What is oil reservoir drive mechanisme?

Answer 1

The process in which reservoir fluids are caused to flow out of the reservoir rock and into a wellbore by natural energy gas drives depend on the fact that, as the reservoir is produced, pressure is reduced, allowing the gas to expand and provide the driving energy. Water-drive reservoirs depend on water pressure to force the hydrocarbons out of the reservoir and into the wellbore.

The primary reservoir drive mechanisms are:

· Gas drive which includes both solution gas drive as well as gas cap drive

· Water drive

· Gravity drainage

· Combination drive

Producing oil and gas needs energy. Usually some of this required energy is supplied by nature. The hydrocarbon fluids are under pressure because of their depth. The gas and water in petroleum reservoirs under pressure are the two main sources that help move the oil to the well bore and sometimes up to the surface. Depending on the original characteristics of hydrocarbon reservoirs, the type of driving energy is different.

Solution Gas Drive Reservoirs When a newly discovered reservoir is below the bubble point pressure; there will be free gas as bubbles within the oil phase in reservoir. The reservoir pressure decreases as production goes on and this causes emerging and expansion of gas bubbles creating extra energy in the reservoir. These kinds of reservoirs are called as solution gas drive reservoirs. Crude oil under high pressure may contain large amounts of dissolved gas. When the reservoir pressure is reduced as fluids are withdrawn, gas comes out of the solution and displaces oil from the reservoir to the producing wells. The efficiency of solution gas drive depends on the amount of gas in solution, the rock and fluid properties and the geological structure of the reservoir.

Water Drive Reservoirs Most oil or gas reservoirs have water aquifers. When this water aquifer is an active one, continuously fed by incoming water, then this bottom water will expand as pressure of the oil/gas zone is reduced because of production causing an extra driving energy. This kind of reservoir is called water drive reservoirs. The expanding water also moves and displaces oil or gas in an upward direction from lower parts of the reservoir, so the pore spaces vacated by oil or gas produced are filled by water. The oil and gas are progressively pushed towards the well bore.

Gravity drainage may be a primary producing mechanism in thick reservoirs that have a good vertical communication or in steeply dipping reservoirs. Gravity drainage is a slow process because gas must migrate up structure or to the top of the formation to fill the space formerly occupied by oil. Gas migration is fast relative to oil drainage so those oil rates are controlled by the rate of oil drainage.