
(HT) (experimental data)
Vasily Melenevskiy 1 , Yury Palyanov 2 , Alexander Sokol 2 , Vladislav Maly 3
1 Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy Science (SB
RAS), Novosibirsk, Russian Federation, 2 Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russian
Federation, 3 Institute of Hydrodynamics SB RAS, Novosibirsk, Russian Federation (corresponding
author:vmelenevsky@yandex.ru)
We studies the behavior of HC and coal in
the conditions of supercritical fluid at HP and HT,
which account for diamond stability conditions, and
that of dispersed OM and coal under shock-wave
loading. The reaction products were examined by
means of chemical, X-ray and pyrolytic (Rock – Eval)
methods. The analysis technique, and the experiment
procedures, and, partly, the findings of the studies
are described in the works [1 - 4].
Supercritical fluids Experiments were
carried out in a multi-anvil high-pressure apparatus of
the ‗‗split-sphere‖ type at temperature 1200 ’ 1420 о С
and pressure 5,2 ÷ 5,7 GPa [3, 4]; eicosane,
anthracene and bituminous coal (R o vt=0.94 %, HI=
225 mg HC/g Соrg) were used as the objects of the
study.
When heated in HT-HP conditions, the first
processes starting to proceed in coal is cracking,
followed by further decomposition of the hydrocarbon
products yielded and ending by the build-up of
metamorphized residuals. The data analysis showed
that the coal has metamorphically altered to pass to
the metaanthracitic stage of coalification (atomic ratio
(Н/С)at was shown to decrease against the initial
value of 0.84 to 0.24). X-ray diffraction data for the
residual solid OM after the experiment on HCs have
proven it to be represented by graphite. The
accuracy of establishing the HC decomposition
degree was defined with the analysis blank value in
the experiment. Under the HT-HP experiment
conditions, the decomposition degree value might not
exceed 0.999, according to our estimations.
However this estimation proved correct only
for HC with nCi>10. For the light HC additional
investigations are needed.
Shock wave experiment. To model the
impact processes going on when a meteorite hits the
surface of the Earth, we used explosion technique in
the geometrical version of cylindrical symmetry [1, 2].
Maximum (calculated) pressure within the front of a
detonation wave varied within the interval 2.0÷ 6.0
GPa. OM proved to have morphed into graphite
during the experiment; neither gaseous or heavy
hydrocarbon have been detected in the sample after
the experiment.
8 cm
Fig. This picture shows longitudinal section
of the container with the sample subjected to
explosion with intensity of 2.00 Gpa. The upper arrow
indicates the detonation wave direction.
In the left portion of the picture we can see a
cone-shaped darkened area, an indication of the
largest transformations, consisting in graphitization of
OM; whereas, the starting OM has hardly been
altered outside this area. Thus after the explosion
there was formed practically non-gradient boundary
between high and low maturity OM.
References
[1] Melenevsky V. N., et al. (2003) Geokhimia, №12,
p.1332-1336.
[2] Melenevsky V. N. et al. (2005) DAN, v. 405, p. 1-
3.
[3] Melenevsky V., Kontorovich. A. (2007) Problemy
TEC (In Russian), #1, p.18-21.
[4] Alexander G. Sokol et al. (2009) Geochim. et
Cosmochim. Acta, v. 73, p.5820–5834.
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