Oil and gas bearing complexes (OGK) are complexes of rocks of the sedimentary cover and the upper part of the basement of oil and gas provinces, which have relatively uniform conditions for the formation and transformation of rocks, organic matter and oil and gas fields, as well as uniform hydrodynamic conditions.

NGCs are characterized by the following indicators:

1) lithological composition and age of rocks;

2) thickness and distribution area (volume);

3) the ratio of reservoirs and seals, oil and gas producing and productive rocks;

4) hydrogeological conditions;

5) genetic and morphological types of traps;

6) conditions of occurrence and patterns of placement of oil and gas deposits.

In terms of lithological and stratigraphic volume, oil and gas complexes cover one or two or three adjacent formations or are part of them.

Classifications of oil and gas bearing complexes. E.A. Bakirov classified oil and gas complexes according to genetic and geotectonic features. The basis of the genetic feature is the nature of the ratio of oil-producing and oil-bearing rocks, and the basis of the geotectonic feature is the nature of the spatial distribution of oil and gas.

According to the nature of the ratio of oil-producing and oil-bearing rocks or the sign of primary and secondary oil and gas potential, oil and gas fields are divided into primary oil-bearing, secondary oil-bearing and mixed.

Primary oil-bearing, or syngenetic, oil and gas consist of oil and gas producing rocks, reservoir rocks and overlapping regional seals. From below, such complexes are isolated by the seal of the underlying regional oil and gas complex or basement rocks.

In secondary oil-bearing, or epigenetic, oil and gas oil and gas producing rocks are absent, have low productivity or have not yet reached the main zone of oil formation. HC enter them from syngenetic complexes as a result of vertical migration through permeable zones. The scale of oil and gas content of epigenetic oil and gas complexes is directly dependent on the generating potential of the underlying syngenetic complex and the shielding properties of its seal.

In mixed, or episyngenetic, NGCs the deposits contain both syngenetic hydrocarbons and hydrocarbons migrated from other complexes.

According to the scale of distribution, oil and gas complexes are divided into regional, subregional, zonal and local. Regional oil and gas companies accepted in this classification in the interpretation of A.A. Bakirov, who first identified them in 1959 as Lithological and stratigraphic units containing accumulations of oil and gas within vast territories corresponding to the NGP or large parts of them. To sub-regional oil and gas complex include rock complexes containing accumulations of oil and gas only within one oil and gas bearing area of ​​any province. The complex of rocks productive within the oil and gas accumulation zone is distinguished as zonal OGK. Local oil and gas companies productive within one or more deposits that are not related by common features.

The structure of the permeable part of the oil and gas complex. The permeable or inner part of the oil and gas complex corresponds in volume to the GGB aquifer complex - a permeable rock mass enclosed between two regional aquicludes (tires). According to the internal structure of the permeable part of the OGK, it can be divided into four types.

to the first type include oil and gas condensates, in which the main part of the section is made up of hydrodynamically connected permeable rocks. Inside such complexes there can be only local, randomly located seals. In complexes of this type, large deposits of oil and gas, as a rule, are confined to the roof of reservoir rocks and are associated with massive and massive-stratal natural reservoirs.

to the second type include oil and gas condensates in which relatively mature reservoir rocks and seals alternate with each other. Therefore, deposits of oil and gas here can be formed throughout the section of the complex in natural reservoirs of reservoir and reservoir-massive type. Multilayer deposits belong to the domed and disjunctively shielded types of the structural class, as well as to the lithologically shielded type of the lithological class. The number of productive layers in the field can reach forty or more.

to the third type include oil and gas condensates, which are dominated by impermeable rocks. Lithologically limited natural reservoirs and traps are developed here, which are confined to individual lenticular bodies of permeable rocks. Natural reservoirs of reservoir type have a subordinate position. Oil and gas deposits in such complexes can be found throughout the entire section of the oil and gas complex. This type of OGK is widespread in deltaic complexes and sediments at the continental foot (turbidites).

to the fourth type The oil and gas complex is a special type of syngenetic complexes associated with clayey rocks such as bazhenites and domanikites, as well as with some carbonate rock varieties. In these OGKs, oil and gas producing rocks are also oil and gas containing. The productivity of this type of oil and gas complex is largely related to high content OM and zones of recent tectonic activation.

Within the little-studied territories, as well as in the lower parts of the section of the sedimentary cover of old oil and gas fields, promising oil and gas complexes. These are parts of the section in which accumulations of oil and gas have not yet been identified, but there are actual data for their detection - this is the presence of: reservoir rocks; seals; organic matter in concentrations exceeding 0.1-0.2% for carbonate rocks and 0.4-0.5% for clay rocks; reservoir temperatures characteristic of the main oil generation zone or the main gas generation zone; tectonic dislocation of the complex; traps and others. For example, in Ciscaucasia, where most of the sedimentary cover has been studied relatively well, such a promising oil and gas complex is the Paleozoic rock complex.

Currently, the regional oil and gas potential of the basement has been established on all continents, excluding Antarctica and in most water areas of the Earth. In this regard, the basement rocks of oil and gas bearing and potentially oil and gas provinces should be classified as promising oil and gas complexes, regardless of ideas about the formation of oil and gas.

In the context of oil and gas provinces, at least two regional oil and gas complexes are distinguished. Their total thickness, together with the overlying seal, usually lies in the range of 2 to 4 km. Above the upper OGK, above the uppermost regional seal, there is conservation area, in which oil and gas deposits can no longer be formed due to the hydrodynamic openness of the section.

Multi-storey the distribution of hydrocarbon accumulations in the section of the earth's crust is associated with the frequency of tectonic development of large geostructural elements of the earth's crust, their stratification into reservoir rocks, seals and, accordingly, with the frequency of OM accumulation processes, oil and gas formation and oil and gas accumulation.

Thus, for the formation and existence of oil and gas complexes, the following are necessary: important conditions:

1) the relative unity of the conditions for the formation and transformation of reservoir rocks and seals, OM, traps, oil and gas fields;

2) availability of single main sources of hydrocarbons;

3) relative hydrodynamic isolation of the oil and gas complex and the hydrodynamic relationship of its permeable part;

4) a certain degree of tectonic dislocation, which determines the formation of structural traps and the distribution of oil and gas deposits along the section and area;

5) certain paleotectonic and paleogeographic conditions of formation, on which the development of traps of the lithological and stratigraphic type depends.

These properties make it possible to use a single methodology for prospecting and exploration work within the boundaries of the identified oil and gas complexes and to widely apply geological analogies.

Remember

What minerals do you know?

There are fuel minerals - peat, coal, oil (sedimentary origin).

Ore minerals - ores of non-ferrous and ferrous metals (magmatic and metamorphic origin).

Non-metallic minerals - mining and chemical raw materials, Construction Materials, mineral water, therapeutic mud.

This I know

1. What is land resources? Mineral resources?

Land resources - a territory suitable for the resettlement of people and the placement of objects of their economic activity.

Mineral resources - natural substances of the earth's crust, suitable for obtaining energy, raw materials and materials.

2. What is the importance of mineral resources in human life?

Mineral resources are the basis of modern economy. From them receive fuel, chemical raw materials, metals. The welfare of the country most often depends on the quantity and quality of mineral resources.

3. What is the reason for the placement of minerals?

The placement of minerals is determined by their origin.

4. What patterns can be established in the placement of minerals?

Deposits of ores of ferrous and nonferrous metals, gold, and diamonds are confined to outcrops of the crystalline basement of ancient platforms. Oil, coal, and natural gas deposits are confined to thick sedimentary covers of platforms, foothill troughs, and shelf zones. Non-ferrous metal ores are also found in folded areas.

5. Where are the main oil and gas fields located?

The main oil and gas bearing areas are concentrated in the shelf zones - the North Sea, the Caspian Sea, the Gulf of Mexico, the Caribbean Sea; sedimentary covers of platforms - Western Siberia; foothill troughs - the Andes and the Ural Mountains.

7. Choose the correct answer. Minerals of sedimentary origin are confined mainly to: a) platform shields; b) to platform plates; c) to folded areas of ancient age.

B) to platform plates

This I can

8. Using the scheme "Education rocks”(See Fig. 24), explain what transformations occur with rocks as a result of the circulation of substances.

As a result of the circulation of substances, there is a transformation of some minerals into others. Igneous rocks can be considered primary. They were formed from magma erupted onto the surface. Under the influence various factors igneous rocks are destroyed. Debris particles are transported and deposited elsewhere. This is how sedimentary rocks are formed. In folded areas, rocks are crushed into folds. At the same time, some of them are immersed in depth. Under the influence of high temperatures and pressure, they are melted down and turn into metamorphic rocks. After the destruction of metamorphic rocks, sedimentary rocks are formed again.

It's interesting to me

9. It is believed that in the Stone Age almost the only mineral was flint, from which arrowheads, axes, spears, and axes were made. How do you think people's ideas about the diversity of minerals have changed over time?

People's ideas about the diversity of minerals have changed very quickly since the Stone Age. After flint, people very quickly found copper. The copper age has arrived. However, the copper products for use were fragile and soft. A little more time passed, and people got acquainted with a new metal - tin. Tin - very brittle metal. We can assume that it happened that the pieces of copper and pieces of tin fell into the fire or bonfire, where they melted and mixed. The result is an alloy that combines the best qualities of both tin and copper. This is how bronze was found. The Bronze Age period is the time from the end of the fourth to the beginning of the first millennium BC.

As we all know, iron in its pure form is not found on Earth - it must be mined from ore. To do this, the ore must be heated to a very high temperature, and only after that iron can be smelted from it.

The fact that centuries were named after minerals speaks of their great importance. The use of ever new minerals opens up new opportunities for man and can radically change the entire economy.

A lot of time has passed since then and now people use great amount mineral resources for different purposes. Exploration and extraction of mineral resources is an urgent task for the economy at all times.

10. Well-known domestic geologist E.A. Fersman wrote: "I want to extract raw, at first glance, unsightly material from the bowels of the Earth ... and make it accessible to human contemplation and understanding." Expand the meaning of these words.

Mineral resources, when extracted from them from the earth's crust, most often look far from the appearance of the product that is obtained from it. They really are ugly stuff. But at right approach, processing of this material can extract a lot of value for a person. Fersman spoke about the value of the bowels of the Earth, about the need to study them and a reasonable approach to this.

Oil It is called a flammable oily liquid of red-brown or black color with a specific odor. Oil is one of the most important minerals on Earth, as the most commonly used fuels are obtained from it. Usually oil is formed together with another, no less important - natural gas. Therefore, very often these two types of minerals are mined in the same place. Oil can occur at a depth of several tens of meters to 6 kilometers, but most often it is located at a depth of 1-3 km. Natural gas is a gas mixture formed during the decomposition of organic substances. It lies in the bowels of the earth in gaseous state in the form of separate accumulations, in the form of an oil cap of oil and gas fields, as well as in a dissolved state (in oil and in water).

The most famous oil and gas fields in Russia:

Urengoy natural gas field. This is the world's second largest gas field in terms of reservoir reserves. Gas volumes here exceed 10 trillion cubic meters. This field is located in the Yamalo-Nenets autonomous region Tyumen region of Russia, just south of the Arctic Circle. The name of the deposit was given by the name of the nearby village of Urengoy. After the development of the deposit began, a whole working city of Novy Urengoy grew up here. The field was discovered in 1966, and gas production began in 1978.

How oil is produced (photo by Maxim Yuryevich Kalinkin)

Tuymazinskoye oil field. This field is located in the Republic of Bashkiria, near the city of Tuimazy. The deposit was discovered in 1937. Oil-bearing layers are located at a depth of 1-1.7 km. The development of the field began in 1944. The Tuymazinskoye field is one of the five largest fields in the world in terms of the amount of oil. The size of the deposit is 40 by 20 kilometers. Thanks to latest method the bulk of the recoverable reserves were produced in 20 years. Twice as much oil has been extracted from the Devonian strata as could be recovered by conventional methods. However, the reserves are so large that mining continues to this day.

Nakhodka gas field. This natural gas field is located in the Bolshekhetskaya depression in the Yamalo-Nenets Autonomous Okrug. The reserves of the field are estimated at 275.3 billion m 3 of gas. Although the field was discovered quite a long time ago (in 1974), its development began only in 2004.

Shtokman gas condensate field. One of the largest deposits in the world, discovered in 1988. It is located in the central part of the shelf approximately 600 km northeast of Murmansk. Gas reserves are currently estimated at 3.7 trillion m2 of gas. Gas production has not yet begun here, since the significant depth of the mineral and the difficult conditions of development require significant costs and high-tech equipment.

Kovykta field(Kovykta). A natural gas field located in the north of the Irkutsk region, 450 km northeast of Irkutsk. The deposit is located on a high plateau covered with dark coniferous. It dominates in some part of the territory. In addition, this area is complicated by numerous canyons. Climatic conditions in the area of ​​the deposit are also quite severe. Natural gas reserves are estimated at 1.9 trillion cubic meters of gas and 115 million tons of liquid gas condensate.

Vankor field oil and gas field. Deposit located in the north Krasnoyarsk Territory. Includes the Vankorsky and Severo-Vankorsky sections. The deposit was discovered in 1991. Oil reserves exceed 260 million tons, and gas - about 90 billion m2. The development of the deposit is to start in 2008. It is planned to drill 266 wells here, and the delivery will be carried out through the Eastern oil pipeline.

Shtokman field

Angaro-Lenskoye gas field. A large natural gas field located in the Irkutsk region. Named after the names of large - and Angara, located nearby. The deposit was discovered at the beginning of the 21st century. According to preliminary estimates, natural gas reserves are more than 1.2 trillion m2.

Samotlor oil field (Samotlor). It is the largest in Russia and one of the largest in the world. oil fields is located in the Khanty-Mansiysk Autonomous Okrug, in the Nizhnevartovsk region near Samotlor. According to experts, oil reserves here amount to 2.7 billion tons. They lie at a depth of 1.6-2.4 km. The deposit was discovered in 1965. Basically, the field was developed in the 80s of the last century. To date, about 2.3 billion tons have already been mined.

Ety-Purovskoye oil field. This is an oil field located in the Yamal-Nenets Autonomous Okrug, near the city of Noyabrsk. Opened in 1982, development began only in 2003. Oil reserves are about 40 million tons.

Verkh-Tarskoye oil field. Located in the north Novosibirsk region. Oil reserves are about 68 million tons. One of the disadvantages of the field is the lack of necessary communications. The oil produced at this field is distinguished by a small amount of impurities. The deposit was discovered in 1970, development began in 2000.

Number of deposits oil and gas in Russia much bigger. Some of them, discovered in the last century, have already been developed, while the development of others, relatively recently discovered, has not even begun (for example, the Vankor field). In addition, there is reason to believe that not all deposits in the country have been discovered.

DEPOSITS AND DEPOSITS OF OIL AND GAS

AA Bakirov subdivides oil and gas accumulations into two categories: local and regional. He refers to the local

1) deposits of oil and gas;

2) oil and gas fields.

A. A. Bakirov and other researchers subdivide regional accumulations of oil and gas into:

1) oil and gas accumulation zones;

2) oil and gas fields;

3) oil-bearing provinces or belts.

The classification of deposits for the purposes of prospecting and exploration is based on the following features:

1) the ratio of gas, oil and water in them;

trap shape.

Classification of deposits by phase composition

An oil and gas deposit is a natural local (single) accumulation of oil and gas in a trap. A deposit is formed in that part of the reservoir in which an equilibrium is established between the forces that make oil and gas move in a natural reservoir, and the forces that prevent it.

Gas, oil and water are located in the reservoir zonal:

q gas, as the lightest, occupies the roof part of the natural reservoir, under the cover;

q below the pore space is filled with oil,

q even lower - with water.

According to the predominance of the liquid phase over the gas (or vice versa), deposits are divided into:

q single-phase - oil, gas, gas condensate

q two-phase - gas and oil, oil and gas.

According to the phase relationships of the hydrocarbons contained in the deposit, 6 types of accumulations are distinguished:

gas,

gas condensate,

oil and gas condensate,

oil and gas,

gas and oil,

oil.

gas deposit(Fig. 7.1) contains mainly methane and its homologues (ethane, propane, etc.).

Rice. 7.1. Scheme of gas deposits

In a number of regions, gas deposits, in addition to hydrocarbon components, contain hydrogen sulfide, carbon dioxide, nitrogen, helium, as well as small amounts of inert gases (argon, neon, krypton).

When visually inspecting the core of the productive horizons of oil fields, one can see smudges and inclusions of oil in the pores and cracks of the rock. In pure gas fields, the core from productive strata does not differ from samples taken from the overlying or underlying deposits. They can be distinguished only immediately after lifting from the well by the smell of gasoline, which quickly disappears and after a short period of time the core no longer carries any traces of hydrocarbons. In this regard, the drilling of wells in gas-bearing areas must be under constant geological control and must be accompanied by gas logging.

Gas condensate deposits(Fig. 7.2) are accumulations of fatty gas and heavier hydrocarbons dissolved in it (C 5 H 12 and above).

Rice. 7.2. Scheme of gas condensate deposit

Their concentration at a high deposit height increases down the section of the productive stratum.

Examples include such largest gas condensate fields in terms of reserves as Astrakhanskoye, Vuktylskoye, Shurtanskoye, Zapadno-Krestishinskoye, Yablonevskoye. The gas fractions of these deposits, in addition to hydrocarbons, also contain the most valuable associated components. Thus, in addition to methane (40–50%) and heavy hydrocarbons (10–13%), the gas composition of the Astrakhan field contains 22–23% hydrogen sulfide and 20–25% carbon dioxide. The content of stable condensate in the hydrocarbon gas of the same Astrakhan field, according to available data, varies over the area from 130 to 350 cm 3 /m 3 .

When calculating reserves, along with hydrocarbon gas and condensate, these components must also be taken into account.

Oil and gas condensate deposits(Fig. 7.3) differ from the previous ones by the presence of liquid hydrocarbons in the lower part of the productive stratum, which are light oil.

Rice. 7.3. Scheme of oil and gas condensate deposit

An example is the Karachaganak field. The height of the massive deposit in this field exceeds 1.5 km. From top to bottom, the amount of condensate gradually increases and about 200 m of the lower part of the productive stratum is filled with oil.

Oil and gas deposit contains an accumulation of gas underlain by oil (over the entire area or in part), the geological reserves of which do not exceed half of the total hydrocarbon reserves of the deposit as a whole. The predominant gas is usually fatty, i.e. in addition to methane, it contains a certain amount of heavy hydrocarbons.

Depending on the type of reservoir and the nature of the filling of the trap, the oil part may look like either an oil rim or an oil cushion (Fig. 7.4).

Rice. 7.4. Diagram of an oil and gas deposit

If a deposit is found in a reservoir , then the oil part of the deposit will be located along the periphery of the trap, and in this case there are continuous external and internal oil-bearing contours and external and internal gas-bearing contours. Within the inner gas-bearing contour, the wells penetrate the pure gas part of the reservoir, between the outer and inner gas-bearing contours – the gas-oil part, and outside the outer gas-bearing contour – the purely oil or water-oil part of the deposit.

Due to geological (reservoir replacement) or hydrodynamic (regional water head) reasons, an oil rim can be shifted towards better reservoirs or lower water pressure and appear as a one-sided rim .

In a massive and incomplete reservoir, the oil part in the form of an oil cushion is located throughout the entire part of the trap or, as in the previous case, can be partially shifted to its periphery .

The formation of the rim can occur due to the displacement of oil by the gas that entered the trap after the formation of the oil deposit. An indicator of this origin of the deposit is the presence of residual, associated oil throughout the section of the productive stratum. The presence of an oil rim may also be due to the flow of oil into the trap after the formation of a gas deposit. In this case, no traces of oil are found in the gas-saturated part of the formation.

Different ratios of the gas and oil parts of the deposit are clearly seen in the Urengoy field as an example. This field in the Cenomanian deposits contains a purely gas reservoir, in the Lower Cretaceous gas condensate, oil and gas condensate deposits, and in the Callovian-Oxfordian - oil. In some productive horizons, oil underlies the entire gas condensate reservoir. In others, the oil rim is displaced to the northern periclinal part of the structure.

Oil and gas deposit is an oil accumulation with a gas cap (Fig. 7.5) .

Rice. 7.5. Oil and gas deposit

Geological oil reserves exceed half of the total hydrocarbon reserves of the deposit. This type of deposits is found in many oil and gas provinces of the world.

The formation of a gas cap can occur either due to the release of gas from oil due to the rise of the trap at the last stages of its development and, consequently, a decrease in reservoir pressure, or as a result of gas inflow after the formation of an oil deposit.

oil deposit contains an accumulation of oil with gas dissolved in it (Fig. 7.6) .

Rice. 7.6. oil deposit

The phase relations of hydrocarbons in deposits of all types, except for purely gas ones, are determined by the thermobaric conditions of occurrence. In the process of development, these conditions change, the balance of the natural system is disturbed. So, in the process of developing an oil deposit in a natural regime, the reservoir pressure decreases, and if it becomes lower than the saturation pressure, then free gas is released in the reservoir and a gas cap is formed; in the gas condensate reservoir. on the contrary, liquid hydrocarbons precipitate. In other words, when the reservoir is affected, its equilibrium state changes and at some stage it passes into a new quality.

The transition of the natural system under consideration to a new qualitative state depends, on the one hand, on the nature of its interrelations with natural systems higher hierarchical levels (regional background), on the other hand, on the degree of technogenic impact on it.

By complexity geological structure The productive horizons of deposits are divided into two main groups:

A) simple structure - productive horizons are characterized by a relative consistency of lithological composition, reservoir properties and productivity throughout the entire volume of the deposit;

b) complex structure - divided by tectonic disturbances into a number of isolated blocks and zones, or deposits with a variable nature of productive horizons.

The Romashkinskoye field is a typical multilayer platform type field with proven oil and bitumen content in a wide range of sedimentary sequences from Givetian to Kazan deposits. The oil content of the sedimentary section was established in 22 Devonian and Carboniferous horizons, of which industrial inflows were obtained from 18 horizons. However, their industrial significance is quite different. The main object of exploitation are deposits of terrigenous Devonian oil (Pashiysky and Kynovsky horizons). The reservoirs of the Pashiysky (layer D 1) and Timansky (layer D 0) horizons form the largest multi-layer reservoir of the dome type with an oil-bearing area of ​​4255 km 2, as follows from Appendix B. The Tournaisian deposits are associated with individual domes and are massive. Along with reservoir vaults, lithological deposits are also common. All deposits are combined into 12 enlarged deposits. In the Middle Carboniferous deposits, the largest deposit (1.5x20 km) was discovered in the southwestern part of the deposit.

Of the locally oil-bearing, the most significant are terrigenous deposits of the Givetian Stage and carbonate rocks of the Semiluksky, Petinsky horizons of the Frasnian Stage, the Yelets horizon, the Zavolzhsky suprahorizon of the Famennian Stage, as well as the Upinsky, Malevsky and Aleksinsky horizons of the Lower Carboniferous.

The terrigenous Devonian accounts for 83.5% of the explored reserves. The next in terms of industrial importance are terrigenous deposits of the Lower Carboniferous, containing 9.6% of the proven reserves of the deposit. Devonian and Carboniferous carbonate deposits contain 5.9% of the proven reserves of the deposit. The deposits of the Upper Tournaisian substage of the Lower Carboniferous and the Verei-Bashkirian deposits of the Middle Carboniferous are of major commercial importance here, to which 5.4% of the explored reserves are associated. The remaining horizons are of less commercial interest due to local oil content and small size. A total of 421 deposits have been identified at the field, of which 41 are in clastic Devonian deposits, 162 are in terrigenous deposits of the Carboniferous, 87 are in carbonate beds of the Upper Tournaisian substage, 3 are in the Middle Carboniferous, and 128 are in other horizons.

At the field, as well as within the eastern part of Tatarstan as a whole, taking into account the nature of the oil content and the degree of consistency of reservoirs of productive deposits along the section and strike, their isolation from each other, seven oil and gas bearing and bitumen-containing complexes are distinguished: 1 - Devonian terrigenous strata; 2-carbonate Devonian and carbonate-terrigenous Lower Carboniferous; 3 - carbonate Lower and carbonate-terrigenous Middle Carboniferous; 4 - carbonate Middle and Upper Carboniferous, carbonate Lower Permian; 5 - terrigenous Ufa sequence; 6-7 - terrigenous-carbonate strata of the Upper Kazanian substage. On the territory of the Romashkinskoye multilayer field, the main oil-bearing complexes are the lower ones, and the upper complexes are bituminous.

Deposits of the Pashiy horizon (D I) and layer D 0 of the Kynov horizon, from which the most significant commercial oil inflows were obtained, form the largest deposit in the section of the sedimentary strata of the Romashkinskoye field. This is a multilayer dome type deposit, structurally confined to a vast flat uplift with the most elevated areas in the area of ​​the Minnibaevskaya and Abdrakhmanovskaya areas and having a number of independent structures separated by depressions that are insignificant in amplitude. The average mark of the water-oil contact (WOC) for the field is minus 1490m. From the crested sections in all directions, a gentle descent of the layers to the wings is observed, mainly with insignificant angles of incidence up to the marks of minus 1490 - minus 1500m. In the central part of the field, all layers of the D I horizon are oil-bearing, but towards the periphery their number decreases, as does the oil-bearing level of the horizon, as follows from Appendix D.

Deposits of the reservoir D 0 are mainly oil-bearing in the northwestern and northern parts of the field, and in the rest of the territory the reservoir is represented by a non-reservoir. In general, the considered deposits can be considered as parts of a single Pashiysko-Kynovskaya deposit.

The main commercial accumulations of oil of the Upper Tournaisian substage are confined to the deposits of the Kizelovsky horizon (layer B IV) within relatively small local structures, mainly of the third order. Oil shows in the Cherepet deposits are noted only in some highly elevated sections of the structures. In total, about 170 deposits have been identified, which in their structure belong to the massive type and are controlled by dome-shaped (within the East Suleevskaya, Aznakaevskaya, North Almetyevskaya terraces) and brachianticlinal (within the Minnibaevskaya and Chishminsky terraces) uplifts with an amplitude of up to 15-45 m. Numerous deposits, like the Bobrikov deposits, are combined into 21 regionally integrated oil and gas production departments, as follows from Appendix Appendix E. The size of the deposits is on average small (0.5 to 2 km), but a number of them (201, 221, 224) are large (length from 6 to 13 km, width from 3 to 7 km). When testing individual wells on deposits, inflows from 0.05 to 35.6 tons / day were obtained. When studying the materials of geophysical surveys, the position of the water-oil contact within the deposits was determined and it was found that its surface plunges in a northerly direction from the absolute mark of minus 826 m to minus 900 m.

An analysis of the lithological and petrographic features and reservoir characteristics of the rocks of the Upper Tournaisian substage showed that the following types of carbonates are typical for the deposits of the Romashkino deposit: 1 - lumpy limestones, 2 - clot-detrital limestones, 3 - slurry-detrital limestones, 4 - foraminiferal-clotty limestones, 5 - dolomites and dolomitic limestones.

These types differ from each other in terms of sedimentation, the development and direction of secondary processes, and reservoir properties. Among them, according to the nature of oil saturation, oil-saturated, slightly oil-saturated, uneven oil-saturated, saturated with oxidized oil and light gray varieties are distinguished.

Lumpy limestones are composed of lumps of microgranular calcite and large plant, less frequently faunal, detritus. The size of the lumps varies from 0.1 to 0.8 mm, the size of the detritus - from 0.06 to 1 mm. The reservoir properties of this difference are the highest. The average porosity is 14.2%, the permeability is 0.063 µm 2 , and the residual water saturation is 26.4%. The structure of the pore space is simple, reminiscent of the structure of pores and channels in sandstones. The pores are interformal, large (0.45 mm), numerous, their shape is often isometric. The channel system is well designed. The channels are relatively short and wide (0.01-0.15 mm). The porosity of this difference is primary, but the pore volume increased by dissolution processes - traces of leaching at high magnification are visible on most of the large pores. Lumpy limestones are intensively oil-saturated.

Clotty-detrital limestones are the most common variety. They are composed of detritus, mainly algal, clots and lumps of microgranular calcite. The cement of this difference is primary microgranular calcite or secondary, inequigranular calcite. The structure of the pore space is complex: the pores are interformal, intraformal, the channels are much more tortuous, longer and narrower than in lumpy limestones. The average porosity is 11.3%, the permeability is 0.006 µm 2 , and the residual water saturation is 38.7%.

Slurry-detrital limestones have reservoir properties below standard values. Oil saturation is rarely observed in them in the form of weak spots. This difference is composed of fine algal detritus and sludge. The cement is abundant, represented by microgranular calcite, the type of cementation is basal, porous-basal. Clay material is present in a dispersed state in the rock; its total content in individual layers reaches 10%. Pores in slurry-detrital limestones are mostly very small (0.01-0.03 mm) intergranular; pores up to 0.1 mm in size are rare, they are mostly isolated. The porosity of this difference is 7.8%, the permeability is 0.0003 µm 2 , and the residual water saturation is 63%.

Foraminiferal-clotty limestones are highly calcitized rocks composed of clots, less often lumps of microgranular calcite and foraminiferal shells. The cement is basal. The pores are rare, secondary, located locally. The porosity of the foraminiferal clotted limestones is 5%, the permeability is 0.00005 µm 2 , and the residual water saturation is 80%. Oil saturation was not found in these varieties, all samples are light gray, very dense.

Dolomites and dolomitic limestones are very rare in the Upper Tournaisian substage, in the form of single thin layers. Oil saturation was not noted in them. The porosity is 6.6%, the permeability is 0.00013 µm 2 .

The general physical and lithological characteristics of the reservoirs of the Kizelovsky horizon by deposits can be represented as follows.

The top part of the Tournaisian Stage is almost everywhere represented by compacted rocks (slurry-detrital limestones and calcitized foraminiferal-clotted limestones). The reservoir properties are below standard: porosity is 7%, permeability is 0.0003 µm 2 , residual water saturation is 65%. The thickness of the roofing part is 0.2-0.5 m and does not exceed 1.5 m.

The main volume of the Kizelovsky horizon is the B IV layer. It is dominated by lumpy and clot-detrital limestone varieties. The slurry-detrital difference is 15.8%, foraminiferal-clotty - 1.9%, dolomites - 0.1%. Slurry-detrital limestones occur in the form of thin, unseasoned interlayers, foraminiferal-clotty limestones occur in the form of single lenses, nodules. The porosity of this formation as a whole is 11.9%, the permeability is 0.029 µm 2 , and the residual water saturation is 38.9%.

The rock unit at the base of the Kizelovsky horizon (benchmark C-4) is represented by sludge-detrital (45.4%) and clot-detrital (43.2%) limestones (no intensely oil-saturated varieties were found in the latter). About 10% of the volume is impermeable highly calcitized varieties, 1.7% is lumpy limestone, which in this unit is saturated with oxidized oil or weakly oil saturated. In isolated cases, water-bearing lumpy limestones are found. In general, the porosity of the considered pack is 8%, the permeability is 0.001 µm 2 , and the residual water saturation is 58%.

For a detailed study of the structure of the Kizelovsky and Cherepetsky deposits, we used data from wells in which these section intervals were completed with 100% large-diameter core sampling. The observed intercalation of carbonate varieties with a thickness of 10-20 cm and up to 1 m confirms the significant heterogeneity of the section of the Upper Tournaisian substage, mainly due to sedimentation processes. Determined that top part Kizelovsky horizon has the best reservoir characteristics and is represented by interbedding of clotted-detrital and lumpy limestones, with the latter predominating. The top of the Kizelovsky horizon and the underlying member Rp C-4 consist almost 100% of slurry-detrital limestones. Layer BIII is represented mainly by intercalation of clot-detrital and sludge-detrital limestones. The permeability also changes significantly over the intervals. It can also be noted that intense oil saturation occurs in all lumpy limestones and in some clot-detrital ones. Oil is absent in all foraminiferal-clotty and dolomitized limestones.

It has been established that in carbonate rocks in general for the Upper Tournaisian substage, in terms of capacitive-filtration properties, taking into account their oil saturation, 4 groups of reservoirs are quite clearly distinguished: I - high permeability, II - medium permeability, III - low permeability, IV - non-reservoirs. Group I includes lumpy limestones, intensely oil-saturated. Group II includes clot-detrital, uniformly oil-saturated limestones. Group III includes clot-detrital weakly and unevenly oil-saturated limestones. Non-reservoirs (Group IV) are oil-free dense clotted-detrital varieties, slurry-detrital and foraminiferal-clotty limestones, and dolomites.

In the oil-saturated part of the deposits, highly permeable reservoirs of group I are noted with an average porosity of 14.2%, permeability of 0.063 µm 2 , and residual water saturation of 26.4%. In general, in the Upper Tournaisian formations of the Romashkinskoye field, the proportion of reservoirs with high and medium permeability is 73%. Low-permeable reservoirs (III group) make up 10% of the reservoir volume; oil in these rocks at this stage of development is not extracted. Non-collectors make up 16.8%.

The volume of high-amplitude deposits of the Romashkinskoye field includes deposits not only of the Kizelovsky horizon, but also of the Cherepetsky horizon. The Cherepet deposits are represented by the same structural and genetic differences as the Kizel deposits, but due to some reduction in the size of the rock constituent elements, more abundant cement in clot-detrital varieties, their reservoir properties are lower. The reservoir properties of the deposits were determined both from core data and from the results of well logging. The permeability determined from the core averaged 0.030 µm 2 . The results of determining porosity and permeability from sufficiently representative information both for core and geophysics can be considered quite comparable. The average porosity is about 12.0% (it can reach 20.0%), and the oil saturation is about 72.0% (it can reach 90.0%). When calculating reserves, based on a detailed study of various types of dependencies, the following lower standard limits of parameters for reservoir rocks were adopted: porosity - 9.8%, permeability - 0.0015 µm 2 and oil saturation - 54.0%.

When studying the characteristics of the heterogeneity of deposits, it was found that the share of reservoirs is on average about 50%, and a sufficiently high degree of heterogeneity of deposits along the section is evidenced by the value of the coefficient of dissection, which can reach 2-3 or more for individual deposits.

Industrial accumulations of oil in terrigenous deposits of the Lower Carboniferous are confined to the deposits of the Radaevsky, Bobrikov and lower part of the Tula horizons. The most common deposits are in the sandstones of the Radaevsko-Bobrikovsky and the lower part of the Tula horizon. In total, about 100 deposits have been identified, which have different sizes and oil levels. They are controlled by individual local uplifts or by a group of structures. The discontinuous structure and heterogeneity of reservoir layers, due to changes in the lithofacies composition of deposits, along with structural factors, cause a very complex configuration of deposits in plan with replacement areas in the most various parts local structure. Therefore, along with reservoir-arched deposits, lithologically complicated deposits are also widespread.

Numerous deposits (more than 80) of the field are currently combined into 37 oil and gas production departments enlarged by belonging to the territories, as follows from Appendix E. The deposits are characterized by a wide range in size (length from 2 to 35 km, width from 1 to 21 km) and height (from 3 to 47 m).

The largest of them are deposits 1, 5, 8, 12 and 31. The clay-carbonate stratum of the Tula horizon with a thickness of 8-12 m serves as a cover for the deposits. The analysis of data on wells that have opened water-oil contact in the deposits of the Bobrikovsky deposits indicates the presence of a regional subsidence of its surface from the southwest to the north and east from the mark of minus 823 m to minus 946 m. ​​Well flow rates average 15 tons per day.

The productive horizons of the sedimentary strata of the Romashkinskoye field are characterized by a significant variety of occurrence features in terms of area and section, as well as lithological and petrographic composition, reservoir and filtration properties, and saturation of the constituent rocks, as shown in Table 1.

Table 1-Characteristics of productive deposits of the sedimentary strata of the Romashkinskoye field

It should be noted, along with the general characteristics of these horizons, the features of the geological structure of the Pashiysko-Kynov deposits are considered in most detail.

The most studied are the main production facilities of the Romashkinskoye field, confined to productive terrigenous deposits of the Pashiy horizon (D I) and the D 0 formation of the Kynov horizon. The Pashiysky horizon (D I) is a multilayer object represented by interbedding of sandy, silty, mudstone varieties of terrigenous rocks. characteristic feature deposits of the Pashian horizon as a whole is the frequent change of sandy-silty rocks by clayey varieties both in the section and in the area. For the main benchmarks, which are regionally consistent and used to correlate sections, "clays" and "upper limestone" are taken. The lower boundary of the horizon is drawn along the top of the argillite unit (benchmark of "clay"), which overlaps the layer D II. The upper boundary is drawn along the base of the carbonate unit (benchmark "upper limestone"). In addition, for a more confident division of the horizon into the Upper and Lower Pashian units, an additional benchmark "argillite" was identified, which lies above the top of the layer "c". In general, the use of these benchmarks, well-aged in terms of area, makes it possible to fairly confidently compare the sections of the D I horizon for wells located in different parts of the field. For this purpose, summary statistical sections are successfully used. Currently, a scheme has been adopted at the field with the allocation within the D I horizon of 4 layers of the Upper Pashiy (layers "a", "b 1", "b 2", "b 3") and 4 layers of the Lower Pashiy (layers "c", "g 1", "g 2 + 3" and "d") packs, which differ in the nature of occurrence in area and section. In general, the layers of the “d” pack are distinguished by the areal structure throughout the entire territory of the deposit, “a” - in the north and northeast, “c” - in the west of the deposit. For other layers of the horizon, lenticularity, banding (mainly meridional direction) is predominant.

In the interval of layer "a", the thickness of which reaches 5-6 m, up to two or three interlayers can be distinguished. The largest number mergers with the underlying layers "b" are observed within the Aznakaevsky areas. According to the nature of the distribution of the reservoir "a", two zones are distinguished: the northeastern one with areal distribution and the greatest thickness of the reservoirs and the southwestern one, where the reservoirs have a strip-like and lenticular structure.

Within the zonal interval "b", three layers are distinguished, indexed as layers "b 1", "b 2", "b 3" and the most developed in the Aznakaevskaya area. The most frequent are the mergers of the layers "b 1" and "b 2". The thickness of the interlayers is mainly 2–3 m, and when they merge, it reaches 10–12 m.

Layer "c" stands out in the form of an interlayer of sandy-silty rocks 3-4 m thick, occurring between interlayers of mudstones, the upper of which is an additional benchmark. The formation has the greatest areal distribution in the Minnibaevskaya area, and in other areas of the deposit, strip-like and lenticular forms of occurrence predominate.

Within the zonal interval of the “g” reservoir, interlayers 4–6 m thick are distinguished, but their numerous mergers are more characteristic, and then the reservoir thickness can reach 10–12 m. As already noted, the reservoir mainly has an areal distribution of reservoirs.

Layer "d" is the lowest of the layers of the horizon. It is represented mainly by one interlayer 1–6 m thick and lies between mudstones of the Mullinsky horizon, which are rather consistent in area, and a layer of silty-argillaceous rocks, often eroded, as a result of which layer “e” merges with the overlying layer “g”. The reservoir has areal distribution only in certain areas of the deposit, and in general it is characterized by a lenticular and strip-like form of occurrence.

It should be noted that in some areas of the field, three or four or more horizon layers can be hydrodynamically connected along the section due to the presence of their confluence zones, and in this case, the reservoir thickness can reach 20-25 m.

In general, the study of the structural features of the layers of the D I horizon indicates the presence of significant geological heterogeneity of the deposits both along the section and over the area of ​​the Romashkinskoye field. This, for example, is evidenced by the changes in the average values ​​of the total (from 28.2 to 46.3 m) and oil-saturated (from 3.7 to 16.6 m) thicknesses, as well as porosity values (from 0.188 to 0.207), permeability (from 0.339 to 0.666 microns 2) and oil saturation (0.691 to 0.849), net-to-gross ratios (K pes) - from 0.259 to 0.520 and dissection (K p) - from 1.7 to 5.3 . Naturally, a wider range of changes in the parameters under consideration is observed for individual reservoirs and groups of reservoirs, the selection criteria for which are discussed below. This is confirmed by the data given for all areas of the Romashkinskoye field in Table 2. Without considering in detail the nature of the change in all the parameters given in it, it should only be emphasized that the most significant differences between the reservoirs and the distinguished groups of reservoirs are in terms of porosity, permeability and oil saturation, as well as in thickness between the layers of the upper and lower Pashian packs of the D I horizon.

The lithological characteristics of the reservoirs of the Pashian horizon are similar for all sand-silt packs. They are characterized by monomineralism. The clastic material is dominated by quartz (about 90%) with a small admixture of feldspar grains, muscovite flakes, and stable minerals. The predominant among authigenic minerals are secondary quartz, pyrite, calcite, siderite, dolomite, less often - phosphorite, kaolinite, chlorite, anatase. In general, one can note a somewhat higher clay content and increased carbonate content of the deposits of the Upper Pashian subhorizon compared to the Lower Pashian.

Table 2-Average values ​​of thicknesses, reservoir properties and parameters of heterogeneity of deposits of the DI horizon over the areas of the Romashkinskoye field

Indicators
Pashian horizon	kynovsky horizon	Lebedyansky horizon	Trans-Volga horizon	tournaisian	bobrikovskiy horizon	Serpukhov- stage	Bashkir	Vereian horizon
Saturation pressure, MPa
GOR at differential
Rational degassing
in working conditions, m 3 / t
P 1 \u003d 0.5 MPa T 1 \u003d 9 0 C
P 2 \u003d 0.1 MPa T 2 \u003d 9 0 C
Total GOR, m 3 / t
Density, kg / m 3
Viscosity, mPa.s
Volumetric coefficient at
differential degassing
research institutes under working conditions, shares of units.
Density of degassed oil
ti during diffusion, kg / m 3

Table 4 - Physical and chemical properties and fractional composition of degassed oil

Table 5 - Sulfur content for the objects of the Romashkinskoye deposit