Lecture 8 - Petroleum

Petroleum applications

• Transport

• Plastics

• Heating

• Raw material for pharmaceutical products, paints, beauty products

Describe the organic chemistry of petroleum.

• 30-60% - cycloalkanes

• 15-60% - alkanes

• 3-30% - arenes (benzene rings)

• Anything else usually asphaltenes – complex organic compounds containing C, H, O, N, S, V, Ni

What does the American Institute of Petroleum (API) gravity unit show?

• Low API density crude oils more viscous – harder to extract, require cracking

• High API density crude oils less viscous - easier to extract, more commercial uses

Describe petroleum reserve distribution and market

• Largest reserves in the Middle East, Canada and Russia

• Projections show a decrease in petroleum usage; even further reduction on net zero plan

• 88% of reserves are owned by nation states. Middle East have been very dominant in the market in the last 20 years

What conditions are required for the accumulation of organic matter in source rocks?

• Anaerobic conditions to prevent decomposition

• Low sediment dilution

What is the minimum organic matter content required for a rock to be classified as a source rock?

• More than 1% total organic matter

What controls the accumulation of organic matter in source rocks?

• Balance between organic productivity and organic matter degradation

How does sediment overburden affect organic matter maturation?

• Increases pressure and temperature

• Drives stages of maturation: kerogen formation, oil window, gas window, and graphite formation

What happens to organic matter at different temperatures during maturation?

• <40–80°C: Kerogen formation

• 100–150°C: Oil window (formation of shorter hydrocarbon chains)

• 150–200°C: Gas window (methane formation)

• 200°C: Graphite formation

What are the types of kerogen and their primary sources and products?

• Type I: Algae, lipid-rich, produces oil (e.g., Eocene Green River Formation)

• Type II: Algae and zoo/phytoplankton, lipid-rich, produces oil and gas (e.g., Jurassic Kimmeridge Clay)

• Type III: Land plants, humic, produces gas (e.g., coals)

What is required for the migration and accumulation of hydrocarbons?

• Migration driven by pressure and buoyancy through permeable carrier beds

• Accumulation requires a reservoir rock below an impermeable seal rock

What are the properties of a good reservoir rock?

• High porosity and permeability

• Examples: sandstone and limestone

What is a trap in hydrocarbon accumulation?

• A convex-up structure combining a reservoir and a seal that prevents upward migration of hydrocarbons

What are the types of traps?

• Structural traps: Formed by deformation (e.g., folds, faults)

• Stratigraphic traps: Formed by variations in sediment deposition

How is geophysics used in oil exploration?

• Seismic waves identify subsurface structures and traps

• Magnetics and density measurements provide additional data

What data is collected during drilling?

• Wireline logging collects parameters from boreholes using sondes

What are the key components of oil and gas production?

• Production wells and pipelines

• Minimised environmental footprint through EIAs, remote operations, and horizontal drilling

What are the environmental impacts of petroleum production?

• Global warming and carbon cycle imbalance

• Potential for harm if HSE (Health, Safety, and Environment) is not managed properly

Why do fossil fuels remain a major energy source despite environmental concerns?

• They are relatively cheap and vital for developing countries

• Reducing poverty through accessible energy

What are the key stages of organic matter maturation?

• Anaerobic decomposition (<40–80°C)

• Kerogen breakdown (40–80°C)

• Oil window (100–150°C)

• Gas window (150–200°C)

• Graphite formation (>200°C)

What are seal rocks and their function in hydrocarbon traps?

• Impermeable lithologies above reservoirs

• Prevent upward migration of hydrocarbons

What are the biggest environmental concerns associated with petroleum use?

• Global warming and climate change

• Corruption linked to petroleum production and export

What is the role of sedimentary basin studies in oil exploration?

• Provide sedimentary and structural context

• Locate reservoir and source rocks based on global patterns

What technological advances minimise the environmental footprint of oil production?

• Remote subsea operations

• Horizontal drilling

• Environmental Impact Assessments (EIAs)