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Gas Condensate Reservoir

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Characteristics

Between oil and gas reservoir

Produce light-colored or colorless stock tank

oil Condensate (distillate, oil): > 45 API

Gas-oil ratio: 5,000 ~ 10,000 SCF/bbl

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Calculation of Average Specific Gravityof Well Fluids

1 1 3 3

1 3

4602.

133,316o

wo

wo

R R

R RM

+ +=

+ +

1, 3

1, 3

o

R : gas-oil ratio from separator (1) and stock tank (3)

: specific gravity of separator and stock tank gases

: specific gravity of the stock tank oil (water = 1.00)

R

Consider a two-stage separator system

o wo

,

42.43141.5, M

131.5 1.008

o

API o

= =+

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Calculation of Initial Gas and Oil in Place

Ex. 5.1

Initial pressure: 2740 psia Reservoir temperature: 215 deg F

Average porosity: 25% average connate water: 30%Daily tank oil: 242 STB Oil gravity at 60F: 48.0 API

Daily separator gas: 3100 MCF Separator gas gravity: 0.650

Daily tank gas: 120 MCF Tank gas gravity: 1.20

Calculate the initial oil and gas in place per acre-ft for a gas-condensate

reservoir.

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Ex. 5.1 solution:

,

1 3

w

Step 1: Calculate important parameters

141.5 5954 59540.788, 151.9 lb/lb-mole

48.0 131.5 8.811 48.0 8.811

3,100,000 SCF 120,000 SCF12,800 SCF/STB, 496 SCF/STB

242 STB 242 STB

12,810

o woo API

M

R R

= = = = =+

= = = =

=

pc pc

pr pr

(0.650) 4602.(0.788) 496(1.20)0.896133,316(0.788)

12,810 496151.9

step 2: Look for z factor using pseudocritical values

From Fig. 1.4, we have T 423 and p =637 psia215 460

T 1.60,p423 pc p

RT p

T p

+ +

=+ +

=

+= = = =

27404.30

637

look up in Standing and Katz chart, we have z = 0.825 at the initial condition.

step 3: Initial volume of gas in place, V= 43560 0.25 (1-0.30)

Step 4: initial total lb-mole of gas in place

c

= =

pV (2740 psia)(43560 0.25 (1-0.30))n= lb-mole

zR'T 0.825(10.73)(215+460)Under standard conditions each lb-mole of gas is equivalent to 379.4 SCF

G = n lb-mole 379.4 SCF/lb-mole =1326 MCF/ac-ft

=

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step 5: partition into fraction of oil and gas. For gas, volume fraction = mole fraction

for 1 STB of gas condensate,

Gas volume = 12810+496 SCF = 13296 SCF

Gas equivalent of produced condensate = 133,3 o

wo

g o

o

0.78816 133,316 691.6 /ac-ft

M 151.9

13, 296f 0.95, f 0.0513,296 691.6

1326 MCF/ac-ft 0.95 = 1260 MCF/ac-ft,

V 1326 MCF 0.95/(12810+496) = 94.8 STB/ac-ft

Step 6:

total daily gas-condensate

g

SCF

V

= =

= = =+

=

=

p

production in MCF is:

daily gas 3100 120G 3386 MCF/day

0.951 0.951total daily reservoir voidage by the gas law is:

675(14.7)(0.825)V=3,386,000 19, 450 /

520(2740)cu ft day

+ = = =

=