This document discusses phase behavior of reservoir fluids based on pressure-temperature diagrams. It describes: 1) Oil reservoirs can be classified as undersaturated, saturated, or gas-cap depending on initial reservoir pressure and temperature relative to the fluid's critical point. Crude oils are commonly ordinary black oil, low-shrinkage, high-shrinkage, or near-critical. 2) Gas reservoirs have a temperature above the critical point and can be retrograde gas-condensate, near-critical gas-condensate, wet gas, or dry gas based on their phase diagrams and reservoir conditions. 3) Pressure-temperature diagrams are shown for different fluid types to illustrate their phase behavior.

1. Phase Behaviour Of Reservoir Fluid
Group : 3

2. P-T Diagram for Multicomponent System
• Cricondentherm (Tct)
• Cricondenbar (pcb)
• Critical point
• Bubble-point curve
• Dew-point curve

3. Oil reservoirs
• Oil reservoirs—If the reservoir temperature T is less than the critical temperature Tc of the
reservoir fluid, the reservoir is classified as an oil reservoir.
Depending upon initial reservoir pressure pi , oil reservoirs can be subclassified into the
following categories
• Undersaturated oil reservoir
• Saturated oil reservoir
• Gas-cap reservoir
Crude oils cover a wide range in physical properties and chemical compositions, and based
upon the properties exhibited, the crude oils commonly classified into the following types:
• Ordinary black oil
• Low-shrinkage crude oil
• High-shrinkage (volatile) crude oil
• Near-critical crude oil

4. P-T Diagram for an Ordinary Black Oil

5. P-T Diagram for a low-Shrinkage Oil

6. P-T Diagram for a Volatile Crude Oil

7. P-T Diagram for near Critical Crude Oil

8. Liquid shrinkage for crude oil systems

9. 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 basis of their phase diagrams and the prevailing reservoir conditions, natural gases
can be classified into four categories:
• Retrograde gas-condensate
• Near-critical gas-condensate
• Wet gas
• Dry gas

10. P-T Diagram for a Retrograde System

11. P-T Diagram for a near-critical Gas Condensate
Reservoir

12. P-T Diagram for a Wet Gas.

13. Phase Diagram for a Dry Gas

14. Thank
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