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Geology
Formation of Oil and Gas Fields
a report by
Alexey A Marakushev
1
and Sergey A Marakushev
2
1. Institute of Experimental Mineralogy; 2. Institute of Problems of Chemical Physics, Russian Academy of Sciences
One of the main problems in geology is the relationship between the Fluids released from the Earth’s core in the pulsed manner are
abyssal evolution of the Earth and the formation of near-surface oil initially characterised by hydrogen composition, while oxygenous
and gas fields. It is impossible to solve this problem on the basis of components are subordinate. However, increasing fluid permeability
the widely accepted hypotheses of the formation of the Earth and and the extension of the Earth’s silicate shells stimulate the selective
other planets from a cold cosmic material; such hypotheses provide migration of hydrogen (the most mobile component) from the shells.
no explanation for the central issue of the formation of the Earth’s This process is responsible for the loss of the dominant position of
initially liquid nickel–iron core, which has been generating hydrogen hydrogen in such fluids.
3
The consequent fractionation of their
fluid flows for the past 4.6 giga-annums (Ga), driving the planet’s components results in the formation of CO
2
-rich water solutions
endogenic development. The problem can be solved only by (stage I: H
2
+ 2CO = H
2
O + 0.5CO
2
+ 1.5C), which are widespread
understanding the complex genetic relationships between giant in fluid inclusions in minerals of all igneous rocks with low and
planets, their satellites and planets of the Earth group.
1,2
Among normal alkalinity. The presence of nitrogen oxides, halogens and
these planets, the Earth is characterised by the remarkable duration other components in fluids stimulates the formation of both
of its endogenic activity and its magnetic fields, which were lost by carbonic and stronger acids. The fluids thus become aggressive to
other planets of its group due to their complete consolidation. the rocks that constitute the granite layer of the Earth’s crust. This
process is the main factor responsible for the formation of
The Earth’s magnetic field, which is generated by the liquid core, depressions in the crust that are subsequently filled with sedimentary
reflects to a certain extent its endogenic activity. The Earth’s and volcanogenic material.
endogenic activity is manifested in a pulsed manner with a
characteristic geodynamic succession in the development of each Dislocations in rocks reflect a transition to the compression regime
pulse, which begins with extension of the crust and mantle and that impedes the migration of hydrogen from fluids, stimulating the
terminates with their compression. These pulses correspond to generation of hydrocarbons within the fluids (stage II: 3H
2
+ CO =
intensification pulses of core degassing. They also stimulate the H
2
O + CH
4
, 5H
2
+ 2CO = 2H
2
O + C
2
H
6
, and others).
4
Under the
selective migration of hydrogen from fluids and the formation of influence of hydrogen, the acidic components of fluids are
acid fluids that dissolve rocks and produce depressions in the crust. decomposed (4H
2
+ H
2
CO
3
= 3H
2
O + CH
4
), which determines the
In contrast, the compression regime hampers the selective migration alkaline affinity of magmatism.
of hydrogen from fluids, increases fluid pressure and promotes the
development of explosive and other dislocations in crustal The model of the two-stage development of fluids generated by the
depressions. Pulsed degassing of the Earth’s core governs the Earth’s core via mantle magma chambers demonstrates that
formation of magma chambers in the crust and mantle. The generation of methane and ethane (light hydrocarbons) gives way to
degassing also has a substantial impact on the sedimentary process the formation of heavier hydrocarbons and graphite. The formation
and its geochemical and metallogenic patterns. of hydrocarbons is related to reactions of dehydration and oxidation
(3C
2
H
6
+ 0.5O
2
= H
2
O + 2C
3
H
8
).
5
The increased oxidising potential
Across geological history, oil generation has been characterised by is accompanied by the successive dehydration of hydrocarbons due
irregularities in maximal intensity. The largest peak corresponds to
the Cretaceous era; in Russia, 71.2% of hydrocarbon reserves are
Alexey A Marakushev is a Doctor of Geological and
attributed to this period. It is remarkable that this epoch correlates
Mineralogical Sciences and Head of the Mineral
to specific developments in the Earth’s core, corresponding to the Thermodynamics Laboratory at the Russian Academy
maximal decrease in the inversion frequency of the geomagnetic
of Sciences. He is also a Professor at Moscow State
University and an Honoured Professor at the Chinese
field generated by the core (see Figure 1). However, this relationship
Geological University.
is an indirect link associated with magmatism generated by fluid
E: marak@cat.icp.ac.ru
flows ascending from the Earth’s melted core.
Sergey A Marakushev is a Doctor of Biological
Transmagmatic fluid flows accompany all manifestations of
Sciences and a Lead Researcher at the Institute of
magmatism, and their composition changes regularly depending on
Problems of Chemical Physics at the Russian Academy
features of magmatism (largely its alkalinity), as is evident from the
of Sciences. He graduated in biochemistry, biophysics
and geomicrobiology from Moscow State University.
composition of fluid inclusions in minerals of magmatic rocks: in
rocks with low or normal alkalinity, inclusions have the
water–carbon dioxide composition, while hydrocarbons appear as an
obligatory component in rocks with higher alkalinity.
© TOUCH BRIEFINGS 2009
35
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