These traps can take many forms but a common type would be in the shape of an inverted bowl formed from impermeable rock. Traps are formed by changes in the earth's crust such as folding or faulting. Scientists categorize traps by how they were formed or how they look. The major types of traps are anticlinal , fault , plug , stratigraphic , and lenticular . In an anticlinal trap , the layers of rock are altered by geological forces to create a concave shape or dome.
Hydrocarbons move into the porous layers and are trapped by an impermeable rock layer or caprock .
A fault trap is formed by a shift or movement of rock layers that caused an impermeable layer to create a barrier next to a layer of porous rocks containing hydrocarbons. Plug traps are traps where a core of impermeable rock has moved through layers of rock to form a trap. These plugs are often composed of salt and salt domes are an important formation that scientists look for when trying to find oil and gas. A stratigraphic trap is created by either an impermeable rock layer over the top of a porous rock layer or by a change of porosity and permeability within the reservoir itself. Lenticular traps are formed by a change of permeability within the formation.