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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.

[[File:Sandstone-Fig-1.png|thumb|300px|Figure 1: Red sandstone in interior of Lower Antelope Canyon, Arizona. (Modified from Pettijohn et al.<ref name=Pettijohn>Pettijohn F. J., P.E. Potter and R. Siever. (1987). Sand and sandstone. (2nd edition), Springer-Verlag. ISBN 0-387-96350-2.</ref>).]]

[[File:Sandstone-Fig-1.png|thumb|300px|Figure 1: Red sandstone in interior of Lower Antelope Canyon, Arizona. (Modified from Pettijohn et al.<ref name=Pettijohn>Pettijohn F. J., P.E. Potter and R. Siever. (1987). Sand and sandstone. (2nd edition), Springer-Verlag. ISBN 0-387-96350-2.</ref>).]]

* '''Rock grains.''' The grains that make up the bulk of sandstones can be classified into several different categories based on their mineral composition:

* '''Rock grains.''' The grains that make up the bulk of sandstones can be classified into several different categories based on their mineral composition:

*# '''Quartz grains''': are the most dominate, moderately rounded, subhedral, have high degree of hardness, and are chemical stable which allows them to survive multiple recycling events.

*# '''[[Quartz]] grains''': are the most dominate, moderately rounded, subhedral, have high degree of hardness, and are chemical stable which allows them to survive multiple recycling events.

*# '''Feldspars''': commonly alkali feldspars and plagioclase feldspars. Alkali feldspar consists of complete solid solution consisting group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8 while Plagioclase feldspars are a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.

*# '''Feldspars''': commonly alkali feldspars and plagioclase feldspars. Alkali feldspar consists of complete solid solution consisting group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8 while Plagioclase feldspars are a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.

*# '''Lithic fragments''': are pieces of ancient source rock that have yet to weather away to individual mineral grains. Lithic grains may be any fine-grained or coarse- grained [[igneous]], metamorphic, or sedimentary rock. Although, the most commonly they are clasts of volcanic rocks.

*# '''Lithic fragments''': are pieces of ancient source rock that have yet to weather away to individual mineral grains. Lithic grains may be any fine-grained or coarse- grained [[igneous]], metamorphic, or sedimentary rock. Although, the most commonly they are clasts of volcanic rocks.

* '''Accessory minerals''' make up a small percentage of the grains in a sandstone. They commonly include micas such as muscovite and biotite, olivine, pyroxene, and corundum, zircon, tourmaline, rutile, garnet, magnetite, or other dense, resistant minerals derived from the source rock.

* '''Accessory minerals''' make up a small percentage of the grains in a sandstone. They commonly include micas such as muscovite and biotite, olivine, pyroxene, and corundum, zircon, tourmaline, rutile, garnet, magnetite, or other dense, resistant minerals derived from the source rock.

* '''Matrix''': is very fine material present within interstitial pore space between the rock grains. Sandstones are often classified on basis of amount of matrix into Arenites (quartz arenite, lithic arenite and feldspar arenite); which are texturally clean sandstones that are free of or have very little matrix, and Wackes are texturally dirty sandstones that have a significant amount of matrix.

* '''Matrix''': is very fine material present within interstitial pore space between the rock grains. Sandstones are often classified on basis of amount of matrix into Arenites ([[quartz]] arenite, lithic arenite and feldspar arenite); which are texturally clean sandstones that are free of or have very little matrix, and Wackes are texturally dirty sandstones that have a significant amount of matrix.

* '''Cement''': is a secondary mineral that forms after deposition and during burial of the sandstone and binds the siliclastic framework grains together. Cements mainly include carbonate, clay minerals and silica cements and Other minerals that act as cements include: hematite, limonite, feldspars, [[anhydrite]], [[gypsum]], barite, clay minerals, and zeolite . Silica cement can consist of either quartz or opal minerals. In sandstone where there is silica cement present the quartz grains are attached to cement, this creates a rim around the quartz grain called overgrowth. The overgrowth retains the same crystallographic continuity of quartz framework grain that is being cemented. However Opal cement often occurs in sandstones rich in volcanogenic materials, and very rarely is in other sandstones. Calcite cement is the most common carbonate cement. Calcite cement is an assortment of smaller calcite crystals. The cement adheres itself to the framework grains, this adhesion is what causes the framework grains to be adhered together.

* '''Cement''': is a secondary mineral that forms after deposition and during burial of the sandstone and binds the siliclastic framework grains together. Cements mainly include carbonate, clay minerals and silica cements and Other minerals that act as cements include: hematite, limonite, feldspars, [[anhydrite]], [[gypsum]], barite, clay minerals, and zeolite . Silica cement can consist of either [[quartz]] or opal minerals. In sandstone where there is silica cement present the quartz grains are attached to cement, this creates a rim around the quartz grain called overgrowth. The overgrowth retains the same crystallographic continuity of quartz framework grain that is being cemented. However Opal cement often occurs in sandstones rich in volcanogenic materials, and very rarely is in other sandstones. Calcite cement is the most common carbonate cement. Calcite cement is an assortment of smaller calcite crystals. The cement adheres itself to the framework grains, this adhesion is what causes the framework grains to be adhered together.

* '''Pore space''': consists of open spaces within the sandstone and has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together.

* '''Pore space''': consists of open spaces within the sandstone and has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together.

===Sandstone classification===

===Sandstone classification===

Sandstone classifications on basis of their composition and this can be typically done by use of a triangular Quartz, Feldspar, and Lithic fragment diagrams. However, the most acceptable method is Dott's (1964) classification scheme which is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains.

Sandstone classifications on basis of their composition and this can be typically done by use of a triangular [[Quartz]], Feldspar, and Lithic fragment diagrams. However, the most acceptable method is Dott's (1964) classification scheme which is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains.

[[File:Sandstone-Fig-3.png|thumb|300px|Figure 3: Dott's (1964) sandstone classification scheme (after North<ref name=North>North. (1985). Petroleum Geology, Chapter 13.</ref>).]]

[[File:Sandstone-Fig-3.png|thumb|300px|Figure 3: Dott's (1964) sandstone classification scheme (after North<ref name=North>North. (1985). Petroleum Geology, Chapter 13.</ref>).]]

====Late diagenesis====

====Late diagenesis====

Late diagenetic alterations include chemical compaction, the albitization of plagioclase, dickitization and illitization of kaolinite, illitization and chloritization of smectite and the precipitation of quartz, ankerite and type II calcite cements. In addition to the increase in temperature and pressure, the spatial and temporal distributions of the late diagenetic alterations, and hence of porosity-permeability evolution of the sandstones, were influenced by the early diagenetic modifications and oil emplacement.

Late diagenetic alterations include chemical compaction, the albitization of plagioclase, dickitization and illitization of kaolinite, illitization and chloritization of smectite and the precipitation of [[quartz]], ankerite and type II calcite cements. In addition to the increase in temperature and pressure, the spatial and temporal distributions of the late diagenetic alterations, and hence of porosity-permeability evolution of the sandstones, were influenced by the early diagenetic modifications and oil emplacement.

====Epidiagenesis====

====Epidiagenesis====





====Effect of cementation on reservoir quality====

====Effect of cementation on reservoir quality====

* Carbonate cements are more abundant, and hence have a greater control on porosity and, particularly, permeability of the deltaic sandstones than of the fluvial sandstones.(figure 12).A higher overall content of carbonate cement of the delta-front and pro-delta sandstones (av. 4.0% and 4.2%, respectively) accounts partly for the considerably lower reservoir quality. However, the formation of a small amount of early diagenetic quartz cement and homogeneously distributed early diagenetic carbonates in sandstones weakened part of the mechanical compactional effect, and hence the preservation of part of the primary porosity in sandstones.

* Carbonate cements are more abundant, and hence have a greater control on porosity and, particularly, permeability of the deltaic sandstones than of the fluvial sandstones.(figure 12).A higher overall content of carbonate cement of the delta-front and pro-delta sandstones (av. 4.0% and 4.2%, respectively) accounts partly for the considerably lower reservoir quality. However, the formation of a small amount of early diagenetic [[quartz]] cement and homogeneously distributed early diagenetic carbonates in sandstones weakened part of the mechanical compactional effect, and hence the preservation of part of the primary porosity in sandstones.

* The clay minerals have variable influence on reservoir quality evolution. The grain- rimming chlorite and, particularly, illite caused a substantial deterioration of reservoir quality by decreasing the permeability through blocking the pore throats and by increasing the micro porosity.

* The clay minerals have variable influence on reservoir quality evolution. The grain- rimming chlorite and, particularly, illite caused a substantial deterioration of reservoir quality by decreasing the permeability through blocking the pore throats and by increasing the micro porosity.

* The grain-coating chlorite rims and illite around quartz. Nevertheless, chlorite fringes induced the preservation of a considerable proportion of the primary inter/granular macroporosity through inhibiting the precipitation of quartz overgrowths. This resulted in a considerable decrease in permeability, yet often low permeability, in the deltaic sandstones and less commonly in the fluvial sandstones.

* The grain-coating chlorite rims and illite around [[quartz]]. Nevertheless, chlorite fringes induced the preservation of a considerable proportion of the primary inter/granular macroporosity through inhibiting the precipitation of quartz overgrowths. This resulted in a considerable decrease in permeability, yet often low permeability, in the deltaic sandstones and less commonly in the fluvial sandstones.

* The illitization of intergranular kaolinite(due to the only small degree of albitization of K- feldspar grains), and hence further deterioration of permeability, was inhibited due to the earlier transformation of kaolinite into dickite, which is more resistant to illitization due to its better ordered crystal structure.

* The illitization of intergranular kaolinite(due to the only small degree of albitization of K- feldspar grains), and hence further deterioration of permeability, was inhibited due to the earlier transformation of kaolinite into dickite, which is more resistant to illitization due to its better ordered crystal structure.

==Conclusions==

==Conclusions==

Sandstone is the best known petroleum clastic reservoir rock composed of mainly quartz and/or feldspars, and typically deposited by relatively high-energy processes. Sandstone reservoirs have good porosity and high permeability. However porosity and permeability mainly depend on the depositional environment and burial history diagenesis.

Sandstone is the best known petroleum clastic reservoir rock composed of mainly [[quartz]] and/or feldspars, and typically deposited by relatively high-energy processes. Sandstone reservoirs have good porosity and high permeability. However porosity and permeability mainly depend on the depositional environment and burial history diagenesis.

The depositional environments associated with sandstones are very important and they range from terrestrial to deep marine, including: Fluvial; Deltaic ; Aeolian; Shoreline ;Glacial and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements.

The depositional environments associated with sandstones are very important and they range from terrestrial to deep marine, including: Fluvial; Deltaic ; Aeolian; Shoreline ;Glacial and Deep-sea sediments, including contourite sands formed by ocean-bottom currents, turbidites and submarine fan deposits, formed by gravity-driven mass movements.