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Unit 2: Origin and Migration of Petroleum
Overview
How Oil Forms: Natural Hydrocarbons
How Oil Forms: Generated Hydrocarbons
Modeling Petroleum Generation
The Origin of Natural Gas
Migration and Accumulation
Abnormal Pressures
Required Reading
Hunt, Petroleum Geochemistry
Chapters 4 -9
Key Concepts
Organic origins of hydrocarbons
Modeling Petroleum Generation -- time-temperature index (TTI) graphs
Types of oil-generating Kerogens
Origin of natural gas
Arrhenius equation
SOURCE ROCK - A unit of rock that has generated oil or gas in sufficient quantities to form commercial accumulations. The term "commercial" is variable and the terms "migratable" or "significant" are often substituted. Source rock is synonymous with "effective source rock".
LIMITED SOURCE ROCK - A unit of rock that contains all the prerequisites of a source rock except volume. Cannot be defined by geochemical data alone but requires geological information as to the thickness and aerial extent.
POTENTIAL SOURCE ROCK - A unit of rock that has the capacity to generate oil or gas in commercial quantities but has not yet done so because of insufficient catagenesis (thermal maturation). The distinction between source rocks and potential (immature) source rocks are essential in petroleum system studies and when correlating oils to their source rocks.
ACTIVE SOURCE ROCK - A source rock that is in the process of generating oil or gas. Active source rocks have oil window maturities and are at or close to their maximum burial depth. The distribution of active source rocks is essential in petroleum system studies. Active source rocks cannot occur at the surface.
INACTIVE SOURCE ROCK - A source rock that was once active but has temporarily stopped generating prior to becoming spent. Inactive source rocks are usually associated with areas of overburden removal and will generate hydrocarbons again if reburied. Oil-rock correlations are best done between oils and active or inactive source rocks.
SPENT SOURCE ROCKS - A source rock that has completed the oil and gas generation process. A spent oil source rock can still be an active or inactive source for gas. We feel that proper and consistent use of these source rock terms will help mitigate the confusion which exists in the literature and in interpreting and using source rock data.
BIOMARKERS most commonly used in crude oil-source rock correlations and in maturation evaluarions are steranes and terpanes.
Names of individual terpanes and steranes are based on four variations in their origin and chemistry: 1) compound class; 2) number of carbon atoms; 3) 3-dimensional; 4) 3D ring system configuration.
Hydrogen content of kerogen determines the quantity of oil generated in a petroleum system.
Migration
Porosity
Seal
Trap
Unconformities, Sheet, and Channel Sandstones
Distribution of Petroleum by Basin Type
Abnormal pressures
Geothermal gradient
Define
Diagenesis
Catagenesis
Metagenesis
Biomarkers -- what do they include?
Basic building blocks of biomarkers
Odd-carbon chain lenths
CPI -- Carbon Preference Index--what does it indicate?
Sediments occurring in petroleum generation systems
Anoxic environments
What hydrous pyrolysis experiments indicate
Immature, mature, postmature stratigraphic intervals
Gas window
Oil window
Bacterial source of gas
Coal source of gas
Oil source of gas
Condensates
Nonhydrocarbon gases
Carbon dioxide sources
Hydrogen sulfide sources
Nitrogen sources
Pattern of gas compositions
Best petroleum reservoir rocks
Vertical migration pathways
Three critical factors for a petroleum trap
Best petroleum seals
Factors limiting porosity: diagenetic alteration, cementation, dissolution
Processes which enhance porosity
Processes which reduce porosity
Permeability
Processes generating deep overpressures
Gas chimneys
Overpressures due to compaction disequilibrium
Practice Multiple-Choice Test Questions
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