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Water injection/water flooding

Conventionally, based on the type of production and nature of reservoir the following patters are followed an injection well. Once the

primary energy of the reservoir tends to deplete it becomes necessary to maintain the pressure inside the reservoir to achieve

optimum production and maximise ultimate recovery. In such condition the pressure maintenance can be done by injecting water

into the reservoir which is compatible to the formation water present in the reservoir through several water injection wells. Such kind

of operation is known as water flooding/Water injection.

In this process, the primary objective is to fill the voidage created by the produced oil fractions thus avoiding the reservoir pressure

to decrease with the increased production. When the water is injected in the reservoir, it tends to push the oil towards upwards thus

increasing the life and the ultimate recovery of the reservoir. Water injection and water flooding are quite similar terms the only

difference being the level at which injection water is being discharged and the displacement phenomena.

Normally only 30% of the oil in a reservoir can be extracted, but water injection increases that percentage (known as the recovery

factor) and maintains the production rate of a reservoir over a longer period.

Water injection:

In water injection operation, the injected water is discharged in the aquifer through several injection wells surrounding the production

well. The injected water creates a bottom water drive on the oil zone pushing the oil upwards. In earlier practices, water injection

was done in the later phase of the reservoir life but now it is carried out in the earlier phase so that voidage and the secondary gas

cap in the reservoir are not created. Using water injection in earlier phase helps in improving the production as once secondary gas

cap is formed the injected water initially tends to compress free gas cap and later on pushes the oil thus the amount of injection

water required is much more. The water injection is generally carried out when solution gas drive is present or water drive is weak.

Thus for better economy the water injection is carried out when the reservoir pressure is more than saturation pressure.

The selection of injection water {displacing fluid} depends upon the mobility rate between the displacing fluid {injection water} and

the displaced fluid {oil}

DISADVANTAGE OF WATER INJECTION

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Reaction of injected water with the formation water can cause formation damage.

Corrosion of surface and sub-surface equipment.

Water flooding:

n this operation, displacing fluid is injected in the oil zone through the surrounding water injection wells creating an edge water drive

flooding oil towards the production well. For better efficiency, the pressure of the reservoir should be such that no secondary gascap is formed. Water flooding is generally more effective than water injection when no voidage is being created. Water flooding in

other regards is similar to water injection including selection parameters of the displacing fluid, the only difference being the

displacing phenomenon. However, in practice the above patterns are not necessarily followed It is to be noted that water injection

and water flooding are essentially the same process, however, while in the case of former we inject the water in the water zone of

the reservoir, in the latter we inject it directly into the hydrocarbon zone

Gas injection

Gas injection is presently the most-commonly used approach in enhanced oil recovery. In addition to the beneficial effect of the

pressure, this method sometimes aids recovery by reducing the viscosity of the crude oil as the gas mixes with it.

Gases used includeCO2,natural gasornitrogen.

Oil displacement bycarbon dioxide injectionrelies on the phase behaviour of the mixtures of that gas and the crude, which are

strongly dependent on reservoir temperature, pressure and crude oil composition.

In high pressure applications with lighter oils,CO2is miscible with the oil, with resultant swelling of the oil, and reduction in viscosity,

and possibly also with a reduction in the surface tension with the reservoir rock. In the case of low pressure reservoirs or heavy

oils,CO2will form an immiscible fluid, or will only partially mix with the oil. Some oil swelling may occur, and oil viscosity can still be

significantly reduced.

In these applications, between one-half and two-thirds of the injected CO2 returns with the produced oil and is usually re-injected

into the reservoir to minimize operating costs. The remainder is trapped in the oil reservoir by various means.

CO2is pumped into the reservoir through an injection well. It mixes with the remaining oil, forming a miscible

zone. The pressure from the CO2 and expanding oil pushes an oil bank toward the production well, where it rises

to the surface. Then the CO2 is separated from the oil and may be added to the stream of CO2 going into the

injection well. A side effect of enhanced oil recovery is that the CO2 that was used to force oil out of the formation

is now sequestered.

http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Carbon_dioxide_floodinghttp://en.wikipedia.org/wiki/Carbon_dioxide_floodinghttp://en.wikipedia.org/wiki/Carbon_dioxide_floodinghttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxide_floodinghttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Carbon_dioxide

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