Common point of view says that deposits of petroleum and natural gas, which are hydrocarbons, formed as a result of decomposition of organic matter of ancient living organisms. However, the theory of abiogenic petroleum origin tends to become more and more popular among researchers these days. An argument between followers of either classic or alternative theories of hydrocarbon origin can soon be solved thanks to a research, performed by Russian geologists and mineralogists, who developed a technique for identifying a source of carbon, which is a part of natural gas.

The fact that abiogenic hydrocarbon synthesis can exist in theory is beyond question. What researchers needed to know is how origin of natural gas could affect its composition. Solution for this problem was suggested in the laboratories of the Institute of Geology and Mineralogy (Siberian branch of Russian academy of sciences) and the Institute of High-Pressure Physics (Russian academy of sciences). In elegant experiments researchers put ampoules with reagents (source of carbon, water and iron) into a high-pressure chamber and then simulated pressure and temperature of Earth’s upper mantle. As a biogenic source of carbon researchers used limestone (calcium carbonate), and graphite was used as an abiogenic carbon source. After incubation pressure was reduced, and ampoules, cooled to the necessary temperature, were taken out of the chamber, and their content was subject to analysis.

 

 

Ampoules with all versions of the experiment appeared to contain a mix of hydrocarbons, corresponding with hydrocarbon component of natural gas. However, ampoules with graphite as an abiogenic source of carbon, contained so-called “dry” or “lean” gas, which mainly consisted of methane. This gas occurs in nature, for instance, it can be found in the North-Stavropol deposit. When carbon for the gas came from limestone, incubation resulted in “wet” gas, enriched with high-molecular hydrocarbons, mainly by ethane. This kind of natural gas is obtained at the Vuktyl deposit, for example. Thus, after analyzing hydrocarbon component of natural gas, researchers can say where carbon of that gas has come from.

The question is: is it possible for two equally important sources of carbon for hydrocarbons to exist? Well, theory says yes, but researchers have shown that cooling time of reaction mixture also had a significant effect on resulting gas composition. When ampoules were cooled quite quickly, then resulting gas contained small amounts of ethane and ethylene. When cooling was slow and took hours (4 hours in the experiment), concentration of abovementioned components increased tenfold, and even more high-molecular hydrocarbons, like butane and butylene were detected. Therefore, gas mixtures of various compositions can origin from either organic, or inorganic source of carbon. Scientists cannot say they reached total clarity in this field, but they strongly believe that their experimental technique can make a great contribution to further experiments, aimed at understanding a mystery of origin of hydrocarbons.

Source: Science News

Kizilova Anna