Sedimentary material to organic material that later

Sedimentary basins differ due to the origin of the rocks. Basins generally are the accumulation of clastic rock which consist of minerals that later formed into shale, discovered in area that undergone tectonic plate shifts.  These areas undergone a variation of tectonic shifts either the divergent continental margins or the transform continental margin. These shifts allow successful sedimentary episodes which formed sedimentary layers consisting thick sediments in the center that thin towards the edges. During transgression, sea level rose thus volume of subsidence around the basin increase compared to the volume of sediments entering the basin, hence increasing the depth of the oceans. The fine-grained sediments are the potential petroleum source rocks have low permeability and often carried by the sea towards the shore forming an accumulation around a low energy environment. While, the during the regression, the deposits move seaward into a high energy environment resulting the basin shallower. This sequence occurs as the supply of sediments is greater that the accumulation amount in the basin. The regression allows coarse-grained to accumulate due to the high energy level in the basin. The rocks have high permeabilities and become the reservoir rocks that layered on top of the source rocks during transgressive phase. The accumulation of sediments depends on the energy levels, where coarser grades(sand) will accumulate on base level while the finer grades(clay) are in suspensions accumulate on top of the coarser grades. During periods of low orogenic activity, erosion of land is at minimum, chemical weathering occurs at a rapid rate upon completion, stable components were furnished from igneous and metamorphic rocks, such as quartz and zircon, for clastic sediments. The clastic sediments may be cemented by carbonate or clay compound precipitated from the sea water. The change in climatic conditions of area allow different types of sediments accumulation in the basin, from clean granular material to organic material that later serves as source rocks for hydrocarbons as well as impermeable cap rocks. The change in climatic conditions results in variable episodes of fine particles on top of coarse particle forming the layers that become caprocks of the reservoirs. The reactive clays and unstable minerals are mixed with other grains forming a large portion of cementing agents. Hydrocarbons form from the degradation of organic materials from dead plants and animals through decomposition by bacteria. The depletion of oxygen leads to anaerobic condition which reduces the organic matter by removal of oxygen. The products of decomposition will essentially compound of carbon, hydrogen, and oxygen. The low energy environment during transgression allows sedimentation of organic matter which would be buried under the fine-grained sediments, so it will be preserved thus forming the source rocks of petroleum. During the burial, the environment is slowly approaching the thermodynamic equilibrium with low temperature, the organic matter is subjected to both microbial and chemical reaction that transforms into kerogen. Consecutive deposition of sediments leads to deeper burial which increases both pressure and temperature that lead to formation of oil from kerogen this process called catagenesis. While on the higher zone, metagenesis takes place where petroleum changes to graphite and methane. Compaction occurs as soon as sediments begin to accumulate, the original accumulations are buried deeper, due to layers of continued sediment on top, the water from the deeper sediments is expelled, resulting in an increase in density and decrease in porosity. The chemical changes occurring in the interstitial fluid produce precipitates that strengthen the cohesive formation of the material. After expulsion of the pore water, petroleum formed in rich shale may form continuous phase and move along thread-like channels under applied stress. The optimum temperature for generation of petroleum us about 200 degree Fahrenheit, assisting the primary migration of oil. The migration of hydrocarbons from the point of release from a source rock to the top of the trap is associated with capillary pressure and buoyancy. Compaction force allow oils to migrate from the source rock into the reservoir rock given optimum buoyant and hydrodynamic forces. The petroleum is then trapped in either stratigraphic or structural trap. The densities of the liquid hydrocarbons define their placements within the reservoir rocks.