## Answered: - PNG 410 APPLIED RESERVOIR ENGINEERING Homework 5 Due: Thursday,

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PNG 410

APPLIED RESERVOIR ENGINEERING

Homework 5

Due: Thursday, March 30th, 2016 in class

1. A gas reservoir under partial water drive produced 12.0 MMM SCF when the average

reservoir pressure had dropped from 3000 psia to 2200 psia. During the same interval, an

estimated 5.20 MM bbl of water entered the reservoir based on the volume of the invaded

area. If the gas deviation factor at 3000 psia and bottom-hole temperature of 170oF is 0.88

and at 2200 psia is 0.78, what is the initial volume of gas in place measured at standard

conditions.

2. The initial daily production from a gas-condensate reservoir is 186 STB of condensate,

3750M SCF of high-pressure gas and 95 M SCF of stock tank gas. The tank oil has a gravity

of 51.2 oAPI at 60oF. The specific gravity of the separator gas is 0.712 and of the stock tank

gas, 1.30. The initial reservoir pressure is 3480 psia, and the reservoir temperature is 220 oF.

Average hydrocarbon porosity is 17.2%. Assume standard conditions of 14.7 psia and 60oF.

a. What is the average gravity of the produced gases?

b. What is the initial gas-oil ratio?

c. Estimate the molecular weight of the condensate.

d. Calculate the specific gravity (air = 1.00) of the total well production.

e. Calculate the gas deviation factor of the initial reservoir fluid (vapor) at initial

reservoir pressure.

f. Calculate the initial moles in place per acre-foot.

g. Calculate the mole fraction that is gas in the initial reservoir fluid.

h. Calculate the initial (sales) gas and condensate in place per acre-foot.

3. The following data are taken from a study on a recombined sample of separator gas and

separator condensate in a PVT cell with an initial hydrocarbon volume of 3958.14 cu cm.

The wet gas GPM and the residue gas-oil ratios were calculated using equilibrium ratios for

production through a separator operating at 300 psia and 70 oF. The initial reservoir pressure

was 4000 psia, which was also close to the dew-point pressure, and reservoir temperature

was 186oF.

a. On the basis of an initial reservoir content of 1.00 MM SCF of wet gas, calculate the

wet gas, residue gas and condensate recovery by pressure depletion for each pressure

interval.

b. Calculate the dry gas and condensate initially in place based on 1.00 MM SCF of wet

gas.

c. Calculate the cumulative recovery and the percentage of recovery of wet gas, residue

gas and condensate by depletion performance at each pressure.

d. Place the recoveries at an abandonment pressure of 605 psia on an acre-foot basis

corresponding to a porosity of 10% and connate water saturation of 20%.

4000

Composition in mole percentages

3500

2900

2100

1300

605

CO2

0.18

0.18

0.18

0.18

0.19

0.21

N2

0.13

0.13

0.14

0.15

0.15

0.14

C1

67.72

63.1

65.21

69.79

70.77

66.59

C2

14.1

14.27

14.1

14.12

14.63

16.06

C3

8.37

8.25

8.1

7.57

7.73

9.11

i-C4

0.98

0.91

0.95

0.81

0.79

1.01

n-C4

3.45

3.4

3.16

2.71

2.59

3.31

i-C5

0.91

0.86

0.84

0.67

0.55

0.68

n-C5

1.52

1.4

1.39

0.97

0.81

1.02

C6

1.79

1.6

1.52

1.03

0.73

0.8

C7+

6.85

5.9

4.41

2

1.06

1.07

143

138

128

116

111

110

0.867

0

5.254

7127

0

0.799

224

4.578

8283

3.32

0.748

474

3.347

11621

19.36

0.762

1303

1.553

26051

23.91

0.819

2600

0.835

49312

22.46

0.902

5198

0.895

45872

18.07

Pressure, psia

Component

Mol. Wt C7+

o

Gas deviation factor for wet gas at 186 F

Wet gas production, cu am at cell P and T

Wet gas GPM (calculated)

Residue gas-oil ratio

Retrograde liquid, percentage of cell volume

4. Given the following data for a gas-condensate reservoir and the accompanying PVT test.

4100psia

0.63

0.1347

0.083

0.0433

0.024

0.085

3400psia

0.6328

0.144

0.0825

0.0431

0.0226

0.075

2700psia

0.6539

0.1424

0.081

0.0411

0.0223

0.0593

Mol.wt C6+

139

132.8

117.75

Sp. Gr. C6+ at 60oF

0.79

0.79

0.79

Z-factor for wet gas

at cell T

0.87

0.8

0.75

C1

C2

C3

C4

C5

C6+

Wet Gas Prodn.

(cc at cell P,T)

0

248

543

5.25

4.5

3.3

(% of cell volume)

0

4

19.8

Initial cell volume

4100 cc

Cell Temperature

186 oF

Reservoir size

Thickness

Average porosity

Connate water

200 acres

15 ft

0.18

0.23

Wet Gas GPM

The PVT test indicates 25% liquid recovery of butane, 50% recovery of pentane.

a) What is the liquid recovery of C6+ indicated by the above data?

b) What is the recovery of gross gas, residue gas and condensate at 3400 psia?

c) If the residual hydrocarbon (gas + condensate) saturation is 20%, what is the recovery of

residue gas, assuming complete water influx occurred when the pressure was 3400 psia and

the reservoir pressure stabilized at 3400 psia.

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