Assignment 1 – PETR 5350/6350 – Natural Gas Engineering – Fall 2019
Natural Gas Properties, Reserves
(Sunday, Sep 9, 2019 – Due on Thursday, Sep 27, 2018)
1. Calculate the pressure at which the volume of 1 lb of ethane will be 0.1 ft3, at a temperature of
150 F. The critical pressure of ethane is 708 psia and critical temperature is 90 F. Calculate the
Z-factor from Papay's equation
0.274 𝑝2
3.52 𝑝
𝑅
𝑅
𝑍 = 1 + 100.8157𝑇
− 100.9813𝑇
𝑅
𝑅
2. A one lb mixture of ethane and methane contains 30% by volume of methane. Mixture
pressure is 500 psia and temperature is 300 F. Calculate the mixture volume. Use Papay's
equation to calculate the Z-factor. The critical pressure of ethane is 708 psia and critical
temperature is 90 F, and the critical pressure of methane is 673 psia and critical temperature is
-116 F.
3. A natural gas has a molecular weight of 16, critical pressure of 673 psia, and critical
temperature of 344 R. Reservoir pressure is 3500 psia, temperature is 270 F. Calculate the gas
formation volume factor, Bg, in reservoir ft3/scf and in reservoir barrels/scf. Also calculate the
density and compressibility of the gas.
4. Calculate the pressure at the bottom of a shut-in gas well using Papay’s equation inside the
integral. The surface pressure is 3000 psia, depth is 5000 ft, reservoir temperature is 180 F,
M=16, critical pressure of the gas is 673 psia and critical temperature is -116 F.
5. The following pressure-cumulative gas production data is for a gas reservoir (M=16, critical
pressure of the gas is 673 psia and critical temperature is -116 F). Determine the initial gas in
place. Comment on the plot.
Pressure, psia
4600
4000
3100
2000
1000
400
Cumulative gas production, 109 scf
0
0.5
1.5
2.9
4.9
6.0