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CH-7 Porosity (1).pptx
- 1.
- 2. Definition: Porosity isthe fraction of a rock that is occupied by voids (pores). Discussion Topics • Origins and descriptions • Factors that effect porosity • Methods of determination RESERVOIR POROSITY
- 3. ROCK MATRIX ANDPORE SPACE Rock matrix Pore space Note different use of “matrix” by geologists and engineers
- 4. Porosity: The fractionof 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
- 5. ROCK MATRIX ANDPORE SPACE Rock matrix Water Oil and/or gas
- 6. CLASSIFICATION OF ROCKS SEDIMENTARY Rock-forming process Source of material IGNEOUSMETAMORPHIC 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
- 7.
- 8. CLASTIC AND CARBONATEROCKS 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
- 9. Relative Abundances Siltstone and shale (clastic) ~75% Sandstone andconglomerate (clastic) ~11% Limestone and dolomite ~14% SEDIMENTARY ROCK TYPES,
- 10. 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 RocksCarbonate Rocks Comparison of Compositions of Clastic and Carbonate Rocks
- 11. Grain-Size Classification forClastic 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)
- 12. Average Detrital MineralComposition 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)
- 13. 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)
- 14. 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
- 15. FOUR COMPONENTS OFSANDSTONE 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
- 16. ORIGINS OF POROSITYIN CLASTICS AND CARBONATES (Genetic Classification) • Primary (original) • Secondary (induced) (Generally more complex than primary porosity)
- 17. 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
- 18. 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
- 19. 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
- 20. FACTORS THAT AFFECTPOROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (diagenetic)
- 21. ROUNDNESS AND SPHERICITY OFCLASTIC GRAINS High Low Very Angular Angular Sub- Angular Sub- Rounded Rounded Well- Rounded ROUNDNESS Porosity Porosity
- 22. FACTORS THAT AFFECTPOROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 23. Line of Traverse (usingmicroscope) 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
- 24. CUBIC PACKING OFSPHERES Porosity = 48%
- 25. Porosity Calculations -Uniform Spheres • Bulk volume = (2r)3 = 8r3 • Matrix volume = • Pore volume = bulk volume - matrix volume 3 r 4 3
- 26.
- 27. RHOMBIC PACKING OFSPHERES Porosity = 27 %
- 28. FACTORS THAT AFFECTPOROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 29. Packing of TwoSizes of Spheres Porosity = 14%
- 30. Grain-Size Sorting inSandstone Very Well Sorted Well Sorted Moderately Sorted Poorly Sorted Very Poorly Sorted SORTING
- 31. Change of CompositionChange 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
- 32. PROGRESSIVE DESTRUCTION OF BEDDINGTHROUGH BIOTURBATION Regular Layers Irregular Layers Mottles (Distinct) Mottles (Indistinct) Homogeneous Deposits (Whole Core) Bioturbated Sandstone
- 33. FACTORS THAT AFFECTPOROSITY • Particle sphericity and angularity • Packing • Sorting (variable grain sizes) • Cementing materials • Overburden stress (compaction) • Vugs, dissolution, and fractures PRIMARY SECONDARY (DIAGENETIC)
- 34. DIAGENESIS Carbonate Cemented Oil Stained Diagenesis is thePost- 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
- 35. DUAL POROSITY INSANDSTONE 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
- 36. SANDSTONE COMPOSITION, Framework Grains NorphletSandstone, 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
- 37. POROSITY IN SANDSTONE Quartz Grain Pore ScanningElectron 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
- 38. POROSITY IN SANDSTONE ScanningElectron 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
- 39. POROSITY IN SANDSTONE ScanningElectron Micrograph Norphlet Formation, Offshore Alabama, USA Pores Provide the Volume to Store Hydrocarbons Pore Throats Restrict Flow through pores Pore Throat
- 40. Electron Photomicrograph Clay Mineralsin 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
- 41. INTERGRANULAR PORE ANDMICROPOROSITY 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)
- 42. Clay Minerals inSandstone 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)
- 43. DISSOLUTION POROSITY Thin SectionMicrograph - 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
- 44. DISSOLUTION POROSITY Scanning ElectronMicrograph 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
- 45. 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 RocksCarbonate Rocks Comparison of Compositions of Clastic and Carbonate Rocks
- 46. FOLK CARBONATE ROCKCLASSIFICATION 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
- 47. DunhamCarbonateRockClassification DepositionalTextureRecognizable Depositional Texture NotRecognizable Mudstone WackestonePackstone 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
- 48. CARBONATES POROSITY TYPES Interparticle Intraparticle Intercrystal Moldic PoresBetween 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
- 49. Interparticle Intraparticle IntercrystalMoldic 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)
- 50. 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
- 51. 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
- 52. PORE SPACE CLASSIFICATION (In Termsof Fluid Properties)
- 53. PORE-SPACE CLASSIFICATION • Totalporosity, t = • Effective porosity, e = Volume Bulk PoreVolume Total Volume Bulk Pore Space cted Interconne • Effective porosity – of great importance; contains the mobile fluid
- 54. COMPARISON OF TOTALAND EFFECTIVE POROSITIES • Very clean sandstones : e t • Poorly to moderately well -cemented intergranular materials: t e • Highly cemented materials and most carbonates: e < t
- 55. MEASUREMENT OF POROSITY •Core samples (Laboratory) • Openhole wireline logs
- 56. 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)
- 57. PDC Cutters Fluid vent Drill collar connection Innerbarrel Outer barrel Thrust bearing Core retaining ring Core bit CORING ASSEMBLY AND CORE BIT
- 58. COMING OUT OFHOLE WITH CORE BARREL
- 59. Whole Core Photograph, Misoa“C” Sandstone, Venezuela WHOLE CORE Photo by W. Ayers
- 60. SIDEWALL SAMPLING GUN Corebullets Core sample Formation rock
- 61. SIDEWALL CORING TOOL Coringbit Samples
- 62. WHOLE CORE ANALYSISvs. 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
- 63. • 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