Is to accumulate a certain amount of oil and gastrap。iftrapThere is only oil accumulation, which is called pure oil reservoir (or oil reservoir), and only natural gas accumulation, which is called pure gas reservoir (or gas reservoir).When the amount of oil and gas accumulation is sufficient for industrial exploitation, it is called an industrial oil and gas reservoir, and vice versa.Oil and gas reservoir is the basic unit of oil and gas accumulation in the crust. An oil and gas reservoir exists in an independent trap, in which oil and gas have certain distribution laws and unified pressure system.[1]
CrustThe oil and gas reservoirs in the Middle East can be divided into conventional and unconventional types.The history of oil and gas exploration and development in the world is a history of exploration and development from conventional oil and gas reservoirs to unconventional oil and gas reservoirs.
In recent years, as the world's oil and gas exploration begins to enter the era of paying equal attention to conventional and unconventional oil and gas, especially due to the continuous discovery and research and exploration of unconventional oil and gas, it is gradually found that the traditional petroleum geology theory, which is mainly based on the research of conventional oil and gas reservoirs, has become increasingly difficult to meet the needs of the new situation of oil and gas exploration and developmentPetroleum geologyConcepts and theories (such as the concept, classification and accumulation theory of oil and gas reservoirs) need to be re understood and improved.
On the other hand, research shows that conventional and unconventional oil and gas reservoirs are closely related in formation and distributionOil and gas explorationContrary to the development process, the formation of oil and gas reservoirs is often a process from unconventional to conventional oil and gas reservoirs, or a process from continuous to discontinuous accumulation. In this process, three types of oil and gas accumulations, continuous, quasi continuous and discontinuous, have been formed, which represent the basic types of oil and gas reservoir formation in the crust.[2]
In petroliferous basins, conventional and unconventional oil and gas reservoirs or continuous, quasi continuous and discontinuous oil and gas accumulations often coexist, but they are "mutually generated and mutually restricted", and there are close links and unique distribution laws between them.In this case, it is particularly necessary and important for the current and future conventional and unconventional oil and gas exploration to carry out research on the whole process of oil and gas reservoirs from continuous to discontinuous, and reveal the internal relationship between the formation of conventional and unconventional oil and gas reservoirs, as well as the characteristics and distribution laws of various oil and gas accumulations.[2]
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Oil and gas reservoir
Oil and gas reservoir (pool): it is the basic unit of oil and gas accumulation in the crust, the accumulation of oil and gas in a single trap, with independent pressure system and unified oil-water interface.Note: "Single trap": (1) controlled by a single element;(2) The fluid has a unified pressure system and a unified oil gas water boundary.
Oil reservoir: only oil accumulates in the trap
Gas reservoir: only natural gas accumulates in traps
Oil and gas reservoirs: accumulation of both oil and gas in traps
Commercial reservoir: an oil and gas reservoir with commercial exploitation value under certain political, technical and economic conditions.
Typical distribution of oil, gas and water in a single oil and gas reservoir (gravity differentiation)
(1) Bottom water reservoir: An oil reservoir with movable water everywhere under the oil column.(The altitude of oil-water interface is higher than the altitude of high points on the bottom of the reservoir)
(2) Edge water reservoir: a reservoir (edge water) in which there is no bottom water under the oil column near the high point of the reservoir and there is bottom water at the edge.
(3) Gas cap oil ring reservoir: there is no bottom oil under the gas column near the high point of the oil and gas reservoir, and the oil body is distributed in a ring shape.
Oil and gas reservoirs are classified according to the origin of traps:Structural reservoir, includingAnticline reservoir、Fault reservoir, fractured anticline reservoirs andPuncture reservoir。Stratigraphic reservoir, includingLithologic reservoir、stratumUnconformity reservoirStratigraphic overlap reservoirAnd reef block reservoirs.Hydrodynamic reservoirIncluding structural hydrodynamic reservoirs and monoclinic hydrodynamic reservoirs.Composite oil and gas reservoirs include structural stratigraphic composite oil and gas reservoirs, structural hydrodynamic composite oil and gas reservoirs, stratigraphic hydrodynamic composite oil and gas reservoirs and structural stratigraphic hydrodynamic composite oil and gas reservoirs.
In addition to the above classification, there is the Broad classification which was widely spread in the past.According to the reservoir morphology, oil and gas reservoirs are divided into:Layered reservoir, including anticlinal dome reservoirs and screened reservoirs;Massive oil and gas reservoirs, including structural bulge oil and gas reservoirs, erosion bulge oil and gas reservoirs and biogenetic bulge oil and gas reservoirs;Irregular oil and gas reservoirs include lenticular oil and gas reservoirs in normal sedimentary rocks, sandstone oil and gas reservoirs in paleotopographic recesses, oil and gas reservoirs in zones with increased porosity and permeability, and oil and gas reservoirs in small protrusions of paleotopography.
Destruction of oil and gas reservoirs
It is mainly caused by tectonism.Tectonism first destroys the tightness of traps, causing oil and gas to escape or suffer from oxidation and hydraulic scouring, which will destroy part or all of the oil and gas reservoirs.Primary reservoirAfter destruction, it may also formSecondary reservoir。The effect of high temperature and pressure deep underground can also damage oil and gas reservoirs.
concept
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Scholars in different periods, countries or regions have some differences in their understanding of the concept of oil and gas reservoirs.
In Chinese petroleum geology textbooks, the more popular concept of oil and gas reservoir is that oil and gas reservoir is the accumulation of oil and gas in a single trap, with a unified pressure system and oil (gas) - water interface.In particular, since the 1990s, petroleum geology textbooks have generally emphasized two elements in the definition of oil and gas reservoirs: "a single trap" and "a unified pressure system and oil (gas) water interface", such as Oil and Gas Geology by Chen Rongshu, Petroleum Geology by Zhang Houfu, etc.
However, in the petroleum geology textbooks in the 1980s and before, although the definition of oil and gas reservoirs also emphasized the importance of traps, it did not mention "having a unified oil-water interface", such as Petroleum Geology written by the Petroleum Geology Teaching and Research Office of the Geology Department of Northwest University, and Petroleum Geology written by Zhang Wanxuan and Zhang Houfu.Different from domestic scholars, foreign scholars have not mentioned "having a unified pressure system and oil (gas) - water interface" when defining the connotation of oil and gas reservoirs, and even "traps" have not been mentioned.As Levorsen pointed out, "the oil or gas contained in a single ore bed is called oil or gas reservoir".Hobbes and Terazwu call a single accumulation an oil and gas reservoir.Chapman proposed that oil and gas accumulation in a single reservoir can sometimes be called a pool, but he believed that the term "pool" was not recognized in the world.Only North's concept of oil and gas reservoir emphasizes the characteristics of "single trap".[2]
However, it is worth noting that the above concepts of oil and gas reservoirs are mainly based on the research of conventional oil and gas reservoirs.With the discovery of more and more unconventional oil and gas reservoirs, it is gradually recognized that many unconventional oil and gas reservoirs, including tight oil and gas, shale oil and gas, and coalbed methane, usually do not have edge and bottom water.In this case, the concept of "oil and gas reservoir with unified oil (gas) - water interface" is obviously not applicable to unconventional oil and gas reservoirs.In addition, some researchers believe that there is no obvious trap and cap rock for continuous accumulation, including tight oil and gas, shale oil and gas, and coal-bed gas.[2]
Basic conditions for the formation of oil and gas reservoirs
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1、 Sufficient oil and gas sources;
2、 Favorable source reservoir cap rock assemblage;
3、 Have effective traps;
4、 Necessary storage conditions are available.
Reservoir description
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Oil and gas reservoir description is a new technology that uses the obtained underground information to study and quantitatively describe the geological characteristics of oil and gas reservoir development, and evaluate them. It is called RDS Technical Service for short.The main contents of the description include: reservoir structural morphology, reservoir sedimentary characteristics and heterogeneity, reservoir physical properties and spatial structure, fluid properties and seepage characteristics.In different exploration and development stages, the description contents are different and focused, but they should be carried out around the specific characteristics of oil and gas reservoirs and production needs.
Physical property of oil and gas reservoir
It refers to the rock of oil and gas reservoirPhysicsProperties, physical and chemical properties of fluid in the reservoir, and its phase state and volume characteristics under formation conditions, as well as the molecular surface phenomenon and interaction of rock fluid, and the displacement mechanism of oil, gas and water.Studying the physical properties of oil and gas reservoirs is for the development design of oil and gas fields, development performance analysis, and improvement ofUltimate recovery factorProvide parameters andbasisIs one of the important research topics of oil and gas field development.
Classification and characteristics of hydrocarbon accumulation types
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According to the accumulation mode or distribution pattern of oil and gas reservoirs, oil and gas reservoirs are divided into three types of oil and gas accumulation: continuous, quasi continuous and discontinuous. Continuous and quasi continuous oil and gas accumulation are commonly referred to as unconventional oil and gas reservoirs, while discontinuous accumulation is conventional oil and gas reservoirs.[2]
Continuous hydrocarbon accumulation
The concept of "continuous aggregation" was first developed byUSGSIt was proposed in the mid-1990s that oil and gas accumulations with large spatial distribution and no clear boundary exist more or less independent of water column (edge and bottom water).
According to Schmoker, continuous accumulation belongs to unconventional oil and gas reservoirs, including coalbed methane, basin center gas, tight gas, shale gas and natural gas hydrate.[2]
True continuous aggregation should beSource rockThe aggregation formed in theShale oil and gas、CBMEtc.However, not all shale oil and gas reservoirs and coal-bed gas reservoirs are continuous accumulations, and both can have quasi continuous and discontinuous (conventional trap) accumulations, especially the discontinuous (conventional trap) accumulation may even be another important type of coal-bed gas reservoirs and even shale oil and gas reservoirs.[2]
The main characteristics of continuous hydrocarbon accumulation can be summarized as follows:
(1) The reservoir is dense to ultra dense.
(2) Oil and gas exist in multiphase state, such as adsorption, dissociation and dissolution.Different from typical quasi continuous and discontinuous oil and gas accumulation, oil and gas mainly exist in free state. The main occurrence phase state of continuous oil and gas accumulation not only exists in free state, but also has adsorption state and even dissolution state. It can be said that the presence of more adsorption state is one of its most distinctive characteristics.
Among them, CBM is mainly adsorbed.For shale gas, the adsorbed state and free state are both important, but the proportion of the two varies greatly.It can be said that the existence of adsorption state makes the oil and gas accumulation in the source rock have typical continuous accumulation characteristics, while the existence of free state is more conducive to the enrichment and high production of oil and gas.
(3) In fact, there is only one oil and gas reservoir in an oil and gas accumulation, and oil and gas are continuously distributed in large areas without clear boundaries.A prominent feature of continuous accumulation is that an oil and gas accumulation is actually composed of only one oil and gas reservoir, so the oil and gas fields are packaged or non packaged.Moreover, oil and gas reservoirs are distributed in large areas and have large reserves. They are generally medium-sized or even large - giant or super giant oil and gas fields.Its distribution area generally ranges from hundreds to tens of thousands of square kilometers or even hundreds of thousands of square kilometers.As the reservoir is formed within the source, the range of effective source rock distribution is usually the range of oil and gas accumulation.
(4) The reservoir is formed within the source and is self generated and self stored. It is mainly in situ or nearby accumulation, and there is generally no significant migration of oil and gas.Continuous accumulation is mainly formed in the source rock, which belongs to intra source accumulation. It can be said that only in the source rock can large-scale continuous oil and gas accumulation be formed.
The oil and gas reservoirs formed in this source are mainly in-situ or nearby accumulations, and the oil and gas generally do not migrate significantly, and there is also a lack of dominant migration channels.Otherwise, if the dominant migration channels are developed in the source rock, on the one hand, conventional oil and gas reservoirs (such as mudstone fractured oil and gas reservoirs) may be formed in the source rock;On the other hand, it is easy to cause a large amount of oil and gas to be discharged from the source rock, which is not conducive to the accumulation in the source rock.
(5) Oil and gas accumulation is basically not controlled by traps.The study on the characteristics of oil and gas accumulation in continuous shale oil and gas, coalbed gas and other source rocks shows that this kind of oil and gas accumulation is basically not controlled by traps, and its oil and gas accumulation and distribution are mainly controlled by the distribution of effective source rocks, roof and floor conditions, etc.Although it is basically not controlled by traps, the existence of structural traps often has a certain or even important control over the local enrichment of such oil and gas reservoirs. At this time, structural traps actually play a "sweet spot" role.In addition, for some continuous oil and gas accumulation (such as coalbed methane reservoir), hydrodynamic conditions will also have an important control over oil and gas enrichment, but they may not completely act as traps (so-called“Hydrodynamic trap”）And similar to the "dessert" nature.
(6) Oil and gas enrichment is mainly controlled by source rock quality, reservoir "sweet spot", sealing conditions, etc., with the characteristics of enrichment in low structural parts.[2]
Quasi continuous hydrocarbon accumulation
Quasi continuous oil and gas accumulation is mainly formed in tight reservoirs adjacent to source rocks, and its typical representative is tight oil and gas reservoirs.But not all quasi continuous accumulations are tight oil and gas, and not all tight oil and gas are quasi continuous accumulations.
There may also be quasi continuous accumulation in shale oil and gas and coalbed gas reservoirs, while some tight oil and gas reservoirs belong to discontinuous (conventional trap type) accumulation. For tight oil and gas, two types of reservoir formation models have been proposed in the past: ① deep basin gas or continuous accumulation model; ②Conventional trap accumulation mode.In recent years, Zhao Jingzhou and other researchers believe that although the above two modes exist for tight oil and gas, they are mainly quasi continuous accumulation modes.Bai Yubin and others also believe that the 6th member of Yanchang Formation in Ordos Basin belongs to this model.The so-called quasi continuous oil and gas accumulation refers to a group of oil and gas reservoirs composed of several small and medium-sized oil and gas reservoirs that are adjacent to each other. The oil and gas reservoirs are distributed in a quasi continuous manner without a clear oil and gas reservoir boundary.[2]
The main characteristics of quasi continuous hydrocarbon accumulation can be summarized as follows:
(1) The reservoir is tight, and most of them are "tight before forming reservoir".
(2) Oil and gas are distributed in a quasi continuous manner in a large area without clear boundaries, edge and bottom water are not or only locally distributed, and there is no regional inversion of oil, gas and water.
(3) Near source reservoir formation, oil and gas are filled in a large area, the primary migration directly forms the reservoir and the short distance secondary migration forms the reservoir, and oil and gas migration and accumulation are mainly driven by non buoyancy.
(4) Oil and gas accumulation is mainly controlled by non anticline traps such as lithology, and anticline traps basically do not control.
(5) Oil and gas are mainly concentrated in gentle depressions and slopes, and hydrocarbon source, reservoir and sealing conditions are the main control factors.[2]
Discontinuous hydrocarbon accumulation
Discontinuous oil and gas accumulation can also be called conventional trap type or conventional oil and gas accumulation, which is mainly distributed in conventional reservoirs (permeability is generally greater than 1mD).However, not all discontinuous accumulations are conventional reservoirs. Unconventional oil and gas reservoirs such as tight oil and gas, coalbed methane, shale oil and gas can also have discontinuous (conventional trap) accumulations.
In fact, discontinuous (conventional trap) accumulation is also one of the important accumulation modes of unconventional oil and gas.For example, although most of the tight oil and gas are quasi continuous accumulations, there are also conventional traps such as anticlines.Especially in the areas with intense structural deformation of tight reservoirs (such as foreland thrust belts), anticline and other structural trap type oil and gas accumulation is even a major reservoir forming model.In addition, if the relationship between tight oil and gas reservoirs and their reservoirs is "reservoir formation before compaction", they may also form conventional trap type accumulation.[2]
The main characteristics of discontinuous hydrocarbon accumulation are summarized as follows:
(1) Oil and gas reservoirs are distributed in isolation and dispersion, with clear boundaries and usually complete edge and bottom water.
(2) The formation of oil and gas reservoirs generally goes through secondary migration, near source or far source accumulation. Buoyancy is the main driving force of oil and gas migration, and there are generally dominant oil and gas migration channels.
(3) Oil and gas accumulation is strictly controlled by traps, with various trap types.
(4) Oil and gas enrichment is controlled by multiple factors, and oil and gas are generally most enriched in the high part of the structure.[2]
Temporal spatial relationship and distribution law of three types of oil and gas accumulation
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Continuous, quasi continuous and discontinuous oil and gas accumulation represent three basic types of oil and gas accumulation in the crust, which can be found in all major oil and gas basins in the world.Moreover, oil and gas generated from the same source stove can often form continuous, quasi continuous and discontinuous oil and gas accumulation at the same time, and there are close relations and unique distribution laws between them.[2]
In terms of spatial distribution
Horizontally, continuous and quasi continuous oil and gas accumulations are mainly distributed in hydrocarbon generating sags and slopes, while discontinuous oil and gas accumulations are mainly distributed in the high structural parts at the edge of the sags, relatively shallow parts inside the sags, or relatively far away from effective hydrocarbon source beds.
Vertically, the three types of oil and gas accumulations often occur in different layers, but can be distributed in different layers, and are often characterized by the distribution of continuous, quasi continuous, and discontinuous accumulations of source rocks upward and downward.
Generally, the quasi continuous oil and gas accumulation represented by tight oil and gas is distributed in the upper and lower adjacent strata of the source rock (continuous oil and gas accumulation), with the characteristics of near source distribution, while the discontinuous conventional oil and gas accumulation is mostly distributed in the farther strata.This is because the source rocks often represent the most marine (lacustrine) transgression period, before which is the marine (lacustrine) transgression stage, so the positive grain sequence sedimentary structure is often formed;On the source rocks, however, it is a regressive stage, often forming reverse grain sequence sedimentary structure.
Therefore, the closer to the source rock, the finer the sediment particles are, the easier it is to form compact reservoirs, while the farther away from the source rock, the easier it is to form conventional reservoirs.It can be predicted that shale oil and gas (or coalbed gas), tight oil and gas, and conventional oil and gas (i.e. continuous, quasi continuous, and continuous accumulation) are commonly associated in oil and gas bearing basins.[2]
In terms of the time sequence of oil and gas accumulation
It is found that the formation of oil and gas reservoirs in the same source stove is usually characterized by continuous to discontinuous accumulation, that is, continuous accumulation is generally formed first, followed by quasi continuous accumulation, and finally discontinuous accumulation.The specific formation process is as follows:
First of all, the oil and gas generated from the source rock usually give priority to meet the saturation of the source rock itself, and accumulate into reservoirs, forming continuous oil and gas accumulation;Then, when the pores of the source rock are saturated with oil and gas, or when the oil and gas generated in the source rock has enough power to expel hydrocarbon, the continuously generated oil and gas begin to expel to the reservoir outside the source rock.
For thick source rocks, the upper and lower edges or parts close to faults are prone to hydrocarbon expulsion, while the interior of source rocks is difficult to expel hydrocarbon, which is easy to stay and form reservoirs, and is the main part of continuous oil and gas accumulation.In the process of outward migration of oil and gas discharged from source rocks, since the reservoir closest to the source rock is often a tight reservoir, the accumulation of oil and gas outside the source rock usually first occurs in the tight reservoir, thus forming a tight oil and gas reservoir or quasi continuous accumulation, unless there is a fault connecting the source rock directly with the conventional reservoir.When oil and gas meet the requirements for accumulation in tight reservoirs, the surplus oil and gas begin to migrate and accumulate to conventional reservoirs that are relatively far away from the source rocks, thus forming conventional oil and gas reservoirs or discontinuous accumulations.[2]
Because the oil and gas accumulations formed in the same source stove, continuous, quasi continuous and discontinuous oil and gas reservoirs are the products of oil and gas accumulation in source rocks, tight reservoirs and conventional reservoirs respectively during the generation and migration of oil and gas from source rocks to reservoirs, so there is a mutual growth and decline relationship between the three in resource potential.Among them, the proportion of continuous accumulation in oil and gas generated from source rocks (retention rate) is the key. The higher the retention rate of oil and gas in source rocks or the lower the hydrocarbon expulsion rate, the higher the proportion of resources in continuous oil and gas accumulation, and the lower the proportion of resources in quasi continuous and discontinuous oil and gas accumulation.The main factors that determine the retention rate of oil and gas in source rocks are the thickness of effective source rocks, the abundance of organic matter and the sealing conditions at the top and bottom. The greater the thickness of effective source rocks, the higher the abundance of organic matter, especially the sealing conditions at the top and bottom, the more conducive to the accumulation of oil and gas in source rocks,The resource proportion of continuous oil and gas accumulation is higher.
On the contrary, source rocks with thin thickness and poor top and bottom sealing conditions generally have a high hydrocarbon expulsion rate, which is beneficial to the accumulation outside the source rock, but not conducive to the accumulation of oil and gas in the source rock.The resource potential of quasi continuous oil and gas accumulation in tight reservoirs and discontinuous oil and gas accumulation in conventional reservoirs depends not only on the amount of oil and gas discharged from source rocks, but also on the scale, quality and sealing conditions of tight reservoirs,The higher the proportion of resources formed by the quasi continuous accumulation, on the contrary, it is conducive to the accumulation and resource enrichment of conventional reservoirs.[2]
epilogue
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The formation of oil and gas reservoirs is a process from continuous accumulation to discontinuous accumulation. In this process, continuous, quasi continuous and discontinuous oil and gas accumulations are formed, which are different from each other and closely related.In petroliferous basins, conventional and unconventional oil and gas reservoirs or continuous, quasi continuous and discontinuous oil and gas accumulations often coexist, but they are "mutually generated and mutually restricted", and there are close links and unique distribution laws between them.
Therefore, in the study of reservoir formation and exploration of oil and gas bearing basins or petroleum systems, we should strengthen the study of the whole process and all directions of the formation of oil and gas reservoirs in order to maximize the exploration results.[2]
