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Geology of Petroleum Systems

Geology of Petroleum Systems. Petroleum Geology. Objectives are to be able to: Discuss basic elements of Petroleum Systems Describe plate tectonics and sedimentary basins Recognize names of major sedimentary rock types Describe importance of sedimentary environments to petroleum industry

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Geology of Petroleum Systems

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  1. Geology ofPetroleum Systems

  2. Petroleum Geology Objectives are to be able to: • Discuss basic elements of Petroleum Systems • Describe plate tectonics and sedimentary basins • Recognize names of major sedimentary rock types • Describe importance of sedimentary environments to petroleum industry • Describe the origin of petroleum • Identify hydrocarbon trap types • Define and describe the important geologic controls on reservoir properties, porosity and permeability

  3. Outline • Petroleum Systems approach • Geologic Principles and geologic time • Rock and minerals, rock cycle, reservoir properties • Hydrocarbon origin, migration and accumulation • Sedimentary environments and facies; stratigraphic traps • Plate tectonics, basin development, structural geology • Structural traps

  4. Petroleum System - A Definition • A Petroleum System is a dynamic hydrocarbon • system that functions in a restricted geologic • space and time scale. • A Petroleum System requires timely • convergence of geologic events essential to • the formation of petroleum deposits. These Include: Mature source rock Hydrocarbon expulsion Hydrocarbon migration Hydrocarbon accumulation Hydrocarbon retention (modified from Demaison and Huizinga, 1994)

  5. Cross Section Of A Petroleum System (Foreland Basin Example) Geographic Extent of Petroleum System Extent of Play Extent of Prospect/Field O O O Stratigraphic Extent of Petroleum Overburden Rock System Essential Seal Rock Elements of Reservoir Rock Basin Fill Sedimentary Petroleum Pod of Active System Source Rock Source Rock Underburden Rock Petroleum Reservoir (O) Basement Rock Fold-and-Thrust Belt Top Oil Window (arrows indicate relative fault motion) Top Gas Window (modified from Magoon and Dow, 1994)

  6. Basic Geologic Principles • Uniformitarianism • Original Horizontality • Superposition • Cross-Cutting Relationships

  7. Cross-Cutting Relationships K J I H G Angular Unconformity C E F D Igneous Dike B Igneous Sill A

  8. Types of Unconformities • Disconformity • An unconformity in which the beds above and below are parallel • Angular Unconformity • An unconformity in which the older bed intersect the younger beds at an angle • Nonconformity • An unconformity in which younger sedimentary rocks overlie older metamorphic or intrusive igneous rocks

  9. Correlation • Establishes the age equivalence of rock layers in different areas • Methods: • Similar lithology • Similar stratigraphic section • Index fossils • Fossil assemblages • Radioactive age dating

  10. Geologic Time Chart Eon Era Period Epoch Quaternary Recent 0 Quaternary period 0 0 Pleistocene Tertiary Phanerozoic Pliocene 50 10 1 Miocene 100 20 Cretaceous Mesozoic Cenozoic Era Tertiary period 150 30 2 Oligocene Billions of years ago Jurassic Millions of years ago Millions of years ago Cryptozoic (Precambrian) 200 40 Triassic Eocene 3 250 50 Permian Paleocene Pennsylvanian 300 60 4 Mississippian 4.6 350 Devonian 400 Paleozoic Silurian 450 Ordovician 500 Cambrian 550 600

  11. Rocks

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

  13. The Rock Cycle Magma C o o l g i S n n o i l g ( i t l C d r i a e f y i n s c M t d a a t l i i z o a n t i o n ) Heat and Pressure Metamorphic Igneous Rock Rock ) A T m r n e s a d d i r W n n Weathering, Transportation, h u e D s p A s and Deposition a p r s e t t o o e p a h r r m o t e e P a s r a H i i t t t i n i e o o g Weathering, n M , n ( Transportation Sedimentary and Deposition Sediment Rock C e m d n e a n t n a t o i C o n m o p i a c t ( ) L n i t o h i f i i t c a

  14. Sandstone and conglomerate ~11% Limestone and dolomite ~13% Siltstone, mud and shale ~75% Sedimentary Rock Types • Relative abundance

  15. Minerals - Definition Naturally Occurring Solid Generally Formed by Inorganic Processes Ordered Internal Arrangement of Atoms (Crystal Structure) Chemical Composition and Physical Properties Fixed or Vary Within A Definite Range Quartz Crystals

  16. Average Detrital Mineral Composition of Shale and Sandstone Mineral Composition Shale (%) Sandstone (%) 60 5 Clay Minerals 30 65 Quartz 4 10-15 Feldspar 15 Rock Fragments <5 Carbonate 3 <1 Organic Matter, <3 <1 Hematite, and Other Minerals (modified from Blatt, 1982)

  17. The Physical and Chemical Characteristicsof Minerals Strongly Influence the Composition of Sedimentary Rocks Quartz Mechanically and Chemically Stable Can Survive Transport and Burial Feldspar Nearly as Hard as Quartz, but Cleavage Lessens Mechanical Stability May be Chemically Unstable in Some Climates and During Burial Calcite Mechanically Unstable During Transport Chemically Unstable in Humid Climates Because of Low Hardness, Cleavage, and Reactivity With Weak Acid

  18. Some Common Minerals Carbonates Sulfides Sulfates Halides Oxides Aragonite Halite Pyrite Anhydrite Hematite Calcite Sylvite Galena Gypsum Magnetite Dolomite Sphalerite Fe-Dolomite Ankerite Silicates Ferromagnesian Non-Ferromagnesian (not common in sedimentary rocks) (Common in Sedimentary Rocks) Quartz Olivine Muscovite (mica) Pyroxene Feldspars Augite Potassium feldspar (K-spar) Amphibole Orthoclase Hornblende Microcline, etc . Biotite (mica) Plagioclase Albite (Na-rich - common) through Red = Sedimentary Rock- Anorthite (Ca-rich - not common) Forming Minerals

  19. The Four Major Components • Framework • Sand (and Silt) Size Detrital Grains • Matrix • Clay Size Detrital Material • Cement • Material precipitated post-depositionally, during burial. Cements fill pores and replace framework grains • Pores • Voids between above components

  20. Sandstone Composition Framework Grains KF = Potassium Feldspar PRF = Plutonic Rock Fragment PRF KF P = Pore CEMENT Potassium Feldspar is Stained Yellow With a Chemical Dye P Pores are Impregnated With Blue-Dyed Epoxy Norphlet Sandstone, Offshore Alabama, USA Grains are About =< 0.25 mm in Diameter/Length

  21. Porosity in Sandstone Pore Throat Pores Provide the Volume to Contain Hydrocarbon Fluids Pore Throats Restrict Fluid Flow Scanning Electron Micrograph Norphlet Formation, Offshore Alabama, USA

  22. Clay Minerals in Sandstone ReservoirsFibrous Authigenic Illite Secondary Electron Micrograph Significant Permeability Reduction Negligible Porosity Illite Reduction High Irreducible Water Saturation Migration of Fines Problem Jurassic Norphlet Sandstone Hatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)

  23. Clay Minerals in Sandstone ReservoirsAuthigenic Chlorite Secondary Electron Micrograph Iron-Rich Varieties React With Acid Occurs in Several Deeply Buried Sandstones With High Reservoir Quality Occurs as Thin Coats on Detrital Grain Surfaces Jurassic Norphlet Sandstone m ~ 10 m Offshore Alabama, USA (Photograph by R.L. Kugler)

  24. Clay Minerals in Sandstone ReservoirsAuthigenic Kaolinite Secondary Electron Micrograph Significant Permeability Reduction High Irreducible Water Saturation Migration of Fines Problem Carter Sandstone North Blowhorn Creek Oil Unit Black Warrior Basin, Alabama, USA (Photograph by R.L. Kugler)

  25. Authigenic Chlorite Authigenic Illite 100 1000 100 10 10 Permeability (md) 1 1 0.1 0.1 0.01 0.01 2 6 10 14 18 2 6 10 14 Porosity (%) (modified from Kugler and McHugh, 1990) Effects of Clays on Reservoir Quality

  26. Influence of Clay-Mineral Distribution on Effective Porosity Clay f e Minerals Dispersed Clay Detrital Quartz Grains f e Clay Lamination f Structural Clay e (Rock Fragments, Rip-Up Clasts, Clay-Replaced Grains)

  27. Diagenesis Diagenesis is the Post- Depositional Chemical and Mechanical Changes that Carbonate Occur in Sedimentary Rocks Cemented Some Diagenetic Effects Include Compaction Oil Precipitation of Cement Stained Dissolution of Framework Grains and Cement The Effects of Diagenesis May Enhance or Degrade Reservoir Quality Whole Core Misoa Formation, Venezuela

  28. Precipitation Atmospheric Circulation Evapotranspiration Evaporation Channel Flow Water Table Infiltration Meteoric Water COMPACTIONAL WATER Meteoric Water Petroleum Zone of abnormal pressure Fluids Isotherms CH ,CO ,H S 4 2 2 (modified from from Galloway and Hobday, 1983) Subsidence Fluids Affecting Diagenesis

  29. Dissolution of Framework Grains (Feldspar, for Example) and Cement may Enhance the Interconnected Pore System This is Called Secondary Porosity Partially Dissolved Feldspar Pore Quartz Detrital Grain Thin Section Micrograph - Plane Polarized Light Avile Sandstone, Neuquen Basin, Argentina Dissolution Porosity (Photomicrograph by R.L. Kugler)

  30. Hydrocarbon Generation, Migration, and Accumulation

  31. Organic Matter in Sedimentary Rocks Kerogen Disseminated Organic Matter in Sedimentary Rocks That is Insoluble in Oxidizing Acids, Bases, and Organic Solvents. Vitrinite Vitrinite A nonfluorescent type of organic material in petroleum source rocks derived primarily from woody material. The reflectivity of vitrinite is one of the best indicators of coal rank and thermal maturity of petroleum source rock. Reflected-Light Micrograph of Coal

  32. Interpretation of Total Organic Carbon (TOC)(based on early oil window maturity) Hydrocarbon TOC in Shale TOC in Carbonates Generation (wt. %) (wt. %) Potential Poor 0.0-0.5 0.0-0.2 Fair 0.5-1.0 0.2-0.5 Good 1.0-2.0 0.5-1.0 Very Good 2.0-5.0 1.0-2.0 Excellent >5.0 >2.0

  33. Organic Debris Diagenesis Oil Reservoir Initial Bitumen Kerogen Progressive Burial and Heating Catagenesis Thermal Degradation Migration Oil and Gas Cracking Methane Metagenesis Carbon (modified from Tissot and Welte, 1984) Schematic Representation of the Mechanismof Petroleum Generation and Destruction

  34. 0.2 1 65 70 0.3 2 0.4 (C) 75 0.5 Incipient Oil Generation 3 0.6 430 max 80 0.7 4 0.8 Max. Oil Generated OIL 0.9 Vitrinite Reflectance (Ro) % 5 Weight % Carbon in Kerogen 85 450 1.0 Spore Coloration Index (SCI) 6 Wet Pyrolysis T 1.2 Gas 1.3 465 7 Oil Floor 90 Dry 8 Max. Dry Gas 9 Gas 2.0 10 Generated Wet Gas Floor 3.0 Dry Gas Floor 4.0 95 (modified from Foster and Beaumont, 1991, after Dow and O’Conner, 1982) Comparison of Several Commonly Used Maturity Techniques and Their Correlation to Oil and Gas Generation Limits

  35. Fault (impermeable) Oil/water contact (OWC) Migration route Seal Reservoir rock Hydrocarbon accumulation in the reservoir rock Source rock Generation, Migration, and Trapping of Hydrocarbons Top of maturity

  36. Cross Section Of A Petroleum System (Foreland Basin Example) Geographic Extent of Petroleum System Extent of Play Extent of Prospect/Field O O O Stratigraphic Extent of Petroleum Overburden Rock System Essential Seal Rock Elements of Reservoir Rock Basin Fill Sedimentary Petroleum Pod of Active System Source Rock Source Rock Underburden Rock Petroleum Reservoir (O) Basement Rock Fold-and-Thrust Belt Top Oil Window (arrows indicate relative fault motion) Top Gas Window (modified from Magoon and Dow, 1994)

  37. Hydrocarbon Traps • Structural traps • Stratigraphic traps • Combination traps

  38. Oil Shale Trap Fracture Basement Structural Hydrocarbon Traps Gas Closure Oil/Gas Contact Oil/Water Contact Seal Oil Fold Trap Salt Diapir Salt Dome Oil (modified from Bjorlykke, 1989)

  39. Hydrocarbon Traps - Dome Gas Oil Water Sandstone Shale

  40. Fault Trap Oil / Gas Sand Shale

  41. Stratigraphic Hydrocarbon Traps Unconformity Pinch out Oil/Gas Uncomformity Oil/Gas Channel Pinch Out Oil/Gas (modified from Bjorlykke, 1989)

  42. Oil Other Traps Meteoric Water AsphaltTrap Biodegraded Oil/Asphalt Partly Biodegraded Oil Water Hydrodynamic Trap Hydrostatic Head Shale Water (modified from Bjorlykke, 1989)

  43. Heterogeneity

  44. Reservoir Heterogeneity in Sandstone Heterogeneity Segments Reservoirs Increases Tortuosity of Fluid Flow Heterogeneity May Result From: Depositional Features Diagenetic Features (Whole Core Photograph, Misoa Sandstone, Venezuela)

  45. Reservoir Heterogeneity in Sandstone Heterogeneity Also May Result From: Faults Fractures Faults and Fractures may be Open (Conduits) or Closed (Barriers) to Fluid Flow (Whole Core Photograph, Misoa Sandstone, Venezuela)

  46. Geologic Reservoir Heterogeneity Bounding Surface Bounding Surface Eolian Sandstone, Entrada Formation, Utah, USA

  47. Scales of Geological Reservoir Heterogeneity Interwell Well Well Area Determined From Well Logs, 100's Seismic Lines, Field Wide m Statistical Modeling, etc. 1-10 km 10's Interwell m 100's m 1-10's 10-100's m mm 10-100's Well-Bore m m Unaided Eye Hand Lens or Binocular Microscope Petrographic or Scanning Electron Microscope (modified from Weber, 1986) Reservoir Sandstone

  48. Scales of Investigation Used in Reservoir Characterization Relative Volume 300 m 14 10 Well Test Gigascopic 50 m 300 m Reservoir Model 12 2 x 10 Megascopic Grid Cell 5 m 150 m 2 m Wireline Log 7 3 x 10 1 m Interval Macroscopic 2 cm 5 x 10 Core Plug m mm - m Geological 1 Microscopic Thin Section (modified from Hurst, 1993)

  49. Stages In The Generation of An Integrated Geological Reservoir Model Geologic Activities Regional Geologic Framework Depositional Model (As Needed) Structural Diagenetic Core Analysis Model Model Fluid Integrated Log Analysis Model Geologic Model Well Test Analysis (As Needed) Applications Studies Reserves Estimation Simulation Model Testing And Revision

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