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 Overburden Rock Seal Rock Reservoir Rock Source Rock Underburden Rock Basement Rock Top Oil Window Top Gas Window. Geographic Extent of Petroleum System Petroleum Reservoir (O) Fold-and-Thrust Belt (arrows indicate relative fault motion) Essential Elements of Petroleum System(Foreland Basin Example) (modified from Magoon and Dow, 1994) O OS e d im e n tary B asin F ill. O Stratigraphic Extent of Petroleum System Pod of Active Source Rock Extent of Prospect/Field Extent of Play

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

Cross-Cutting Relationships Angular Unconformity. Igneous Sill ABC DE F G H IJK Igneous Dike

• 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 Types of Unconformities

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

0 50 100 150 200 250 300 350 400 450 500 550 600 0 10 20 30 40 50 60 C ryp to zo ic (P re cam b rian )Phanerozoic Quaternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian M illio n s o f y e a rs a g o B illio n s o f y e a rs a g o 0 1 2 3 4 4. 6 Paleocene Eocene. Oligocene Miocene. Pliocene Pleistocene Recent Q uaternary period Tertiary period. Eon Era Period Epoch. Geologic Time Chart P aleozoic M esozoic C e n o zo ic E ra

Rocks

Classification of Rocks SEDIMENTARYR ock-form ing process S ource of m aterial. IGNEOU S 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

The Rock Cycle Magma Metamorphic Rock Sedimentary Rock Igneous Rock Sediment. Heat and Pressure Weathering, Transportation and Deposition. Weathering, Transportation, and Deposition Cooling and Solidification M elting(Crystalization) H eat A nd Pressure (M etam orphism ) W eathering, Transportation A nd D eposition Cementat ion and Compaction (Lithification)

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

Quartz Crystals 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. Minerals — Definition

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)

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

Some Common Minerals Silicates. Oxides Sulfides Carbonates Sulfates Halides Non-Ferromagnesian (Common in Sedimentary Rocks) Anhydrite Gypsum Halite Sylvite. Aragonite Calcite Dolomite Fe-Dolomite Ankerite. Pyrite Galena Sphalerite Ferromagnesian (not common in sedimentary rocks)Hematite Magnetite 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

Norphlet Sandstone, Offshore Alabama, USA Grains are About =< 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. CEMENTSandstone Composition Framework Grains

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

Secondary Electron Micrograph 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. Clay Minerals in Sandstone Reservoirs Fibrous Authigenic Illite

Secondary Electron Micrograph 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 m. Clay Minerals in Sandstone Reservoirs Authigenic Chlorite

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)Clay Minerals in Sandstone Reservoirs Authigenic Kaolinite

100 10 1 0. 01 0. 1 1101001000 2 6 10 14 18 P e rm e a b ility (m d ) Porosity (%)Authigenic Illite Authigenic Chlorite (modified from Kugler and Mc. Hugh, 1990)Effects of Clays on Reservoir Quality

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

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

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

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 Called Secondary Porosity. Pore Quartz Detrital Grain. Partially Dissolved Feldspar (Photomicrograph by R. L. Kugler)Dissolution Porosity

Hydrocarbon Generation, Migration, and Accumulation

Organic Matter in Sedimentary Rocks Reflected-Light Micrograph of Coal. Vitrinite Kerogen 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.

Interpretation of Total Organic Carbon (TOC) (based on early oil window maturity) Hydrocarbon Generation Potential TOC in Shale (wt. %) TOC in Carbonates (wt. %) Poor Fair Good Very Good Excellent 0. 0 -0. 5 -1. 0 -2. 0 -5. 0 >5. 0 0. 0 -0. 2 -0. 5 -1. 0 -2. 0 >2.

Schematic Representation of the Mechanism of Petroleum Generation and Destruction (modified from Tissot and Welte, 1984) Organic Debris Kerogen Carbon Initial Bitumen Oil and Gas Methane Oil Reservoir Migration. Thermal Degradation Cracking. Diagenesis Catagenesis Metagenesis. P ro g re ssive B u rial an d H eatin g

Incipient Oil Generation Max. Oil Generated Oil Floor Wet Gas Floor Dry Gas Floor Max. Dry Gas Generated (modified from Foster and Beaumont, 1991, after Dow and O’Conner, 1982)V itrin ite R efle ctan ce (R o) % W e ig h t % C arb o n in K e ro g e n S p o re C o lo ratio n In d e x (S C I) P yro lysis T (C ) m ax 0. 2 0. 3 0. 4 0. 5 4. 0 3. 02. 01. 3 1 2 3 4 5 6 7 8 9 10 430 450 46565 70 75 80 85 90 950. 6 0. 7 0. 8 0. 9 1. 0 1. 2 OIL Wet Gas Dry Gas. Comparison of Several Commonly Used Maturity Techniques and Their Correlation to Oil and Gas Generation Limits

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

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

Hydrocarbon Traps • Structural traps • Stratigraphic traps • Combination traps

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

Oil Sandstone Shale. Hydrocarbon Traps — Dome Gas. Water

Fault Trap Oil / Gas. Sand Shale

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

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

Heterogeneity

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

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)

Bounding Surface Eolian Sandstone, Entrada Formation, Utah, USAGeologic Reservoir Heterogeneity

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

Scales of Investigation Used in Reservoir Characterization Gigascopic Megascopic Macroscopic Microscopic Well Test Reservoir Model Grid Cell Wireline Log Interval Core Plug Geological Thin Section Relative Volume 110 14 2 x 10 12 3 x 10 7 5 x 10 2300 m 50 m 300 m 5 m 150 m 2 m 1 m cm mm — m (modified from Hurst, 1993)

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

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