Under elevated subsurface temperatures, the kerogen contained in sedimentary rocks breaks down to smaller chemical compounds. This process is known as the petroleum generation and is governed by the chemical structure of the parent kerogen on the one hand and the burial/temperature history of the source horizon on the other hand. The generated hydrocarbons will be expelled from the chemical structure of the kerogen during a process known as the petroleum expulsion. The movement of expelled petroleum through the porous network of the source rock is called primary migration. The next stage involves movement of petroleum in the porous carrier beds, a process known as the secondary petroleum migration. The rates of secondary migration may slow down when the petroleum faces extremely tiny pores. This process leads to the formation of petroleum accumulations in the subsurface with different sizes and compositions. Tertiary migration is a process in which structural events force the accumulated petroleum to leave the initial accumulation site and re-migrate into more-stable and often younger trapping geometries.