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Geology _ Geophysics in Oil Exploration

Unconformity trap trap whose closure is controlled by

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Unformatted text preview: cks) • Metamorphic Rocks: Formed by action of temp. &/or pressure on sedimentary or igneous • Sedimentary Rocks: the most important for the oil industry as it contains most of the source rocks and cap rocks and virtually all reservoirs. Sedimentary rocks come from the debris of older rocks ; and are split into two categories: • Clastic rocks: Formed from the materials of older rocks by the actions of erosion, transportation and deposition. (Mechanical process). Such as conglomerate, sandstone, shale. • Non clastic rocks: are formed by chemical precipitation (settling out from a solution). Such as Limestone, calcite and halite. 28 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration 2. Origin of rock: • Fragmental reservoir rocks: Aggregates of particles and fragments of the older rocks (called also detrital rock). Fragmental reservoir rocks: (sandstones, Conglomerates, Arkoses, gray wakes) are the most common reservoir rocks. Most of these rocks are siliceous, but many are carbonates such as Oolites and Coquinas. • Chemical reservoir rocks: It is composed of chemical or biochemical precipitates such as limestone and dolomite not transported as clastic grains. Limestone and dolomite are by far the most important of the chemical reservoir rocks, because they contain nearly half of world's petroleum reservoir. • Miscellaneous reservoir rocks: It includes igneous and metamorphic rocks. It is geologically important but rarely important commercially. The reservoir space is usually in fractures in the brittle basement rocks. 3.Depositional environment Sedimentary reservoir rocks may be subdivided into those of marine origin and those of nonmarine, or continental origin but between these classes there are many gradations and intermixtures Most petroleum found in rocks believed to have been deposited under marine conditions, but substantial deposits have also been found in rocks of nonmarine origin. 4.Geologic ti...
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