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# PTRE 461 Natural Gas Engineering

1. (20 points) If a natural gas has a specific gravity of 0.75 and contains 20% of H2S, 0% of N2, and 10% of CO2 (in molar percent), calculate its pseudo-critical pressure in psia and pseudo-critical temperature in ℉.

2. (30 points) For the following given data, estimate upstream pressure at choke:

```Down stream pressure:  	400  psia
Choke size:  	48  1/64 inch
Flowline ID:  	2  in
Gas production rate:  	14000  Mscf/d
Gas specific gravity:  	0.70  1 for air
Gas specific heat ratio:  	1.3
Upstream temperature:  	120  ℉
Choke discharge coefficient:  	1.05
Assuming gas viscosity is 0.02 cp and z-factor is 0.9.
```

3. (30 points) A 0.70 specific gravity natural gas flows from a 2-in pipe through a 1.0-in orifice-type choke. The discharge coefficient of choke is 1.03. The upstream pressure and temperature are 120 psia and 70 ℉, respectively. The down stream pressure is 90 psia (measured 2 ft from the nozzle). The gas specific heat ratio is 1.25. Assuming gas viscosity is 0.02 cp and z-factor is 0.9.

1. What is the expected daily flow rate?
2. Is icing a potential problem?
3. What is the expected pressure at the nozzle outlet?

4. (20 points) A gas well produces 0.7 specific gravity natural gas. The average reservoir pressure is 2,800 psia. Reservoir temperature is 150 ℉. The well was tested at two flow rates:

```Test point 1, flow rate: 	1100 	Mscf/d
bottom hole pressure: 	1700 	psia
Test point 2, flow rate: 	1500 	Mscf/d
bottom hole pressure: 	1000 	psia
```

Use backpressure model with pressure squared approach to estimate the gas rate at a flowing bottomhole pressure of 800 psia.