AN OIL MIGRATION AND RE-ENTRAPMENT MODEL FOR THE MARDIN GROUP RESERVOIRS OF SOUTHEAST ANATOLIA

Oil migrates from a source into a reservoir rock and then, inside the reservoir rock, into a trap, and from the trap into a series of traps and reservoir rocks. The movement of oil is continuous and the interchange of oil between several reservoir rocks is totally independent of the source rock after a certain stage of migration. Each migration stage may cause quality changes in the properties of oil. A model is devised to account for oil migration and re-entrapment, and to explain the distribution of different quality oils in time and space. Variations in the API-gravity of oil, formation-water salinity, reservoir temperature and pressure, sulphur-content of oil, initial water content and recoverable oil reserves of oilfields can be important clues for the determination of migration directions and new prospects. These concepts were applied in a petroleum migration study of the Mardin Group (Aptian-Turonian) which is the most important reservoir rock of SE Anatolia.
Quantitative modelling shows that oil migration is directed towards two main uplifts which control the distribution of oilfields in SE Anatolia. Active water movement inside the reservoir rock has resulted in the accumulation of oil inside very young structural traps. Because almost all the fields have tilted oil-water contacts, wildcat locations must be selected with special emphasis on hydrodynamics.