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POROSITY Many slides contain more detailed notes that may be shown using the Notes Page View

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Acknowledgments Dr. Walt Ayers, PETE 311, Fall 2001 NExT PERF Short Course Notes, 1999 Note that many of the NExT slides appears to have been obtained from other primary sources that are not cited

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Definition: Porosity is the fraction of a rock that is occupied by voids (pores). Discussion Topics Origins and descriptions Factors that effect porosity Methods of determination RESERVOIR POROSITY

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ROCK MATRIX AND PORE SPACE Rock matrix Pore space Note different use of matrix by geologists and engineers

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Porosity: The fraction of a rock that is occupied by pores POROSITY DEFINITION Porosity is an intensive property describing the fluid storage capacity of rock

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ROCK MATRIX AND PORE SPACE Rock matrix Water Oil and/or gas

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OBJECTIVES To provide an understanding of The concepts of rock matrix and porosity The difference between original (primary) and induced (secondary) porosity The difference between total and effective porosity Laboratory methods of porosity determination Determination of porosity from well logs

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CLASSIFICATION OF ROCKS SEDIMENTARY Rock-forming process Source of material IGNEOUS METAMORPHIC Molten materials in deep crust and upper mantle Crystallization (Solidification of melt) Weathering and erosion of rocks exposed at surface Sedimentation, burial and lithification Rocks under high temperatures and pressures in deep crust Recrystallization due to heat, pressure, or chemically active fluids

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SEDIMENTARY ROCKS Clastics Carbonates Evaporites

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CLASTIC AND CARBONATE ROCKS Clastic Rocks Consist Primarily of Silicate Minerals Are Classified on the Basis of: - Grain Size - Mineral Composition Carbonate Rocks Consist Primarily of Carbonate Minerals (i.e. Minerals With a CO Anion Group) Limestone - Predominately Calcite (Calcium Carbonate, CaCO 3 ) Dolomite - Predominately Dolostone (Calcium Magnesium Carbonate, CaMg(CO 3 ) 2 ) 3 -2

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Relative Abundances Siltstone and shale (clastic) ~75% Sandstone and conglomerate (clastic) ~11% Limestone and dolomite ~14% SEDIMENTARY ROCK TYPES,

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Sand Grains Clay Matrix Chemical Cement Quartz Feldspar Rock Fragments Quartz Calcite Hematite Illite Kaolinite Smectite Average Sandstone Average Mudrock (Shale) Allochemical Grains Chemical Cement Microcrystalline Matrix Calcite Fossils Pelloids Oolites Intractlasts Calcite Average Sparry Limestone Average Micritic Limestone Clastic Rocks Carbonate Rocks Comparison of Compositions of Clastic and CarbonateRocks

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Grain-Size Classification for Clastic Sediments NameMillimetersMicrometers Boulder Cobble Pebble Granule Very Coarse Sand Coarse Sand Medium Sand Fine Sand Very Fine Sand Coarse Silt Medium Silt Fine Silt Very Fine Silt Clay 4,096 256 64 4 2 1 0.5 0.25 0.125 0.062 0.031 0.016 0.008 0.004 500 250 125 62 31 16 8 4 (modified from Blatt, 1982)

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Average Detrital Mineral Composition of Shale and Sandstone Mineral Composition ShaleSandstone Clay Minerals Quartz Feldspar Rock Fragments Carbonate Organic Matter, Hematite, and Other Minerals 60 (%) 30 4