Natural Gas and Ideal Gas

NATURAL GAS

1. 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.
2. Generally, the natural gas is a mixture of hydrocarbon and nonhydrocarbon gases.
3. The hydrocarbon gases that are normally found in a natural gas are methanes, ethanes, propanes, butanes, pentanes, and small amounts of hexanes and heavier.
4. The nonhydrocarbon gases (i.e., impurities) include carbon dioxide, hydrogen sulfide, and nitrogen

Knowledge of pressure-volume-temperature (PVT) relationships and other physical and chemical properties of gases is essential for solving problems in natural gas reservoir engineering.

  These Gas properties include

• Apparent molecular weight, 
• Specific gravity, 
• Compressibility factor, z 
• Density, 
• Specific volume, v 
• Isothermal gas compressibility coefficient, cg 
• Gas formation volume factor, Bg 
• Gas expansion factor, Eg 
• Viscosity 

 Rule Of thumb About Natural Gas

1. A gas is a homogeneous fluid
2. No definite volume
3. Completely fills the vessel in which it is contained 
4.  Behaviour vital to petroleum engineers 
5.  Simple gas laws straightforward 
6. Hydrocarbon gases at reservoir conditions are more complicated.

 IDEAL GAS

Several Assumptions in Ideal Gas is:

S        Volume of molecules are insignificant with respect to the total volume of the gas.

S      There are no attractive or repulsive forces between molecules or molecules and    container walls.

S        No internal energy loss when molecules collide

Formula used in Ideal Gas is Boyle's Law

And also Charles Law

absolute unite

Rankin ^oR = ^oF + 460

Kelvin   K = ^oC + 273

Avogadro’s Law

 Under the same conditions of temperature and pressure equal volumes of all ideal gases contain the same number of molecules.

That is; one molecular weight of any ideal gas occupies the same volume as the molecular weight of another ideal gas.

      2.73 x 10²⁶ molecules/lb.mole of ideal gas 

            1 lb.mole of any ideal gas at 60^oF and 14.7 psia. occupies 379.4 cu.ft.

1 gm.mole at 0^oC and atmos. pressure occupies 22.4 litres

Ideal Gas Law

The Ideal Equation of State

Combining Boyle’s Law and Charles Law gives an equation relating P,T & V