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Oil RESERVOIR


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There are basically six driving mechanisms

that provide the natural energy necessaryfor oil recovery:

Rock and liquid expansion drive

Depletion drive

Gas cap drive

Water drive

Gravity drainage drive Combination drive


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The Depletion Drive Mechanism

This driving form may also be referred to by the following

various terms:

Solution gas drive

Dissolved gas drive

Internal gas drive


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In this type of reservoir, the principal source of

energy is a result of gas liberation from the crude

oil and the subsequent expansion of the solution

gas as the reservoir pressure is reduced. Aspressure falls below the bubble-point pressure,

gas bubbles are liberated within the micro- scopic

pore spaces. These bubbles expand and force the

crude oil out of the pore space as shownconceptually in Figure below.

The Depletion Drive Mechanism


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Solution Gas Drive Reservoir

OIL

OIL + GAS


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Water Drive Oil

Reservoir


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WATER DRIVE RESERVOIR


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Gas Cap Drive Reservoir

Gas-cap-drive reservoirs can be identified by

the presence of a gas cap with little or no

water drive as shown in Figure below.

Due to the ability of the gas cap to expand,

these reservoirs are charac- terized by aslow decline in the reservoir pressure.


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Combination Drive

Reservoir


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Gas Cap Drive Reservoir


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The Gravity-Drainage-Drive Mechanism

The mechanism of gravity drainage occurs in

petroleum reservoirs as a result of differences in

densities of the reservoir fluids.


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Factors that affect ultimate recoveryfrom gravity-drainage reservoirs are:

Permeability in the direction of dip Dip of the reservoir

Reservoir producing rates

Oil viscosity

Relative permeability characteristics


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Gravity Drainage Reservoir


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Gravity Drainage Reservoir

Injection WellProduction

Well


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Petroleum reservoirs are broadly classified as oil or gas

reservoirs. These broad classifications are further

subdivided depending on:

The composition of the reservoir hydrocarbonmixture

Initial reservoir pressure and temperature

Pressure and temperature of the surface

production

CLASSIFICATION OF RESERVOIRS AND

RESERVOIR FLUIDS


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Pressure-Temperature Diagram

Figure 1-1 shows a typical pressure-temperature

diagram of a multi- component system with aspecific overall composition. Although a dif-

ferent hydrocarbon system would have a different

phase diagram, the general configuration is

similar.


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Typical P-T Diagram of

Hydrocarbon Fluids


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Oil ReservoirsDepending upon initial reservoir pressure pi, oil reservoirs can be sub- classified into

the following categories:

1. Undersaturated oil reservoir. If the initial reservoir pressure pi (as represented by

point 1 on Figure 1-1), is greater than the bubble-point pressure pb of the

reservoir fluid, the reservoir is labeled an undersaturated oil reservoir.

2. Saturated oil reservoir. When the initial reservoir pressure is equal to the bubble-point pressure of the reservoir fluid, as shown on Figure 1-1 by point 2, the

reservoir is called a saturated oil reservoir.

3. Gas-cap reservoir. If the initial reservoir pressure is below the bubble- point

pressure of the reservoir fluid, as indicated by point 3 on Figure 1-1, the reservoir

is termed a gas-cap or two-phase reservoir, in which the gas or vapor phase isunderlain by an oil phase. The appropriate quality line gives the ratio of the gas-

cap volume to reservoir oil volume.


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Gas Reservoirs

In general, if the reservoir temperature is above the

critical temperature of the hydrocarbon system,

the reservoir is classified as a natural gas reservoir.

On the basis of their phase diagrams and the

prevailing reservoir conditions, natural gases can beclassified into four categories:

Retrograde gas-condensate

Near-critical gas-condensate

Wet gas

Dry gas


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Initial Conditions Development Conditions


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1. Development of a heavy oil Field.

2. How to expoit a light oil Field.

3. How to exploite Deep Oil Reservoir.

4. Plan of Development of Oil Reservoir Field with Strong Water Drive.

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