Enclosing rocks of oil have relatively high porosity and sufficient to eject permeability. Breed, allowing free movement and accumulation in these fluids are called collectors. Porosity depends on all sorted grains, their shape and styling, as well as on the presence of cement. Permeability determined by the size of pores and their communicability. The most important oil reservoirs are sands, sandstones, conglomerates, dolomite, limestone, and other well-permeable rocks, prisoners of impermeable rocks such as clay or plaster. Under favorable conditions, the collectors may be fractured metamorphic and igneous rocks that are in the vicinity of the oil-bearing sedimentary rocks.

Often the oil reservoir is only part of the reservoir and therefore, depending on the nature and degree of cementation porosity rocks (reservoir heterogeneity) found varying degrees of oil saturation in some segments within the reservoir itself. Sometimes this is due to the presence of the cause of non-productive areas of the reservoir. Usually oil deposits accompanied with water, which limits the accumulation downdip layers or along its base. In addition, each oil reserves with it is so-called. film or residual water enveloping the rock particles (sand) and the pore walls. In the case of reservoir rock pinching or cutting his faults, thrusts and t n disjunctive dislocations can deposit either in whole or in part beyond low permeable rocks. In the upper parts of the oil column is sometimes concentrated gas (so-called. "Gas cap"). Well production rate, in addition to the physical properties of the reservoir, its capacity and saturation, determined by the pressure of the dissolved gas in oil and boundary waters. In oil wells can not entirely remove all the oil from the reservoir, a significant amount of it remains in the depths of the earth's crust (see oil recovery and oil production). For a more complete extraction of oil using special techniques, of which the importance is the method of flooding (aquifer, vnutrikonturnogo, focal). Oil in the reservoir is under pressure (elastic expansion and / or the edge of the water and / or gas, as well as dissolved gas cap) so that the opening of the reservoir, especially the first well, accompanied by the risk gazonefteproyavleny (very rare Fountains discharges of oil). Very long time (from the 2nd half of the XIX century.) Geologists believe that the oil fields are timed almost exclusively to the saddle, and only in 1911, IM Gubkin was opened in Maikop's a new type of deposit, marking the alluvial sands and received the name "sleeve-." After more than 10 years, similar deposits have been discovered in the United States. Further development of the exploration in the USSR and the United States completed the discovery of deposits associated with the salt domes, raised, and sometimes poke through the sedimentary strata. The study of oil fields showed that the formation of oil deposits due to different structural forms bends strata stratigraphic relationships and lithological features suites of rocks. Proposed several classifications of fields and oil deposits in Russia and abroad. Oil fields differ from each other by the type of structural forms and conditions of their formation. And oil and gas are different from each other according to the forms of traps, reservoirs and educational conditions in which concentrations of oil....

The chemical composition

The overall composition

Petroleum is a mixture of about 1,000 individual substances of which the majority - liquids (> 500 substances or usually 80-90% by weight) and heteroatomic organic compounds (4-5%), mainly sulfur (about 250 agents), nitrogen ( > 30 substances) and oxygen (85 substances), and organometallic compounds (mainly vanadium and nickel), and the remaining components - dissolved hydrocarbon gases (C1-C4, from tenths to 4%), water (from trace to 10% ), mineral salts (mainly chlorides, 0,1-4000 mg / l or more), solutions of salts of organic acids, etc., mechanical impurities.
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Hydrocarbon composition

Basically in paraffin oil are (usually 30-35, sometimes 40-50% by volume) and naphthenic (25-75%). To a lesser extent - aromatic compounds (10-20, at least 35%) and mixed or hybrid, structure (eg, paraffin-naphthenic, naphthene-aromatic).
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The elemental composition of oil and heteroatomic components

Along with the hydrocarbons in the oil are substances containing impurity atoms. Sulfa - H2S, mercaptans, mono-and disulfides, thiophenes and Thiophane and polycyclic etc. (70-90% is concentrated in the residual products - fuel oil and tar), nitrogen - mainly homologues of pyridine, quinoline, indole, carbazole, pyrrole, and porphyrins (mostly concentrated in the heavy fractions and residues), oxygen - naphthenic acids, phenols, resin-asphaltene and other substances (usually concentrated in high fractions). The elemental composition (%): 82-87 C; 11-14,5 N; 0,01-6 S (rarely to 8); 0,001-1,8 N; 0,005-0,35 O (rarely to 1.2) etc. A total of 50 oil found items. So, along with the above, the oil contains V (10-5 - 10-2%), Ni (10-4-10-3%), Cl (from traces to 2.10 -2%), etc. The content of these compounds and impurities in the raw materials of different deposits varies widely, so to speak of the average chemical composition of the oil can only conditionally.

Oil properties

Oil - the liquid from light brown (almost colorless) to dark brown (almost black) color (even though there are examples of emerald-green oil). The average molecular weight of 220-300 g / mol (rare 450-470). Density 0,65-1,05 (0,82-0,95 usually) g / cm ³; oil whose density is lower than 0.83, is called light, 0,831-0,860 - average above .860 - heavy weight oil, like other hydrocarbons, is strongly dependent on temperature and pressure [9]. It contains a large number of different organic substances and therefore not characterized by a boiling point, and the initial boiling point of liquid hydrocarbons (typically> 28 ° C, at least ≥ 100 ° C in the case of heavy oils) and fractional composition - Out separate fractions, distilled first at atmospheric pressure and then under vacuum in certain temperature range, usually up to 450-500 ° C (boiling over ~ 80% of the sample), at least 560-580 ° C (90-95%). The crystallization temperature of -60 to + 30 ° C; depends primarily on the content of petroleum wax (what it is, the higher the crystallization temperature) and light fractions (the more, the lower the temperature.) Viscosity varies widely (from 1.98 to 265.90 mm ² / s for various oil produced in Russia), determined the fractional composition of oil and its temperature (the higher and higher the number of light ends, the lower the viscosity), and content of resin-asphaltene substances (the more, the viscosity of the above). Specific heat capacity of 1.7-2.1 kJ / (kg ∙ K), specific heat (low) 43,7-46,2 MJ / kg, the dielectric constant of 2.0-2.5, the electric conductivity of the [specific] from 2 ∙ 10-10 to 0,3 ∙ 10-18 ohm-1 ∙ cm-1.

Oil - a flammable liquid, the flash point of - 35 [10] to +121 ° C (depending on the fractional composition and its content of dissolved gases). Oil soluble in organic solvents, in normal circumstances, is insoluble in water, but it can form stable emulsions. The technology to separate oil from water and dissolved salts conduct dehydration and desalting.

Origin

Oil - the result lithogenesis. It is a liquid (basically) a hydrophobic phase products fossilization (disposal) of organic matter (kerogen) in the water-sediment.

Oil formation - the step-wise, very long (typically 50-350 Ma) [6], a process that begins as early as living matter. Highlighted a number of stages:
Sedimentation - in which the remains of living organisms fall to the bottom of the basins;
Biochemical - compaction process, dehydration and biochemical processes with limited access to oxygen;
protokatagenez - lower layer of organic residues to a depth of 1.5-2 km, with a slow rise in temperature and pressure;
mezokatagenez or main phase of oil generation (GFN) - lower layer of organic residues to a depth of 3-4 km, with the rise in temperature to 150 ° C. In this case, the organic substances undergo catalytic thermal decomposition, resulting in formation of bituminous substances that make up the bulk of mikronefti. Further there is a distillation of the oil due to the pressure difference and stem emigration mikronefti in sand reservoirs, and on them in the trap;
apokatagenez kerogen or main phase of gas generation (GFG) - lower layer of organic residues to a depth of 4.5 km, with the rise in temperature to 180-250 ° C. In this organic matter becomes neftegeneriruyuschy metanogeneriruyuschy potential and realize potential.
IM Gubkin also singled stage destruction of oil mestozarozhdeny.

Strong evidence of the biogenic nature of the parent substance of oil were obtained from a detailed study of the evolution of the molecular composition of hydrocarbons and their biochemical precursors (progenitors) in the source organisms, organic matter and sediments and rocks in various oil from reservoirs. Important was the discovery of oil in the hemofossily - a very unique and often complex molecular designs clearly biogenic nature, that is inherited (in whole or in fragments) of organic matter. Study of the distribution of stable isotopes of carbon (12C, 13C) in the oil, organic matter of rocks and organisms (Vinogradov, EM Galimov) [7] also confirmed ineligibility inorganic hypotheses.

However, in the present, some scientists (mainly in Russia) advocate inorganic hypothesis of the origin of oil. In particular, it is argued that the newly formed in ancient times by organic oil is constantly added oil, which is formed by inorganic. If this is true, it means almost inexhaustible reserves of oil.

Historical information about the oil

In the Middle Ages interest in oil, mainly based on its ability to burn. In VII century BC Byzantines used the so-called Greek fire (a mixture of oil with lime), which ignited when wet. Used against enemy ships: she smeared arrowheads or produced primitive grenades. [4] Tell about the "fuel water - thick" brought from Ukhta to Moscow in Boris Godunov.
Until the early 18th century, oil mainly used in bulk, that is unprocessed and untreated. Great attention to the oil as a mineral was paid only after:
factory in Russia practice Dubinin brothers (from 1823)
American chemist B. Sillimanite (1855),

it was proved that we can select a kerosene - light oil, such photogenic, even then, is developed from some types of coals and shales and widespread. Preferential use of refined oil only started in the 2nd half of the 19th century, helped emerged at this time a new method of oil production by drilling wells instead of wells. The world's first oil production from the well bore was held in 1848 at the Bibi Eybatskom field near Baku.
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Overview

Oil is found together with gaseous hydrocarbons at depths of tens of meters to 5-6 km. However, at depths greater than 4.5-5 km dominated by gas and gas condensate reservoirs with a minor amount of light fractions. The maximum number of oil deposits located at a depth of 1-3 km. At shallow depths and natural outcrops on surface oil is converted into a thick Malta, semisolid asphalt and other education - such as tar sands and bitumen.

Chemical composition and origin of oil is close to natural gas fuel, ozokerite and asphalt. These resources are collectively called petrolytes. Petrolytes referred to even larger group of so-called caustobioliths - combustible biogenic minerals, which also includes solid fossil fuels.

Petroleum

Oil (from the tour. Neft, from Persian. Oil [1]) - the natural oily flammable liquid consisting of a complex mixture of hydrocarbons and other organic compounds. In color, the oil is red-brown, sometimes almost black in color, although sometimes there and poorly painted in yellow-green color and even colorless oil, has a peculiar smell, common in sedimentary rocks of the Earth. Today, oil is one of the most important minerals for mankind.