
- •1 Drilling
- •Four Types Of Structural and Stratigraphic Traps
- •Stratigraphic Problems When Drilling
- •Structural Problems When Drilling
- •Question 2. Non-hydrocarbons impurities.
- •Special question.
- •Ideal gas mixtures
- •It follows that the ratio of the partial pressure of component j, pj, to the total pressure of the mixture p is:
- •It follows that the ratio of the partial volume of component j to the total volume of the mixture is
- •Apparent Molecular Weight
Special question.
Ideal gas mixtures
The previous treatment of the behavior of gases applies only to single component gases. As the engineer rarely works with pure gases, the behavior of multi-component mixture of gases must be treated. This requires introduction of two additional ideal gases laws.
Dalton`s Law. Dalton`s Law states that each gas in a mixture of gases exerts a pressure equal to that which it would exert if it occupied the same volume as the total mixture. This pressure is called the partial pressure. The total pressure is the sum of the partial pressures. This law is valid only when the mixture and each component of the mixture obey the ideal gas law. It is sometimes called the Law of Additive Pressures.
The partial pressure exerted by each component of the gas mixture can be calculated using the ideal gas law.
Consider a mixture containing nA moles of component A, nB moles of component B, nC moles of component C. The partial pressure exerted by each component of the gas mixture may be determined with the ideal gas equation^
According to Dalton`s Law, the total pressure is the sum of the partial pressures
It follows that the ratio of the partial pressure of component j, pj, to the total pressure of the mixture p is:
(1)
where yj is defined as the mole fraction of its component in the gas mixture. Therefore, the partial pressure of a component of a gas mixture is the product of its mole fraction times the total pressure.
Amagat`s Law. Amagat`s Law states that the total volume of a gaseous mixture is the sum of the volumes that each component would occupy at the given pressure and temperature. The volumes occupied by the individual components are known as the partial volumes. This law is correct only if the mixture and each of the components obey the ideal gas law.
The partial volume occupied by each component of the gas mixture consisting of nA moles of component A, nB moles of component B, nC moles of component C, and so on, can be calculated using the ideal gas law.
Thus, according to Amagat, the total volume is
It follows that the ratio of the partial volume of component j to the total volume of the mixture is
.
(2)
This implies that for an ideal gas the volume fraction is equal to the mole fraction.
Apparent Molecular Weight
Since a gas mixture is composed of molecules of various sizes, it is not strictly correct to say that a gas mixture has a molecular weight. However, a gas mixture behaves as if it were a pure gas with definite molecular weight. This molecular weight is known as an apparent molecular weight and is defined as
(3)
Exaple: dry air is a gas mixture consisting essentially of nitrogen (N2, mole fraction yN2=0.78, molecular weight MN2– 28.01), oxygen (O2, mole fraction yO2=0.21, molecular weight MO2– 32.00) and small amounts of other gases (such as argon – A, mole fraction yA=0.01, molecular weight MA– 39.94).
Lets computer the apparent molecular weight of air given its approximate composition.
A value of 29.0 is usually considered sufficiently accurate for engineering calculations.
The specific gravity of a gas is defined as the ratio of the density of the gas to the density of dry air taken at standard conditions of the temperature and pressure. Symbolically,
(4)
Assuming that the behavior of both the gas and air may be represented by the ideal gas law, specific gravity may be given as
where Mair is the apparent molecular weight of air. If the gas is a mixture, this equation becomes
(5)
where Ma is the apparent molecular weight of the gas mixture.
For engineering calculations the density of dry air taken at standard conditions of the temperature and pressure can be accepted at value 1.293.
So we can change the formula (4) into
(6)
The physical constants of hydrocarbons may be found in table 1.
Special lituretature (list):
Table 1 – Natural gas properties
№ |
Compound |
Formula |
Molecular weight |
Describing (what is part of the natural gases at standard conditions?) |
Critical pressure, psia |
Critical temperature, 0F |
1 |
Methane |
CH4 |
16.043 |
dry gas |
667.8 |
-116.63 |
2 |
Ethane |
C2H6 |
30.070 |
dry gas |
707.8 |
90.09 |
3 |
Propane |
C3H8 |
44.097 |
liquid gas |
616.3 |
206.01 |
4 |
n-Butane |
C4H10 |
58.124 |
liquid gas |
550.7 |
305.65 |
5 |
Isobutane |
C4H10 |
58.124 |
liquid gas |
529.1 |
274.98 |
6 |
n-Pentane |
C5H12 |
72.151 |
condensate |
488.6 |
385.7 |
7 |
Isopentane |
C5H12 |
72.151 |
condensate |
490.4 |
369.10 |
8 |
Neopentane |
C5H12 |
72.151 |
condensate |
464.0 |
321.13 |
9 |
n-Hexane |
C6H14 |
86.178 |
condensate |
436.9 |
453.7 |
10 |
Neohexane |
C6H14 |
86.178 |
condensate |
446.8 |
420.13 |
11 |
n-Heptane |
C7H16 |
100.205 |
condensate |
396.8 |
512.8 |
12 |
n-Octane |
C8H18 |
114.232 |
condensate |
360.6 |
564.22 |
13 |
Isooctane |
C8H18 |
114.232 |
condensate |
372.4 |
519.46 |
14 |
n-Nonane |
C9H20 |
128.259 |
condensate |
332.0 |
610.68 |
15 |
n-Decane |
C10H22 |
142.286 |
condensate |
304.0 |
652.1 |
16 |
Carbon Dioxide |
CO2 |
44.010 |
non-hydrocarbon component |
1071.(17) |
87.9(23) |
17 |
Hydrogen Sulfide |
H2S |
34.076 |
non-hydrocarbon component |
1306.(17) |
212.7(17) |
18 |
Sulfur Dioxide |
SO2 |
64.059 |
impurity |
1145.(24) |
315.5(17) |
19 |
Air |
N2O2 |
28.964 |
air |
547.(2) |
-221.3(2) |
20 |
Hydrogen |
H2 |
2.016 |
non-hydrocarbon component |
188.1(17) |
-399.8(17) |
21 |
Oxygen |
O2 |
31.999 |
non-hydrocarbon component |
736.9(24) |
-181.1(17) |
22 |
Nitrogen |
N2 |
28.013 |
non-hydrocarbon component |
493.0(24) |
-232.4(24) |
23 |
Water |
H2O |
18.015 |
impurity |
3208.(17) |
705.6(17) |
24 |
Helium |
He |
4.033 |
non-hydrocarbon component |
- |
- |