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PHASE DIAGRAM


Generally speaking, all substances can exist as solid, liquid or gas. These three forms of existence are termed phases of matter. Whether a substance exist as solid, liquid or gas phases of matter is determined by temperature and pressure.

Hydrocarbon compounds, either individually or in a mixture, also change state or phase in response to changing temperature and pressure conditions. This is called "Phase behaviour" and many times important consideration in reservoir and well operations.

The Phase behaviour of hydrocarbons can be explained by the behaviour of hydrocarbons can be explained by the behaviour of molecules making up the mixtures.The four physical factors are important: Molecular attraction, Kinetic energy, and Molecular repulsion.

Increased pressure tends to force molecules closer together so that gas will be compressed or possibly changed to a liquid.If pressure is decreased, gas expands and liquid tends to vaporize to gas. These phase changes caused by changes in pressure are termed phase behaviour.

PHASE DIAGRAM TERMINOLOGIES
Bubble point: Is the point on a reservoir by which the first bubble comes out of the reservoir fluid during production.

Isothermal lines: These are lines of equal liquid percent present in the phase diagram.
Critical Point: This is a point at which the properties of liquid and gas are indistinguishable.

Cricondermtherm: The highest temperature of the phase diagram at which hydrocarbons can no longer be formed.

Cricondermbar: The highest pressure of the phase diagram at which hydrocarbons can no longer be formed.

TYPES OF RESERVOIRS

DEWPOINT RESERVOUR
These are reservoir for which the reservoir temperature lies between the critical temperature and critical temperature

BUBBLEPOINT RESERVOIR
This is the reservoir in which reservoir temperature is less than the critical temperature.This reservoir are mostly undersaturated reservoirs because the fraction of light components present in the oil is too low for a gas phase to form at that temperature and presure.Isothermal pressure reduction causes the appearance of a vapour phase at the bubble point.

RETROGRADE CONDENSATE RESERVOIR
This is the formation of liquid hydrocarbon in a gas reservoir as the pressure in the reservoir decreases below dewpoint pressure due to production.It is called retrograde because some of the gas condenses into liquid at isothermal conditions instead of expanding or vapourizing when pressure is decreased.

CONDENSATE RESERVOIR
The reservoir temperature is between the critical temperature and the cricondermtherm.

ENGINEERING 4239692614937930941

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