On approval of the classification of reserves and resources of oil and combustible gases. Petroleum and gas geological zoning and patterns of distribution of oil and gas accumulations in the earth's crust

06.08.2016

Any classification of oil and gas deposits, first of all, should reflect the genetic features of the formation of traps in which deposits are formed. It was this principle that A.A. Bakirov, when, summarizing all the available information about natural traps and oil and gas deposits confined to them, he identified four main classes of deposits (Table 12.1).

As can be seen from the table, four classes of oil and gas deposits are distinguished in the classification, which, in turn, are divided into groups and subgroups. Let's take a look at what some of them are. Let's start with the class of structural deposits. It distinguishes three subgroups: deposits of anticlinal structures, deposits of monoclines and deposits of synclinal structures.
Deposits of anticlinal structures are confined to local uplifts different kind, simple or broken structure. In turn, the group of deposits of anticlinal structures includes four subgroups (Table 12.2).
Ho, before proceeding to the consideration of deposits, it is necessary to study the symbols that characterize their structure in section and plan.

Thus, deposits of anticlinal structures are confined to local uplifts of various types. Dome deposits are formed in local structures, as simple structure, and complicated by tectonic disturbances, diapirism, mud volcanoes or salt dome tectonics. Sometimes there are, as already mentioned, the so-called "hanging" deposits, which are usually located on the wings, less often on the periclinals of local structures of a simple or complex structure, which will be discussed in more detail below.
On the structural maps of these deposits, the contours of the oil-water contact usually do not correspond to the isohypses of the top or bottom of productive formations, but cut them at different angles.
Now let's consider a group of monocline deposits, in which three subgroups are distinguished; reservoirs screened by faults, reservoirs associated with flexural formations, and reservoirs associated with structural noses (Table 12.3).

Currently, there are three main hypotheses for the formation of these deposits, which are very unusual from the point of view of the anticlinal theory. The first hypothesis is tectonic. She explains their formation by changing the position of the paleoarch of the fold. The second is due to oxidative processes occurring at contour zone. And the third, the most common, explains the displacement of the deposit under the pressure of formation waters.
Tectonically screened deposits are formed along faults and reverse faults that complicate local anticlinal folds. Depending on the spatial position and orientation of faults, these deposits can be located on domes, limbs, or periclines.
Near-contact deposits are formed at the contact of productive horizons with a salt stock, a diapiric core, or volcanogenic formations. Monocline deposits can be associated with flexural formations: with structural noses or faults that complicate the monoclines.
A special place in the classification is occupied by deposits of synclinal structures. They were found in some areas of the Analach oil and gas province of the USA, in the Sichuan province in China, in Brazil, etc. (Table 12.4).

Let's move on to the group of deposits associated with reef masses (Table 12.5). A separate reef mass or a group of reefs may contain a single oil or gas reservoir with a common oil-water contact. Due to the fact that cavernousness and jointing of limestones very often have a local distribution, the capacitive-filtration properties of reef masses change significantly even at short distances. In this regard, when developing such deposits, well flow rates in various parts reef massif are almost never the same.
The next subject of our consideration is the class of lithological deposits.
This class contains two groups: lithologically screened and lithologically limited deposits (Table 12.6).


Anthological deposits are common in almost all oil and gas areas. Of these, screened deposits are associated with areas of wedging out of the reservoir by its rise or with areas of replacement of permeable rocks with impermeable ones. In the literature, such deposits are sometimes referred to as bay-shaped.
The same group also includes deposits, the formation of which is associated with the screening of the collector with asphalt or bitumen, formed as a result of oxidative processes.
Lithologically limited deposits can form in coastal sandy swell-like formations of fossil bars (bar deposits) or in lenticular sandy reservoirs surrounded on all sides by poorly permeable clay deposits. Often such deposits are formed in sandy formations of channels and paleo-river deltas.
This subgroup of deposits was first discovered by I.M. Gubkin in 1911 in the Maykop region. Remember, we talked about this at the very beginning of the book, when we said that in the early days of the oil industry, the “wild cat” method was widely used in the search for oil.
Deposits associated with sandy formations of channels and deltas of paleo-rivers, I.M. Gubkin, with his inherent humor, called "skin" or "sleeve-shaped".
And the last class of deposits is stratigraphic deposits. These are deposits in reservoirs cut by erosion and blocked by impermeable rocks. Two subgroups are distinguished here: deposits associated with stratigraphic unconformities on tectonic structures and deposits associated with stratigraphic unconformities confined to the eroded surface of buried remains of the paleorelief or ledges of crystalline rocks (Table 12.7).

In conclusion, it should be noted that sometimes in nature there are deposits, the formation of which is due to the action of several factors, for example, lithological and stratigraphic. There are well-known cases when deposits are confined to areas of wedging out reservoirs, cut off by erosion and then covered with tight deposits for more than young age, such as the West Tebuk deposits in Siberia, East Texas in the USA, etc.

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. We need a natural reservoir - a natural reservoir for oil, gas and water, the shape of which is determined by the ratio of the reservoir to the enclosing poorly permeable rocks.

A natural reservoir is a reservoir bounded by impermeable rocks.

3. A trap is needed - a part of a natural reservoir in which an oil and gas deposit can be formed or has already been formed.

An oil and gas reservoir is a single accumulation of oil and gas. Sometimes such an accumulation is called elementary, local, isolated, etc. This 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 classified as off-balance.

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

1) reservoir deposits;

2) massive deposits;

3) deposits lithologically limited 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.

A reservoir deposit is an accumulation of oil and gas in a reservoir, limited in the roof and bottom by impermeable rocks.

The trap for oil and gas is created by the arched bends of the formation. According to the nature of the trap, reservoir arched and reservoir shielded deposits are distinguished.

Reservoir domed deposits are deposits in anticlinal structures, they are most often encountered in practice. The trap in the formation crest is formed by the bending of the overburden.

On fig. 5.1 shows a diagram of a reservoir dome deposit. The line of intersection of the surface of the oil-water contact (OWC) with the top of the formation is called the outer contour of the oil-bearing capacity. The line of intersection of the surface of the oil-water contact with the base of the formation is called the internal contour of the oil-bearing capacity.

Rice. 5.1. circuit diagram domed reservoir

Reservoir deposits can be screened tectonically, stratigraphically, lithologically.

Tectonic shielding is associated with a discontinuous disturbance, along which the reservoir is, as it were, cut off. Violation is impenetrable.

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

Lithologically screened deposits are formed mainly when regional rises in reservoir thickness decrease upwards on the slopes to its almost complete disappearance or as a result of deterioration of the reservoir properties of the reservoir: porosity, permeability, etc. (Fig. 5.3).

Fig.5.3.Principal diagram of reservoir lithologically screened deposits

Massive deposits. Massive reservoirs are represented by a thick layer 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 are most often formed in ledges of carbonate rocks. Water-oil contact crosses the entire body of the massif, regardless of the composition and stratigraphic affiliation of the heterogeneous reservoir.

Lithologically limited deposits on all sides. This group includes deposits of oil and gas in reservoirs irregular shape bounded on all sides by poorly permeable rocks. Water in these deposits plays a passive role, it is not the reason for the movement of oil and gas to the wells in case of exploitation.

These are numerous sand bars, coastal ridges, sandstone lenses. Stocks

The height of lithologically limited traps is usually small, the thickness of the sand layers is several meters.

Reservoir domed and massive deposits in structural ledges are associated with anticlinal forms of traps. For other traps, screening is determined by other factors. All traps can be divided into anticlinal and non-anticlinal.

An oil reservoir associated with salt tectonics structures is shown in fig. 5.7. In the salt-dome structure, the salt massif is located at a depth, from above it is covered with a layer of anhydrite or gypsum, and they, in turn, are covered with porous limestone. The Americans, according to Gubkin, call the top tire a "cap" (cap). There is an anticline above the rock salt. Oil is available in the "cap", in the overlying layers and on the sides of the US fields. They are widely developed in the Gulf of Mexico. Rock salt under the pressure of overlying rocks with a thickness of 700 m (170 kg / cm 3) flows into the vaults of the domes.

Rice. 5.7. An idealized section of a salt dome oil field deposits in the Gulf Coast basin (according to A. Levorsen)

The salt stock is an array of cylindrical shape, when the height is several times greater than the width of the array. Below is the classification of oil and gas deposits according to A.A. Bakirov (Fig. 5.8-5.15).

Rice. 5.8. Pivot deposits: a - undisturbed; b - violated; (c) structures complicated by cryptodiapirus or volcanogenic formations; d – salt dome structures; 1 – oil in profile; 2 - oil in plan; 3 - stratoisohypses along the top of the productive formation; 4 - violations; 5 - limestones; 6 - volcanogenic formations; 7 – salt stock; 8 - sands; 9 - clays; 10 – mud volcano and diapirs; 11 - marls

Rice. 5. 9. Hanging deposits of structures: a - a simple undisturbed structure; b - complicated by discontinuous violation; c - complicated by diapirism or volcanic formations

Rice. 5.10. Tectonically screened deposits: a - near-fault; b - reverse faults; c – structures complicated by diapirism or mud volcanism; d – salt dome structures; e - subthrust

Rice. 5.11. Contact deposits: a - with salt stocks; b – with diapiric cores or with formations of mud volcanism; c - with volcanogenic formations

Rice. 5. 1 2. Deposits of monoclinal structures: a – shielded by faults on monoclines; b – associated with flexural complications of monoclines; c - associated with structural noses on monoclines

Rice. 5. 1 3. Lithologically shielded deposits: a - confined to the areas of wedging out of the reservoir - reservoir by rising layers; b - to areas of replacement of permeable rocks with impermeable ones; c - sealed with asphalt

Rice. 5.14. Lithologically limited deposits: (a) Paleo-rivers confined to sandy formations of fossil beds (laced or sleeve-shaped); b – to coastal sandy swell-like formations of fossil bars (bars); c - to nested sandy reservoirs surrounded on all sides by poorly permeable clay formations

5.15. Stratigraphic type deposits associated with stratigraphic unconformities: a – within local structures; b - on monoclines; c – on the surface of the buried remains of the paleorelief; g-on the surface of buried ledges of crystalline massifs

Seminar session, practical and test

Topic 2. NATURAL RESERVOIRS, TRAPS AND RESERVOIRS OF OIL AND GAS

Objective:

Consolidation of knowledge on the topics "Natural reservoirs, traps and deposits of oil and gas";

Acquisition of skills in graphic construction of various types of traps and deposits of oil and gas;

To form the ability to determine on structural maps and geological sections different types traps and deposits.

Initial data: Description of the deposit by trap type and phase state.

Work order:

To study the theoretical part of the following topics: "Natural reservoirs", "Traps", "Oil and gas deposits";

Answer Control questions;

Using the description of the deposit by trap type and phase state, a) depict the geological section of the trap and b) build a structural map.

The geological section is depicted in an arbitrarily chosen depth interval and an arbitrary vertical scale. generally accepted conventional signs show the reservoir, the cap, the underlying fluid seal and the position of the hydrocarbon (HC) deposit, which is determined by the position of the contacts: water-oil (OWC) and gas-water (GWC) in single-phase deposits; gas-oil (GOC) and water-oil contact in two-phase deposits.

Draw a structural map under the section. The map must correspond to the line of the geological section and the description. On the map, show the position of the outer contour of oil or gas.

Title the work symbols and submit it for review.

When constructing a geological section of traps and deposits, you can use the figures and tables given in methodological guide as well as the literature below.

natural reservoirs

Natural Reservoir (PR) is a complex of rocks of reservoirs and seals, within which the movement of fluids and the accumulation of oil and gas are possible. There are three main types of natural reservoirs (I.O. Brod; 1951): bedded, massive and lithologically limited (rice. one).

Reservoir reservoir- this is a permeable reservoir, limited by fluid seals in the roof and sole ( rice. one, a ).

Rice. 1. Natural reservoirs:

a- reservoir; b- uniformly massive; v– heterogeneous-massive; G– lithologically limited; d– reservoir-massive

massive reservoirs They are a large thickness of permeable rocks, from several tens to a thousand meters or more, covered by an impermeable layer. This may be a high-amplitude folded structure, a reef mass, a tectonic or erosion-tectonic ledge of the basement or sedimentary cover ( rice. one v ). Deposits of oil or gas in such reservoirs are controlled by seal rocks only from above and from the sides, and below, over the entire area, they are supported by water.

Lithologically constrained reservoirs morphologically represented by permeable bodies enclosed in the thickness of impermeable rocks ( fig 1, G ). Genetically and morphologically, they are represented by various types and species (lenses, paleobars, buried sections of river channels and deltas of small rivers at the foot of mountains).

Oil and gas traps

Trap is a part of the PR, in which, due to the balance of hydraulic forces, accumulation of oil and gas can occur and a hydrocarbon deposit can form. A trap is a certain closed or semi-closed volume. Closed traps are associated with lithologically closed PRs. favorable conditions for the accumulation of hydrocarbons and the formation of oil and gas deposits, there are:

In the vaults of anticlinal structures;

In areas of anticlines and monoclines shielded by discontinuities;

In zones of wedging out of reservoirs or in zones of their replacement by impermeable rocks;

In zones of reservoir screening by the surface of stratigraphic unconformity and reef masses;

In zones of hydrodynamic shielding.

The most important indicators by which traps are classified are their genesis and form. Depending on the causes of the formation of traps, five genetic types of traps are distinguished: structural, lithological, stratigraphic, reef and hydrodynamic. The simplest trap is the anticlinal bend of the reservoir. In the contour of the lowest closed isohypse of a semi-closed trap, there is its hydraulic lock, which determines the maximum filling of the trap with oil or gas. The main parameters of the trap are: collector thickness, square(in the contour of the lowest closed isohypse) and height, measured from the highest point of the roof of the collector to the hydraulic lock of the trap.

Since the deposit in the trap can be in three states: in equilibrium, in the state of formation and in the state of destruction, it can occupy a different volume of the trap. Degree (factor) of filling the HC trap is determined by the ratio of the height of the deposit to the height of the trap. The coefficient varies from 0 to 1 or is expressed as a percentage.

Genetic types of traps.

Structural type traps (rice.2 ) are formed as a result of plicative and disjunctive tectonic deformations rocks, and are divided into vaulted or anticlinal ( rice. 2, a ) and tectonically shielded traps ( rice. 2, b ).

Rice. 2. Section and plan of structural type traps in reservoir:

(a) dome trap; ( b) disjunctively (tectonically) screened trap

Tectonically screened traps are formed both on anticlinal structures and on monoclines in the presence of tectonic faults. It would be more correct to call them disjunctively escaped, since anticlines are also tectonic plicative screens on the path of hydrocarbon movement.

Lithological type traps formed in the following four cases:

1) when wedging out reservoir rocks by rising layers ( rice. 3);

Rice. 3. Lithologically shielded trap:

1 - line of wedging out of the reservoir

2) replacement of reservoir rocks with coeval low-permeable rocks;

3) the appearance of increased local fracturing of rocks;

4) the presence of sandy or silty lenses inside clayey strata ( rice. 4).

In the last two cases, the concepts of a natural reservoir and a trap coincide.

Rice. 4. Lithologically limited traps

Stratigraphic type traps are formed as a result of denudation cutting of reservoir rocks and their unconformity overlapping with seals ( rice. 5).

Rice. 5. Stratigraphically screened traps:

a– in the crest part of the anticlinal structure;

b– on the monocline (impermeable rocks are represented by limestones)

reef type traps. This type of trap includes reef massifs covered with seals ( rice. 6).

Rice. 6. Trap dedicated to the reef massif:

1 – cavernous and fractured carbonate rocks; 2 – impenetrable sedimentary rocks overlying the reef body

Hydraulic (hydrodynamic) traps are formed as a result of the hydrodynamic head of the oncoming water flow, which exerts counterpressure on the migrating hydrocarbons. Great importance in this type, they have capillary pressure, hydrophobicity and hydrophilicity of rocks.

In fact, hydraulic traps and, accordingly, oil deposits are formed when the hydraulic head, usually together with capillary pressure, exceeds the gravitational force.

Oil floating force p g depends on the density difference between water and oil ρ in -ρ n, as well as on the height of the deposit H and the sine of the reservoir inclination angle sin α, along which the oil migrates:

p g = gН (ρ in -ρ n) sin α

Traps of reef, lithological, stratigraphic and hydrodynamic types are commonly referred to as non-structural , and, together with disjunctively screened traps on monoclines, non-anticlinal traps (NAL) or complex screening traps.

Oil and gas deposits

Deposits are local clusters oil and gas. Deposits also belong to local accumulations. Deposits and deposits are the main objects of geological exploration (GE) and development.

deposit- this is a single accumulation of oil and (or) gas in the trap of a natural reservoir, which is controlled by a single water-oil or gas-water contact and can be in three states: in equilibrium, in the state of formation and in the state of destruction.

Field- this is a set of deposits that are controlled by one tectonic structure and located on the same local area. In the projection onto the earth's surface, the contours of oil and (or) gas content of deposits completely or partially overlap ( rice. 7, 8).

Rice. 7 Geological section of the productive part of Pravdinsky oil field

Rice. 8. Geological section of the Kharyaginskoye field (according to V.E. Yakovlev):

1 – sandstones and siltstones; 2 – clays and mudstones; 3 - limestones; 4 – reef limestones; 5 - dolomites; 6 – clayey limestones; 7 - oil

According to the scale of distribution and oil and gas content, in addition to local accumulations, two more categories are distinguished - regional and global. Regional clusters are the main objects and systematic units of oil and gas geological zoning. They are: 1) oil and gas zone; 2) oil and gas region; 3) oil and gas area; 4) oil and gas province or oil and gas basin.

Global Clusters reflect the general planetary patterns of oil and gas distribution and draw attention to the geological conditions for the formation of accumulations with the maximum concentration of oil and gas. Among them are oil and gas belts, isometric associations of oil and gas provinces, as well as nodes, or poles, of oil and gas accumulations - these are territories and water areas with unique scales of oil and gas content.

Principles of classification of oil and gas deposits.

Oil and gas deposits are classified according to different indicators, the most important of which are: 1) types of traps; 2) phase state of the deposit; 3) the amount of reserves; 4) complexity geological structure deposits; 5) collector type, etc.

Classifications of deposits by type of traps are based on the genetic and morphological features of oil and gas traps.

Classification of deposits according to the genetic type of traps. In practical geology, the genetic classification of oil and gas deposits by A.A. Bakirov, in which five classes of deposits are distinguished according to the genesis of traps: structural, reef, lithological, stratigraphic and lithological-stratigraphic (tab., app.). Quite often in natural reservoirs there are combined traps created with the participation of two or more factors.

The concept is also widely used massive deposits » . This type of deposits was identified in the morphological classification of deposits by I.O. Broda (1951). massive deposits - these are oil and gas deposits of great height, in which the position of hydrocarbons in the trap is controlled by fluid seals only from above and from the sides (tire). HC from below are propped up over the entire area of ​​the deposit by bottom water, therefore, in them oil-water contact (WOC) or gas water contact (GWC) located above the bottom of productive rocks (reservoir rocks).

They have a similar structure vaulted incomplete reservoir, or waterfowl, deposits. The fundamental difference between them and massive deposits is only in the thickness of productive rocks and, accordingly, in the volume of the deposit.

The surface of the WOC (GWC) in most cases has a horizontal position, but it can also be inclined. The slope of the surface can be associated with the manifestation of hydrodynamic or capillary forces, as well as with the processes of recent tectonic deformation of the trap. With a horizontal position of the WOC (GWC) surface, the oil-bearing (gas-bearing) contour lies on the structural map parallel to the isohypses of the top of the productive formation, and in an inclined position it crosses the isohypses of the top of the formation, shifting towards the slope of the contact surface ( rice. 9).

Rice. Fig. 9. Principal diagram of an oil incomplete reservoir (water-floating) reservoir with an inclined water-oil contact (hanging reservoir): a - geological section; b - structural map:

1, 2 - oil, respectively, in the section and on the map; 3 – isohypses, m; 4 - outer contour of oil and gas

Table. Classification of oil and gas deposits (according to A.A. Bakirov)

Similar information.

By type of trap - the most commonly used classification of oil and gas deposits, which is based on the forms and conditions for the formation of traps that are genetically and morphologically diverse. The classification is also widely known, in which the main feature is the type of natural reservoir (classification of types of deposits according to I. O. Brod), where three main groups of deposits are distinguished: reservoir, massive, deposits, lithologically limited from all sides. It is believed that it is the type of natural reservoir that determines the conditions for the movement and differentiation of fluids. The first two groups are formed in natural reservoirs that have a regional distribution and saturation with water throughout their length. Unlike them, in the third group, the reservoir is limited on all sides by impermeable rocks in which there is no water circulation.

Oil and gas deposits in a reservoir accumulate when there are traps within the reservoir. The trap in the formation reservoir is formed either due to structural bending or due to the presence of a screening surface that cuts the formation along its rise. The accumulation of oil and gas is possible if the underlying water closes the deposit. Depending on the conditions for the formation of a trap, a group of reservoir deposits is divided into two subgroups: arched (layer-arched) and shielding deposits (layer-shielded). Tectonically screened (disjunctively screened) deposits are formed if, as a result of disjunctive dislocations, a monoclinally occurring reservoir comes into contact with impermeable rocks. By their genetic nature, screens can be faults, reverse faults, overthrusts and shifts. Tectonic disturbances often break up reservoir-arched deposits. Such combined deposits are called reservoir-arched tectonically shielded.

Stratigraphically screened deposits are confined to traps, which are formed in reservoirs cut by erosion and unconformably overlain by poorly permeable rocks of younger age. Conventional stratigraphically shielded deposits are formed after the reservoir formation is overlain by an unconformable impermeable stratum. However, oil and gas deposits screened or sealed with asphalt during the erosion period should also be attributed to the same type. Lithologically screened deposits are confined to traps, which are screened by lithological replacements of permeable rocks with poorly permeable ones and wedging out of reservoir layers. This type of replacement leads to a gradual deterioration in porosity and permeability as it approaches the wedging surface. A group of massive deposits is associated with massive natural reservoirs, limited by an impermeable seal only from above. A distinctive feature of massive deposits is the hydrodynamic connection of all parts of the deposit, despite the difference in capacitive-filtration properties and the presence of sections. There are massive reservoirs lithologically relatively homogeneous and heterogeneous, the latter are much more widespread.

A group of lithologically limited (on all sides) deposits is confined to irregularly shaped traps, bounded on all sides by impermeable rocks. The deposits of this group are usually shallow, the thickness of productive rarely exceeds a few tens of meters, so reservoir pressures cannot have high values. Such deposits are associated with reservoirs that have only local distribution. There are three sub-groups within this group: reservoirs bounded by tight rocks (the most numerous), bounded by aquifers, and bounded by partially tight and partially aquifers. Classification of oil and gas deposits, according to A.A. Bakirov, proposed in the lectures of this cycle.

An oil and gas reservoir is a single accumulation of oil and gas. Sometimes such an accumulation is called elementary, local, isolated, etc.

I. O. Brod, according to the nature of the natural reservoir, identified three types of deposits, which are firmly established in the theory and practice of prospecting for oil and gas:

1) reservoir deposits;

2) massive deposits;

3) deposits lithologically limited 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.
A reservoir deposit is an accumulation of oil and gas in a reservoir, limited in the roof and bottom by impermeable rocks.
The trap for oil and gas is created by the arched bends of the formation. According to the nature of the trap, reservoir arched and reservoir shielded deposits are distinguished.

Reservoir domed deposits are deposits in anticlinal structures, they are most often encountered in practice. The trap in the formation crest is formed by the bending of the overburden.

Rice.principledreservoir dome scheme

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

Arched deposits are associated with anticlinal uplifts of various genesis. They may be broken or unbroken, or complicated by cryptodiapirs.
Reservoir deposits can be screened tectonically, stratigraphically, lithologically.
Tectonic shielding is associated with a discontinuous disturbance, along which the reservoir is, as it were, cut off. Violation is impenetrable.
Stratigraphic screening is associated with unconformity occurrence of one set of sediments on another. It occurs when the reservoirs, cut by erosion, are blocked by impermeable rocks of a different age. There are cases when the reservoir is limited by washout surfaces both from below and from above.

Lithologically screened deposits are formed mainly when regional rises in reservoir thickness decrease upwards on the slopes to its almost complete disappearance or as a result of deterioration of the reservoir properties of the reservoir: porosity, permeability, etc.

Rice. Schematic diagram of reservoir lithologically screened deposits.

Massive deposits. Massive reservoirs are represented by a thick layer 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 are most often formed in ledges of carbonate rocks. Water-oil contact crosses the entire body of the massif, regardless of the composition and stratigraphic affiliation of the heterogeneous reservoir.
A group of massive deposits is associated with structural, erosional and biohermal ledges.
Structural ledges - anticlines, vaults, domes.

Erosion protrusions are common. They are associated with the remains of an ancient relief. For example, the limestone and dolomite strata were eroded and covered with clays. In the process of erosion, a "ledge" was created, which was later buried. It formed a deposit of oil.
Bioherm ledges are reefs. Massive deposits are characterized by an uneven distribution of porous and permeable zones in the massif.

Rice. Section of a typical bioherm

Lithologically limited deposits on all sides.
This group includes deposits of oil and gas in irregularly shaped reservoirs bounded on all sides by poorly permeable rocks. Water in these deposits plays a passive role, it is not the reason for the movement of oil and gas to the wells in case of exploitation.
These are numerous sand bars, coastal ridges, sandstone lenses. Oil reserves in them are usually small.
A significant number of lithologically limited deposits are associated with buried paleo-river beds.

Below is the classification of oil and gas deposits according to A.A. Bakirov

Pivotdeposits:

a - undisturbed; b - violated; (c) structures complicated by cryptodiapirus or volcanogenic formations; d – salt dome structures; 1 – oil in profile; 2 - oil in plan; 3 - stratoisohypses along the top of the productive formation; 4 - violations;
5 - limestones; 6 - volcanogenic formations; 7 – salt stock; 8 - sands; 9 - clays; 10 – mud volcano and diapirs; 11 - marls

Hanging deposits of structures:

a - a simple undisturbed structure; b - complicated by discontinuous violation;
c - complicated by diapirism or volcanic formations

Tectonically screened deposits:

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

Contactdeposits:

a - with salt stocks; b – with diapiric cores or with formations of mud volcanism;
c - with volcanogenic formations

Deposits of monoclinal structures:

a – shielded by faults on monoclines; b – associated with flexural complications of monoclines;
c - associated with structural noses on monoclines

Lithologically screened deposits:

a - confined to the areas of wedging out of the reservoir - reservoir by rising layers;
b - to areas of replacement of permeable rocks with impermeable ones; c - sealed with asphalt

Lithologicallylimited deposits:

(a) Paleo-rivers confined to sandy formations of fossil beds (laced or sleeve-shaped);
b – to coastal sandy swell-like formations of fossil bars (bars);
c - to nested sandy reservoirs surrounded on all sides by poorly permeable clay formations

Stratigraphic type deposits associated with stratigraphic unconformities:

a – within local structures; b - on monoclines; c – on the surface of the buried remains of the paleorelief;
g-on the surface of buried ledges of crystalline massifs

The methods of graphical representation of deposits include the construction of maps and sections.

Similar information.