Is the oil the remains of dead dinosaurs? No, but the mystery of its origin is quite interesting.

The generally accepted theory is that the current oil reserves originate from organic materials that existed millions of years before dinosaurs appeared on Earth. About 300 million years ago, dead organic materials such as zooplankton and algae accumulated at the bottom of the seas and oceans, where they could not decompose. Organic matter turned into kerogen, which over time, at high temperature and pressure, became oil.

In this infographic, we will take a closer look at the process of the emergence of "black gold", as well as talk about its application and history.

Where did the oil come from - an alternative theory

The above-mentioned theory of the organic origin of oil explains the appearance of most of the deposits on Earth, but an alternative theory has existed for more than a century. And if it is confirmed, our attitude to the world and natural resources will change completely.

According to the theory of abiotic oil, some of the oil originated from inorganic materials. In other words, it originated as a result of natural processes deep in the earth's crust or was brought to the planet by meteorites. Frankly speaking, we already know about the existence of hydrocarbons in space, although organic materials are not there. In 2009, it was proved that ethane and heavier hydrocarbons can be synthesized under the temperature and pressure conditions typical of upper layers the mantle of the planet.

So what's the flaw in the theory? The fact is that until now, not a single field of abiotic oil has been discovered on Earth. In addition, not a single discovery has been made by geologists with the help of the abiotic theory, and many of the postulates of the alternative theory are today recognized as pseudoscience.

At the moment, this theory is just a curious, but not confirmed hypothesis.

Experts perceive the widespread forecast of an imminent (in 30-50 years) depletion of oil reserves differently. Most - with respect ("it is"), others skeptical ("oil reserves are unlimited!"), And the third with regret ("could have been enough for centuries ..."). Popular Mechanics decided to investigate this issue.

Oil formation according to biogenic theory

The volumes of oil production at the "White Tiger" field on the sea shelf of Vietnam have surpassed the most optimistic forecasts of geologists and inspired many oilmen with the hope that huge reserves of "black gold" are stored at great depths

1494-1555: Georgius Agricola, physician and metallurgist. Until the 18th century, there were many curious versions of the origin of oil (from "earth fat under the influence of the waters of the Flood", from amber, from whale urine, etc.). In 1546, George Agricola wrote that oil is inorganic in origin, and coal is formed by its thickening and solidification.

1711−1765: Mikhailo Vasilievich Lomonosov, encyclopedic scientist - chemist, physicist, astronomer, etc. One of the first to express a scientifically substantiated concept of the origin of oil from plant residues subjected to carbonization and pressure in the earth's layers ("On the layers of the earth", 1763) : "Brown and black oily matter is expelled by the underground heat from the preparing coal ..."

1834-1907: Dmitry Ivanovich Mendeleev, chemist, physicist, geologist, meteorologist, etc. At first he shared the idea of ​​the organic origin of oil (as a result of reactions taking place at great depths, at high temperatures and pressures, between carbonaceous iron and water seeping from the surface land). Later adhered to the "inorganic" version

1861-1953: Nikolai Dmitrievich Zelinsky, organic chemist. He made a significant contribution to solving the problem of the origin of oil. He showed that some carbon compounds that are part of animals and plants, at low temperatures and appropriate conditions, can form products similar to oil in chemical composition and physical properties

1871-1939: Ivan Mikhailovich Gubkin, oil geologist. Founder of Soviet petroleum geology, supporter of biogenic theory. He summarized the results of studies of the nature of oil and came to the conclusion: the process of its formation is continuous; the most favorable for the formation of oil are areas of the earth's crust that were unstable in the past at the boundaries of areas of subsidence and uplift

Roughly speaking, no one knows for how many years the oil reserves will last. What is more surprising, until now no one can say for sure in what way oil is formed, although the dispute about this has been going on since the 19th century. Scientists, depending on their beliefs, were divided into two camps.

Now the biogenic theory prevails among specialists in the world. It says that oil and natural gas formed from the remains of plant and animal organisms in the course of a multi-stage process lasting millions of years. According to this theory, one of the founders of which was Mikhail Lomonosov, oil reserves are irreplaceable and all of its deposits will eventually run out. Irreplaceable, of course, taking into account the transience of human civilizations: the first alphabet and nuclear energy are separated by no more than four thousand years, while the formation of new oil from the current organic remains will take millions. This means that our not too distant descendants will have to do without oil, and then without gas ...

Supporters of the abiogenic theory are optimistic about the future. They believe that our oil and gas reserves will last for many more centuries. While in Baku, Dmitry Ivanovich Mendeleev once learned from the geologist Herman Abikh that oil deposits are geographically very often confined to discharges - a special type of cracks in the earth's crust. At the same time, the famous Russian chemist became convinced that hydrocarbons (oil and gas) are formed from inorganic compounds deep underground. Mendeleev believed that during mountain-building processes along cracks that cut the earth's crust, surface water seeps into the depths of the Earth to metal masses and reacts with iron carbides, forming metal oxides and hydrocarbons. Then hydrocarbons along the cracks rise to the upper layers of the earth's crust and form oil and gas deposits. According to the abiogenic theory, the formation of new oil will not have to wait for millions of years, it is a completely renewable resource. Proponents of the abiogenic theory are confident that new deposits are expected to be discovered at great depths, and that the oil reserves explored at the moment may well turn out to be insignificant in comparison with those still unknown.

Looking for evidence

Geologists, however, are pessimists rather than optimists. At least they have more reasons to trust the biogenic theory. Back in 1888, German scientists Gefer and Engler set up experiments that proved the possibility of obtaining oil from animal products. During the distillation of fish oil at a temperature of 4000C and a pressure of about 1 MPa, they isolated saturated hydrocarbons, paraffin and lubricating oils from it. Later, in 1919, Academician Zelinsky from organic silt from the bottom of Lake Balkhash, mainly of plant origin, obtained crude tar, coke and gases - methane, CO, hydrogen and hydrogen sulfide by distillation. Then he extracted gasoline, kerosene and heavy oils from the resin, having experimentally proved that oil can be obtained from organic matter of plant origin.

Supporters of the inorganic origin of oil had to adjust their views: now they did not deny the origin of hydrocarbons from organic matter, but believed that they could be obtained by an alternative, inorganic method. Soon they had their own evidence. Spectroscopic studies have shown that the simplest hydrocarbons are present in the atmosphere of Jupiter and other giant planets, as well as their satellites and in the gas envelopes of comets. This means that if the processes of synthesis of organic substances from inorganics are taking place in nature, nothing interferes with the formation of hydrocarbons from carbides on Earth. Soon, other facts were discovered that did not agree with the classical biogenic theory. On a number of oil wells oil reserves began to recover in an unexpected way.

Oil magic

One of the first such paradoxes was discovered in an oil field in the Tersko-Sunzhensky region, not far from Grozny. The first wells were drilled here back in 1893, in places of natural oil shows.

In 1895, one of the wells from a depth of 140 m gave a grandiose gusher of oil. After 12 days of gushing, the walls of the oil barn collapsed and the flow of oil flooded the rigs of nearby wells. Only three years later, the fountain was tamed, then it dried up and from the fountain method of oil production they switched to the pumping method.

To the beginning of the Great Patriotic War all wells were heavily watered, and some of them were mothballed. After the onset of peace, production was restored, and, to everyone's surprise, almost all high-water-cut wells began to produce waterless oil! In an incomprehensible way, the wells received a "second wind". Half a century later, the situation repeated itself. To the beginning Chechen wars the wells were again heavily watered, their production rates dropped significantly, and during the wars they were not operated. When production was resumed, production rates increased significantly. Moreover, the first shallow wells began to seep oil to the earth's surface through the annulus. Supporters of the biogenic theory were perplexed, while the "inorganics" easily explained this paradox by the fact that in this place the oil is of inorganic origin.

Something similar happened at one of the world's largest Romashkinskoye oil fields, which has been developed for over 60 years. According to Tatar geologists, 710 million tons of oil could be extracted from the wells of the field. However, to date, almost 3 billion tons of oil have already been produced here! The classical laws of oil and gas geology cannot explain the observed facts. Some wells seemed to be pulsating: a drop in production rates was suddenly replaced by their long-term growth. A pulsating rhythm was also noted in many other wells in the territory of the former USSR.

It is impossible not to mention the White Tiger field on the Vietnamese shelf. From the very beginning of oil production, "black gold" was extracted exclusively from sedimentary strata, here the sedimentary stratum (about 3 km) was drilled through, entered the foundation of the earth's crust, and the well gushed. Moreover, according to the calculations of geologists, it was possible to extract about 120 million tons from the well, but even after this volume was produced, oil continued to flow from the bowels with good pressure. The field posed a new question for geologists: does oil accumulate only in sedimentary rocks, or can it be stored in basement rocks? If the foundation also contains oil, then the world reserves of oil and gas may turn out to be much larger than we assume.

Fast and inorganic

What caused the "second wind" of many wells, which is inexplicable from the point of view of the classical geology of oil and gas? “In the Tersko-Sunzhensky field and some others, oil can be formed from organic matter, but not over millions of years, as classical geology envisages, but over a few years, - says the head of the Department of Geology of the Russian State University of Oil and Gas. THEM. Gubkina Victor Petrovich Gavrilov. - The process of its formation can be compared with the artificial distillation of organic matter, similar to the experiments of Gefer and Zelinsky, but carried out by nature itself. This rate of oil formation became possible due to the geological features of the area, where, together with the lower part of the lithosphere, part of the sediments is drawn into the upper mantle of the Earth. There, under conditions of high temperatures and pressures, there are rapid processes of destruction of organic matter and synthesis of new hydrocarbon molecules ”.

At the Romashkinskoye field, according to Professor Gavrilov, a different mechanism operates. Here, in the thickness of the crystalline rocks of the earth's crust, in the basement, lies a thick layer of high-alumina gneisses more than 3 billion years old. The composition of these ancient rocks contains a lot (up to 15%) of graphite, from which hydrocarbons are formed at high temperatures in the presence of hydrogen. They rise along faults and cracks into the porous sedimentary layer of the crust.

There is another mechanism for the rapid replenishment of hydrocarbon reserves, discovered in the West Siberian oil and gas province, where half of all Russia's hydrocarbon reserves are concentrated. Here, according to the scientist, in the buried rift valley of the ancient ocean, the processes of methane formation from inorganics took place and are taking place, as in "black smokers" (see inset). But the local rift valley is blocked by sediments, which interferes with the dispersion of methane and forces it to concentrate in rock reservoirs. This gas fed and continues to feed the entire West Siberian Plain with hydrocarbons. Here, oil is rapidly formed from organic compounds. So, will there always be hydrocarbons here?

“If we build our approach to field development on the basis of new principles,” the professor answers, “to coordinate the rate of extraction with the rate of supply of hydrocarbons from the sources of generation in these areas, the wells will operate for hundreds of years”.

But this is a too optimistic scenario. The reality is more cruel: in order for the reserves to have time to replenish, mankind will have to abandon "violent" mining technologies. In addition, it will be necessary to introduce special rehabilitation periods, temporarily abandoning the operation of the fields. Will we be able to do this in the face of the growing population of the planet and growing needs? Unlikely. After all, apart from nuclear energy, oil does not yet have a worthy alternative.

Dmitry Ivanovich Mendeleev criticized in the century before last that burning oil is like stoking a stove with banknotes. If the great chemist lived today, he would probably call us the craziest generation in the history of civilization. And perhaps he would be wrong - our children can still surpass us. But the grandchildren, most likely, will not have such a chance ...

Today, most scientists believe that oil is of biogenic origin. In other words, oil was formed from the decay products of small organisms of animals and plants (plankton) that lived millions of years ago. The oldest oil fields were formed 600 million years ago.

At that time, most of the Earth was covered with water. After death, living organisms sank to the bottom of ancient seas and bays and were covered with silt, sand and layers of subsequent sediments. These deposits gradually compacted, dehydrated and sank lower and lower. At the same time, the pressure and temperature in these deposits increased. Under the influence of anaerobic bacteria (that is, bacteria that can live without oxygen), hydrocarbons began to form from organic matter, collected in small oily droplets. Unfortunately, scientists cannot yet accurately answer the question of what processes in organic sediments led to the formation of oil.

It is important to understand that hydrocarbons did not lie underground in the form of oil lakes. They were mixed with water and sand, which gradually seeped through the porous layers of sandstone and limestone along with gas bubbles. Often the mixture was propelled through rocks under the influence of high pressure... Oil and gas seeped into the voids between the sedimentary particles like water flows into a sponge. Sooner or later, the oil and gas tracked a layer of rock through which they could not seep - impermeable rock that had no pores or cracks - and thus they found themselves in a geological "trap."

While the process of oil formation was going on, the Earth was also changing. There were movements of the earth's crust, faults and connections of massifs. These processes formed Various types oil geological "traps".

We know that the composition of oil found in different parts of the globe varies greatly. This is explained by the difference in the reactions that occurred during the formation of oil or different types of plants and animals, from whose organisms it was formed.

Oil reserves are estimated at hundreds of billions of tons, and it is distributed everywhere, on land and at sea. What lay on the surface has long been used, and now oil is extracted from depths of 2-4 kilometers or more. But even deeper it is even more, it is just that it is economically unprofitable to extract it from there, that is, it is expensive.

Did you know ...

The first conjecture about the origin of oil from organic matter was expressed by the Russian scientist Mikhailo Vasilyevich Lomonosov in his work "On the layers of the earth" (1763)

"Oil is the most valuable chemical raw material,
It must be protected. And you can heat boilers
and banknotes. "
D.I. Mendeleev

Despite the fact that by the end of the twentieth century, nuclear energy began to grow rapidly, oil still occupies the most important place in the energy balance of all countries. How could it be otherwise? After all, you can't put a nuclear power plant on cars and airplanes! Nuclear ships, of course, exist, but there are few of them. What about everything else? And man is alive not only by energy. He walks on asphalt roads, and this is oil. And all these gasolines, kerosene, fuel oil, oils, rubbers, rubbers, polyethylene, asbestos products and even mineral fertilizers! It would be bad for us if there were no oil on the globe. But there is a lot of oil on Earth, they began to extract it back in the VI millennium BC, and now the annual production is hundreds of millions of tons.

Oil brings in big profits. Whole countries thrive selling their oil and envy their neighbors. Other countries are pumping oil into natural and artificial caves, creating strategic reserves just in case. Oil kings and monopolies, pipelines and oil refineries, redistribution of oil property, oil wars, contracts and speculation, etc., etc. What has not happened in the history of mankind because of oil! Life would be boring for people if it were not for her in the world.

But oil exists, its reserves are estimated at hundreds of billions of tons, and it is distributed everywhere, on land and at sea, and at great depths, calculated in kilometers: what lay on the surface has long been used, and now oil is extracted from depths of 2-4 or more kilometers. But even deeper it is even deeper, it is simply unprofitable to extract it from there.

But here's the strange thing: although there is a lot of oil and it is widely used, until now no one knows where the oil came from on Earth at all. There are many guesses and hypotheses on this score, some refer to the pre-scientific period, which lasted until the Middle Ages, and others to the scientific period, called by scientists the period of scientific guesses.

In 1546 Agricola wrote that oil and coal are of inorganic origin. Lomonosov in 1763 suggested that oil originated from the same organic matter as coal. In the third period - the period of development of the oil industry, a number of assumptions were made about both organic and inorganic origin of oil. Without being able to even simply list them, we will limit ourselves to only a few.

1866 French chemist M. Berthelot: oil is formed by the action of carbon dioxide on alkali metals.

1871 French chemist G. Biasson: oil was formed due to the interaction of water, carbon dioxide and hydrogen sulfide with hot iron.

1877 DI Mendeleev: oil was formed as a result of water penetration deep into the Earth and its interaction with carbides.

1889 VD Soloviev: hydrocarbons were contained in the gas shell of the Earth even when it was a star, and then they were absorbed by molten magma and formed oil.

And then there was a series of hypotheses of inorganic origin of oil, but they were not supported by the International Petroleum Congresses, and of organic origin, which were supported.

Plankton is believed to be the main starting material for oil. Rocks formed from sediments containing this type of organic matter are potentially oil source. After prolonged heating, they form oil. Many variations on this topic have been created, however, one difficulty is not explained in any way, how such a mass of plankton (or mammoths, it doesn't matter) could get to such depths throughout the globe, and even settle in sandstones, albeit porous. And it is still unclear why oil fields always contain not only oil, but also sulfur in the form of hydrogen sulfide or tar. And why in the associated waters accompanying oil production, there is almost the entire set chemical elements hardly contained in plankton.

But those who scientifically guess about the origin of oil try not to focus on such trifles.

However, I would like to draw your attention to another possibility, which most likely will not be recognized by the International Petroleum Congresses. The fact is that the sandstones that contain oil are mainly silicon oxide - SiO. And if from one silicon nucleus, having an atomic weight of 28, one subtract one alpha particle with an atomic weight of 4 and add it to another silicon atom, then a sulfur atom with an atomic weight of 32 is obtained. And the remaining magnesium isotope with an atomic weight of 24 is partially will be preserved as magnesium, which is also contained in the associated waters, and will partially fall apart and give two carbon molecules with an atomic weight of 12 each, thus creating some basis for the formation of both oil and coal. But if this is so, then the question arises about the mechanism that could accomplish all this.

From the point of view of ether dynamics, such a mechanism exists. To the Earth, as to any other heavenly body etheric streams flow in from space, the speed of their entry is equal to the second cosmic speed, which is 11.18 km / s for the Earth. These streams penetrate into the interior of the Earth to any depth, passing through rocks along the way and becoming turbulized. The result of the turbulization of the ether flows are vortices, which are compressed by the external pressure of the ether, and the speed of flows in them increases many times, as well as the gradients of velocities, which means that large pressure gradients appear, tearing apart molecules, atoms and nuclei and rebuilding the substance. At the same time, over many years, any hydrocarbons and in general any elements could be created from ordinary inorganic rocks, and at any depth.

Such processes may well take place in the bowels of any planets, which means that oil, coal, and other minerals and elements can exist on all planets. Solar system and not only her. This, however, does not mean that there was life on these planets. Just as the prints of dragonflies or leaves in coal do not at all indicate that coal was formed from these dragonflies or leaves. You never know where someone could have flown over the past millions of years!

It follows from the foregoing that the oil crisis may be associated not with a shortage of oil on Earth, but with the high cost of its extraction from deep layers. So DI Mendeleev is right not only in the sense that oil must be conserved because it is a valuable raw material, this is true even if there is a lot of it. He is also right because starting from a certain moment the cost of its extraction will increase so much that it is possible to heat the boilers with banknotes, i.e. paper money will be cheaper.

V. E. KHAIN

Oil and its accompanying or separately occurring natural combustible gas are essential minerals. In the 20th century, they became essentially "blood" National economy, without them, the functioning of such important industries as energy, transport, production would be unthinkable. important materials... Therefore, by analogy with the Stone, Bronze, Iron Ages experienced by mankind at an early stage in the development of its civilization, the past XX century can be called the oil age (the XIX century was coal, and the XXI century is likely to become gas). Currently, oil and gas exports account for about 40% of all Russian exports.
Oil is a mixture of natural hydrocarbons, variable in composition and density, but usually lighter than water. Hydrocarbons can occur naturally and in solid form, in the form of bitumen, but large deposits of the latter are relatively rare. Hydrocarbon gases are much more common, consisting mainly of the lightest component - methane CH4. Under certain conditions of temperatures and pressures, gas releases petroleum hydrocarbons dissolved in it in the form of gas condensate - a liquid that is lighter and lighter than oil, and therefore easier to process. All of these natural hydrocarbon feedstocks have a similar origin and are found either together or in close proximity.

OIL AND GAS IN THE EARTH'S SEDIMENTARY ENVELOPE

Industrial accumulations of oil, gas and gas condensate are found almost exclusively in the upper, sedimentary shell of the earth's crust. Occasionally they are found in volcanic (basalts), intrusive-magmatic (granites), or metamorphic (gneisses) rocks. Oil and gas deposits are found in almost all types of sedimentary rocks, but mainly in sands, sandstones, limestones, dolomites, since they are characterized by increased porosity and represent natural reservoirs - reservoirs, reservoirs of liquid and gaseous hydrocarbons. But also denser rocks - clays, dense carbonates can represent such reservoirs, if they are sufficiently fractured. A common feature of sedimentary strata containing oil deposits is their subaquatic origin, that is, deposition in an aquatic environment. Initially, it seemed that such strata should have necessarily been deposited in marine conditions, but after the discovery of large deposits of oil in continental lacustrine, deltaic sediments in China, it became obvious that the sedimentation environment should have been aqueous, but not necessarily marine.

By the middle of the 20th century, one more prerequisite became clear - the oil-containing strata should have a certain minimum thickness (thickness), about 2-3 km. Thicknesses of this thickness were usually accumulated in large depressions of the earth's crust, since their accumulation and preservation required a prolonged and stable subsidence of the corresponding sections of the crust. Such depressions in the 1950s in the USA (W. Pratt, L. Weeks) and the USSR (I.O. Brod, V.V. Weber, the author of these lines) began to stand out as oil and gas basins. The doctrine of oil and gas bearing basins arose, which is successfully developing at the present time.

The classification of oil and gas basins until the 70s of the XX century was based on the geosynclinal-orogenic-platform concept. Geosynclines were understood as deep troughs of the earth's crust, filled with strata of sediments and volcanic rocks and then transformed into folded mountain structures - orogens. The latter, after their leveling by denudation (erosion), turn into the foundation of stable crustal blocks - platforms, partially overlapped by a sedimentary cover. But in the late 1960s, a new geological concept appeared - the concept of plate tectonics, which quickly gained wide acceptance. In this regard, the classification of oil and gas basins was transferred to a new basis (Fig. 1).

According to the theory of plate tectonics, the upper part of the solid Earth, to a depth of about 200-300 km, is divided into a fragile upper shell - the lithosphere and the underlying relatively plastic asthenosphere. The lithosphere of the Earth is divided into a limited number of large and medium-sized plates, on the boundaries of which the main tectonic, seismic and magmatic activity is concentrated. The boundaries of the plates are of three kinds: divergent, along which they diverge, the formation of new basalt crust and oceanic basins; convergent, along which the plates approach each other, pushing against each other, and, finally, transform, along which they move relative to each other in the horizontal direction along vertical faults.

Divergent boundaries arise within the continental parts of the lithospheric plates in the form of rift systems - deep cracks that open more and more under the action of extension and uplift from the depth of the asthenospheric bulge - the mantle diapir. Depressions are formed above the rifts, in which continental (river, lacustrine) deposits begin to accumulate first, and then marine deposits. At the base of the rifts, thinning of the crust and the entire lithosphere occurs, the uplift of the underlying submelted asthenosphere, and the partial intrusion of basalt magma released from it into the lithosphere. Subsequently, the cooling of the asthenospheric bulge and the magmatites intruded into the lithosphere leads to the expansion and accelerated subsidence of the above-rift depression (Fig. 2). The lowering of the bottom is also facilitated by the pressure of the strata of the sediments accumulated in it. This is how one of the types of oil-and-gas-bearing sedimentary basins is formed - the intraplate one, the largest and brightest representative of which is the West Siberian basin.
Continental rifting with more intense stretching is accompanied by a rupture of the continental crust and transforms into the so-called spreading, that is, filling of the resulting expansion with newly formed oceanic crust released from the asthenosphere with a gradual expansion of the space occupied by it and its transformation into the ocean floor. In this case, the shoulders of the continental rift are transformed into the so-called passive (relatively aseismic, avulcanic) continental margins, framing the newborn ocean. They become the main area of ​​accumulation of sediments carried from the continent, especially in the deltas of large rivers flowing into the ocean. According to the famous lithologist-oceanologist A.P. Lisitsyn, this is an area of ​​avalanche sedimentation, the thickness of sediments here reaches 15-20 km. Thus, large oil and gas basins appear on the passive continental margins. In Russia, these are the Volga-Ural and Timan-Pechora basins, which extend to the north. When folded mountain structures appear within the adjacent part of the ocean, they move to the edge of such a basin, which undergoes additional intense subsidence and turns into the forward (foothill) trough of this structure. These are the Cis-Ural, Ciscaucasian, Ciscarpathian and other similar troughs, which also represent a special type of oil and gas basins.

The active margins of the continents undergo compression during their development, due to which the island arcs merge with each other and ultimately form mountain structures approaching the neighboring continent (or continents, if the ocean is completely closed), as mentioned above. But between individual structures, intermontane depressions often arise, like the Kura depression between the Greater and Lesser Caucasus or the Pannonian (Hungarian) depression between the Carpathians and the Dinaric mountains, which are also filled with thick sediments and are oil and gas basins.

Compression, which manifests itself at convergent plate boundaries and leading to the formation of complex mountain structures like the Caucasus, the Alps or the Himalayas, often extends far into the interior of the continents, in areas that have long lost tectonic activity, were covered with an almost undisturbed sedimentary cover and represented the so-called platforms ... At the same time, the crust of such platforms begins to warp, experiencing uplifts and subsidences with the formation of mountain structures and intermontane depressions, the latter, again, are oil and gas bearing sedimentary basins. This process of intracontinental orogenesis (mountain building) is most clearly manifested in Central Asia, and it is here that such basins as Fergana, Tajik, Dzhungar, Tarim are located.

These are the main types of oil and gas basins. The question arises: how are oil and gas formed in sedimentary basins?

ORIGIN OF OIL AND GAS. OIL AND GAS COLORS

Unlike another combustible fossil - coal, the origin of which is quite obvious thanks to the finds of leaf prints and even whole petrified tree trunks and was unraveled by M.V. Lomonosov, the origin of oil has long been the subject of heated debate, which has not completely died down even today. There are two opposite versions of the origin of oil: inorganic and organic. The choice between these versions is complicated by the fact that oil and gas are very mobile fluid substances, they are capable of movement - migration inside the earth's crust and its sedimentary shell over long distances, and their accumulations are often far enough from the supposed place of formation.

The inorganic hypothesis of the origin of oil was relatively the most popular in the USSR, where it was defended by two scientific schools - in St. Petersburg (then Leningrad), headed by N.A. Kudryavtsev and Kiev, headed by V.B. Porfiriev. The adherents of this trend relied on the authority of D.I. Mendeleev, who suggested that oil could have been formed by the action of water on iron carbide. The main geological facts that formed the basis for the constructions of "inorganics" were the finding of some deposits of oil in volcanic, intrusive-magmatic and metamorphic rocks. Such deposits do exist. Particularly indicative is the example of a large accumulation of oil in fractured and weathered granites at the White Tiger field in the south of Vietnam, in the Mekong Delta.

From the standpoint of the opposite, organic concept of oil genesis, all such deposits are the result of oil migration from adjacent sedimentary rocks. But it should be recognized that hydrocarbons, in principle, can have inorganic origin in nature - otherwise how to explain their presence in meteorites and the atmosphere of some planets and their satellites, as well as the release of methane in rift zones of mid-ocean ridges, which are practically devoid of precipitation. However, all these locations are only of scientific interest, and we should talk about deposits of industrial importance.

Opponents of "inorganics" cited the presence of spores and pollen of plants and specific organic compounds - porphyrins - in oils as arguments in favor of organic origin. However, the "inorganics" explained all this by borrowing from the host deposits of sedimentary rocks. The decisive proof of the organic origin of oil was provided by the data of organic geochemistry, which established the identity of oil and biogenic hydrocarbons in molecular level... The molecules of such organic compounds are called "biomarkers", that is, labels indicating the biogenic origin of this oil. Despite this, some researchers both in our country and abroad continue to defend the inorganic origin of oil. Corresponding views were expressed quite recently in the pages of the Explorer magazine, published by the authoritative American Association of Petroleum Geologists. And in Sweden, a rather deep well was even drilled in the crystalline rocks of the Baltic Shield, but no oil inflows were received.

In general, according to the entire amount of accumulated facts, only the concept of organic, biogenic origin of oil, put forward by the German botanist G. Potonier at the beginning of the 20th century, can be considered sufficiently justified. In our country, it was developed by G.P. Mikhailovsky, I.M. Gubkin, but most fully and at the modern level N.B. Vassoevich, who called it the sedimentary-migration theory of oil formation. According to this theory, the source of oil is organic matter buried in sediments - a product of decomposition of organisms - deposited together with mineral particles of sediments.

In turn, the source of this organic matter is two groups of organisms: terrestrial vegetation, the remains of which were carried by rivers to sea or lake basins, bacteria and marine zoo and phytoplankton, and it is the latter that plays the main role in oil formation.

Differences in the composition of organic matter deposited from these two sources, humus and sapropel, can be traced in the composition of oils that arose from them. The accumulation of significant masses of organic matter in sediments was possible in the absence or limited access of free oxygen, which could only occur in an aquatic environment.

Organic matter is dispersed in sediments. Some types of precipitation are enriched in it to a greater extent, others are less or even practically devoid of it, but the average content very rarely exceeds 1% of the sediment mass. And only a relatively small part of this substance (10-30%) is then converted into oil, the rest remains in the sediment and passes into the sedimentary rock formed from it. The most enriched in organic matter are dark clay strata such as the Oligocene-Miocene Maikop series of the Caucasus, the Devonian, the so-called Domanik of the Volga-Ural and Timan-Pechora basins. They have long been considered as classic oil-producing or oil-source strata. However, it later became clear that other types of sedimentary formations, in particular carbonate, had the ability to produce oil.

The transformation of the original organic matter into oil is a long, complex and not yet fully understood process. It is known that petroleum hydrocarbons are formed already in the bodies of living organisms and are found in modern sediments. However, as N.B. Vassoevich, the process proceeds very slowly until the precipitation sinks to a depth of more than 2 km, being covered by younger layers, and heats up to 80-100 ° C. Only then will the main phase of oil formation begin. At a greater depth, about 6 km, and at a higher temperature, over 120 ° C, gas will start to form instead of oil (Fig. 3).

According to more modern concepts (Sh.F. Mekhtiev, B.A. Sokolov), oil formation is significantly promoted (in addition to subsidence and an increase in temperature with depth), coming from the mantle fluids. This is especially noticeable in young rift basins such as the Gulf of Suez in the Red Sea, but should have played a large role at an early stage in the development of older basins such as the West Siberian one. In this sense, it can be recognized that in the ideas of the "inorganics" there was a grain of truth, albeit a small one, - a deep endogenous factor takes a certain part in the process of oil and gas generation. And since the effect of this factor in time is manifested unevenly, in separate impulses, then the generation of hydrocarbons can proceed not in one phase, but in several such phases, as the Ukrainian scientist A.E. Lukin.

But in essence, the process of oil formation ends only when oil droplets begin to collect in larger accumulations. And this only happens when the oil is squeezed out together with bound water from the source rock under the weight of the overlying layers, gas pressure and during its transition into porous reservoir rocks, in particular sands and sandstones.

Reservoirs can be in a thin interlayer with parent clays, and sometimes the clays themselves, if they are sufficiently fractured, can serve as reservoirs of newly formed oil. Examples are the Bazhenov Formation of Western Siberia overlying the Jurassic Roof or the Miocene Monterey Formation of California. However, much more often the reservoirs occur higher along the section of the sedimentary basin than the oil source strata, or replace it along the strike, for example, the Permian cavernous reef carbonates of the Uralian trough. Here we are talking about the migration of oil from the source strata into the stratum containing reservoirs - vertical or lateral.
It must be borne in mind that water is squeezed out of the parent rock together with oil and even earlier, and in immeasurable large quantities... And reservoir rocks are necessarily aquifers. Water can have different origins in them - it can be buried together with sediments (buried water) or penetrate from the surface at the outlet of strata to this surface (infiltration water). All oil and gas bearing sedimentary basins, as I.O. Ford, are both artesian, and oil and gas move, migrate not by themselves, but together with water, oil essentially initially in the form of an oil-water mixture (oil droplets in water). But soon there is a separation of oil and gas from water, due to the lower specific gravity, oil floats above the water and accumulates in the reservoir, trying to occupy the highest hypsometric position in the reservoir. This is all the more true for gas and gas condensate, but the origin of the gas deserves special mention.

The range of gas formation depths is much wider than that of oil, and its source can be not only substances of organic origin buried in subaqueous sediments, but also substances resulting from the coalification of terrestrial vegetation. Gas deposits produced by the Middle Carboniferous coal-bearing strata are known in the Upper Carboniferous and Lower Permian in the southern part of the North Sea and other regions. Methane emissions are observed in almost all coal-bearing strata, and its explosions in mines often have catastrophic consequences. The formation of methane begins already in bogs, and industrial gas deposits are found in very young, Pliocene-Quaternary sediments. Gas formation continues at great depths, but, as noted above, its main phase falls on the region of higher temperatures than the main phase of oil formation (see Fig. 2). Recently, in the Rocky Mountains of the United States, gas accumulations have been discovered in low-permeable sediments of the upper Cretaceous, they are called unconventional, and the clay strata mentioned above also belong to them. Finally, mention should be made of the wide distribution in the sedimentary strata of the seas and oceans and in the bottom layer of sediments of deposits of gas hydrate - liquefied and frozen gas dissolved in water.

A prerequisite for the preservation of a formed oil or gas reservoir is the presence of impermeable or low-permeable rocks - fluid seals, in common parlance, usually called seals, above the reservoir layers. Saline formations are the best seals. The development of such formations of the Lower Permian, Kungurian age owes their safety to giant deposits of gas, condensate and oil in massive carbonates - carbonate platforms on the periphery of the Caspian depression (Astrakhan, Orenburg, Tengiz fields). But much more often the role of seals is played by clay members and formations. Thus, oil and gas complexes consist of oil source strata, reservoirs and seals.

OIL AND GAS DEPOSITS AND THEIR TYPES

Floating above the water in the reservoir, oil and gas move in inclined (rather a very slight slope observed in flat-platform areas) strata up their rise to the point where they encounter any obstacle to this movement. Such an obstacle can be the reverse bending of the formations in the crest of the fold, and then it is here that the oil reservoir is localized, and above it there is often a "gas cap", or an independent gas reservoir, often with a fringe of gas condensate. Such arched (or anticlinal) deposits are among the most widespread (Fig. 3). At the beginning of the development of oil and gas geology, the anticlinal theory of oil occurrence was generally considered generally accepted. Deposits of this type were widely known in the Caucasus - in Azerbaijan, the Grozny region, Dagestan, Western Turkmenistan, and then were discovered in the Volga-Ural region, Western Siberia in very gentle platform uplifts, as well as on Sakhalin.

However, it was soon discovered that anticline traps were not the only type of trap for oil and gas deposits. An obstacle for the further lateral migration of hydrocarbons can be the planes of tectonic fractures, along which the reservoir-reservoirs abut against low-permeability rocks. As a result, tectonically screened deposits are formed in front of them, which is also quite common. However, part of the fluids can then go upward along the fracture surfaces (vertical migration) and form deposits already in the overlying reservoirs. In addition, it is through fractures that oil and gas can come to the surface. Initially, oil was extracted from wells at such outcrops, which gave rise to the connection of oil deposits with tectonic ruptures even before the anticlinal theory appeared. These natural oil shows have long served as the only exploratory feature.

Both domed and tectonically screened deposits are classified as structural. But already in the 30s of the XX century, traps for deposits of two fundamentally different types became known: stratigraphic and lithological (Fig. 4). The first of them are associated with wedging out of reservoirs or their cutting off by unconformity surfaces overlain by low-permeable rocks. The second - with the replacement of reservoirs at the same stratigraphic level with low permeable rocks. A special type of traps are hydraulically screened traps, when the reservoir is held, often in a highly inclined position, by the counter pressure of formation waters.

Deposits of even different types can be concentrated in the same area within the same structural element, most often anticlines, being at different depths. These are oil, oil and gas and gas fields, which are multi-layer. Reservoir strata containing deposits are here separated by horizons of fluid-tight rocks, for example, sandstones or limestones by clays or marls. In other cases, there are massive deposits that are distinguished by high heights. Such deposits are most often confined to large reef massifs or buried protrusions of fractured and / or weathered igneous (granites) or metamorphic rocks. Above has already been given an illustrative example of a large deposit "White Tiger" in Vietnam.
It should be noted a certain general trend observed in the analysis of the development of oil and gas geology. It is a continuous expansion of the range of source deposits, hydrocarbon reservoir rocks, trap types for oil and gas accumulation.

It is quite obvious that this trend contributes to an increase in the explored reserves of hydrocarbon raw materials and the expansion of the prospects for prospecting for its new deposits. It is precisely because of this that gloomy forecasts of an imminent depletion of oil reserves turn out to be untenable every time. Finally, it should be borne in mind that for modern methods less than half of its reserves are extracted from the subsoil. Improvement of these methods will make it possible to extract part of the oil remaining in the depths of old fields.

GEOGRAPHY OF OIL AND GAS DEPOSITS

The distribution of oil and gas deposits on the Earth's surface is very uneven (Fig. 5). The abyssal plains of the oceans and mid-oceanic ridges, crystalline shields of ancient platforms with outcrops of deeply metamorphosed rocks of the Precambrian, axial zones of fold-cover mountain structures, composed of intensively dislocated and, to one degree or another, metamorphosed rock strata, are obviously devoid of industrial deposits. But already in the latter case, a reservation should be made: along the periphery of such structures under the tectonic covers of crystalline rocks, unmetamorphosed and oil-and-gas-containing strata are often found, the Rocky Mountains of Canada and the USA can serve as a vivid example.

For quite a long time, oil and gas have been produced not only on land, but also in the sea, the beginning of which was laid in the Caspian Sea and in the Gulf of Mexico. At the same time, in search of oil deposits, drilling goes to ever greater depths of the sea; the champion in this regard is Brazil, where production is already carried out at a depth of more than 1,700 m. The discovery of oil and gas in the North Sea has turned the UK and Norway from consumers of oil and gas into exporters.

The richest oil and gas region on a global scale is the Persian Gulf region. Thanks to the discovery of huge deposits of oil, the countries of the Arabian coast of the Gulf, previously lifeless and inhabited by rare nomadic tribes, are now covered with green oases with white-stone cities and beyond. short term achieved significant prosperity. The other two largest oil and gas basins are the West Siberian Basin, thanks to its gas reserves, Russia ranks first in the world, and the Gulf of Mexico basin (USA, Mexico). The rest of the basins are shown in Fig. 5.

The main resources of oil and gas are concentrated in relatively young, Mesozoic and Cenozoic deposits formed over the last 200 million years of the Earth's history. However, oil and gas production is also carried out from the Paleozoic, and in Eastern Siberia there are oil deposits in even more ancient deposits of the Upper Proterozoic, which is not surprising, since they are rich in organic matter, mainly of algal origin. Therefore, it can be expected that oil and gas production will "grow" in the Proterozoic.

Reviewers of the article V.A. Korolev, M.G. Lomize

Victor Efimovich Khain, Doctor of Geological and Mineralogical Sciences, Professor of the Department of Dynamic Geology of Moscow State University, full member of the Russian Academy of Sciences. Laureate of state prizes of the USSR and the Russian Federation. Research interests - the structure and development of the earth's crust of continents and oceans. Author of over 30 monographs and textbooks and over 700 scientific articles.