By type natural reservoir deposits (traps) are distinguished: stratified, massive and lithologically limited on all sides (I.O. Brod).

In the deposits reservoir type, hydrocarbon fluids are controlled by the roof and bottom of a specific reservoir layer (most often a sand pack), which is bounded above and below by fluid-confining rocks; the fluid moves along the layer (laterally).

Reservoir-type deposits are divided into full-layer and incomplete-layer (waterfloating). The former have external and internal contours of gas (oil) content, the latter - only the external. In plan they most often have an isometric and elongated shape.

In the deposits massive type, hydrocarbon fluids are retained only by the rocks of the seal; the formation fluid moves in all directions. A massive deposit is characterized only by external contours of gas and oil content. Massive deposits are often confined to carbonate reservoirs and are most often circular in plan.

Lithologically limited on all sides the deposits are surrounded by impermeable rocks, formation fluid movement does not occur, and the external and internal contours of gas (oil) potential in plan have irregular outlines. Deposits are often confined to clastic and unconventional reservoirs, to lenticular and non-anticlinal traps.

Depending on the productivity of production wells A.E. Kontorovich developed a classification based on working flow rates (Table 4). It should be noted that, for example, in the USA the average oil well flow rate is 2-5 tons/day. In the Russian Federation, there is a disdainful attitude towards small deposits and a pursuit only of large economic benefits.

Table 4 – Classification of deposits according to operating flow rates (according to A.E. Kontorovich)

By difficulties geological structure deposits are highlighted:

simple structure - single-phase deposits associated with undisturbed or slightly disturbed structures, productive layers are characterized by consistency of thickness and reservoir properties in area and section;

complex structure - single- and two-phase deposits, characterized by unconsistency in the thickness and reservoir properties of productive strata in area and section, or the presence of lithological replacement of reservoirs with impermeable rocks, or tectonic disturbances;

very complex structure- single- and two-phase deposits, characterized both by the presence of lithological replacements or tectonic disturbances, and by irregular thicknesses and reservoir properties of productive strata.

According to the initial phase state and composition of the main hydrocarbon compounds in the depths of the deposits are divided into single-phase and two-phase.

Single-phase deposits include:

a) oil deposits confined to reservoir layers containing oil saturated to varying degrees with gas;

b) gas or gas condensate deposits confined to reservoir layers containing gas or gas with hydrocarbon condensate.

Two-phase deposits include deposits confined to reservoir strata containing oil with dissolved gas and free gas above the oil (oil reservoir with a gas cap or gas reservoir with an oil rim). In some cases, the free gas of such deposits may contain hydrocarbon condensate. Based on the ratio of the volume of the oil-saturated part of the deposit to the volume of the entire deposit, two-phase deposits are divided into:

a) oil with a gas or gas condensate cap (oil more than 0.75);

b) gas or gas condensate-oil (oil from 0.50 to 0.75);

c) oil and gas or oil and gas condensate (oil from 0.25 to 0.50);

d) gas or gas condensate with an oil rim (oil less than 0.25).

Most of the classifications of oil and gas deposits developed to date are based on the genesis and structure of the traps and natural reservoirs containing the deposits. However, these signs primarily characterize not the oil and gas deposits themselves, but natural reservoirs or elements of the earth’s crust containing them.

Deposit is a natural local accumulation of oil or gas that occupies part (a trap) of a natural reservoir. If the development of a deposit is profitable, it is called an industrial deposit.

In most cases, the formation of oil and gas deposits occurs according to anticlinal-gravity model, described in 1859 by M. Drake in the USA. According to this model, oil and gas, being less dense, are forced out of the gas-oil-water fluid into the upper parts of the reservoirs and are localized in traps, which are usually located in the protrusions of the upper parts of the reservoirs. In a reservoir formed according to this model, all parts are hydrodynamically connected, which creates the opportunity for gravitational differentiation of fluids. Being in a reservoir, an oil or gas deposit is concentrated in the reservoir rock and is covered on top by a sealing rock. Below, under the deposit, there is the same reservoir, but saturated with water.

As an attempt to comprehensively consider deposits, one should consider the classification of hydrocarbon deposits according to the following criteria: reserves, structure of the reservoir in the trap, type of reservoir, type of screen in the trap, value of working flow rates. As practice shows, the most important, from the point of view of economics and methods of conducting prospecting and exploration work, is the classification of deposits according to their phase state. Below (Table 1) is an example of such a classification.

Table 1.

Classification and nomenclature of hydrocarbon deposits by phase state

and quantitative ratio of gas, oil and condensate

Suggested nameformation of deposits (designationreading)	Main features of deposits
Single-phase deposits
Gas (G)	Consist mainly of CH 4 with a content of pentane and heavier hydrocarbons of no more than 0.2% of the deposit volume
Gas condensate gas (GCG)	Gas deposits with C5 + higher content. within 0.2-0.6% of the deposit volume, which approximately corresponds to a condensate content of up to 30 cm 3 /m 3
Gas condensate (GC)	Gas deposits containing C, + higher. within 0.6-4% of the deposit volume, which approximately corresponds to a condensate content of 30-250 cm 3 /m 3
Condensate (K)	Gas deposits containing Cs + higher. more than 4% of the deposit volume, which approximately corresponds to a condensate content of more than 250 cm 3 /m 3
Transition State Deposits (TSD)	Hydrocarbon deposits, which in their physical properties (viscosity, density) in reservoir conditions are close to a critical state, occupying an intermediate position between liquid and gas
Oil (N)	Oil reservoirs with varying contents of dissolved gas (usually less than 200-250 m 3 /t)
Two-phase deposits
Oil and gas (NG)		Gas deposits with an oil rim; gas reserves are greater than geological oil reserves
Gas and oil (GN)		Oil deposits with a gas cap; Geological oil reserves exceed gas reserves
Oil and gas condensate (OGC)		Gas condensate or condensate deposits with an oil rim; gas and condensate reserves exceed oil reserves
Gas-condensate-oil (GKN)		Oil deposits with gas condensate caps; Geological oil reserves exceed gas and condensate reserves

Rice. 1. Scheme of a strata-vault gas-oil deposit.

1 – bottom of the oil deposit; 2 – external contour of oil content; 3 – internal contour of oil content; 4 – gas-oil interface; 5 – external contour of gas content; 6 – internal contour of gas content; 7 – deposit length; 8 – deposit width; 9 – height of oil deposit; 10 – height of the gas cap; 11 – total height of the gas-oil deposit; 12 – gas part of the deposit; 13 – gas-oil part of the deposit; 14 – oil part of the deposit; 15 – water-oil part of the deposit

Rice. 2. Diagram of a massive oil and gas reservoir.

1 – base of the oil deposit; 2 – external contour of oil content; 3 – gas-oil interface; 4 – external contour of gas content; 6 – deposit length; 5 – deposit width; 7 – height of oil deposit; 8 – height of the gas cap; 9 – total height of the gas-oil deposit; 10 – gas-oil part of the deposit; 11 – water-oil part of the deposit

It is advisable to accept genetic classification A.A. Bakirov (1960), who, developing the ideas of I.M. Gubkin, identified four main classes of local oil and gas accumulations: structural, lithological, reefogenic and stratigraphic (Fig. 3).

When studying this section, it is necessary to obtain knowledge sufficient to establish the genetic type of the deposit, determine from geological documentation and a schematic representation of such deposit elements as height, length, width, and area of the deposit, trap amplitude, oil-water contact (OWC), gas-oil contact (GOC) , gas-water (GWK), external and internal contours of oil content (gas content), etc.

Class	Group	Subgroup
Structural	Deposits of anticlinal structures	Vaulted (Fig. 4). Tectonically shielded (Fig. 5). Contact (Fig. 6). Hanging (Fig. 7).
	Monocline deposits	Screened by discontinuous faults (Fig. 8a). Associated with flexural formations (Fig. 8b). Associated with structural noses (Fig. 8c).
	Deposits of synclinal structures
Reefogenic	Associated with reef masses	Deposits in a single reef (Fig. 9a). Deposits in a group of reef massifs (Fig. 9b).
Lithological	Lithologically screened	Confined to areas where reservoirs are pinched out (Fig. 10a). Confined to areas of replacement of permeable rocks with impermeable ones (Fig. 10b). Shielded with asphalt or bitumen (Fig. 10c).
Lithological	Lithologically limited	Confined to sandy formations of paleo-river beds (corded or branch-shaped) (Fig. 11a). Confined to coastal sandy swell-like formations of fossil bars (Fig. 11b). Lenticular (Nest-shaped) (Fig. 11c).
Stratigraphic	Deposits in reservoirs cut off by erosion and covered by impermeable rocks	Associated with stratigraphic unconformities on local structures (Fig. 12a). Associated with monoclines (Fig. 12b). Associated with stratigraphic unconformities confined to the eroded surface of the buried remains of the paleorelief (Fig. 12c). Associated with projections of crystalline rocks (Fig. 12d).

Fig.3 Genetic classification oil and gas deposits according to A.A. Bakirov.

Rice. 4. Dome deposits: a - undisturbed; b - disturbed; c - structures complicated by cryptodiapir or volcanic formations; d - salt dome structures. Legend: 1 - oil in profile; 2 - oil in plan; 3 - stratogypsum along the roof of the productive formation; 4 - violations; 5 - limestones; 6 - volcanogenic formations, 7 - salt stock; 8 - sands; 9 - clay; 10 - mud volcano and diapirs; eleven - marls

Rice. 5. Tectonically shielded deposits.

a – near-fault, b – near-fault, c – structures complicated by diapirism or mud volcanism; d – salt-dome structure, e – subthrust structure.

Rice. 6. Near-contact deposits on structures:

a – with a salt stock, b – with a diapiric core or c the formation of mud volcanism, c – with volcanogenic formations.

Rice. 7. Hanging deposits of anticlinal structures:

a – undisturbed structure, b – faults complicated by rupture, c – complicated by cryptodiapir or volcanogenic formations.

Rice. 8. Monocline deposits:

a – screened by rupture disorders, b – associated with flexure complications, c – associated with structural noses.

Rice. 9. Deposits of reef formations in a single reef massif (a), in a group of reef massifs (b).

Fig. 10. Lithologically screened deposits confined to areas of pinchout of the reservoir layer (a) and replacement of permeable rocks with impermeable ones (b), and a deposit sealed with asphalt (c).

Rice. 11. Lithologically limited deposits confined to:

a – to sandy formations of paleo-river beds, b – to coastal sandy formations of fossil bars, c – to lenses of sandy rocks in low-permeability clayey deposits.

Rice. 12. Stratigraphic deposits:

a – within the local structure, b – on monoclines, c – on the surface of buried remains of paleorelief, d – on the surface of projections of crystalline rocks.

Annex 1.

Federal Agency for Education

Perm National Research Polytechnic University

TEST

(for part-time students)

1.5.1. Main types of deposits

The following main types of oil and gas deposits are distinguished: reservoir (Fig. 1); massive; lithologically or stratigraphically limited; tectonically screened.

^ Fig. 1. Scheme of the strata dome deposit.

Parts of the formation: 1-water, 2 - water-oil, 3-oil, 4 -gas-oil, 5-gas; 6 - reservoir rocks; N - deposit height; Ng, Nn- heights of the gas cap and the oil part of the deposit, respectively

An oil and gas deposit can be confined to one isolated natural reservoir or associated with a group of hydrodynamically communicating natural reservoirs, in which the marks of gas-liquid and water-oil contacts are the same, respectively. In the second case, the deposit is identified as massive or sheet-massive.

1.5.2. Classification of deposits according to the phase state of hydrocarbons

Depending on the phase state and the basic composition of hydrocarbon compounds in the subsoil oil and gas deposits are divided on (Fig. 2):

- oil containing only oil saturated to varying degrees with gas;

gas-oil and oil-gas(two-phase); in gas and oil

The main part of the deposits in terms of volume is oil and a smaller part is gas (gas cap); in oil and gas, the gas cap exceeds the oil part of the system in volume; oil and gas deposits also include deposits with an extremely insignificant oil part in volume - the oil rim;

- gas, containing only gas;

gas-condensate-oil and oil-gas-condensate: firstly, the main oil part in terms of volume, and secondly, the gas-condensate part (see Fig. 2).

1.5.3. Main features characterizing the conditions for deposit development

Any oil or gas deposit has potential energy, which during development is spent on displacing oil and gas from the reservoir (productive formation). The displacement of fluids from the reservoir occurs under the influence of natural forces that carry reservoir energy. Such carriers are, first of all, the pressure of regional waters, as well as the elastic forces of oil, water, and rock; gas compressed in gas deposits and gas caps, and gas dissolved in oil. In addition, oil gravity acts in the reservoirs.

The nature of the manifestation of driving forces in the reservoir, causing the influx of fluids to production wells, is called the reservoir regime. In accordance with the nature of the manifestation of the dominant source of reservoir energy during development in oil deposits, the following modes are distinguished: water pressure, elastic water pressure, gas pressure (gas cap), dissolved gas and gravity, and in gas deposits - gas and elastic water pressure.

The manifestation of one or another regime in a deposit is determined by the heterogeneity of the productive formation within the deposit and outside it, the composition and phase state of the hydrocarbon deposit, its distance from the recharge area, and the technological solutions used in the development process. The regimes of a deposit are judged by changes in oil, gas and water flow rates over time, water cut of products, reservoir pressures, gas factors, the movement of marginal waters, etc. The conditions for the development of deposits are also determined by many other factors: phase permeabilities of rocks, well productivity , hydraulic conductivity, piezoelectric conductivity of productive formations, degree of hydrophobization of rocks, completeness of oil displacement by a displacing agent.

1.6. OIL AND GAS FIELDS AND THEIR MAIN CLASSIFICATION FEATURES

MASTER BIRTH is a collection of oil and gas deposits confined to a single tectonic structure and located within the same area.

Deposits may be single fallow And multi-fallow. Based on the size of recoverable oil reserves and balance gas reserves, fields are divided into unique, large, medium and small (Table 1)

Classification of oil and gas field reserves by size

According to the complexity of the geological structure, the conditions of occurrence and consistency of productive formations Regardless of the size of reserves, deposits (deposits) are distinguished:

simple structure associated with undisturbed or slightly disturbed structures, the productive layers of which are characterized by consistency in thickness and reservoir properties in area and section;

complex structure , characterized by unconsistency in the thickness and reservoir properties of productive formations in area and section OR lithological replacement of reservoirs with poorly permeable rocks or the presence of tectonic disturbances;

very complex structure , which are characterized by both lithological replacements or tectonic disturbances, and ^I uneven thickness and reservoir properties of productive strata.

Complexity geological structure of deposits is installed based on the corresponding characteristics of the main deposits comprising the main part (more than 70%) deposit reserves. The size and complexity of the deposit structure determine the methodology of exploration work, its volume and economic indicators of exploration and development.

1.7. OIL AND GAS BEARING OBJECTS CONTAINING OIL AND GAS RESOURCES. AND THE BASIC PRINCIPLES OF THEIR CLASSIFICATION AND OIL AND GAS GEOLOGICAL ZONING

Oil and gas are extremely unevenly distributed in the depths. In this regard, forecasting oil and gas content and conducting geological exploration are aimed at identifying territories and parts of the section characterized by the maximum concentration of oil and gas fields and deposits. The identification of individual parts within the study area according to the degree of similarity of the geo-tectonic structure and composition of their constituent formations, i.e., factors that collectively control the oil and gas content of the subsoil, is called oil and gas geological zoning .

When oil and gas geological zoning, four main groups of factors should be taken into account - criteria that control the processes of generation, migration and accumulation of hydrocarbons:

Modern geotectonic structure of the studied territories and features of the formation of their geostructural elements;

Lithological and stratigraphic characteristics of the section, based on paleogeographic, formational and facies conditions for the formation of sediments in various parts these territories;

Hydrogeological conditions;

Geochemical conditions of the territories, including the phase state and physicochemical properties and composition of hydrocarbons, oil and gas source potential of rocks and the concentration and composition of bitumoids and organic matter(0V).

Deposits and deposits , associated with geostructural elements of the corresponding rank, belong to the elements of oil and gas geological zoning of the lowest level.

An association of adjacent and geologically similar oil and gas fields, the deposits of which are confined to traps that make up a single group that complicates the structure of a higher order (level), is called oil and gas accumulation zone.

Oil and gas region is an association of oil and gas accumulation zones, characterized by a common geological structure and development, lithological-facial conditions and conditions of regional oil and gas accumulation.

Oil and gas bearing area is an association of adjacent oil and gas bearing areas within a large geostructural element of more high level compared to the level of the element corresponding to the oil and gas bearing region. All oil and gas bearing areas within the region must be characterized by a common geological structure and history of development, including paleographic conditions of oil and gas formation and oil and gas accumulation.

Oil and gas province is an association of adjacent oil and gas bearing areas within one largest geostructural element or group thereof.

^ Zones, districts, regions and provinces, the oil and gas potential of which has not yet been proven, but is assumed, are usually called oil and gas promising .

Along with zoning by area, oil and gas geological zoning provides for the division of the sedimentary cover of the assessed territory according to the section. The main units of such division are the formation, the reservoir 1, the oil and gas bearing complex and the oil and gas bearing formation.

Oil and gas bearing formation is a thickness of permeable reservoir rocks bounded above (at the top) and below (at the bottom) by fluid seals.

Oil and gas horizon represents a group of overlain zonal seal and hydrodynamically connected layers within an oil and gas bearing complex.

Oil and gas complex is a lithologic-stratigraphic unit covered by a regional seal. The complex includes one oil and gas bearing horizon or a group of them.

Oil and gas formation is a natural-historical association of rocks genetically connected in time and space by regional paleogeographic and paleotectonic conditions favorable for the development of processes of oil and gas formation and oil and gas accumulation. An oil and gas bearing formation may contain one oil and gas bearing complex or a group of them.

Layers, horizons, complexes, the productivity of which has not yet been proven, but is assumed, are called oil and gas promising layers, horizons and complexes.

Genetic classification of oil and gas deposits by trap shape

Development of classification various types Numerous works have been devoted to oil and gas deposits. The most famous classifications are I.O. Broda, N.A. Eremenko, N.Yu. Uspenskoy, A.A. Bakirova.

IN general case All deposits can be divided into strata and massive. In strata deposits, it is noted that the deposit is confined to individual layers.

The formation of a massive deposit is associated with a terrigenous or carbonate massive reservoir, when, with a large level of oil and gas content, the deposit is controlled from above by the shape of the upper surface of the trap, and from below the horizontal contact cuts the entire body of the massif. Massive deposits are formed in reefs, anticlinal structures, erosion ledges, which are the remains of ancient relief. The most significant accumulations of oil and gas discovered in our country are associated with massive deposits.

According to the classification of A. A. Bakirov, taking into account main features formation of traps with which deposits are associated, four main classes of local oil and gas accumulations are distinguished:

· structural

reefogenic

· stratigraphic

· lithological.

To the class structural deposits include deposits confined to various types local tectonic structures. The most common deposits of this class are domed, tectonically shielded and near-contact.

Arch deposits(layered vaulted, according to G.A. Gabrielyants) are formed in the vaulted parts of local structures (Fig. 7.7)

Rice. 7.7. Arch deposits in section and in plan (according to A.A. Bakirov):

A - undisturbed; b - disturbed; in structures complicated by:

V- cryptodiapir or volcanic formations, G - salt domes.

1,2 - oil on the profile and in plan, respectively; 3 - stratogypsum on the roof

productive formation, m; 4 - violations; 5 - limestones; 6 - volcanic formations; 7 - salt rod; 8 - sandy rocks; 9 - clay; 10 - oil-bearing contour

Tectonically shielded deposits(tectonically shielded strata, according to G.A. Gabrielyants) are formed along fault displacements, complicating the structure of local structures (Fig. 7.8).

Such deposits can be located in different parts of the structure: on the roof, wings or periclines

Contact deposits are formed in productive strata in contact with a salt stock, clay diapir, or with volcanogenic formations (Fig. 7.9).

Unlike the reservoir deposits presented above, reef deposits are classified as massive. Deposits of this class are formed in the body of reef massifs (Fig. 7.10).

A typical example can serve as deposits in the reef massifs of the Ishimbayevsky region of the Bashkir Urals.

As part of the class lithological deposits Two groups of deposits are distinguished: lithologically screened and lithologically limited.

Deposits lithologically screened are located in areas where the reservoir formation pinches out (Fig. 7.11).

They are associated with the wedging out of the reservoir through the uprising of layers; with the replacement of permeable rocks by impermeable ones; With sealing the reservoir with asphalt.

Deposits lithologically limited are confined to sandy formations of fossil paleo-river beds (corded or sleeve-shaped), to coastal sandy swell-like formations or to nest-like reservoir rocks surrounded on all sides by poorly permeable rocks (Fig. 7.12).

Lithologically limited deposits, according to I. O. Brod, are associated with reservoirs represented by sand accumulations various shapes in low-permeability strata - in sandy formations of fossil paleo-river beds - cord or sleeve-shaped; in coastal sandy swell-like formations of fossil bars (bar); in nest-like sandy reservoirs, surrounded on all sides by poorly permeable clayey formations, in deltas; in cavernous zones - karst and in areas of permeable rocks among dense ones.

Deposits are identified simple And complex buildings. Deposits of simple structure include deposits confined to lithologically consistent layers and contained in a single local uplift.

The complex category includes multi-layer and multi-dome deposits. A multilayer oil and gas reservoir (Fig. 7.13) covers several layers, between which there is a hydrodynamic connection.

In this case, despite the complexity of the trap structure, the oil-water section, reservoir pressure and oil properties in all layers will be approximately the same.

In cases where oil or gas fills several adjacent anticlinal traps, a multidome reservoir is formed (Fig. 7.14).

At the same time, synclinal troughs between folds are also filled with oil or gas, and formation water moves to the periphery.

Oil and gas reserves in individual deposits can be very different: from insignificant to several billion tons of oil or several trillion cubic meters gas The main indicators of the industrial value of a deposit are the reserves contained in it and the economically justified minimum profitable flow rates of oil and gas, ensuring the economic profitability of the industrial development of the deposit. Based on these indicators, deposits are divided into:

q balance, the development of which is currently advisable,

q off-balance sheet, the development of which is currently unprofitable, but which can be considered as an object for industrial development in the future.

According to the working flow rates deposits are divided into 4 classes: high-yield, medium-yield, low-yield and low-yield (Table 7.1).

Scientifically based searches, exploration and development of oil and gas fields are impossible without clear knowledge of their properties, conditions of occurrence in earth's crust and the patterns of their spatial placement.

In order for an oil or gas deposit to form, at least three conditions are needed.

1. Need a collector. This is a porous, permeable rock capable of receiving and releasing oil, gas, and water. For example sandstones, limestones.

2. Need a natural reservoir- a natural reservoir for oil, gas and water, the shape of which is determined by the relationship of the reservoir with the poorly permeable rocks that host it.

A natural reservoir is a reservoir bounded by impermeable rocks.

3. Nit's a trap- a part of a natural reservoir in which an oil and gas deposit can be formed or has already formed.

An oil and gas reservoir means a single accumulation of oil and gas. Sometimes such a cluster is called elementary, local, isolated, etc. It is the same. If oil or gas reserves are large and their development is economically justified, then they are of industrial importance; if they are small, they are considered off-balance sheet.

Ignatius Osipovich Brod, one of the students of Academician Gubkin, in 1951, based on the nature of the natural reservoir, identified three types of deposits, which have become firmly established in theory and practice search work for oil and gas:

1) reservoir deposits;

2) massive deposits;

3) lithologically limited deposits on all sides.

I. O. Brod successfully identified these three types of deposits, and his classification of oil and gas deposits has stood the test of time.

Reservoir deposit is an accumulation of oil and gas in a reservoir formation, limited at the top and bottom by impermeable rocks.

A trap for oil and gas is created by the arched bends of the formation. According to the nature of the trap there are stratified vaulted And layer shielded deposits.

Stratified dome deposits are deposits in anticlinal structures and are most often encountered in practice. A trap in a strata dome deposit is formed by the bending of the overlying caprock.

Schematic diagram of the arched stratal deposit (according to N.A. Eremenko):

1 – bottom of the oil deposit (surface of the oil-water section); oil-bearing contours: 2 – external, 3 – internal; 4 – rotation of the gas-oil section; gas content contours: 5 – external (gas cap contour), 6 – internal; 7, 8, 9 – length, width and height of the oil deposit, respectively; 10 – height of the gas cap; 11 – total height of the gas-oil deposit; parts of the deposit: 12 – gas, 13 – gas-oil, 14 – oil, 15 – water-oil

In the case of a horizontal OWC position, the oil-bearing contour is parallel to the isohypses of the reservoir roof and has the shape of a ring. The arch deposits are associated with anticlinal uplifts of various origins. They can be disturbed or undisturbed, or complicated by cryptodiapirs.

Layered deposits can be screened tectonically, stratigraphically, lithologically.

Tectonic screening associated with a discontinuity, along which the reservoir is, as it were, cut off. The violation is impenetrable.

Stratigraphic screening associated with the unconformable occurrence of one complex of sediments on another. It occurs when reservoirs, cut off by erosion, are covered by impermeable rocks of a different age. There are cases when the reservoir is limited both below and above by erosion surfaces.

One of the largest fields in the world - East Texas in the USA - with recoverable reserves of 810 million tons of oil is confined to the structural nose on the western flank of the Sabine Rise.

As A. Levorsen writes, the intersection of two unconformity surfaces caused the pinchout of permeable Woodbine sandstones (Upper Cretaceous). The subsequent formation of the large Sabine uplift caused deformation of the zone of pinching out of permeable rocks and contributed to the formation of a trap with the largest oil deposit.

The Woodbine sandstones are unconformably overlain by impermeable sediments of younger age.

Lithologically screened deposits are formed mainly when the thickness of the reservoir is reduced up the upslope on the slopes of regional uplifts until it almost completely disappears or as a result of deterioration in the reservoir properties of the formation: porosity, permeability, etc.

Massive deposits. Massive reservoirs are represented by a thick strata, consisting of many permeable layers, not separated from one another by poorly permeable rocks.

Massive deposits are associated with massive reservoirs. For the formation of massive deposits, the shape of the covering surface of the reservoir is important. Oil and gas saturate the massif in the uplifting part. The shape of the trap is determined by the shape of the roof bend. Massive deposits most often form in outcroppings of carbonate rocks. The oil-water contact crosses the entire body of the massif, regardless of the composition and stratigraphic affiliation of the heterogeneous reservoir.

The group of massive deposits is associated with structural, erosional and biohermic highs.

Structural protrusions - anticlines, arches, domes.

Gas deposits in the Cenomanian deposits of the Urengoy field and others (Medvezhye, Yamburg, Zapolyarny) are confined to a mass of many alternating sandy and clayey layers, overlain by a thick cover of Turonian clays and overlying deposits of the Upper Cretaceous and Paleogene. Sandstones are filled with gas and have a single gas-water contact. The height of the Cenomanian gas deposit on Urengoy is 200 m, and the number of gas-bearing layers is in the dozens.

Erosion protrusions often occur. They are associated with the remains of an ancient relief. For example, the thickness of limestones and dolomites was eroded and covered with clays. During the process of erosion, a “protrusion” appeared, which was later buried. An oil deposit formed in it.

Bioherm protrusions- these are reefs that are widespread in the Samara, Orenburg, and Ulyanovsk regions and are associated with the Kama-Kinel system of troughs. Massive deposits are characterized by an uneven distribution of porous and permeable zones in the massif.

Lithologically limited on all sides deposits.
This group includes oil and gas deposits in irregularly shaped reservoirs, bounded on all sides by poorly permeable rocks. Water in these deposits plays a passive role and does not cause the movement of oil and gas to wells during operation.

These are numerous sand bars, coastal ramparts, and sandstone lenses. Their oil reserves are usually small.

A significant number of lithologically limited deposits are associated with buried paleo-river beds. In the Samara Volga region, there is a “lace” deposit at the Pokrovskoye oil field.

Sand bars appear in gently sloping coastal conditions, when minor fluctuations in water levels lead to the drying of large areas.