Petroleum geology

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.