Lecture 1 - Source rocks Flashcards
What is a source rock?
A sedimentary rock with sufficient organic material that, when buried and heated, will produce/yield petroleum (e.g. oil and/or gas)
What environment do source rocks require? Give examples
Requires high organic productivity and stagnant water
E.g. swamps, shallow seas, lakes
What is required for the preservation of source rocks?
Low or zero oxygen contents
What kind of material is required for oil producing rocks? Why?
Organic material rich in soft, waxy tissues (e.g. algae)
Proteins, carbohydrates, lipids and lignin are required for hydrocarbon generation
What kind of tissue is required for generating gas source rocks?
Woody tissue
What kind of environment is required for source rocks in the sea/lakes? Give examples
High productivity and oxygen deficiency in water column and sea/lake bed
Why do lakes and seas have anoxic bottom waters?
Lack of circulation allowing organic material to be preserved
What is bitumen?
Compounds soluble in organic solvents
What are kerogens?
Abundant Insoluble CHO complex compounds
Name the four types of kerogens and briefly describe them in terms of yield, source, what they produce and fluoresces
Liptinite (Type 1): high yield, algal source, produces oil, fluoresces under UV
Exinite (Type 2): lower yield (40-60%), plant source, produces oil, fluoresces under UV
Vitrinite (Type 3): low yield, plant source, produces gas, does not fluoresces under UV
Inertinite (Type 4): High C, low H, ‘dead’ carbon
When are large molecules of kerosene stable?
Low temperatures
What happens with progressive heating of kerosene? What is released?
Breaks down to smaller molecules of liquid and gaseous hydrocarbons. CO2, H20 and residues released
What is the oil window? (temps and depth)
60-120 degrees C
2-4km depth
What is the gas window?
100-200+ degrees C
2-6km
What is the most important control for hydrocarbon maturation?
Temperature
