1. n. []
A relatively impermeable rock, commonly shale, anhydrite or salt, that forms a barrier or cap above and around reservoir rock such that fluids cannot migrate beyond the reservoir. A seal is a critical component of a complete petroleum system. The permeability of a seal capable of retaining fluids through geologic time is ~ 10-6 to 10-8 darcies.
Synonyms: caprock
See: evaporite, fault, field, halite, impermeable, migration, oil field, permeability, petroleum system, pinch-out, prospect, reservoir, salt dome, shale, structural trap, trap