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Pore type, pore geometry, and fluid properties are critical factors affecting [[permeability]]. Sandstone texture directly affects pore type and geometry. Knowing what textures and fluids to expect, as well as what authigenic clays might be present, can help us predict permeability.

Pore type, pore geometry, and fluid properties are critical factors affecting [[permeability]]. Sandstone texture directly affects pore type and geometry. Knowing what textures and fluids to expect, as well as what authigenic clays might be present, can help us predict permeability.

==Effects of texture==

==Effects of texture==

[[file:predicting-reservoir-system-quality-and-performance_fig9-60.png|300px|thumb|{{figure number|1}}Grain size affects permeability and porosity.<ref name=ch09r11>Coalson, E., B., Hartmann, D., J., Thomas, J., B., 1990, Applied Petrophysics in Exploration and Exploitation: Notes from short course sponsored by Univ. of Colo.–Denver, var. pages.</ref>]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-60.png|300px|thumb|{{figure number|1}}Grain size affects permeability and porosity.<ref name=ch09r11>Coalson, E. B., Hartmann, D. J., and Thomas, J. B., 1990, Applied Petrophysics in Exploration and Exploitation: Notes from short course sponsored by Univ. of Colo.–Denver, var. pages.</ref>]]

Sandstone texture affects permeability as follows:

Sandstone texture affects permeability as follows:

==Effect of authigenic clays==

==Effect of authigenic clays==

[[file:predicting-reservoir-system-quality-and-performance_fig9-61.png|300px|thumb|{{figure number|2}}. Copyright: North, 1985; courtesy Allen & Unwin.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-61.png|300px|thumb|{{figure number|2}}. Copyright: F. K. North;<ref name=North_1985>North, F. K., 1985, Petroleum Geology: London, Allen & Unwin, 607 p.</ref> courtesy Allen & Unwin.]]

Pore-bridging clays, like illite, decrease porosity slightly but can destroy sandstone permeability. Discrete particle clay, like kaolinite, lowers porosity and permeability only slightly. [[:file:predicting-reservoir-system-quality-and-performance_fig9-61.png|Figure 2]] compares porosity-permeability relationships for kaolinite-, chlorite-, and illite-cemented sandstones. Note there is no significant change in porosities, but permeabilities range over four orders of magnitude.

Pore-bridging clays, like illite, decrease porosity slightly but can destroy sandstone permeability. Discrete particle clay, like kaolinite, lowers porosity and permeability only slightly. [[:file:predicting-reservoir-system-quality-and-performance_fig9-61.png|Figure 2]] compares porosity-permeability relationships for kaolinite-, chlorite-, and illite-cemented sandstones. Note there is no significant change in porosities, but permeabilities range over four orders of magnitude.

==Pore geometry and clay minerals==

==Pore geometry and clay minerals==

[[file:predicting-reservoir-system-quality-and-performance_fig9-62.png|thumb|300px|{{figure number|3}}After Neasham.<ref name=ch09r40>Neasham, J., W., 1977, The morphology of dispersed clay in sandstone reservoirs and its effect on sandstone shaliness, pore space, and fluid flow properties: Proceedings of the SPE Annual Meeting, October 9–12, paper SPE-6858.</ref> Copyright: SPE.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-62.png|thumb|300px|{{figure number|3}}After Neasham.<ref name=ch09r40>Neasham, J. W., 1977, The morphology of dispersed clay in sandstone reservoirs and its effect on sandstone shaliness, pore space, and fluid flow properties: Proceedings of the SPE Annual Meeting, October 9–12, paper SPE-6858.</ref> Copyright: SPE.]]

[[:file:predicting-reservoir-system-quality-and-performance_fig9-62.png|Figure 3]] shows pore lining and discrete particle clays that decrease porosity and permeability only slightly in contrast to pore-bridging clays, which decrease porosity slightly but substantially lower permeability.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-62.png|Figure 3]] shows pore lining and discrete particle clays that decrease porosity and permeability only slightly in contrast to pore-bridging clays, which decrease porosity slightly but substantially lower permeability.

==Detrital clay and permeability==

==Detrital clay and permeability==

[[file:predicting-reservoir-system-quality-and-performance_fig9-63.png|300px|thumb|{{figure number|4}}After Wilson and Pittman.<ref name=ch09r68>Wilson, M., D., Pittman, E., D., 1977, Authigenic clays in sandstones: recognition and influence on reservoir properties and [[paleoenvironmental analysis]]: Journal of Sedimentary Petrology, vol. 47, no. 1, p. 3–31.</ref> Copyright: Journal of Sedimentary Petrology.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-63.png|300px|thumb|{{figure number|4}}After Wilson and Pittman.<ref name=ch09r68>Wilson, M. D., Pittman, E. D., 1977, Authigenic clays in sandstones: recognition and influence on reservoir properties and [[paleoenvironmental analysis]]: Journal of Sedimentary Petrology, vol. 47, no. 1, p. 3–31.</ref> Copyright: Journal of Sedimentary Petrology.]]

Detrital clays can be part of sandstone matrix or grains. As matrix, detrital clays can obliterate permeability. Detrital grains of clay are often ductile and can be compacted into pore spaces during burial. The percentage of detrital clay in a rock determines permeability. [[:file:predicting-reservoir-system-quality-and-performance_fig9-63.png|Figure 4]] shows different types of detrital clays in a sandstone.

Detrital clays can be part of sandstone matrix or grains. As matrix, detrital clays can obliterate permeability. Detrital grains of clay are often ductile and can be compacted into pore spaces during burial. The percentage of detrital clay in a rock determines permeability. [[:file:predicting-reservoir-system-quality-and-performance_fig9-63.png|Figure 4]] shows different types of detrital clays in a sandstone.

==Effect of quartz overgrowths==

==Effect of quartz overgrowths==

In general, as quartz cement precipitates, the pore–pore throat size ratio approaches 1 (Hartmann et al., 1985{{citation needed}}). Throats are reduced less than pore space; therefore, permeability is affected less than porosity. During cementation, the size of the pore spaces between the pore-filling crystals decreases until it approaches the size of the pore throats. Throats become more tabular or sheet-like. Sandstone porosity may be quite low (

In general, as quartz cement precipitates, the pore–pore throat size ratio approaches 1 (Hartmann et al., 1985{{citation needed}}). Throats are reduced less than pore space; therefore, permeability is affected less than porosity. During cementation, the size of the pore spaces between the pore-filling crystals decreases until it approaches the size of the pore throats. Throats become more tabular or sheet-like. Sandstone porosity may be quite low (<5%) and still have some permeability (<10 md) where cemented with quartz.

==Effect of fractures==

==Effect of fractures==