primary migration

The term "primary migration" in geology refers to the initial movement of hydrocarbons from fine-grained source rocks, such as clays and shales, into coarser-grained carrier beds. This process is driven by geothermal action on kerogen, an insoluble organic residue within the source rock. As sediments accumulate, the pressure of overlying layers compacts the source rock, dehydrating clay minerals and releasing water molecules.12

With increasing temperature, newly generated hydrocarbons become mobile and can leave the source beds. This movement occurs in solution, suspension, or emulsion with the expelled water. The hydrocarbons then migrate through more permeable rocks like sandstones or carbonates, a process known as secondary migration, which can be influenced by geological events such as plate tectonics. This migration continues until the hydrocarbons are trapped or eventually seep to the surface.1