Lecture 1 - Migration and Traps Flashcards
Describe primary, secondary and tertiary migration
Primary - expulsion from source rock
Secondary - movement from source rock to trap
Tertiary - leakage from trap to the Earth’s surface
What is the driving factor in non-water assisted primary migration?
Pressure differential between source and ‘carrier’ beds
Favoured mechanism via a water-wet rock ‘matrix’
How does methane migration occur?
Soluble in water at elevated pressures and temperatures
What can cause secondary migration?
Trap disruption or fill-to-spill
What drives secondary migration?
Density buoyancy of hydrocarbons
What is hydrostatic and hydrodynamic secondary migration?
Hydrostatic: No water movement involved - purely buoyancy driven
Hydrodynamic case: water movement can retard or enhance
What two things related to pores can influence secondary migration?
Pore geometry
Nature of pore throats
What happens to oil that migrates to lower pressures?
Dissolved gases escape
What happens to oil migrating to low temps
Bacterial action degrades oil, losing n-alkanes, branching alkanes etc.
This is especially prevalent where there is water flow
Give three examples of tertiary migration
Gas chimneys
Hydrate layers and mounds
Mud volcanoes
What drives tertiary migration? What other factors have an influence?
Density buoyancy driven: Helped/hindered by over-pressure and/or hydrodynamic conditions
What cause hydrodynamic traps?
Not common - caused by differences in water pressures due to water flow
How do structural traps in extensional tectonic regimes appear? Give an example
Tilted fault blocks
E.g. North Sea
How do structural traps commonly appear in compressional tectonic regimes? Give an example
Large scale folds and thrusts at convergent plate boundaries
E.g. Zagros Mountains, Iran
Explain the diapiric structural trap. Give an example
Buoyant ascent of low density ‘plastic’ salt can produce a variety of structural traps
E.g. Greater Burgan, Kuwait
