Primary and secondary migrations are well definedterms in hydrocarbon reservoir genesis. Both of themdesignate spontaneous displacement of the hydrocarbon, fromthe source rock to the final trap, I.e. to the reservoir rock.Producing the reservoir implies a forced movementof hydrocarbons towards the wells, consuming the energyaccumulated over the ages.Mainly due to the gravitational forces and waterinflux, a new kind of fluid movement is taking place into thereservoir towards its production final stage. The main featureof the fluids displacements into the reservoir is theirspontaneous character. This kind of fluid movement that occurafter reservoir abandonment, defines the tertiary migrationprocess.As a consequence of tertiary migration, the reservoirfluids, water, oil and gas, tend to place themselves to anormal-gravitational position. Additionally, the dynamicpressure distribution at the end of the production history tendsto relax, amplifying the migration process towards normalstationary pressure gradients. The result of the tertiarymigration is a new saturation distribution into the reservoirand it is expected that in the most favorable cases, theproduction potential of some parts of the reservoir should berestored.From this point of view, an enormous interest forRomania concerns the old oil reservoirs, abandoned over 70-80 years ago with a final recovery factor sometimes less then20%.The present paper examines the principles and factorsinvolved in the tertiary migration process. A special attentionis paid to pressure redistribution and gravitational segregationduring such a process. To demonstrate the concept, this studydiscusses two successful production restarting projects inRomania. If today the world is not very proud aboutproduction restarting projects, tomorrow will be for sure.
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