RE:GEOLOGY
As a liquid fuild and gas the petroleum migrates upwards to the reservoir bedrock locations over millions of years. It reaches an equilibrium based on favorable stratigraphic conditions associated with stratigraphic trap features of the resovior bedrock. Note as this occurs the overlying straigraphic bedrock have been deposit with bedrock units/types that confine the petroleum from migrating upward. This is refered to a confining straigraphic unit(s). Tectonic forces and resultant structural geologic trap features, faults.. can influence the migration of petroleum in many ways different from straigraphic traps.