petrol formation

Jurassic Period climate

Warm greenhouse climate with high CO₂ levels and no polar ice caps; caused by increased volcanism and seafloor spreading releasing greenhouse gases

Increase in volcanism during Jurassic

Breakup of Pangaea caused tectonic activity and seafloor spreading; magma rose and formed volcanic rock (igneous rock)

Why oceans became stagnant

Warm temperatures reduced ocean circulation; less mixing led to low oxygen levels (hypoxic/anoxic conditions)

Effect of carbonic acid on weathering

Carbonic acid increases chemical weathering, especially dissolving minerals in rocks like granite and gneiss, speeding erosion

Phytoplankton definition

Microscopic photosynthetic organisms that form the base of marine food webs

Why phytoplankton blooms increased

Nutrient runoff from weathering (especially iron and phosphorus) fertilized oceans, causing large blooms

Anoxic zone definition

An area of water with little to no oxygen

How Jurassic oceans became anoxic

Stratification and lack of circulation prevented oxygen mixing; decomposition used up oxygen

Why anoxic conditions preserved organic matter

Low oxygen prevented decomposition, allowing organic material to accumulate and eventually form petroleum

Formation of kerogen in sedimentary basin

Organic material is buried by sediments; heat and pressure transform it into kerogen over time

Source rock definition

Rock that contains organic material that can generate petroleum; typically shale (sedimentary rock)

Hydrocarbon kitchen concept

Zone where heat, pressure, and time convert kerogen into hydrocarbons

Lowest temperature petroleum

Oil (liquid hydrocarbons)

Highest temperature petroleum

Natural gas (methane and lighter hydrocarbons)

Carbon atom ranges of hydrocarbons

Oil: ~5-20 carbons; Natural gas: 1-4 carbons; heavier compounds have more carbons

ONS definition

Oxygen, Nitrogen, Sulfur compounds found in hydrocarbons

Petroleum with least ONS

Natural gas has the least ONS impurities

Reservoir rock definition

Rock that stores petroleum; typically sandstone or limestone due to high porosity and permeability

Importance of cap rock

Impermeable layer (like shale or salt) that traps petroleum and prevents it from escaping

Anticline petroleum trap definition

Upward-folded rock structure that traps oil and gas beneath a cap rock

Layering in anticline trap

Gas at top, oil in middle, water at bottom (based on density)

Importance of anticline traps

Common and effective structures for trapping petroleum, making them key exploration targets

Casing in petroleum recovery

Steel pipe inserted into wells to prevent collapse and protect groundwater from contamination

Primary oil recovery

Uses natural pressure; extracts about 10-20% of oil

Secondary oil recovery

Uses water or gas injection to increase pressure; extracts ~20-40%

Enhanced oil recovery

Uses heat, chemicals, or CO₂; can extract up to ~60% total

Tar sands definition

Mixture of sand, clay, water, and bitumen; requires processing to extract oil; found in reservoir-like deposits

Oil shale definition

Rock containing kerogen that hasn't fully converted to oil; requires heating; found in source rock

Tight oil/gas definition

Hydrocarbons trapped in low-permeability rock (like shale); requires fracking

Double climate concern of tar sands and oil shale

More CO₂ released during extraction and combustion compared to conventional oil

Hydraulic fracturing importance

Increases access to oil and gas in tight formations, boosting U.S. energy production

Rock type fracked in tight oil/gas

Shale (low permeability sedimentary rock)