Unformatted text preview: me scale. • Pleistocene: 0% of reservoir rocks The short time the exposed sediments have had to form and to accumulate petroleum. General lack of an impervious cover to create traps conditions. General nonmarine character of the sediments. • Precambrian:<1% of reservoir rocks General metamorphism. Lack of permeability. Most of the pre‐Cambrian occurrences are found in fractures and secondary openings resulting from weathering and deformation. • • • • • Cambrian: <1% of reservoir rocks Triassic: <1% of reservoir rocks Paleozoic: 15% of reservoir rocks Cretaceous: 18% of reservoir rocks Tertiary: 58% of reservoir rocks Rocks of Tertiary age continue to dominate in the total productivity, and several reasons may be suggested to account for this: It contains thick sequences of un‐metamorphosed marine sediments characterized by lateral gradation, permeable reservoir rocks, adequate impervious cover, numerous traps and an adequate supply of petroleum. Since it is late in the geologic time scale, only a minor part of it has been removed by erosion. It consists of material eroded from per‐Tertiary anticlines, which include some of the oil that seeped out from the larger oil pools in the eroded rocks. 29 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Physical Characteristics of a Reservoir: Physical characteristics of a reservoir include original deposition and subsequent changes, the type of reservoir, sandstone or carbonate, which was discussed previously, depth, area, thickness, porosity, permeability, and capillary pressure. 1. Depth • Shallow reservoir: Created by the folding of relatively thick, moderately compacted reservoir rock with accumulation under an anticline or some trap. The hydrocarbons would generally be better separated as a result of lower internal reservoir pressures, less gas in solution and oil of increased viscosity, resulting from lower temperatures. • Deep reservoir: Typically created...
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- Spring '10
- Geology, Volcano, Tephra, Volcanic Ash, Geology & Geophysics, Mahmoud Ahmed Sroor