PETE311_06A_Class02 porosity.ppt
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This document provides information about porosity in rocks. It defines porosity as the fraction of bulk volume that is occupied by pores. Primary porosity develops during deposition, such as intergranular pores in clastics. Secondary porosity develops after deposition through processes like dissolution. Factors that influence porosity include particle shape, sorting, cementation, and compaction. Methods to determine porosity include well logs and laboratory analysis. Rocks can have different pore systems like matrix and fractures. The document also discusses porosity in carbonates and includes classifications of carbonate rocks.
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PETE311_06A_Class02 porosity.ppt
- 1. POROSITY Many slides contain more detailed notes that may be shown using the “Notes Page View”
- 2. 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
- 3. Definition: Porosity is the fraction of the bulk volume of a material (rock) that is occupied by pores (voids ). Discussion Topics • Origins and descriptions • Factors that effect porosity • Methods of determination RESERVOIR POROSITY
- 4. ROCK MATRIX AND PORE SPACE Rock matrix Pore space Note different use of “matrix” by geologists and engineers
- 5. Porosity: The fraction of the bulk volume of a rock that is occupied by pores b ma b b p V V V V V Porosity POROSITY DEFINITION • Porosity is an intensive property describing the fluid storage capacity of rock
- 6. ROCK MATRIX AND PORE SPACE Rock matrix Water Oil and/or gas
- 7. 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
- 8. 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
- 10. 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, CaCO3) Dolomite - Predominately Dolostone (Calcium Magnesium Carbonate, CaMg(CO3)2 ) 3 -2
- 11. Relative Abundances Siltstone and shale (clastic) ~75% Sandstone and conglomerate (clastic) ~11% Limestone and dolomite ~14% SEDIMENTARY ROCK TYPES,
- 12. 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 Carbonate Rocks
- 13. Grain-Size Classification for Clastic Sediments Name Millimeters Micrometers 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)
- 14. Average Detrital Mineral Composition of Shale and Sandstone Mineral Composition Shale Sandstone Clay Minerals Quartz Feldspar Rock Fragments Carbonate Organic Matter, Hematite, and Other Minerals 60 (%) 30 4 <5 3 <3 5 (%) 65 10-15 15 <1 <1 (modified from Blatt, 1982)
- 15. SANDSTONE CLASSIFICATION Quartz + Chert Feldspar Unstable Rock Fragments 5 5 25 25 25 25 25 25 50 50 50 10 10 Quartzarenite Subarkose Sublitharenite Lithic Subarkose Lithic Arkose Felspathic Litharenite (modified from McBride, 1963)
- 16. Framework Matrix Cement Pores Sand (and Silt) Size Detrital Grains Silt and Clay Size Detrital Material Material Precipitated Post-Depositionally, During Burial. Cements Fill Pores and Replace Framework Grains Voids Among the Above Components FOUR MAJOR COMPONENTS OF SANDSTONE
- 17. FOUR COMPONENTS OF SANDSTONE MATRIX FRAMEWORK (QUARTZ) FRAMEWORK (FELDSPAR) CEMENT PORE Note different use of “matrix” by geologists and engineers 0.25 mm 1. Framework 2. Matrix 3. Cement 4. Pores Engineering “matrix” Geologist’s Classification
- 18. ORIGINS OF POROSITY IN CLASTICS AND CARBONATES (Genetic Classification) • Primary (original) • Secondary (induced) (Generally more complex than primary porosity)
- 19. PRIMARY (ORIGINAL) POROSITY • Developed at deposition • Typified by – Intergranular pores of clastics or carbonates – Intercrystalline and fenestral pores of carbonates • Usually more uniform than induced porosity
- 20. SECONDARY (INDUCED) POROSITY • Developed by geologic processes after deposition (diagenetic processes) • Examples – Grain dissolution in sandstones or carbonates – Vugs and solution cavities in carbonates – Fracture development in some sandstones, shales, and carbonates
- 21. SANDSTONES POROSITY TYPES Intergranular (Primary) Dissolution Micropores Fractures Interstitial Void Space Between Framework Grains Partial or Complete Dissolution of Framework Grains or Cement Small Pores Mainly Between Detrital or Authigenic Grains (Can Also Occur Within Grains Breakage Due to Earth Stresses
- 22. FACTORS THAT AFFECT POROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (diagenetic)
- 23. ROUNDNESS AND SPHERICITY OF CLASTIC GRAINS High Low Very Angular Angular Sub- Angular Sub- Rounded Rounded Well- Rounded ROUNDNESS Porosity Porosity
- 24. FACTORS THAT AFFECT POROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 25. Line of Traverse (using microscope) Cement Matrix (clays, etc.) Tangential Contact Sutured Contact Long Contact Concavo-Convex Contact GRAIN PACKING IN SANDSTONE (modified from Blatt, 1982) This Example Packing Proximity = 40% Packing Density = 0.8 4 Types of Grain Contacts Packing Proximity Packing Density A measure of the extent to which sedimentary particles are in contact with their neighbors A measure of the extent to which sedimentary particles occupy the rock volume
- 26. CUBIC PACKING OF SPHERES Porosity = 0.48
- 27. Porosity Calculations - Uniform Spheres • Bulk volume = (2r)3 = 8r3 • Matrix volume = • Pore volume = bulk volume - matrix volume 3 r 4 3
- 29. RHOMBIC PACKING OF SPHERES Porosity = 0.27
- 30. FACTORS THAT AFFECT POROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 31. Packing of Two Sizes of Spheres Porosity = 0.14
- 32. Grain-Size Sorting in Sandstone Very Well Sorted Well Sorted Moderately Sorted Poorly Sorted Very Poorly Sorted SORTING
- 33. Change of Composition Change of Size Change of Shape Change of Orientation Change of Packing Sand Shale Eolian Fluvial Slow Current Fast Current River Beach TYPES OF TEXTURAL CHANGES SENSED BY THE NAKED EYE AS BEDDING
- 34. PROGRESSIVE DESTRUCTION OF BEDDING THROUGH BIOTURBATION Regular Layers Irregular Layers Mottles (Distinct) Mottles (Indistinct) Homogeneous Deposits (Whole Core) Bioturbated Sandstone
- 35. STS61A-42-0051 Mississippi River Delta, Louisiana, U.S.A. October 1985
- 36. STS084-721-029 Selenga River Delta, Lake Baykal, Russia May 1997
- 37. FACTORS THAT AFFECT POROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 38. DIAGENESIS Carbonate Cemented Oil Stained Diagenesis is the Post- Depositional Chemical and Mechanical Changes that Occur in Sedimentary Rocks Some Diagenetic Effects Include Compaction Precipitation of Cement Dissolution of Framework Grains and Cement The Effects of Diagenesis May Enhance or Degrade Reservoir Quality Whole Core Misoa Formation, Venezuela Photo by W. Ayers
- 39. DUAL POROSITY IN SANDSTONE MATRIX FRAMEWORK (QUARTZ) FRAMEWORK (FELDSPAR) CEMENT PORE Note different use of “matrix” by geologists and engineers 0.25 mm Sandstone Comp. • Framework • Matrix • Cement • Pores DISSOLUTION PORE FRACTURE 1. Primary and secondary “matrix” porosity system 2. Fracture porosity system
- 40. SANDSTONE COMPOSITION, Framework Grains Norphlet Sandstone, Offshore Alabama, USA Grains ~0.25 mm in Diameter/Length PRF KF P KF = Potassium Feldspar PRF = Plutonic Rock Fragment P = Pore Potassium Feldspar is Stained Yellow With a Chemical Dye Pores are Impregnated With Blue-Dyed Epoxy Q Q = Quartz Photo by R. Kugler
- 41. POROSITY IN SANDSTONE Quartz Grain Pore Scanning Electron Micrograph Norphlet Sandstone, Offshore Alabama, USA Porosity in Sandstone Typically is Lower Than That of Idealized Packed Spheres Owing to: Variation in Grain Size Variation in Grain Shape Cementation Mechanical and Chemical Compaction Photomicrograph by R.L. Kugler
- 42. POROSITY IN SANDSTONE Scanning Electron Micrograph Tordillo Sandstone, Neuquen Basin, Argentina Pore Throats in Sandstone May Be Lined With A Variety of Cement Minerals That Affect Petrophysical Properties Photomicrograph by R.L. Kugler
- 43. POROSITY IN SANDSTONE Scanning Electron Micrograph Norphlet Formation, Offshore Alabama, USA Pores Provide the Volume to Store Hydrocarbons Pore Throats Restrict Flow through pores Pore Throat
- 44. Secondary Electron Micrograph Clay Minerals in Sandstone Reservoirs, Authigenic Chlorite Jurassic Norphlet Sandstone Offshore Alabama, USA (Photograph by R.L. Kugler) Occurs as Thin Coats on Detrital Grain Surfaces Occurs in Several Deeply Buried Sandstones With High Reservoir Quality Iron-Rich Varieties React With Acid ~ 10 mm
- 45. Electron Photomicrograph Clay Minerals in Sandstone Reservoirs, Fibrous Authigenic Illite Jurassic Norphlet Sandstone Hatters Pond Field, Alabama, USA (Photograph by R.L. Kugler) Illite Significant Permeability Reduction Negligible Porosity Reduction Migration of Fines Problem High Irreducible Water Saturation
- 46. INTERGRANULAR PORE AND MICROPOROSITY Intergranular Pore Microporosity Kaolinite Quartz Detrital Grain Intergranular Pores Contain Hydrocarbon Fluids Micropores Contain Irreducible Water Backscattered Electron Micrograph Carter Sandstone, Black Warrior Basin, Alabama, USA (Photograph by R.L. Kugler)
- 47. Clay Minerals in Sandstone Reservoirs, Authigenic Kaolinite Secondary Electron Micrograph Carter Sandstone North Blowhorn Creek Oil Unit Black Warrior Basin, Alabama, USA Significant Permeability Reduction High Irreducible Water Saturation Migration of Fines Problem (Photograph by R.L. Kugler)
- 48. DISSOLUTION POROSITY Thin Section Micrograph - Plane Polarized Light Avile Sandstone, Neuquen Basin, Argentina Dissolution of Framework Grains (Feldspar, for Example) and Cement may Enhance the Interconnected Pore System This is Secondary Porosity Pore Quartz Detrital Grain Partially Dissolved Feldspar Photo by R.L. Kugler
- 49. DISSOLUTION POROSITY Scanning Electron Micrograph Tordillo Formation, Neuquen Basin, Argentina Partially Dissolved Feldspar Dissolution Pores May be Isolated and not Contribute to the Effective Pore System Photo by R.L. Kugler
- 50. 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 Carbonate Rocks
- 52. Maldive Islands
- 53. FOLK CARBONATE ROCK CLASSIFICATION 0-1% 1-10% 10-50% Over 50% Sparse Biomicrite Micrite & Dismicrite Fossili- ferous Micrite Packed Biomicrite Poorly Washed Biosparite Unsorted Biosparite Sorted Biosparite Rounded Biosparite Over 2/3 Lime Mud Matrix Over 2/3 Spar Cement Subequal Spar & Lime Mud Sorting Poor Sorting Good Rounded, Abraded Claystone Sandy Claystone Clayey or Immature Sandstone Sub- mature SS Mature SS Super- mature SS Depositional Texture Recognizable Depositional Texture Not Recognizable
- 54. DunhamCarbonateRockClassification DepositionalTextureRecognizable Depositional Texture NotRecognizable Mudstone Wackestone Packstone Grainstone Boundstone Crystaline Carbonate Grain Supported LacksMud, Grain- Supported ComponentsNotBoundTogetherDuringDeposition MudSupported ContainsMud (clayandsiltsizeparticles <10% Grains >10% Grains OriginalComponents BoundTogether DuringDeposition DUNHAM CARBONATE ROCK CLASSIFICATION Depositional Texture Recognizable Depositional Texture Not Recognizable Mudstone Wackestone Packstone Grainstone Boundstone Crystalline Carbonate Grain Supported Lacks Mud, Grain- Supported Components Not Bound Together During Deposition Mud Supported Contains Mud (clay and silt size particles <10 % Grains >10 % Grains Original Components Bound Together During Deposition
- 55. CARBONATES POROSITY TYPES Interparticle Intraparticle Intercrystal Moldic Pores Between Particles or Grains Pores Within Individual Particles or Grains Pores Between Crystals Pores Formed by Dissolution of an Individual Grain or Crystal in the Rock Fenestral Fracture Vug Primary Pores Larger Than Grain-Supported Interstices Formed by a Planar Break in the Rock Large Pores Formed by Indiscriminate Dissolution of Cements and Grains
- 56. Interparticle Intraparticle Intercrystal Moldic Fenestral Shelter Growth-Framework Fabric Selective Fracture Channel Vug Non-Fabric Selective Breccia Boring Burrow Shrinkage Fabric Selective or Not Fabric Selective Idealized Carbonate Porosity Types (modified from Choquette and Pray, 1970)
- 57. CARBONATE POROSITY - EXAMPLE Thin section micrograph - plane-polarized light Smackover Formation, Alabama (Photograph by D.C. Kopaska-Merkel) Moldic Pores • Due to dissolution and collapse of ooids (allochemical particles) • Isolated pores • Low effective porosity • Low permeability Blue areas are pores. Calcite Dolomite Moldic Pore
- 58. CARBONATE POROSITY - EXAMPLE Thin section micrograph Smackover Formation, Alabama Black areas are pores. (Photograph by D.C. Kopaska-Merkel) • Combination pore system • Moldic pores formed through dissolution of ooids (allochemical particles) • Connected pores • High effective porosity • High permeability Moldic Pore Interparticle Pores Moldic and Interparticle Pores
- 59. PORE SPACE CLASSIFICATION (In Terms of Fluid Properties)
- 60. PORE-SPACE CLASSIFICATION • Total porosity, t = • Effective porosity, e = Volume Bulk PoreVolume Total Volume Bulk Pore Space cted Interconne • Effective porosity – of great importance; contains the mobile fluid
- 61. COMPARISON OF TOTAL AND EFFECTIVE POROSITIES • Very clean sandstones : e t • Poorly to moderately well -cemented intergranular materials: t e • Highly cemented materials and most carbonates: e < t
- 62. MEASUREMENT OF POROSITY • Core samples (Laboratory) • Openhole wireline logs
- 63. Quartz (Framework) Small Pores Isolated Pores Large, Interconnected Pores Clay Surfaces & Interlayers Clay Layers Irreducible or Immobile Water Hydration or Bound Water Hydrocarbon Pore Volume Structural (OH -) Water Rock Matrix Total Porosity - Neutron Log Total Porosity - Density Log Absolute or Total Porosity Oven-Dried Core Analysis Porosity Humidity-Dried Core Analysis Porosity Capillary Water VShale Sandstone Porosity Measured by Various Techniques (modified from Eslinger and Pevear, 1988) Quartz (Framework) Small Pores Isolated Pores Large, Interconnected Pores Clay Surfaces & Interlayers Clay Layers Irreducible or Immobile Water Hydration or Bound Water Hydrocarbon Pore Volume Structural (OH -) Water Rock Matrix Total Porosity - Neutron Log Total Porosity - Density Log Absolute or Total Porosity Oven-Dried Core Analysis Porosity Humidity-Dried Core Analysis Porosity Capillary Water VShale Sandstone Porosity Measured by Various Techniques (modified from Eslinger and Pevear, 1988) SANDSTONE POROSITY MEASURED BY VARIOUS TECHNIQUES Quartz (Framework) Small Pores Isolated Pores Large, Interconnected Pores Clay Surfaces & Interlayers Clay Layers Irreducible or Immobile Water Hydration or Bound Water Hydrocarbon Pore Volume Structural (OH - ) Water Rock Matrix Total Porosity - Neutron Log Total Porosity - Density Log Absolute or Total Porosity Oven-Dried Core Analysis Porosity Humidity-Dried Core Analysis Porosity Capillary Water VShale (modified from Eslinger and Pevear, 1988)
- 64. INFORMATION FROM CORES* • Porosity • Horizontal permeability to air • Grain density • Vertical permeability to air • Relative permeability • Capillary pressure • Cementation exponent (m) and saturation exponent (n) Standard Analysis Special Core Analysis *Allows calibration of wireline log results
- 65. PDC Cutters Fluid vent Drill collar connection Inner barrel Outer barrel Thrust bearing Core retaining ring Core bit CORING ASSEMBLY AND CORE BIT
- 66. COMING OUT OF HOLE WITH CORE BARREL
- 67. Whole Core Photograph, Misoa “C” Sandstone, Venezuela WHOLE CORE Photo by W. Ayers
- 68. SIDEWALL SAMPLING GUN Core bullets Core sample Formation rock
- 69. SIDEWALL CORING TOOL Coring bit Samples
- 70. WHOLE CORE ANALYSIS vs. PLUGS OR SIDEWALL CORES WHOLE CORE • Provides larger samples • Better and more consistent representation of formation • Better for heterogeneous rocks or for more complex lithologies
- 71. • Smaller samples • Less representative of heterogeneous formations • Within 1 to 2% of whole cores for medium-to high- porosity formation • In low-porosity formations, from core plugs tends to be much greater than from whole cores • Scalar effects in fractured reservoirs WHOLE CORE ANALYSIS vs. PLUGS OR SIDEWALL CORES PLUGS OR SIDEWALL CORES
- 72. Sparks and Ayers, unpublished CORE PLUG
- 74. Student Questions / Answers • intraparticle porosity in carbonates (JC1): – vugs and fractures • why are clays important (JC1): – one major reason is that clays conduct electricity, this can effect water saturation calculations if not accounted for • fines (ABW): – solid particles so small that they can flow with fluids through pores - but they can also plug pore throats • tortuousity (ABW): – the indirect curvy flow path through the pore system to get from point A to point B • holocene: – referring to the Holocene Epoch (geology) or in general meaning about the last 10,000 years.