Exploring

Infographics

How Deposits Form: Reservoir, Cap Rock and Trap

How Deposits Form: Reservoir, Cap Rock and Trap

HydrocarbonsThe final phase in petroleum system formation, after a deposit has accumulated... tend to travel upward and accumulate in reservoirs made of porous, permeable rock in a process called vertical migration (hydrocarbons)The stage in oil formation when the hydrocarbons are gradually expelled from the source rock and rise to the surface... .  The presence of an impermeable layer of cap rockAn impermeable barrier that blocks the migration of oil and gas to the surface... prevents the oil or gas from moving all the way up to the surface. But for a depositAn accumulation of natural resources, such as oil, natural gas, coal, uranium, metal ore or another commodity... to form, these hydrocarbons must also be sealed in a closed space called a trapA volume of “sealed” rock whose configuration or type prevents the oil and gas trapped in the reservoir... . There are two main types of trap:

  • Structural traps are the most common. They are created by changes in geological layers. Anticlinal traps are the most well known type of structural trapTrap that forms as a result of changes in the structure of subsurface... and form when the rock is pushed into a dome.
  • Stratigraphic traps are made up of sedimentary layers that have not undergone tectonic deformation. In this case, a cap rock completely seals off the reservoir rock. A salt dome, for example, can act as a cap rock in this type of trap.