PNG 410: Applied Reservoir Engineering

Home work assignment #3

March 22, 2010 Due date: April 1, 2010

NOTE: Please detail the formula, steps, and units for the calculation. Missing formula, calculation steps, and units can lead to lost points. Problem 1: We have a single phase gas reservoir with the following field data:

Contour number

Contour area (acre)

Thickness (ft)

Pressure psia

Water saturation

Porosity

1 551 5 4200 0.34 0.22 2 410 6 4185 0.25 0.22 3 290 5 4102 0.20 0.22 4 142 4 4055 0.20 0.22 5 80 5 4044 0.20 0.22

1.1 Please calculate the reservoir volume using trapezoidal rule and pyramidal rule. What

is difference you get using the two different integration rules? 1.2 Please calculate the average pressure of the reservoir. 1.3 Please calculate the original gas in place, using the reservoir volume calculated from

trapezoidal rule. 1.4 If the gas formation volume factor at the average initial pressure is 0.00453 cu ft/SCF,

what is the original gas in place in units of SCF? Problem 2: A small gas reservoir has an initial pressure of 3200 psia and temperature 220 deg F. The pressure-production history and gas volume factors are as follows:

Pressure (psia) Cumulative Gas Production (MM SCF)

Gas Volume Factor (cu ft/SCF)

3200 0 0.0052622 2925 79 0.0057004 2525 221 0.0065311 2125 452 0.0077360

2.1 Calculate the initial gas in place using production data at the end of each production intervals, assuming volumetric behavior. 2.2 Is this reservoir a volumetric reservoir or water drive reservoir? Explain. 2.3 Plot p/z vs cumulative production. 2.4 If the initial volume of gas in place is 1018 MM SCF, and if there is no appreciable water production, what is the volume of water invaded at the end of each period? Problem 3:

The production of a gas field is given below: p/z (psia) Gp (MMM SCF) 6553 0.393 6468 1.642 6393 3.226 6329 4.260 6246 5.504 6136 7.538 6080 8.749

3.1 draw p/z vs Gp. Is this a volumetric reservoir? 3.2 What is the initial gas in place? 3.3 What percentage of the initial gas in place will be recovered at a p/z of 900? Problem 4: Calculate the daily gas production including the condensate and water gas equivalents for a reservoir with the following daily production: Separator gas production = 6 MM SCF Condensate production = 100 STB Stock tank gas production = 21 M SCF Fresh water production = 10 bbl Initial reservoir pressure = 6000 psia Current reservoir pressure = 2000 psia Reservoir temperature = 225°F Water vapor content of 6000 psia and 225 deg F = 0.86 bbl/MM SCF Condensate gravity = 50°API