Changes

[http://www.thefreedictionary.com/Detrital Detrital] clays can be part of sandstone [http://www.britannica.com/EBchecked/topic/369508/matrix matrix] or grains. As matrix, detrital clays can obliterate permeability. Detrital grains of clay are often [[Ductility|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.

[http://www.thefreedictionary.com/Detrital Detrital] clays can be part of sandstone [http://www.britannica.com/EBchecked/topic/369508/matrix matrix] or grains. As matrix, detrital clays can obliterate permeability. Detrital grains of clay are often [[Ductility|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.<ref name=Harris1985>Harris, P. M., C. G. St.-C. Kendall, and I. Lerche, 1985, Carbonate cementation—a brief review, in N. Schneidermann and P. M. Harris, eds., Carbonate Cements: SEPM Special Publication 36, p. 79–95.</ref> 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. (See also [[Connectivity and pore throat size]].)

In general, as quartz cement precipitates, the pore:pore throat size ratio approaches 1.<ref name=Harris1985>Harris, P. M., C. G. St.-C. Kendall, and I. Lerche, 1985, Carbonate cementation—a brief review, in N. Schneidermann and P. M. Harris, eds., Carbonate Cements: SEPM Special Publication 36, p. 79–95.</ref> 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. (See also [[Connectivity and pore throat size]].)

Predicting sandstone reservoir permeability is possible as long as we realize that potential errors may be large. Any process that decreases pore throat size decreases permeability, so predict accordingly. Use the procedure below to help predict sandstone reservoir permeability.

Predicting sandstone reservoir permeability is possible as long as we realize that potential errors may be large. Any process that decreases pore throat size decreases permeability, so predict accordingly. Use the procedure below to help predict sandstone reservoir permeability.

# Estimate [[grain size]], [[Core_description#Maturity|sorting]], and [[porosity]] using the [[Depositional environments|depositional environment]]. For example, if a reservoir is a [[beach]] sand, it should be fine to medium grained and well sorted with well-rounded quartz grains

# Estimate [[grain size]], [[Core_description#Maturity|sorting]], and [[porosity]] using the [[Depositional environments|depositional environment]]. For example, if a reservoir is a [[beach]] sand, it should be fine to medium grained and well sorted with well-rounded [[quartz]] grains

# Apply information from Step 1 to the porosity–permeability–grain size plot ([[:file:predicting-reservoir-system-quality-and-performance_fig9-60.png|Figure 1]]). Use porosity and grain size from sandstone to estimate the permeability on the chart.

# Apply information from Step 1 to the porosity–permeability–grain size plot ([[:file:predicting-reservoir-system-quality-and-performance_fig9-60.png|Figure 1]]). Use porosity and grain size from sandstone to estimate the permeability on the chart.

# If the sandstone is poorly sorted or is cemented, then discount permeability downward.

# If the sandstone is poorly sorted or is cemented, then discount permeability downward.