DISTRIBUTION OF CERTAIN GROUPS OF BACTERIA IN GROUNDWATER AND ROCKS IN THE AERATION ZONE OF THE NORTH KOLPASHEVO AREA

P. A. UDODOV, E. P. SHAMOLINA, V. G. BYKOV

(Presented by the scientific seminar of the Problem Geological Laboratory of TPI)

Experience from investigations in a number of oil-and-gas-bearing regions of the country has shown that, in petroleum exploration, the application of geochemical methods yields good results. A cheap and promising method is the bacterial method, which is based on detecting bacteria capable of oxidizing hydrocarbon gases that diffuse to the surface from an oil or gas accumulation. A number of physiological groups of bacteria of exploratory significance for oil and gas have been identified (Mogilevsky, 1953; Birshtekher, 1957; Kuznetsov, Ivanov, Lyalikova, 1962). For the conditions of Tomsk Oblast, this question is at the stage of development.

As experimental investigations at the first stage, the North Kolpashevo local uplift was selected; tectonically, it is situated in the saddle between the Payduginsky megaswell and the Mokhovsky dome-shaped uplift.

The prospectivity of the structure was substantiated by its proximity to oil and gas-condensate fields with analogous geological structure and by favorable hydrodynamic conditions.

During the fieldwork, surface watercourses, waters of the first aquifer from the surface, waters penetrated by the North Kolpashevo well 81-R, and rocks in the aeration zone were examined (no oil or gas shows were observed during testing of the well).

To detect bacteria of various physiological groups, inoculations were made into the corresponding selective media. Hydrocarbon-oxidizing bacteria were determined on Munz’s mineral medium in a hydrocarbon atmosphere; methane-forming bacteria, on Barker’s medium with calcium acetate; sulfate-reducing bacteria, on Tauson’s medium. Along with indicator bacteria, the content of microorganisms in 1 ml of water was determined by the direct-count method (Kuznetsov, Romanenko, 1963).

The results of microbiological investigations of rocks and waters are given in Tables 1 and 2. Attention is drawn to the weak development of the gas-oxidizing microflora and to the fact that the intensity of bacterial development increases with depth. All water samples are richly populated with methane-forming bacteria and with bacteria that oxidize liquid hydrocarbons. Methane-forming bacteria develop through the reduction of carbon dioxide to methane in the presence of molecular hydrogen. This dependence is maintained in our case: the more carbon dioxide there is, the more intensive the development of bacteria. This same group of bacteria, detected in surface waters, may develop at the expense of \(CO_2\) and \(H_2\), formed

Table 1

Composition of the microflora in deep and ground waters of the North Kolpashevo area

Table 2

Detection of hydrocarbon-oxidizing microflora in rock samples collected within a radius of 10 km from well 81-R of the Severo-Kolpashevskaya area

as a result of the decomposition of terrestrial vegetation. Gas-oxidizing bacteria are found in the waters of exploration well 81-R, beginning at a depth of 2340 m and deeper. The development of these bacteria in surface watercourses can be explained by the presence of biogenic methane. Bacteria oxidizing heptane, hexane, and decane are more widely distributed in nature, since they are less specific with respect to the utilization of hydrocarbons. Among bacteria oxidizing aromatic hydrocarbons, phenol-oxidizing forms are widely distributed. Benzene-oxidizing bacteria were found in the waters of well 81-R, beginning at a depth of 2141 m and deeper. The development of desulfurizing bacteria is limited by the high oxidation-reduction potential \((rH_2\ 13.0—22.3)\), whereas the optimum is

\[ rH_2 = 6\text{–}8. \]

The bacterial content in the waters of well 81-R ranges within tens of thousands per 1 ml of water, which indicates the closed nature of the structure.

In the waters of Quaternary and Paleogene deposits located close to the ground surface, tens and hundreds of thousands per 1 ml of water are counted.

It is evident from Table 2 that in most rock samples the development of hydrocarbon-oxidizing microflora is absent, and only at certain points is very slight development observed.

In view of the fact that this question for Tomsk Oblast is at the experimental stage, it is necessary to conduct similar investigations in areas known to be oil- and gas-bearing. This will make it possible to develop definite oil-prospecting criteria based on microbiological data and to recommend the most promising and rational type of bacterial survey for the conditions of our region.

References

1. E. Birshtekher. Petroleum Microbiology. Gostoptekhizdat, Moscow, 1957.

2. S. I. Kuznetsov, M. V. Ivanov, N. N. Lyalikova. Introduction to Geological Microbiology. Publishing House of the USSR Academy of Sciences, Moscow, 1962.

3. S. I. Kuznetsov, V. I. Romanenko. Microbiological Study of Inland Waters. Laboratory Manual. Publishing House of the USSR Academy of Sciences, Moscow, 1963.

4. G. A. Mogilevskii. Microbiological Method for Prospecting Gas and Oil Deposits. BTEI TsIMTNEFTI. Gostoptekhizdat, Moscow, 1953.