Changes

===Matrix===

===Matrix===

Clay minerals commonly occur as both matrix and cement in reservoir sandstones.<ref name=pt05r71>Hagoort, J., 1984, Measurement of relative permeability for computer modeling/reservoir simulation: Oil and Gas Journal, Feb. 20, p. 62–68.</ref> [http://dictionary.reference.com/browse/detrital Detrital] matrix can be introduced into sand during or immediately following sedimentation by depositional processes, infiltration, and [[bioturbation]]. It can occur as grain coatings, dispersed matrix, laminae, or discrete grains. [ http://dictionary.reference.com/browse/authigenic Authigenic] clay cements commonly precipitate as grain coatings, pore fillings, and grain replacements. Virtually any clay mineral can occur in any of these modes, with [[kaolinite]], [[chlorite]], [[smectite]], mixed layer illite-smectite, and [[illite]] occurring as common constituents of reservoir sandstones.

Clay minerals commonly occur as both [http://www.britannica.com/EBchecked/topic/369508/matrix matrix] and cement in reservoir sandstones.<ref name=pt05r71>Hagoort, J., 1984, Measurement of relative permeability for computer modeling/reservoir simulation: Oil and Gas Journal, Feb. 20, p. 62–68.</ref> [http://dictionary.reference.com/browse/detrital Detrital] matrix can be introduced into sand during or immediately following sedimentation by depositional processes, infiltration, and [[bioturbation]]. It can occur as grain coatings, dispersed matrix, laminae, or discrete grains. [ http://dictionary.reference.com/browse/authigenic Authigenic] clay cements commonly precipitate as grain coatings, pore fillings, and grain replacements. Virtually any clay mineral can occur in any of these modes, with [[kaolinite]], [[chlorite]], [[smectite]], mixed layer illite-smectite, and [[illite]] occurring as common constituents of reservoir sandstones.

The presence of clay minerals of any origin has both direct and indirect effects on [[reservoir quality]]. Directly, clay minerals commonly result in lowered [[permeability]] because they constrict [[Connectivity and pore throat size|pore throats]] and promote higher [http://petrowiki.org/Glossary%3AIrreducible_water_saturation irreducible water saturation]. Indirectly, clay minerals commonly influence [[Diagenesis|diagenetic]] processes that impact reservoir quality. For example, clay grain coatings in some sandstones have inhibited the nucleation of quartz overgrowths and thereby contributed to porosity preservation. However, clay grain coatings in other sandstones have promoted intergranular [[pressure solution]] and have thereby contributed to porosity destruction.

The presence of clay minerals of any origin has both direct and indirect effects on [[reservoir quality]]. Directly, clay minerals commonly result in lowered [[permeability]] because they constrict [[Connectivity and pore throat size|pore throats]] and promote higher [http://petrowiki.org/Glossary%3AIrreducible_water_saturation irreducible water saturation]. Indirectly, clay minerals commonly influence [[Diagenesis|diagenetic]] processes that impact reservoir quality. For example, clay grain coatings in some sandstones have inhibited the nucleation of quartz overgrowths and thereby contributed to porosity preservation. However, clay grain coatings in other sandstones have promoted intergranular [[pressure solution]] and have thereby contributed to porosity destruction.

==Carbonate reservoirs==

==Carbonate reservoirs==

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thin-section-analysis_fig2.png|{{figure number|2}}Carbonate classification schemes of (a) Folk<ref name=pt05r56 /> and (b) Dunham,<ref name=pt05r50 /> both based on textures observed in hand specimen or thin section. In Folk's scheme, the black pattern represents lime mud matrix, the lined pattern represents sparry calcite cement, and the white objects represent various carbonate grains.

thin-section-analysis_fig2.png|{{figure number|2}}Carbonate classification schemes of (a) Folk<ref name=pt05r56 /> and (b) Dunham,<ref name=pt05r50 /> both based on textures observed in hand specimen or thin section. In Folk's scheme, the black pattern represents lime mud [http://www.britannica.com/EBchecked/topic/369508/matrix matrix], the lined pattern represents sparry calcite cement, and the white objects represent various carbonate grains.

Porosity_fig3.png|{{figure number|3}}

Porosity_fig3.png|{{figure number|3}}

</gallery>

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