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==Definition of porosity terms==

==Definition of porosity terms==

[[file:porosity_fig1.png|thumb|300px|{{figure number|1}}Schematic of a pore system relating mineralogy, water content, and porosity assessment. (Notes: *lf sample is completely disaggregated during measurement. “Varies as a function of height above the free water level.) (After Chatzis et al.<ref name=pt05r33>Chatzis, I., N. R. Morrow, and H. T. Lim, 1983, Magnitude and detailed structure of residual oil saturation: Society Petroleum Engineers Journal, v. 23, p. 311–326., 10., 2118/10681-PA</ref>; modified from Hill et al., 1969.{{citation needed}})]]

[[file:porosity_fig1.png|thumb|300px|{{figure number|1}}Schematic of a pore system relating mineralogy, water content, and porosity assessment. (Notes: *lf sample is completely disaggregated during measurement. “Varies as a function of height above the [[free water level]].) (After Chatzis et al.<ref name=pt05r33>Chatzis, I., N. R. Morrow, and H. T. Lim, 1983, Magnitude and detailed structure of residual oil saturation: Society Petroleum Engineers Journal, v. 23, p. 311–326., 10., 2118/10681-PA</ref>; modified from Hill et al., 1969.{{citation needed}})]]

Discrepancies often exist between laboratory determined porosity values and porosities derived from downhole logs. Some of these discrepancies result from differences inherent in comparing direct measurements of physical properties made on small samples with indirect assessments of averaged properties. Many of these discrepancies, however, can be explained by noting differences in the definition and assessment of porosity ([[:file:porosity_fig1.png|Figure 1]]).

Discrepancies often exist between laboratory determined porosity values and porosities derived from downhole logs. Some of these discrepancies result from differences inherent in comparing direct measurements of physical properties made on small samples with indirect assessments of averaged properties. Many of these discrepancies, however, can be explained by noting differences in the definition and assessment of porosity ([[:file:porosity_fig1.png|Figure 1]]).

===Sample preparation===

===Sample preparation===

Most porosity analysis techniques require removal of soluble hydrocarbons before sample analysis. Factors influencing sample cleaning include the types of hydrocarbon present, the presence of salts precipitated from pore waters, rock mineralogy, degree of cementation, and time constraints. Different solvents and cleaning techniques can be used to remove hydrocarbons from rocks. Toluene is generally an effective solvent for most liquid hydrocarbons. If hydrocarbons cannot be removed with toluene, toluene/methanol (azeotrope), chloroform/methanol (azeotrope), methylene chloride or carbon disulfide may be used. Methanol is used to remove salts formed from the evaporation of saline pore waters. Rocks containing gypsum and smectite require special low temperature cleaning techniques to minimize removal of structural and bound water.<ref name=pt05r89>Keelan, D. K., 1971, A critical review of core analysis techniques: 22nd Annual Technical Meeting of the Petroleum Society of the Canadian Institute of Mining, Calgary, Banff, Alberta, June 2–5, Paper No. 7612, p. 1–13.</ref>

Most porosity analysis techniques require removal of soluble hydrocarbons before sample analysis. Factors influencing sample cleaning include the types of hydrocarbon present, the presence of salts precipitated from pore waters, rock [[mineralogy]], degree of cementation, and time constraints. Different solvents and cleaning techniques can be used to remove hydrocarbons from rocks. Toluene is generally an effective solvent for most liquid hydrocarbons. If hydrocarbons cannot be removed with toluene, toluene/methanol (azeotrope), chloroform/methanol (azeotrope), methylene chloride or carbon disulfide may be used. Methanol is used to remove salts formed from the evaporation of saline pore waters. Rocks containing [[gypsum]] and smectite require special low temperature cleaning techniques to minimize removal of structural and bound water.<ref name=pt05r89>Keelan, D. K., 1971, A critical review of core analysis techniques: 22nd Annual Technical Meeting of the Petroleum Society of the Canadian Institute of Mining, Calgary, Banff, Alberta, June 2–5, Paper No. 7612, p. 1–13.</ref>

Laboratory determination of porosity generally requires dry samples. Most clay-free samples can be dried in an oven ([[temperature::115&deg;C]]). If clay minerals, especially smectite, are present, humidity drying (45% relative humidity, [[temperature::63&deg;C]]) is required to prevent removal of clay-bound water.

Laboratory determination of porosity generally requires dry samples. Most clay-free samples can be dried in an oven ([[temperature::115&deg;C]]). If clay minerals, especially smectite, are present, humidity drying (45% relative humidity, [[temperature::63&deg;C]]) is required to prevent removal of clay-bound water.

[[Category:Laboratory methods]]

[[Category:Laboratory methods]]