As for the Ternopil region's oil and gas prospects, it is located in the middle area of the Volyn-Podilsk oil-and-gas-bearing region, which, in turn, constitutes the central element of the vast Baltic-Fore-Dobrudja oil-and-gas-bearing province, covering the entire western edge of the Eastern European platform with a system of pericratonic marginal platform deflections.

The section of the Dnieper pericratonic area which forms the basis of the Volyn-Podilsk oil-and-gas-bearing region within the Ternopil region begins with the Lower Vendian vulcanites / avg. 300m /, and sometimes with the sediments of the younger Mohyliv-Podilsky Series of the Upper Vendian / 50-200 m /. The latter is composed of sandstones, arlihites and, in the upper part, bituminous oil shales. This section is thickened by the fine-rhythmic sandy-clay stratum of the Kanyliv series / up to 150 m / of the Upper Vendian and terrigenous Cambrian deposits / 100-650 m /, which introduces the Paleozoic system. Moreover, the lower / Baltic / series is mostly clay / up to 130 m /, with only a 10-20 m pack of sandstones / Rivne series / at the base, and powerful packs of sandstones in the upper Berezhky, which are separated into / up to 5 / independent horizons by 30-50m clay-silt layers. During the Ordovician period, most of the Ternopil region represented a large paleoisland / Chortkiv paleoelevation /, so these deposits are present only in the northwest / up to 30 m / and in the far east / 2-5 m /. More commonly, Cambrian deposits in this area are overlain by quite large Silurian formations / 300-500 m /, composed mainly of clay limestones, marls and dolomites, and in the 25-30km-wide submeridional strip along the Strypa River, bioherm bodies with a thickness of 30-50 m, which, according to many scientists, had once formed barrier reefs, appear in its section on two levels. With its continuous sedimentation, the Silurian section is built up by powerful, mainly terrigenous Lower Devonian rocks with layers of limestone (from 0 m in the far east to 350 m near Ternopil, and up to 1270 m in the west of the region).

The north-western part of the Ternopil region is occupied by a younger tectonic formation, the Lviv Paleozoic trough / middle-upper Devonian-Carboniferous /, which is a superimposed structure on the Dniester pericratonic area and is represented within the region by its centroclinal closure. The Middle Devonian / 0-170m / is composed of dolomites, anhydrides, limestones, argillites and sandstones. The amount of carbonate components increases further upward, and dolomites and limestones dominate in the Upper Devonian stratum. The Paleozoic deposits of the Dniester pericratonic area and the Lviv Depression west of the Ternopil-Buchach line are covered by thin layers / up to 100 m / of the Cretaceous Mesozoic, which is represented by conglomerates, sandstones and inoceramus limestones of the Cenomanian and limestones with flint.

A long-term study of oil and gas potential of Volyn-Podillya showed that the main prospects in this regard are three lithological-stratigraphic complexes: the Cambrian terrigenous, Silurian carbonate / riphogenic limestones / and Middle Devonian, with its underlying Lower Devonian deposits - / covering with a thickness of up to 50m /. The Middle Devonian complex proved to be promisingly oil-and-gas-bearing only within the Volyn and Lviv regions, where two gas reservoirs have been discovered: Velyki Mosty / Lviv region / and Lokachi / Volyn region /.

The prospects of the Cambrian complex, which already cover the Ternopil region west of the meridian of the city of Ternopil, are broader in terms of area.

Biohermic Silurian / reef / formations are associated mainly with oil resources and are projected in the aforementioned strip along the Strypa River.

The number of seismic reconnaissance surveys has been carried out to date within the Ternopil region, 6 / Kremenets, Zolochiv, Khmeliv, Buchach - 1,2, Zavadiv / deep parametric wells and a number of structural exploration wells / Zavadivka, Buchach, Koropets-Pyshkivtsi, Pidhaitsi, Darakhiv, Konopkiv(ka) /, among which 14 wells revealed the Silurian and partly Cambrian complex.

In the cores of Pidhaitsi 1,2, Koropets-Pyshkivtsi 1-4, Buchach-1, the extension of the strip of Silurian rifogenic formations to the territory of Ternopil region has been proven.

In the course of testing wells in the Buchach area, gas manifestations from Cambrian and Silurian deposits took place.

Results of near-surface geochemical studies in the Berezhany-Pomoryany area (the Olkhivka site).

Surface geochemical studies were conducted at the Olkhivka site, which belongs to the promising area of Berezhany-Kozova and were identified by comprehensive interpretation of remote and geological, geophysical data (M. Aristov and others).

The Olkhivka site is located on the right slope of the Zolota Lypa river valley . It is clearly manifested in space images as a photon anomaly located at the intersection of linear zones. In its relief, this site is manifested by the arched outlines of the Zolota Lypa riverbed and the beams that limit it, the anomalous fractured nature of the relief and the structure of the river valley.

The area of geochemical research is located within the southern part of the eastern side of the Lviv Paleozoic Depression. Sediments of the Valdai series of the Upper Proterozoic, Cambrian, Ordovician, Silurian, Devonian, Lower Devonian, Upper Cretaceous, and Anthropogenic constitute the geological structure of the work area. Their underlying foundation is represented by rocks of the Archean-Proterozoic age.

The work area is characterized by the monoclinic deposits of the sedimentary cover. The hydrocarbon deposits on monoclines are, generally, adapted to flexures, hemianticlines and gradually falling fractures. On the other hand, the confinement of hydrocarbon accumulations to structural systems located at the intersection of lineament zones was proven.

The series of geochemical studies included the study of the content of hydrocarbons, individual non-hydrocarbon components (H₂, Н_е, О₂, СО_2,N₂) in free and sorbed gases. The results of the gas analyses, along with the coordinates of the observation points, were entered into a PC.

Data samples for hydrocarbon components have been formed. With the help of "Statistica" software, the statistical processing of analysis results was performed, the arithmetic mean (±) and standard deviation (σ) were calculated. The limit values of the background field were determined at the level of χ + σ and χ + 2 σ.

Using Surfer software, maps were made of methane and ethane content, the amount of heavy hydrocarbons, the ratio of saturated to unsaturated hydrocarbons, as well as the methane content in free gases.

As a result of the analysis and map comparison, a geochemical anomaly was revealed in the southern part of the Berezhany-Pomoryany area. Anomalous methane contents are located in the eastern and northeastern part of the site and spatially tend to terraces above the floodplains of the river network, which may be due to the influence of biogenic (syngenetic) methane, and therefore are not considered by researchers to be among the most informative. The highest informativeness, in our opinion, since the generation of these components in a loose cover is considered almost impossible. The revealed geochemical anomaly is close in shape to the ring one.

For geological interpretation, anomalies for ethane are provided and the amount of heavy hydrocarbons, geochemical parameters materials of geological survey, deep and structural-gravimetric and magnetometric works, data on lithology of near-surface deposits and geochemical researches were collected and analyzed by the researchers.

The detected gas anomaly coincide well spatially with the geophysical material selected as a result of reinterpretation (L. Filshtynsky, 1972). The Mechyshchiv geochemical anomaly coincides well with the Mechyshchiv forecast rise (Siletsky TM, 1973)

According to general geological data, the Silurian reef zone passes through the Mechyshchiv uplift.

The geochemical anomaly partially coincides with the detected aerospace survey by the Olkhivka forecast site, but is slightly shifted in the southern direction.

Analysis of the results of the complex geochemical and geophysical surveys on the Berezhany-Pomoryany area (the Olkhivka site).

Analyzing the results of near-surface surveys conducted on the Berezhany-Pomoryany area, the researchers came to the conclusion that the geochemical fields on the territory of the Kuropatnytsia object are characterized by background values in all the main parameters. Concentrations of ethane in gases sorbed by rocks at a depth of 1.5 m within the site range from traces smaller than 0.001 cm³/kg , while the anomalous contents determined by statistical processing of geochemical data exceed 0.005 cm³/kg. Concentrations of one of the main informative parameters - the sum of heavy hydrocarbons, ranging from traces smaller than 0.002 cm³/kg , anomalous for the same study area are the contents that exceed 0.002 cm³/kg. Therefore, the Kuropatnytsia facility is considered unpromising in terms of hydrocarbon deposit exploration.

Among the positive factors that indicate the possibility of the existence of a hydrocarbon deposit in the area of the Olkhivka site is the high gas content of sediments in the Berezhany-1 well, starting from a depth of 850 m (Lower Devonian), which reaches maximum values in the sole of the Silurian sediments (360 cm³/kg ).

The distribution of hydrocarbon concentrations in rocks and clay solution in the section of the well is shown in the table.

At the same time, the West Ukrainian Geophysical Prospecting Expedition (ЗУГРЕ) conducted electrical reconnaissance work by method of formation of the field in the near zone (ЗСБЗ) on profile 1, which passes through the geochemical anomaly detected within the Olkhivka site. show that there is a significant change in apparent resistance (from 50 to 300 Ohms * m) in the geoelectric section in the interval of pickets 5000-9500. Such a change in resistance may be associated with a change in the lithology or type of fluid saturation of rocks (carbonation or the presence of explosives).
Within the limits of the revealed anomaly additional electrical reconnaissance work by method of formation of the field in the near zone (ЗСБЗ) have been conducted by employees of the department of geophysical research of the Ukrainian State Geological Prospecting Institute (A. Kanonskyi and others) (profiles I, II, III). As a result of these works, a bundle of carbonate deposits with a thickness of 250-300 m was identified, which is characterized by high apparent resistances (60-80 Ohm * m) and belongs to the Lopushnia series of the Middle Devonian.

Regarding the electric reconnaissance profile, it is observed that this stratum is not homogeneous, because in the intervals of pickets 2000-3500 and 6000-8500 there is a sharp decrease in apparent resistance. This may be due to the cracking and waterlogging of these deposits. Note that the highest concentrations of hydrocarbon gases in near-surface sediments (Fig. 4) are confined to these particular areas.

Thus, the carbonate stratum identified in the course of the electrical reconnaissance works by method of formation of the field in the near zone can serve as a certain geochemical barrier, which plays an important role in shaping the configuration of the detected geochemical anomaly.

Analysis of the component composition of hydrocarbon gases in the process of geochemical research within the geochemical anomaly leads one to identification of the following:

- Low CH₄ / LNG ratio;

- There being more saturated than unsaturated hydrocarbons.

A similar situation can be observed over the Lokachi and Velyki Mosty gas reservoirs (according to O. Borkovskyi, West Ukrainian Geophysical Prospecting Expedition, 1979-81).

Thus, having comprehensively considered the results of the geochemical research, geological and geophysical data, we can conclude that the geochemical anomaly found in the southern part of the research area is promising in terms of hydrocarbon deposit exploration, and with the presence of rocks with sufficient reserving and screening properties (favorable trapping conditions) in the subsoils, the probability of the formation of explosive clusters is quite high.

Work on near-surface geochemical methods were carried out on the Berezhany field. The task set before us was to assess the prospects of the morphostructures that were identified by remote sensing methods.

Laboratory work included the study of samples of free and sorbed gases and petroleum products.

The content of hydrocarbons (methane, heavy homologues up to C₆) was studied in free and sorbed gases. Unsaturated).

The degassing of oil products in soil samples was performed on mobile electric dewaxing and devices; gas analyses were conducted on a chromatograph (Crom-5, Tsvet (color) -100, Tsvet (color) -500) according to the approved methods.

The study of oil content in soil samples from a depth of 3 m was conducted by infrared-spectrophotometric and luminescent-bituminous methods.

According to the results of research conducted using Surfer software, maps-schemes were built of methane content, the amount of heavy hydrocarbons, the ratio of heavy hydrocarbons to methane, the ratio of saturated hydrocarbons to unsaturated gases sorbed by rocks, and the total explosive content in free gases.

The highest search informativeness is provided by anomalies regarding the amount of heavy hydrocarbons (C₂-C₆), because the generation of these components in near-surface sediments is impossible, while methane in these conditions can be formed biogenically.

According to the results of the study, it is observed that the anomalous methane contents (Fig. 1) are located in the north-eastern part of the site and tend to the terraces of the river network.

During the comparison of the different map-schemes in the southern part of the Berezhany field, a geochemical anomaly of heavy hydrocarbons was revealed. This anomaly is close to the ring anomaly and coincides well with the Mechyshchiv Geophysical Predictive Object of the Proterozoic (Volyn series) selected as a result of L. Filshtynsky's reinterpretation. At the same time, it partly coincides with the Olkhivka forecast site, but is somewhat shifted to the southern direction.

Preliminary gasometric studies, on the core and clay solution (interval 300-2038m), and luminescent-bituminous studies (interval 350-1978m) have been conducted in the section of the Berezhany - 1 well.

Gasometric studies show that starting from a depth of 850 m (Lower Devonian), there is an increase in the gas saturation of rocks, which reaches maximum values in the sole of the Silurian sediments (360 cm³/kg). The distribution of hydrocarbon concentrations in the rocks and the clay solution in the section of the Berezhany-1 well is provided in the table.

Table 1. The content of hydrocarbon gases in rocks and clay solution in St. Berezhany-1.

For intervals with a high content of hydrocarbon gases, the ratio of homologues to methane is shown in table 2.

Table 2. The content of methane and heavy hydrocarbons (HH/ТВ) and their ratio in St. Berezhany -1.

It should be noted that the fat content of the gas decreases with increasing depth, which indicates a high degree of catagenetic transformations of Silurian and Cambrian deposits; these deposits are in the main phase of gas generation

The analysis of the component composition of hydrocarbon gases based on the results of near-surface geochemical studies indicates a number of features of the near-surface geochemical field:

- A relatively high ratio of heavy hydrocarbons (HH) / CH₄ (close to 1);

- The presence of unsaturated hydrocarbons, and their content in some cases exceeds the content of methane homologues.



Consider these features.

1) When comparing the results of the study of the component composition of Lower Devonian, Silurian, Cambrian gases and the results of the near-surface geochemical works, there are doubts as to the participation of the gases of these sediments in the formation of a near-surface geochemical field, because they are characterized by a low HH / CH₄ ratio 1) in contrast to the gases of near-surface sediments

The source of fatty gases should be located in the Lower or Middle Devonian sediments, which, according to the geochemical zonation for the sedimentary complex, are in the main zone of oil generation, which is in section above the main zone of gas generation (Silurian-Cambrian deposits, high ratio of methane to homologues).



2) Regarding the presence of unsaturated hydrocarbons, the results of our own research indicate that the anomalous values of unsaturated hydrocarbons coincide with the anomalous fields of liquid hydrocarbons, which have been established according to the results of luminescent-bituminous and IR spectrophotometric studies. For example, within the Boryslav oil reservoir, anomalous fields of unsaturated hydrocarbons are observed only in areas contaminated with petroleum products, regardless of the source of origin of the natural process of migration through tectonic disturbances to the day surface or technogenic pollution caused by oil production. This further confirms that the source of the unsaturated hydrocarbons in near-surface conditions lies in the processes of biodegradation of deep hydrocarbons.

Studies of core material from geochemical wells up to 3 m deep within the Berezhany field for the content of petroleum products showed positive results. The concentration of liquid methane-naphthenic hydrocarbons in near-surface sediments reaches values of 0.085 g / kg of rock.

Given the above material, we can assume the presence of accumulations of petroleum hydrocarbons, which are, moreover, located in the deposits of the Upper-Middle Devonian.

Only the following fact can call into question the obtained results. After the lifting of the core from the Cambrian sediments (int.1764-1765), a tool was caught in the well. For the purpose of accident prevention, it was mixed with a clay solution. The effect of the oil in the clay solution on the composition of the desorbed gas was manifested in the following. Keeping in account that the composition of desorbed gases from the overlying rocks to a depth of 1760 m consisted of 94.2 vol.% CH₄ and 5.8 vol.% HH, methane's part, in the interval of 1800-2000 m, was in the range of 32.2-85.7 vol.% (average of 61.4 vol.%), while its homologues formed 14.3-77.8 vol.% (average of 38.6 vol.%).

However, given the fact that the near-surface distribution of petroleum products is significantly spread throughout area and partially coincides with the anomalies of hydrocarbon gases, we can assume that the study area is promising in terms of oil potential.

It is also necessary to take note of the distribution of methane, which forms a ring anomaly within the study area around the Olkhivka forecast site. If this methane is not of biogenic origin, then we can assume that we are dealing with the unloading of hydrocarbons from the Silurian-Lower Devonian sediments, where one could, under favorable geological and structural conditions, expect an accumulation of hydrocarbon gases.

1. «Геодинамічні умови формування і нафтогазоносність Карпатського та Волино-Подільського регіонів України» (The geodynamic conditions of the formation and oil and gas potential of the Carpathian and Volyn-Podillya regions of Ukraine). Yu. Z. Krupskyi, Ukrainian State Geological Prospecting Institute, Lviv.

2. «Геодинамічні умови формування і принципи районування Волино-Поділля» (The geodynamic conditions of the formation and principles of zoning of Volyn-Podillya). Yu. Z. Krupskyi, Ukrainian State Geological Prospecting Institute, Lviv.

3. «Особливості тектонічної будови Волино-Поділля, згідно із даними сейсморозвідувальних та бурових робіт і положення зони Тейссейреторнквіста» (The peculiarities of the tectonic structure of Volyn-Podillya, according to the data of seismic and drilling works and the position of the Teisseire-Tornkvist zone). Yu. Z. Krupskyi, Ukrainian State Geological Prospecting Institute, Lviv.

4. «Закономірності розміщення та умови формування покладів вугле воднів» (The regularities of placement and conditions of formation of hydrocarbon deposits). Yu. Z. Krupskyi, Ukrainian State Geological Prospecting Institute, Lviv.

5. «Геологічні передумови відкритття родовищ вуглеводнів на території Тернопільської області» (The geological preconditions for the discovery of hydrocarbon deposits in the Ternopil region). Yu. Z. Krupskyi, V. Marusiak, Ukrainian State Geological Prospecting Institute, Lviv.

6. «Комплексна інтерпретація геолого-геофізичних даних на Бережанській ділянці» (Comprehensive interpretation of geological and geophysical data in the Berezhany area). I. M. Kurovets, I. B. Hubych, «Геопошук» (Geosearch) Lviv.

7. «Перспективи нафтогазоносності Куропатницького локального об'єкту за результатами приповерхневих геохімічних досліджень» (Prospects regarding the oil and gas potential of the Kuropatnytsia local object based on the results of near-surface geochemical studies). I. B. Hubych, Geochemistry and Ecology Laboratory, Ukrainian State Geological Prospecting Institute, Lviv.

As for the Ternopil region's oil and gas prospects, it is located in the middle area of the Volyn-Podilsk oil-and-gas-bearing region, which, in turn, constitutes the central element of the vast Baltic-Fore-Dobrudja oil-and-gas-bearing province, covering the entire western edge of the Eastern European platform with a system of pericratonic marginal platform deflections.

Within the Volyn-Podillya outskirts of the Eastern European platform, the following well-studied oil and gas fields and reservoirs are identified: The Velyki Mosty and Lokachi gas reservoirs, Peremyshlyany, Olesko-Zolochiv and Buchach oil-and-gas-bearing areas.

In the northwest, the Berezhany field borders the Peremyshlyany oil and gas field (Lviv region), where an industrial inflow of gas from Cambrian deposits was obtained from the 1-Peremyshlyany well. Further southwest, the area borders the Ivano-Frankivsk region where, at a distance of 40 km from the project area, the Kadobna gas reservoir is located.