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Sandstone is a clastic sedimentary reservoir rock composed of mainly quartz and/or feldspars, and typically deposited by relatively high-energy processes, which winnow out much of the fine particle size fraction while transporting and depositing the coarser (sand-sized) particles. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, grey, pink, white and black depending on the mineral composition. According to Dott's (1964) classification scheme, sandstones are classified into: quartz arenite, sublithic arenite, lithic arenite, arkosic arenite and arkose based on the mineralogy of framework grains, and arenites, wackes, and mudrocks based on the type of matrix present in between the framework grains. Arenites are the best known petroleum reservoir rock with good porosity and high permeability mainly dependent on reservoir fluid and rock properties; mainly influenced and modified by the depositional environment and burial history diagenetic processes. The depositional environments associated with sandstones are very important and they range from terrestrial to deep marine, including: Fluvial(alluvial fans, river sediments); Deltaic (levees, distributary deposits ,mouth bars and other sediments formed where river meets a lake or sea); Aeolian(wind-blown dune sands formed in coastal and desert environments); Shoreline ( beaches, barrier bars, tidal deltas and similar deposits formed in coastal areas);Glacial(sandy materials in tillites and other glacier deposits); and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements. Depositional conditions at any instant vary from one location to another which results in lateral as well as vertical changes within the reservoir and within individual rock units. These changes result in variations in porosity, fluid distribution, and permeability. However the main diagenetic process in sandstone such as compaction, cementation and dissolution also change these variations and affect the reservoir quality. Hence good analytical interpretations, research, innovativeness and learnt knowledge of sandstone composition, associated depositional environment and burial diagenetic history are vital for the success of any petroleum industry since over 60% of the world’s giant fields have sandstone reservoirs.

Sandstone is a clastic sedimentary reservoir rock composed of mainly quartz and/or feldspars, and typically deposited by relatively high-energy processes, which winnow out much of the fine particle size fraction while transporting and depositing the coarser (sand-sized) particles. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, grey, pink, white and black depending on the mineral composition. According to Dott's (1964) classification scheme, sandstones are classified into: quartz arenite, sublithic arenite, lithic arenite, arkosic arenite and arkose based on the mineralogy of framework grains, and arenites, wackes, and mudrocks based on the type of matrix present in between the framework grains. Arenites are the best known petroleum reservoir rock with good porosity and high permeability mainly dependent on reservoir fluid and rock properties; mainly influenced and modified by the depositional environment and burial history diagenetic processes. The depositional environments associated with sandstones are very important and they range from terrestrial to deep marine, including: Fluvial ([[alluvial]] fans, river sediments); Deltaic (levees, distributary deposits ,mouth bars and other sediments formed where river meets a lake or sea); Aeolian(wind-blown dune sands formed in coastal and desert environments); Shoreline ( beaches, barrier bars, tidal deltas and similar deposits formed in coastal areas);Glacial(sandy materials in tillites and other glacier deposits); and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements. Depositional conditions at any instant vary from one location to another which results in lateral as well as vertical changes within the reservoir and within individual rock units. These changes result in variations in porosity, fluid distribution, and permeability. However the main diagenetic process in sandstone such as compaction, cementation and dissolution also change these variations and affect the reservoir quality. Hence good analytical interpretations, research, innovativeness and learnt knowledge of sandstone composition, associated depositional environment and burial diagenetic history are vital for the success of any petroleum industry since over 60% of the world’s giant fields have sandstone reservoirs.

Sandstone is most significant type of petroleum reservoir rock in over 60% of the world’s giant fields; composed of mainly quartz and/or feldspars and typically deposited by relatively high- energy processes, which winnow out much of the fine particle size fraction while transporting and depositing the coarser (sand-sized) particles. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, grey, pink, white and black. However, since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions depending on the for example red sandstone Red sandstone found in interior of Lower Antelope Canyon, Arizona.

Sandstone is most significant type of petroleum reservoir rock in over 60% of the world’s giant fields; composed of mainly quartz and/or feldspars and typically deposited by relatively high- energy processes, which winnow out much of the fine particle size fraction while transporting and depositing the coarser (sand-sized) particles. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, grey, pink, white and black. However, since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions depending on the for example red sandstone Red sandstone found in interior of Lower Antelope Canyon, Arizona.

==Sandstone depositional environments==

==Sandstone depositional environments==

The depositional environments are very important and determine the reservoir quality. They sandstone beds range from terrestrial to deep marine, including: Fluvial(alluvial fans, river sediments); Deltaic (levees, distributary deposits ,mouth bars and other sediments formed where river meets a lake or sea); Aeolian(wind-blown dune sands formed in coastal and desert environments); Shoreline ( beaches, barrier bars, tidal deltas and similar deposits formed in coastal areas);Glacial(sandy materials in tillites and other glacier deposits); and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements.(figure 4). However, Depositional conditions at any instant vary from one location to another which results in lateral as well as vertical changes within the reservoir and within individual rock units. These changes result in variations in porosity, fluid distribution, and permeability.

The depositional environments are very important and determine the reservoir quality. They sandstone beds range from terrestrial to deep marine, including: Fluvial ([[alluvial]] fans, river sediments); Deltaic (levees, distributary deposits ,mouth bars and other sediments formed where river meets a lake or sea); Aeolian(wind-blown dune sands formed in coastal and desert environments); Shoreline ( beaches, barrier bars, tidal deltas and similar deposits formed in coastal areas);Glacial(sandy materials in tillites and other glacier deposits); and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements.(figure 4). However, Depositional conditions at any instant vary from one location to another which results in lateral as well as vertical changes within the reservoir and within individual rock units. These changes result in variations in porosity, fluid distribution, and permeability.

[[File:Sandstone-Fig-4.png|thumb|300px|Figure 4: depositional environments associated with sandstone (modified from Reading<ref> Reading, H. (1996). Sedimentary Environments and Facies (3rd edition), Black wells, Oxford, pp.704.</ref>).]]

[[File:Sandstone-Fig-4.png|thumb|300px|Figure 4: depositional environments associated with sandstone (modified from Reading<ref> Reading, H. (1996). Sedimentary Environments and Facies (3rd edition), Black wells, Oxford, pp.704.</ref>).]]

===Fluvial sandstones===

===Fluvial sandstones===

Fluvial or alluvial sandstones are not so well sorted sand deposits containing carbonaceous debris and clay trapped in the spaces within the framework grains. They are formed in river channel deposits and terrestrial environments, and are commonly developed on unconformity surfaces. Individual sands in meandering and braided stream deposits are as thick as the depth of the river. They often rest on eroded base with a fining upward particle size sequence especially with meandering streams; where sands grade into shales and possibly even coals deposited in associated flood plain areas. Trough and planar cross beds occur in main part of sandstone beds (figure 5) dipping essentially downstream, with ripples occurring towards the top. In plain view, fluvial sandstones have abrupt terminations of sand bars. The individual channel bar and point bars deposits are interleaved with shales and other muddy sediments of flood plain origin; they tend to elongated parallel to flow direction especially in braided streams compared to direction parallel to the depositional strike. The beds then developed on unconformity surfaces may thicken in the valley (down cut) areas and be rich in sand, and become shaly and thin in the between-valley (intervening) sections.

Fluvial or [[alluvial]] sandstones are not so well sorted sand deposits containing carbonaceous debris and clay trapped in the spaces within the framework grains. They are formed in river channel deposits and terrestrial environments, and are commonly developed on unconformity surfaces. Individual sands in meandering and braided stream deposits are as thick as the depth of the river. They often rest on eroded base with a fining upward particle size sequence especially with meandering streams; where sands grade into shales and possibly even coals deposited in associated flood plain areas. Trough and planar cross beds occur in main part of sandstone beds (figure 5) dipping essentially downstream, with ripples occurring towards the top. In plain view, fluvial sandstones have abrupt terminations of sand bars. The individual channel bar and point bars deposits are interleaved with shales and other muddy sediments of flood plain origin; they tend to elongated parallel to flow direction especially in braided streams compared to direction parallel to the depositional strike. The beds then developed on unconformity surfaces may thicken in the valley (down cut) areas and be rich in sand, and become shaly and thin in the between-valley (intervening) sections.





[[File:Sandstone-Fig-5.png|thumb|300px|Figure 5: Fluvial sandstone with trough cross beds, Kibuku road cut, Semliki basin, Uganda.]]

[[File:Sandstone-Fig-5.png|thumb|300px|Figure 5: Fluvial sandstone with trough cross beds, Kibuku road cut, Semliki basin, Uganda.]]