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Careful examination and recording of information from continuous cores provide critical data for stratigraphic correlation, environmental interpretation, and wireline log calibration. Core plugs provide samples for analysis of [[porosity]], [[permeability]], fluid saturation, and a host of compositional and textural studies. Recommendations for the well site and laboratory handling of cores as well as sedimentological analyses are described by Siemers et al.<ref name=pt05r145>Siemers, C. T., R. W. Tillman, and C. R. Williamson, eds., 1981, Deep-water clastic sediments—a core workshop: SEPM Core Workshop, n. 2, 416 p.</ref> and Miall.<ref name=pt05r109>Maness, M., and J. G. W. Price, 1977, Well formation characterization by residual hydrocarbon analysis: Annual Meeting of the Society of Petroleum Engineers, Denver, CO, Oct. 9–12, SPE 6860.</ref>

Careful examination and recording of information from continuous cores provide critical data for stratigraphic correlation, environmental interpretation, and wireline log calibration. Core plugs provide samples for analysis of [[porosity]], [[permeability]], fluid saturation, and a host of compositional and textural studies. Recommendations for the well site and laboratory handling of cores as well as sedimentological analyses are described by Siemers et al.<ref name=pt05r145>Siemers, C. T., R. W. Tillman, and C. R. Williamson, eds., 1981, Deep-water clastic sediments—a core workshop: SEPM Core Workshop, n. 2, 416 p.</ref> and Miall.<ref name=pt05r109>Maness, M., and J. G. W. Price, 1977, Well formation characterization by residual hydrocarbon analysis: Annual Meeting of the Society of Petroleum Engineers, Denver, CO, Oct. 9–12, SPE 6860.</ref>

* Often provide a more complete section of the stratigraphic unit

* Often provide a more complete section of the stratigraphic unit

* Better preservation of contacts between units having significantly different resistances to weathering

* Better preservation of contacts between units having significantly different resistances to weathering

* Better preservation of delicate primary and soft sediment deformation structures in shale and siltstone units

* Better preservation of delicate primary and soft sediment [[deformation]] structures in shale and siltstone units

* Better preservation of trace fossils

* Better preservation of trace fossils

* Ability to obtain material for petrographic study below the present groundwater table

* Ability to obtain material for petrographic study below the present groundwater table

* Allow comparison of lithologic properties with petrophysical properties and wireline log responses.

* Allow comparison of lithologic properties with petrophysical properties and wireline log responses.

These advantages, however, are offset by the lack of a three-dimensional view and the inability to observe lateral facies changes and large-scale sedimentary features directly.

These advantages, however, are offset by the lack of a three-dimensional view and the inability to observe [[lateral]] facies changes and large-scale sedimentary features directly.

==Format for core logging==

==Format for core logging==

[[file:core-description_fig1.png|thumb|300px|{{figure number|1}}Idealized graphic log. Explanation for some symbols used for sedimentary structures, lithologies, fossils, and contacts are given. Grain size of sillclclastic rocks and Dunham's<ref name=pt05r50>Dunham, R. J., 1962, [http://archives.datapages.com/data/specpubs/carbona2/data/a038/a038/0001/0100/0108.htm Classification of carbonate rocks according to depositional texture], in W. E. Ham, ed., Classification of Carbonate Rocks: AAPG Memoir 1, p. 108–121.</ref> classification of limestones are indicated in the column on the left. All sedimentary structures are depicted graphically as accurately as possible. Porosity amounts in percent can be scaled as needed. (Modified from Casey.<ref name=pt05r32>Casey, J. M., 1980, Depositional systems and basin evolution of the Late Paleozoic Taos trough, northern New Mexico: Ph. D. Dissertation, The University of Texas at Austin, 236 p.</ref><ref name=pt05r28 />.)]]

[[file:core-description_fig1.png|thumb|300px|{{figure number|1}}Idealized graphic log. Explanation for some symbols used for sedimentary structures, lithologies, fossils, and contacts are given. [[Grain size]] of sillclclastic rocks and Dunham's<ref name=pt05r50>Dunham, R. J., 1962, [http://archives.datapages.com/data/specpubs/carbona2/data/a038/a038/0001/0100/0108.htm Classification of carbonate rocks according to depositional texture], in W. E. Ham, ed., Classification of Carbonate Rocks: AAPG Memoir 1, p. 108–121.</ref> classification of limestones are indicated in the column on the left. All sedimentary structures are depicted graphically as accurately as possible. Porosity amounts in percent can be scaled as needed. (Modified from Casey.<ref name=pt05r32>Casey, J. M., 1980, Depositional systems and basin evolution of the Late Paleozoic Taos trough, northern New Mexico: Ph. D. Dissertation, The University of Texas at Austin, 236 p.</ref><ref name=pt05r28 />.)]]

A graphic log format, which visually expresses a stratigraphic succession, is strongly recommended for describing continuous cores. Such logs should reflect the following:

A graphic log format, which visually expresses a stratigraphic succession, is strongly recommended for describing continuous cores. Such logs should reflect the following:

===Porosity===

===Porosity===

Identification of porosity type and a qualitative estimate of porosity abundance should be made in the column labeled “Porosity.” For carbonate rocks, the porosity classification scheme discussed by Choquette and Pray<ref name=pt05r34>Choquette, P. W., Pray, L. C., 1970, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0054/0002/0200/0207.htm Geological nomenclature and classification of porosity in sedimentary carbonates]: AAPG Bulletin, v. 54, p. 207–250.</ref> is recommended. For siliciclastic rocks, four types of porosity are common:

Identification of porosity type and a qualitative estimate of porosity abundance should be made in the column labeled “Porosity.” For carbonate rocks, the porosity classification scheme discussed by Choquette and Pray<ref name=pt05r34>Choquette, P. W., and L. C. Pray, 1970, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0054/0002/0200/0207.htm Geological nomenclature and classification of porosity in sedimentary carbonates]: AAPG Bulletin, v. 54, p. 207–250.</ref> is recommended. For siliciclastic rocks, four types of porosity are common:

* Intergranular

* Intergranular

* Intragranular or moldic

* Intragranular or moldic

* Microporosity

* Microporosity

* [[Fracture]] (Pittman<ref name=Pittman>Pitman, E. D., 1979, Porosity, diagenesis, and productive capability of sandstone reservoirs, in Scholle, P. A., and P. R. Schluger, eds., Aspects of Diagenesis: Society Economic Paleontologists and Mineralogists Special Publication 26, p. 159-173</ref>)

* [[Fracture]] (Pittman<ref name=Pittman>Pitman, E. D., 1979, Porosity, diagenesis, and productive capability of sandstone reservoirs, in P. A. Scholle, and P. R. Schluger, eds., Aspects of Diagenesis: Society Economic Paleontologists and Mineralogists Special Publication 26, p. 159-173</ref>)

Of these, microporosity is the most difficult to recognize with a binocular microscope. The existence of microporosity is suggested by the presence of detrital or authigenic clays in sandstones. Accurate laboratory or thin section determinations of porosity types and percentages should always augment the estimates made during core logging. (For more on porosity classification schemes, see [[Porosity]].)

Of these, microporosity is the most difficult to recognize with a binocular microscope. The existence of microporosity is suggested by the presence of detrital or authigenic clays in sandstones. Accurate laboratory or thin section determinations of porosity types and percentages should always augment the estimates made during core logging. (For more on porosity classification schemes, see [[Porosity]].)

[[Category:Laboratory methods]]

[[Category:Laboratory methods]]