Geology of Petroleum Systems Petroleum Geology Objectives

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 • Describe the origin of petroleum • Identify hydrocarbon trap types • Define and describe the important geologic controls on reservoir properties, porosity and permeability

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

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)

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

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

Cross-Cutting Relationships K J I H G Angular Unconformity C E D ou e Ign l Sil s Igneous Dike F B A

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

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

4 4. 6 150 Mesozoic 100 Cretaceous Jurassic 200 Triassic 250 Permian Pennsylvanian 300 Mississippian 350 400 450 Devonian Silurian Ordovician 500 550 600 Cambrian Recent 0 Pleistocene 10 20 Pliocene Miocene 30 Oligocene 40 Eocene 50 60 Paleocene Cenozoic Era 3 Tertiary 50 Paleozoic 1 Millions of years ago Phanerozoic 2 Quaternary 0 Cryptozoic (Precambrian) Billions of years ago 0 Epoch Tertiary period Era Period Millions of years ago Eon Quaternary period Geologic Time Chart

Rocks

Classification of Rocks Rock-forming Source of process material 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

The Rock Cycle Magma nd M el t g in Co So oling (Cr lidi ys fic a tal at iza n i o n) tio Sedimentary Rock Heat and Pressure We ath eri an ng, T d D ran ep osi sport tion atio n, Weathering, Transportation and Deposition Ceme ntation and Compaction (Lithification) Igneous Rock Weather Transportaing, tion And Dep ositi on And Heat ure Press rphism) tamo (Me Metamorphic Rock Sediment

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

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

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

The Physical and Chemical Characteristics of 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

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

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

Sandstone Composition Framework Grains KF = Potassium Feldspar PRF = Plutonic Rock Fragment KF CEMENT P Norphlet Sandstone, Offshore Alabama, USA Grains are About =< 0. 25 mm in Diameter/Length P = Pore Potassium Feldspar is Stained Yellow With a Chemical Dye Pores are Impregnated With Blue-Dyed Epoxy

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

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

Clay Minerals in Sandstone Reservoirs Authigenic 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 Offshore Alabama, USA ~ 10 mm (Photograph by R. L. Kugler)

Clay Minerals in Sandstone Reservoirs Authigenic 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)

Effects of Clays on Reservoir Quality Authigenic Chlorite Authigenic Illite Permeability (md) 1000 10 10 1 1 0. 01 2 6 10 14 18 Porosity (%) (modified from Kugler and Mc. Hugh, 1990)

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

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

Fluids Affecting Diagenesis heric Circ ula Atmosp tion Evaporation Precipitation Evapotranspiration el n han C w Flo Water Table Infiltration Meteoric Water COMPACTIONAL WATER Petroleum Fluids Meteoric Water Zone of abnormal pressure Isotherms CH 4, CO 2, H 2 S Subsidence (modified from Galloway and Hobday, 1983)

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

Hydrocarbon Generation, Migration, and Accumulation

Organic Matter in Sedimentary Rocks Kerogen Vitrinite Disseminated Organic Matter in Sedimentary Rocks That is Insoluble in Oxidizing Acids, Bases, and Organic Solvents. 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

Interpretation of Total Organic Carbon (TOC) (based on early oil window maturity) Hydrocarbon Generation Potential TOC in Shale (wt. %) TOC in Carbonates (wt. %) 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 >5. 0 >2. 0 Excellent

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

Comparison of Several Commonly Used Maturity Techniques and Their Correlation to Oil and Gas Generation Limits 65 0. 4 0. 5 Incipient Oil Generation 0. 6 0. 7 0. 8 0. 9 1. 0 80 2. 0 3. 0 4. 0 Max. Oil Generated OIL 1. 2 1. 3 75 Oil Floor Wet Gas Floor Dry Gas Max. Dry Gas Generated 85 90 95 (modified from Foster and Beaumont, 1991, after Dow and O’Conner, 1982) 2 3 4 5 6 7 8 9 10 430 450 465 Pyrolysis Tmax (C) 70 Spore Coloration Index (SCI) 0. 3 1 Weight % Carbon in Kerogen Vitrinite Reflectance (Ro) % 0. 2

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

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

Hydrocarbon Traps • Structural traps • Stratigraphic traps • Combination traps

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

Hydrocarbon Traps - Dome Gas W at er Oil Sandstone Shale

Fault Trap Oil / Gas Sand Shale

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

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

Heterogeneity

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)

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)

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

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

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

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