Technology Highlights
Theory of Abyssal Abiotic Petroleum Origin: Challenge for Petroleum Industry
Experimental Confirmation
The theory of abyssal non-biotic petroleum origin recognizes that petroleum is a primordial material of deep origin which has been erupted into the crust of the Earth. According to the theory of the abyssal non-biotic petroleum origin, developed during the last 50 years in Russia and Ukraine, hydrocarbon compounds are generated in the mantle of the Earth. There are three possible scenarios for mantle petroliferous fluid migration. According to the first; when pressure in the fluid flow is decreased dramatically at an almost constant temperature, the complete destruction of the hydrocarbons occurs. According to the second scenario, if pressure is not high enough to overcome a resistance of the “locking” layer, the mantle fluid is locked at depth between the upper mantle and the surface. Depending on the depth (i.e. thermobaric conditions) the fluid could be completely or partly destroyed within a certain time. The third scenario deals with petroleum deposit formation. Rising from subcrustal zones through deep faults and their feather joints or fissures, the mantle petroliferous fluid is injected under high pressure into any rock and is distributed there in the form of a mushroom-like cloud. The hydrocarbon composition of oil and gas accumulations formed this way depends on the fluid cooling velocity during the movement of these fluids to the surface of the Earth. However, being at shallow depths, the oil and gas accumulations become principally stationary. They do not migrate upwards in anticlines or synclines, or through tilted or horizontal beds until the petroleum masses are moved further by new quantities of the mantle petroliferous fluid (fig. 1).
Figure 1. Possible scenario of the mantle petroliferous fluid migration. Accumulation of oil and gas is one part of the natural process of the Earth’s outgassing that was responsible for creation of its hydrosphere, atmosphere and biosphere.
According to the theory of abyssal non-biotic petroleum origin, the following conditions are necessary for the synthesis of hydrocarbons from non-biotic substances: adequate pressure and temperature, donors of carbon and hydrogen, and a thermodynamically favorable reaction environment. Theoretical calculations based on methods of modern statistical thermodynamics have established that polymerization of hydrocarbons takes place in the temperature range 600-1500 °C and at pressures 20-70 kbar (Kenney et al. 2002). According to the modern scientific consideration of the physical and chemical characteristics of continental mantle (Carlson et al. 2005), these conditions could take place deep in the Earth at depths of 70- 250 km. Different substances can act as donors of carbon: carbon dioxide (CO2), graphite, magnesite (MgCO3), calcite (CaCO3). Water and the hydroxyl group of various minerals could be possible donors for hydrogen.
According to modern science analysis, all the above-mentioned substances are present in the mantle in sufficient amounts (Murakami et al. 2002, Isshiki et al. 2004). Favorable reducing conditions could be created by a presence of FeO unconnected to metal-silicates.
Thus, hydrocarbon non-biotic synthesis could take place in the basic and ultrabasic rocks of the upper mantle, in the presence of FeO and donors of carbon and hydrogen. The possible reaction of formation in this case could be presented as follows: reduced mantle substance + mantle gases → oxidized mantle substance + hydrocarbons. Another mechanism of the hydrocarbon synthesis could also be the following. Structural radicals such as carbon, methylene (CH2), methyl (CH3) could exist in the mantle. Different combinations of these radicals define the wide range of oil-and-gas hydrocarbons, and also cause the analogous properties and genetic similarity of oils from different parts of the world.
One of the main obstacles to development of the theory of abyssal non-biotic petroleum origin has been the lack of reliable and reproducible experimental results that confirm the possibility of the spontaneous synthesis of complex hydrocarbon systems under the conditions of the upper mantle of the Earth.
The first set of such kinds of experiments were made between 1998 and 2000, at the Institute of High Pressure Physics in Russia (Kutcherov et al. 2002) with the purpose being to model mantle conditions in a laboratory. To provide the conditions essential for the experiment and to prevent atmospheric contamination, a special high-pressure apparatus was designed. This equipment permits investigations at pressures up to 50 kbar and temperatures up to 1200°C. The cooling system allows rapid cooling while maintaining high pressures. For analyses of reaction products, the standard mass-spectrometer and chromatograph were used. Two different schemes of the reactions of hydrocarbon synthesis were determined. At pressure 30 kbar the synthesis is due to the following reactions in the temperature range 550–900 °C:
CaCO3 + 9FeO + 2H2O = 0.5CaC2H6O2 + 3Fe3O4 |
(1) |
0.5Ca2C2H6O2 = 0.5Ca(OH)2 + [—CH2—] |
(2) |
At pressure 50 kbar the synthesis is passed in one stage at temperature 1200 °C:
nCaCO3 + (9n+3)FeO + (2n+1)H2O →nCa(OH)2 + (3n+1)Fe3O4 + CnH2n+2 |
(3) |
Results of chromatographic analyses (Kutcherov et al. 2002), together with the characteristics of gas-liquid inclusions within granitoid rocks from the “White Tiger” oilfield in Vietnam (Areshev et al. 1997) are shown in Table 1. The data in Table 1 shows that during the aforementioned high-pressure experiments, the system spontaneously evolved hydrocarbon mixtures with compositions similar to those of naturally occurring crude oils.
| Hydrocarbon | |||
1,473 K |
1,153 K |
||
| Methane (CH4) | 57.3 |
89.6 |
94.0 |
| Ethane (C2H6) | 5.9 |
2.8 |
0.57 |
| Ethylen (C2H4) | 5.9 |
2.5 |
0.55 |
| Propane (C3H8) | 3.6 |
0.9 |
1.77 |
| Propylen (C3H6) | 8.7 |
3.2 |
0.13 |
| Isobuthane (i-C4H10) | 0.2 |
0.1 |
0.9 |
| Butane (n-C4H10) | 2.1 |
0.3 |
0.9 |
| Isopenthane (i-C5H12) | 0.4 |
0.15 |
0.4 |
| Pentane (n-C5H12) | 1.2 |
0.25 |
0.3 |
| Isohexane (i-C6H14) | 0.12 |
0.01 |
0.26 |
| Hexane (n-C6H14) | 0.6 |
0.1 |
0.27 |
| Other | 13.98 |
0.09 |
0 |
Table 1. Content of Synthezated and Natural Hydrocarbon Mixture.
Part of our experimental results has been confirmed by experiments conducted by Scott et al. (2004). The American researchers have presented in situ observations of hydrocarbon formation via carbonate reduction at upper mantle pressures and temperatures. They have shown that methane was formed from FeO, CaCO3-calcite, and water at pressures between 50 and 110 kbar and temperatures ranging from 500 °C to 1500 °C.
Therefore, the results obtained by two independent groups of researchers confirm one of the main breakthroughs in the theory of abyssal non-biotic petroleum origin: complex hydrocarbon systems can be spontaneously generated deeply in the Earth, under the conditions present in the upper mantle.