DEPARTMENT OF PETROLEUM ENGINEERING
FACULTY OF TECHNOLOGY
TPE 413: NATURAL GAS PROCESSING
SPECIAL EXAMINATION,
SEPTEMBER 2019
INSTRUCTIONS: ANSWER ALL
TIME: 13 Hours
!.(a)
Calculate the gross heating value (dry) of the separator gas with composition shown in
the Table 1.0 below:
TABLE 1.0: Composition and properties of a separator gas stream
Component Mole
Fraction
𝒚𝒊
𝐶𝑂2
𝑁2
𝑪𝐻4
𝐶2 𝐻4
𝐶3 𝐻6
0.04
0.02
0.72
0.14
0.08
Molecular
weight
(𝒍𝒃⁄𝒎𝒐𝒍)
𝑴𝒊
44.010
28.010
16.043
30.070
44.097
HHV
(𝑩𝒕𝒖/𝒇𝒕𝟑 )
LHV
(𝑩𝒕𝒖/𝒇𝒕𝟑 )
00.0
00.0
1010.0
1770.0
2416.1
00.0
00.0
909.0
1619.0
2315.0
Compressibility
factor (STP)
𝒛𝒊
0.09943
0.9097
0.9180
0.8919
0.8825
* Volumetric Heating Values are based on standard temperatures and pressure of dry gas - 60oF and 14.73 psi
(b) Determine also:
(i) The gross heating value of the gas mixture
(ii) The compressibility factor of the gas.
(iii) The Wobbe Index of the gas
2.(a) List three parts of a vertical separator and explain briefly the functions of each
(b) A vertical separator has the following properties: Shell height = 15ft (h = 4.25),
Inside diameter of separator = 24in., Gas gravity = 0.8, Oil gravity = 45oAPI at
60oF, operating pressure = 500psia, operating temperature = 80oF, Separation
coefficient, K = 0.166.
Calculate
(i)
the rated oil capacity in bbl/sec
(ii)
the entrainment velocity in feet per second, and
(c) Reservoir fluid from a conventional reservoir is passed through a high pressure
separator (HPX) which separates 324MMSCF of associated gas from the
reservoir liquid. The resulting effluent liquid was passed through a low pressure
separator (LPX) where additional gas, equal to exactly one-eight, (1⁄5)𝑡ℎ of the
original gas volume from the HPX, was recovered. Water and crude oil were also
separated from the LPX resulting into 2.5 stock tank barrel of water and 12.5
stock tank barrels of crude oil. Assuming stock tank oil molecular weight is
92lb and gas has the average composition shown below:
COMPONENT Mole
fraction,𝑦𝑖
𝐶𝑂2
𝑁2
𝐶𝐻4
𝐶2 𝐻6
𝐶3 𝐻8
𝐶4 𝐻10 +
0.0000
0.0000
0.1130
0.1351
0.1489
0.5930
Molecular
weight,
𝑀𝑖
44.01
28.01
16.04
30.07
44.10
𝟏𝟎𝟎. 𝟐𝟎
Gross
Heating
Value
0.00
0.00
1010
1783
2572
4556.4
Net
Heating
Value
0.00
0.00
910
1630
2371
4323.1
Assume the molecular weight of the butane plus fraction, (𝐶4 𝐻10 +) is the same as that of
𝑯𝒆𝒑𝒕𝒂𝒏𝒆, 𝑪𝟕 𝑯𝟏𝟔 , Molecular weight of air is 28.96 lb (air density at STP is approximately
0.0765 lb/(cu ft)) and the density of water is 62.4279 𝑙𝑏⁄𝑓𝑡 3 .
Calculate:
(i)
the well stream gas gravity, 𝛾𝑤 = 𝑅
𝑅𝑔 𝛾𝑔 +4584𝛾𝑜
𝑔 +132,800𝛾𝑜 ⁄𝑀𝑜
given that the surface gas
specific gravity, 𝛾𝑔 = 0.68, API gravity is 58 degrees and the total gas oil ratio at
surface condition, 𝑅𝑔 = 5,500𝑆𝐶𝐹/𝑆𝑇𝐵 ;
(ii)
The density of the stock tank crude oil in pounds per cubic feet;
(iii)
Total gas recovered
*NOTE* Total gas recovered is the sum of gas separated + gas equivalence of condensate +gas
equivalence of water recovered.