Chapter 1 : Reservoir Short Notes

Chapter 1  : Reservoir Short Notes

1. Cricondentherm (Tct)—The Cricondentherm is defined as the maximum temperature above which liquid cannot be formed regardless of pressure . The corresponding pressure is termed the Cricondentherm pressure pct.
2. Cricondenbar (pcb)—The Cricondenbar is the maximum pressure above which no gas can be formed regardless of temperature . The corresponding temperature is called the Cricondenbar temperature Tcb.
3. Critical point—The critical point for a multicomponent mixture is referred to as the state of pressure and temperature at which all intensive properties of the gas and liquid phases are equal. At the critical point, the corresponding pressure and temperature are called the critical pressure pc and critical temperature Tc of the mixture.
4. Phase envelope (two-phase region)—The region enclosed by the bubble- point curve and the dew-point curve, wherein gas and liquid coexist in equilibrium, is identified as the phase envelope of the hydrocarbon system.
5. Quality lines—The dashed lines within the phase diagram are called quality lines. They describe the pressure and temperature conditions for equal volumes of liquids. Note that the quality lines converge at the critical point .
6. Bubble-point curve—The bubble-point curve  is defined as the line separating the liquid-phase region from the two-phase region. 
7. Dew-point curve—The dew-point curve  is defined as the line separating the vapor-phase region from the two-phase region.
8. 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.
9. Gas reservoirs—If the reservoir temperature is greater than the critical temperature of the hydrocarbon fluid, the reservoir is considered a gas reservoir.
10. Undersaturated oil reservoir - If the initial reservoir pressure pi is greater than the bubble-point pressure pb of the reservoir fluid, the reservoir is labeled an undersaturated oil reservoir.
11. Saturated oil reservoir-  When the initial reservoir pressure is equal to the bubble-point pressure of the reservoir fluid, the reservoir is called a saturated oil reservoir.
12. Gas-cap reservoir - If the initial reservoir pressure is below the bubblepoint pressure of the reservoir fluid the reservoir is termed a gas-cap or two-phase reservoir, in which the gas or vapor phase is underlain by an oil phase. The appropriatequality line gives the ratio of the gas-cap volume to reservoir oil volume.
13. Retrograde gas-condensate reservoir - If the reservoir temperature T lies between the critical temperature Tc and cricondentherm Tct of the reservoir fluid, the reservoir is classified as a retrograde gas-condensate reservoir. 
14. Near-critical gas-condensate reservoir - If the reservoir temperature is near the critical temperature the hydrocarbon mixture is classified as a near-critical gas-condensate.
15. The critical compressibility factor is another property that is often used in thermodynamic-property prediction models. It is defined as the component compressibility factor calculated at its critical point. This property can be conveniently computed by the real gas equation-of-state at the critical point, or
    
16. A gas is defined as a homogeneous fluid of low viscosity and density that has no definite volume but expands to completely fill the vessel in which it is placed. Generally, the natural gas is a mixture of hydrocarbon and nonhydrocarbon gases.
17. Standard Volume : In many natural gas engineering calculations, it is convenient to measure the volume occupied by l lb-mole of gas at a reference pressure and temperature. These reference conditions are usually 14.7 psia and 60°F, and are commonly referred to as standard conditions. The standard volume is then defined as the volume of gas occupied by 1 lb-mol of gas at standard conditions:
    
18. Density The density of an ideal gas mixture is calculated by simply replacing the molecular weight of the pure component in following equation with the apparent molecular weight of the gas mixture to give  
19. Specific Volume The specific volume is defined as the volume occupied by a unit mass of the gas. For an ideal gas, this property can be calculated by applying following equation 
20. Specific Gravity The specific gravity is defined as the ratio of the gas density to that of the air. Both densities are measured or expressed at the same pressure and temperature. Commonly, the standard pressure psc and standard temperature Tsc are used in defining the gas specific gravityand   
21. The gas compressibility factor, gas deviation factor, or simply the z-factor:
22. Pseudo-reduced pressure & Pseudo-reduced temperature :
23. By definition, the isothermal gas compressibility is the change in volume per unit volume for a unit change in pressure or, in equation form 
24. GAS FORMATION VOLUME FACTOR The gas formation volume factor is used to relate the volume of gas, as measured at reservoir conditions, to the volume of the gas as measured at standard conditions, i.e., 60°F and 14.7 psia. This gas property is then defined as the actual volume occupied by a certain amount of gas at a specified pressure and temperature, divided by the volume occupied by the same amount of gas at standard conditions. In an equation form, the relationship is expressed as 
25. GAS VISCOSITY : The viscosity of a fluid is a measure of the internal fluid friction (resistance) to flow. The viscosity of a fluid is generally defined as the ratio of the shear force per unit area to the local velocity gradient. Viscosities are expressed in terms of poises, centipoise, or micropoises. One poise equals a viscosity of 1 dyne-sec/cm2 and can be converted to other field units by the following relationships: