This document discusses secondary migration of petroleum, which is the movement of oil and gas within reservoir rocks after primary migration. The main forces driving secondary migration are buoyancy, as oil and gas are less dense than water, and hydrodynamic forces from water flow. Capillary pressure acts as a resistant force. Secondary migration can occur over distances ranging from hundreds of meters to over 100 km and is facilitated by porous and permeable pathways as well as pressure gradients within the rocks. Water drive and gas flushing are two mechanisms enabling secondary migration to traps and accumulations. Fractures also provide routes for secondary oil and gas to migrate through reservoir strata.

1. Name: WAQAR HUSSAINSubject: PETRLOEUM GEOLOGYCHINA UNIVERSITY OF PETROLEUM

2. Petroleum MigrationAny Movement of oil and gas in the crust is called petroleum migration, including primary and secondary migration

4. Secondary Migration Movement of oil and gas in the reservoir is called secondary migration. Secondary migration takes place within the porous reservoir rock, or from one reservoir rock to another . It is the process which collects oil and gas into commercial pools. In secondary migration, the oil droplets are moved about within the reservoir to from pools.Secondary migration can include a second step during which crustal movements of the earth shiftthe position of the pool within the reservoir rock

6. In secondary migration in the carrier bed, petroleum moves updip in a carrier rock predominantly because of its buoyancy, since it has a lower density than the surrounding formation waters. Petroleums in the subsurface will typically have densities ranging from 800 to 500 kg m−3 for oils and as low as 100 kg m−3 for gases according to the pressure and temperature

7. Main forces of secondary migration

8. Buoyance : It is upward acting force caused by fluid pressure that keeps thing float .The main driving force for the upward movement of oil through sea water is buoyancy. Buoyancy is also the main driving force for oil or gas migrating through water-saturated rocks in the subsurface.Pb is greatest for the gas and lowest for the heavy oil

10. Hydrodynamic force A vector in the direction of water flow and equal to the rate of change of pressure measured along the flow path and corrected to horizontal datum plane is the hydrodynamic force , Ph, acting on the unit volume of the oil as consequence of the water flow.

11. The hydrodynamic force interferes with the buoyant force .The resultant of these two forces controls the position of the oil in the aquifer in relation to moving water.

12. Capillary pressure—Resistant forceThe pressure difference between the oil phase and the water phase across a curved oil-water interface.The factors that determine the magnitude of this resistant force are (1) the radius of the pore throats of the rock, and (2) the hydrocarbon-water interfacial tension, and (3) wettability.

14. Physical requirements for secondary migrationAn adequate supply of hydrocarbons to sustain itadequately continuous permeable pathways to facilitated it The necessary pressure gradient to impel it

15. Secondary migration by water drive Buoyancy, reflecting the difference in densities of hydrocarbons and waters, is the main mechanism of secondary migration under hydrostatic conditions , especially in coarse sand in which the pressure readily equalize to hydrostatic , All crude oils float on salt water and nearly all on fresh water.

16. Secondary migration by gas flushing Where two or more fluids of different densities try to occupy the same trap, the heaviest fluid is displaced because the lighter ones move above it and force it below the spill point. William Gussow examined the case of the migration of gas oil and water though a succession of traps .

17. Secondary migration via fractures Open fractures in the reservoir are the channels of nearly infinite permeability they ,they must constitute possible routes of secondary migration through porous strata.Fractures are a means of facilitating secondary migration.

18. Distance The total distance of secondary migration of oil up to traps may vary fr0m a few hundred meters to more than one hundred kilometers In the Alberta basin of Canada , for instance the formation of the Athabasca tar sand requires secondary migration over distance of at least 100 km.

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