JNTU
JNTU B.Tech IV NATURAL GAS ENGINEERING Previous Question Paper (February/March - 2022 - R18)
Answer any five questions
All questions carry equal marks
Main
Draw the graph of viscosity, Bg, Cg and Z factors versus pressure and explain briefly.
Answer
The physical properties of natural gas vary significantly with pressure. As pressure increases:
- Z-factor (Compressibility Factor): Initially decreases as pressure increases due to attractive intermolecular forces, reaching a minimum, then increases as repulsive forces dominate at high pressures.
- Bg (Gas Formation Volume Factor): Decreases rapidly with increasing pressure because the gas is compressed into a smaller volume. It is inversely proportional to pressure and directly proportional to the Z-factor.
- Cg (Isothermal Compressibility): Decreases sharply as pressure increases, reflecting the decreasing ability to compress the gas further at higher densities.
- Viscosity (μg): Increases with pressure because higher density leads to more frequent molecular collisions.
Given the natural gas gravity to air gg = 0.75, the pseudocritical pressure, ppc and temperature, Tpc are 667 psi and 405 R, respectively. If the pressure and temperature are 1,500 psi and 200°F, respectively, calculate how many lb of gas can fit in 1,000 ft3 of space? At what pressure increase would the mass increase by 50%, if the temperature remains constant? (Z=0.51)
Answer
Given: P = 1,500 psi, T = 200°F = 660 R, V = 1,000 ft3, Z = 0.51, Mair = 28.97 lb/lb-mol, gg = 0.75. The molecular weight of the gas is M = gg × 28.97 = 21.73 lb/lb-mol.
Using the real gas law, PV = nRT, where n = m/M and R = 10.73 (psi·ft3)/(lb-mol·R):
To increase the mass by 50%, the new mass m' = 1.5 × 9,336.5 = 14,004.75 lb. Since T and V are constant, the ratio m'/m = (P'/Z') / (P/Z) = 1.5. Assuming Z remains approximately constant at 0.51 for this calculation:
The required pressure increase is ΔP = 2,250 - 1,500 = 750 psi.
Explain briefly the natural gas composition and phase behavior.
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Use the real gas law to calculate the volume of 5 lb-mol of a gas mixture at reservoir conditions of T = 180°F and p = 4,000 psi. Assume that this natural gas has the following molar composition: C1 = 0.874, C2 = 0.083, C3 = 0.022, i-C4 = 0.006, n-C4 = 0.002, iC5 = 0.008, n-C5 = 0.003, n-C6 = 0.001 and C7+ = 0.001.
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Explain the nodal analysis with the Bottom hole node of a gas well for identification of operating points.
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Describe briefly the gas well inflow under non-Darcy flow.
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A gas well produces from a reservoir whose pressure is 3,150 psi, and the reservoir temperature is 148°F. Gas specific gravity is 0.61 with no sour gases. The net pay is 50 ft. The damage skin factor is equal to 5 and the reservoir permeability is 20 md. The non-Darcy coefficient D is 1.5 E-3 (Mscf/d)-1. Calculate the rate of the well at pwf = 1,200 psi assuming pseudo steady state. Also assume that: ln (0.472 re/rw) = 7. What is the apparent skin at that rate? What would be the miscalculated rate if the non-Darcy effects were ignored?
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Explain in detail the Unified Fracture Design (UFD).
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Explain briefly the principle pipeline applications for gel pigs.
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Consider a 6-in. pipeline that is 20 miles long. Assuming that the compression and delivery pressures will maintain unchanged, calculate gas capacity increases by using the following measures of improvement: i) replace 10 miles of the 8-in. pipeline by a 6-in. pipeline segment; ii) Place an 8-in. parallel pipeline to share gas transmission.
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Which conditions tend to promote the formation of natural gas hydrates in gas pipeline?
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Natural gas must be delivered as CNG to a destination located 600 nautical miles away from a shipping point at a rate of 500 MMscf/d. What CNG fleet should service this market? Assume that the maximum loading and offloading rate is 150 MMscf/d, the time needed to connect or disconnect to facilities is 1 hour, the sailing velocity is 14 knots, and that 4% of natural gas loaded is consumed as fuel.
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Describe in detail the entropy analysis of the APCI process with neat diagram.
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Calculate the mass of methanol (in lb) that can be produced from 4 Bcf of natural gas. Assume that it is all methane. How many pounds of oxygen would be required?
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What are the alternatives to natural gas fired electricity?
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Calculation of the average wind velocity to generate 1 MW of power assuming a power coefficient cp = 0.4, a rotor diameter 54 m, and ρ ≈ 1.2 kg/m3.
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