- The movement of hydrocarbons from the source interval or kitchen to the reservoir is referred to as migration. Hydrocarbons migrate vertically due to variations in buoyancy. They basically migrate from a position of relatively high potential energy to an area with lower potential energy. As the hydrocarbons are less dense than water they're buoyant on water. Thus in the reservoir, you'll find either the oil or gas on top of the associated water lake. Saying that we can identify the source of hydrocarbons found in a reservoir does not mean we have a clear understanding of exactly how they got there. Migration is inferred, rather than saying it's observed. Through chemical identification or fingerprinting, the source of hydrocarbons found in a reservoir can be tied to their associated kitchen. But understanding how those hydrocarbons got there, that's clearly a different matter. Fortunately, it's not necessary to understand the migration and migration process in order to produce hydrocarbons from the reservoir. Hydrocarbon migration takes place over geologic time, which means millions of years, and does not necessarily take place through a single conduit. So even though understanding migration process is not required to produce hydrocarbons, either oil or gas from the reservoir, when proposing a new prospect for drilling, identifying the possible source rock and its association with the reservoir will increase the prospectivity of the play and thus make it easier to sell it to either management or investors.