Some Data on the Microflora of Groundwater of the Sovetskoye Oil Field in Tomsk Oblast

SOME DATA ON THE MICROFLORA OF GROUNDWATER OF THE SOVETSKOYE OIL FIELD IN TOMSK OBLAST

E. P. SHAMOLINA, A. D. NAZAROV

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

Data on the microbiological composition of waters in the oil-and-gas-bearing regions of Tomsk Oblast are lacking. Meanwhile, the study of the microflora of waters, rocks, oils, and gases of oil-and-gas-bearing regions is of great interest from both the practical and the theoretical standpoint. Microbiological investigations help us to understand the conditions of formation of hydrocarbon deposits and their interaction with the surrounding rocks and waters. In addition, they make it possible to identify certain microbiological prospecting indicators.

As is known, on the qualitative composition of the microflora of groundwaters and rocks of various oil-bearing regions of the Union, including Western Siberia, a large body of factual material has been accumulated and published in a number of works (2, 3). As a result of these works, the following physiological groups of bacteria present in formation waters, oils, and rocks have been identified: sulfate-reducing bacteria; bacteria decomposing oil under anaerobic conditions; methane-forming bacteria; thionic bacteria; and bacteria oxidizing, in the presence of oxygen, crude oil, hydrocarbons of the paraffin series, and aromatic hydrocarbons. Most of these organisms are used as indicators in bacterial prospecting for oil (1).

The development of microflora depends on ecological conditions. The presence of oxygen has an especially great influence on it. The penetration of oxygen-rich infiltration waters promotes the intensive development of aerobic microflora in the upper layers of the geological section. With depth, the oxygen content in waters decreases, and the development of aerobic microflora is inhibited. Anaerobic microflora becomes the determining factor. Under these conditions, the oxygen of sulfates, nitrates, and other oxygen-containing compounds of waters and rocks enters the cycle.

In the course of their vital activity, bacteria use carbon, nitrogen, and other components of oils, as well as the oxygen of sulfates and nitrates, significantly affecting the distribution of these components in the equilibrium system water—rock—hydrocarbons. Hydrogen sulfide, methane, ammonia, and nitrogen appear in the waters. Such a process may proceed even to the complete destruction of the deposit.

In studying the microflora of the waters of the Sovetskoye field, the task was set of outlining regularities in the distribution of microorganisms indicative of oil and gas. For this purpose, water samples were taken from the aquifer horizons of the Kulomzino, Vartov, Pokur formations and Pa-

* — method of Yu. Yu. Lur’e

The brief characterization of the composition of the waters analyzed, given in Table 1, shows a regular increase with depth in temperature at a distance of 30 m from the water–oil contact (WOC), sample No. 2—from Neogene and Quaternary deposits. Sample 1 was taken from water-bearing bed \(A_1\) at a distance of 200 m from the top of bed \(A_1\).

and its homologues, and a decrease in oxygen in the composition of the dissolved gases. In the same direction the gas saturation of the waters increases. An analysis of the microflora of these waters is given in Table 2. Bacteria that, under aerobic mineralization (from 0.22 g/l to 27.0 g/l) of sodium and calcium chlorides, meta-

Table 1

Hydrogeochemical indicators

Ion-salt

Continuation of Table 1

Continuation of Table 1

method of coprecipitation of TPI

under natural conditions, oil and certain hydrocarbons (hexane, phenol) are present not only in oil-bearing waters but also in waters not associated with oil.

At the same time, benzene-oxidizing bacteria were found only in samples of water taken from oil-bearing strata. A qualitative reaction for benzene notes its presence in these same samples. If this dependence is confirmed in the analysis of a larger number of water samples, bacteria that oxidize benzene may be used as indicators of the presence of oil and gas in formation waters. Moreover, in the opinion of many researchers, benzene itself is specific only to oil-bearing waters. Its content in waters in an amount greater than 0,015 mg/l is considered a direct

Table 2

as a direct indication of the presence of a hydrocarbon pool in the nearest trap (4).

This article presents the first data from reconnaissance studies of the microbiological composition of groundwater in oil fields of Tomsk Oblast, carried out by the problem-oriented geological laboratory of TPI. They make it possible only to outline certain directions for further microbiological investigations of groundwater in oil- and gas-bearing regions.

The need to study the microflora of waters, rocks, and oils in combination with other hydrogeochemical investigations is becoming entirely clear. In addition, at present the question arises of modeling microbiological processes under conditions close to reservoir conditions.

LITERATURE

1. Geochemical methods for prospecting for oil and gas fields. Proceedings of the All-Union Conference on Geochemical Methods. Publishing House of the USSR Academy of Sciences, Moscow, 1959.

2. E. N. Dutova. On bacteria that destroy naphthenic acids, and their distribution in groundwater. Problems of Petroleum-Prospecting Hydrogeology. Materials of VSEGEI, new series, issue 18, Leningrad, 1956.

3. Z. I. Kuznetsova. Distribution of bacteria in groundwater and the use of microbiological data for assessing oil-bearing capacity, rotaprint VSEGINGEO, Moscow, 1963.

4. Methodology for prospecting and exploration of oil and gas fields. VNIIENG, Moscow, 1968.