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==Petrographic techniques==

==Petrographic techniques==

Basic petrographic analysis is performed in transmitted light using a polarizing microscope. Certain petrographic problems require the use of a cathodoluminescence (CL) microscope (see [[SEM, XRD, CL, and XF methods]]). CL petrography is used to detect cement stratigraphy and original fabrics in recrystallized carbonate rocks<ref name=pt05r48>Dorobek, S. L., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0005/0450/0492.htm Petrography, geochemistry, and origin of burial diagenetic facies, Siluro-Devonian Helderberg Group (carbonate rocks), central Appalachians]: AAPG Bulletin, v. 71, p. 492–514.</ref> and to distinguish between detrital quartz grains and authigenic quartz overgrowths (cement) in sandstones.<ref name=pt05r80>Houseknecht, D. W., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0006/0600/0633.htm Assessing the relative importance of compaction processes and cementation to reduction of porosity in sandstones]: AAPG Bulletin, v. 71, p. 633–642.</ref>

Basic petrographic analysis is performed in transmitted light using a [http://dictionary.reference.com/browse/polarizing+microscope polarizing microscope]. Certain petrographic problems require the use of a cathodoluminescence (CL) microscope (see [[SEM, XRD, CL, and XF methods]]). CL petrography is used to detect cement stratigraphy and original fabrics in recrystallized carbonate rocks<ref name=pt05r48>Dorobek, S. L., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0005/0450/0492.htm Petrography, geochemistry, and origin of burial diagenetic facies, Siluro-Devonian Helderberg Group (carbonate rocks), central Appalachians]: AAPG Bulletin, v. 71, p. 492–514.</ref> and to distinguish between detrital quartz grains and authigenic quartz overgrowths (cement) in sandstones.<ref name=pt05r80>Houseknecht, D. W., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0006/0600/0633.htm Assessing the relative importance of compaction processes and cementation to reduction of porosity in sandstones]: AAPG Bulletin, v. 71, p. 633–642.</ref>

Petrographic analysis of thin sections in either transmitted light or CL can involve either qualitative description or quantitative estimation of rock properties, depending upon objectives of the analysis. Quantitative estimation of composition and porosity types by modal analysis (point counting) is recommended for both carbonate and sandstone reservoir rocks. In addition, quantitative estimation of textural parameters (grain size and sorting) is recommended for sandstones.

Petrographic analysis of thin sections in either transmitted light or CL can involve either qualitative description or quantitative estimation of rock properties, depending upon objectives of the analysis. Quantitative estimation of composition and porosity types by modal analysis (point counting) is recommended for both carbonate and sandstone reservoir rocks. In addition, quantitative estimation of textural parameters (grain size and sorting) is recommended for sandstones.