sea floor. The buildup of thousands of feet of mud and sediment layers caused the sea floors to slowly sink and be squeezed. This eventually became the sedimentary rocks (the sandstones and shales, and the carbonates) where petroleum is found today.very large amount of small plant and animal life, which came into the sea with river mud and sedimentary materials, and the much larger amount of small marine life remains already on the sea floors constituted the source of petroleum. These small organisms died and were buried by the depositing silt and, thus, were protected from ordinary decay. Over many years, pressure, temperature, bacteria, and other reactions caused these dead organisms to change into oil and gas.gas was formed under the higher-temperature conditions, whereas the oil was ormed under the lower-temperature conditions. The rocks where oil and gas were formed are known as the source rock.of Oil and Gasoil, gas, and salt water occupied the pore spaces between the grains of the sandstones, or the pore spaces, cracks, and vugs of the limestones and dolomites . Whenever these rocks were sealed by a layer of impermeable rock, the cap rock, the petroleum accumulating within the pore spaces of the source rock was trapped and formed the petroleum reservoir. However, when such conditions of trapping the petroleum within the source rocks did not exist, oil gas moved (migrated), under the effects of pressure and gravity, from the source rock until it was trapped in another capped (sealed) rock.of the differences in density, gas, oil, and water segregated within the trap rock. Gas, when existed, occupied the upper part of the trap and water occupied the bottom part of the trap, with the oil between the gas and water. Complete displacement of water by gas, or oil, never occurred. Some salt water stayed with the gas and / or oil within the pore spaces and as a film covering the surfaces of the rock grains; this water is known as the connate water, and it may occupy from 10% up to 50% of the pore volume.geologic structure in which petroleum has been trapped and has accumulated, whether it was the source rock or the rock to which petroleum has migrated, is called the petroleum reservoirmmary then, the formation of a petroleum reservoir involves first the accumulation of the remains of land and sea life and their burial in the mud and sedimentary materials of ancient seas.is followed by the decomposition of these remains under conditions that recombine the hydrogen and carbon to form the petroleum mixtures. Finally, the formed petroleum is either trapped within the porous source rock when a cap rock exists or it migrates from the source rock to another capped (sealed) structure.
OF PETROLEUM RESERVOIR
reservoirs are generally classified according to their geologic structure and their production (drive) mechanism.Classification of Petroleum Reservoirsreservoirs exist in many different sizes and shapes of geologic structures. It is usually convenient to classify the reservoirs according to the conditions of their formation as follows:
. Dome-Shaped and Anticline Reservoirs: reservoirs are formed by the folding of the rock layers as shown in Figure <file:///C:Documents%20and%20SettingsLoner-XPРабочий%20столНастеAbdel-Aal.et.al.Petroleum.and.Gas.Field.Processing.doc> 3.2.3. <file:///C:Documents%20and%20SettingsLoner-XPРабочий%20столНастеAbdel-Aal.et.al.Petroleum.and.G...
