Oil formation - the step-wise, very long (typically 50-350 Ma) [1], 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, the slow rise of temperature and pressure;
mezokatagenez or main phase of oil generation (GFN) - lower layer of organic residues to a depth of 3 - 4 km, when the temperature rises 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) [2] also confirmed ineligibility inorganic hypotheses.
It is believed that the main source of oil is usually a matter of zooplankton and algae, providing the greatest bio-products in water and the accumulation of organic matter in the sediments of sapropelic type, characterized by a high content of hydrogen (due to the presence of aliphatic and alicyclic kerogen molecular structures).
In ancient times there were warm, nutrient-rich seas, such as the Gulf of Mexico and the ancient Tethys Ocean, where a large amount of organic material falls to the bottom of the ocean, higher than the rate at which it could decompose. As a result of large masses of organic material were buried under subsequent deposits such as shale or salt. This is confirmed by the presence of a thick layer of salt over the oil fields in the Middle East. The formation of salt deposits suggests that these waters for a long time were quite small, poorly communicated to the rest of the ocean and evaporation greatly exceeds that of the sea water from the outside. Subsequently, the band were on the ground as a result of the movement of continents. Conditions are quite unique, so most of the modern organic sediments on the bottom of the ocean waiting for a different fate - the motion of the oceanic crust, they fall into the subduction zone.
Rocks formed from sediments that contain this type of organic matter, potentially oil source. Most often it is clay, at least - carbonate and sandstone-siltstone rocks that during immersion reach the upper half of the zone mezokatageneza which comes into force the main factor of oil generation - long heating of organic matter at temperatures of 50 ° C and above. The upper boundary of the main zone of oil formation located at depths of 1.3-1.7 km (with an average geothermal gradient 4 ° C/100 m) to 2.7-3 km (with a gradient of 2 ° C/100 m) and fixed by changing degree of coalification lignite coal organic matter. Main phase of oil generation confined to the area where coalification of organic matter reaches a degree corresponding coals Mark G. This phase is characterized by a significant increase in thermal and (or) thermal catalytic decomposition polimerlipoidnyh and other components of kerogen. Produced in large quantities petroleum hydrocarbons, including low molecular weight (C5-C15), almost absent in the earlier stages of the transformation of organic matter. These hydrocarbons, giving rise to the gasoline and kerosene fractions of oil, significantly increase the mobility mikronefti. At the same time, due to a decrease of the sorption capacity of source rocks, increasing the internal pressure in them and the allocation of water in the dehydration of clay increases the movement in the coming mikronefti collectors. When migrating to a collector in the trap oil always rises, so its maximum reserves are located at depths of several smaller than the display area of the main phase of oil generation, the lower boundary of which usually corresponds to the zone where the organic matter reaches the degree of coalification rocks, typical coking coals. Depending on the intensity and duration of heating, this boundary is at a depth of (meaning the maximum depth for the entire geological history of this series of sediment) from 3-3.5 to 5-6 km.
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