Name: WAQAR HUSSAINSubject: PETRLOEUM

GEOLOGYCHINA UNIVERSITY OF

PETROLEUM

Petroleum Migration

Any Movement of oil and gas in the crust is called petroleum migration, including primary

and secondary migration

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 shift• the position of the pool within the reservoir rock

• 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

Main forces of secondary migration 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

• 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.

• 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.

Capillary pressure—Resistant force

• The 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.

Physical requirements for secondary migration

1. An adequate supply of hydrocarbons to sustain it

2. adequately continuous permeable pathways to facilitated it

3. The necessary pressure gradient to impel it

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.

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 .

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.

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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