PNG 410: Applied Reservoir Engineering

Home work assignment #5

April 21, 2010 Due date: April 28, 2010

NOTE: Please detail the formula, steps, and units for the calculation. Missing formula, steps, and units can lead to lost points. Problem 1: The following data are taken from an oil field that had no original gas cap and no water drive: Initial reservoir pressure = 3500 psia Initial reservoir temperature = 140 deg F Bubble point pressure of the reservoir pb= 2400 psia Initial oil volume under reservoir condition = 75 MM cu ft Solubility of gas in crude oil below bubble pressure = 0.42 SCF/STB/psi Formation volume factor Boi at 3500 psia = 1.333 bbl/STB Gas deviation factor z at 1500 psia and 140 deg F = 0.95 Oil produced when pressure at 1500 psia Np= 1.0 MM STB Net cumulative produced gas-oil ratio Rp at 1500 psia = 2800 SCF/STB 1.1 Calculate the initial STB of oil in reservoir 1.2 Calculate the initial gas-oil ratio and SCF of gas in reservoir (using the definition of

gas solubility in crude oil). 1.3 Calculate the SCF of gas remaining in the reservoir at 1500 psia 1.4 Calculate the SCF of free gas in the reservoir at 1500 psia 1.5 Calculate the gas volume formation factor at 1500 psia at standard condition of 14.7

psia and 60 deg F. 1.6 Calculate the reservoir volume of the free gas at 1500 psia 1.7 Calculate the single phase oil formation volume factor at 1500 psia 1.8 Calculate the total, or two phase, oil volume formation factor at 1500 psia. Problem 2: The R sand is a volumetric oil reservoir whose PVT properties are shown below. Reservoir temperature is 150 deg F. When the reservoir pressure dropped from an initial pressure of 2500 psia to an average pressure of 1600 psia, a total of 26.0 MM STB of oil had been produced. The cumulative gas-oil ratio at 1600 psia was 954 SCF/STB. No Appreciate amount of water was produced, and standard condition were 14.7 psia and 60 deg F. Initial water saturation is 0.18.

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2.1 Calculate the initial oil in place. 2.2 Calculate the SCF of free gas remaining in the reservoir at 1600 psia. 2.3 Calculate the average gas saturation in the reservoir at 1600 psia. 2.4 Calculate the barrels of oil that would have been recovered at 1600 psia if all the produced gas had been returned to the reservoir. 2.5 Assuming no free gas flow, calculate the recovery expected by depletion drive performance down to 2000 psia. Problem 3: The following table provides fluid property data for an initially undersaturated oil reservoir. The initial connate water saturation was 25%. Initial reservoir T and p were 97 deg F and 2110 psia, respectively. Average compressibility factors between the initial and bubble-point pressures were 4.0(10)-6 psia-1 and 3.1(10)-6 psia-1 for the formation and water, respectively. The initial oil formation factor is 1.256 bbl/STB. The critical gas saturation at which gas flow starts to form is estimated to be 10%. Determine the recovery factor at the bubble point pressure. Assume it is a volumetric reservoir. Pressure (psia) Oil formation

volume factor (bbl/STB)

Solution gas-oil ratio (SCF/STB)

Gas formation volume factor (ft3/SCF)

2110 1.256 540 1700 1.265 540 0.007412 1500 1.241 490 0.008423 1300 1.214 440 0.009826 1100 1.191 387 0.011792 900 1.161 334 0.014711 700 1.147 278 0.019316 500 1.117 220 0.027794

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