l11-evaluating production performancecvd

7/22/2019 L11-Evaluating Production PerformanceCVD

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Termodinamica de

Hidrocarburos

Maria A. Barrufet


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Sketch of a

Production

Mechanism

for a Gas

Condensate

Constant Volume Depletion (CVD)

Pi = Initial Reservoir Pressure

T = Reservoir Temperature

Vi = Reservoir Pore Volumezi = Initial Reservoir Fluid Composition

(Gas Condensate)

(1)

1. Mass in place (either in moles or pounds)

Given

Pi =3,000

psia

P1 = 2,800 P1= 2,800 P2 = 2,500

np1np2

Vp1Vp2

( zi)o ( zi)1

( yi)2

( xi)2

( yi)

1

( x i) 1

Vi V1= Vi + Vp1 Vi V2= Vi + Vp2

V1= VL1+ VG1 V2= VL2+ VG2

ni = P iVi/zRT


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Sketch of a

Production

Mechanism

for a Gas

Condensate

V

( y i)n

( x i) n

( z i)n-1

pnnpn

Target for gascycling

End of Depletion

Constant Volume Depletion of a Conden sate Reservoir (cont.)

At any depletion stage need:

Moles and composition of liquid phase (n l , x i's)

Moles of gas phase formed (n v, y i's)

Comp ressibility factor of the liquid phase, zl

Comp ressibility factor of the gas phase, zv

n zi= yinv+ xinlFrom flash calculations

VG=nvzv RT

P

VL=nlzl RT

P

From EOS


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Simulation of a Constant

Volume Depletion (CVD) Test

for a Gas Condensate or aVolatile Oil Using an EOS


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CVD with EOS

Numerical Example of a CVD. The

data required for the EOS for this

calculation are,initial fluid compositions

reservoir temperature

initial pressure and pressure depletion

stage

The production data required are

Pressures and Gp.


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Flow chart

for asimulated

CVD test

Given Reservoir Fluid CompositionTemperature, Dew Point PressureControl parameters

Determine Moles ofGas to be produced

Recombine RemainingPhases

Calculate initialnumber of moles

Drop pressure below Pd

Select Hydrocarbon Pore

Volume

Flow Diagram for simulating a CVD

P = P - P

Calculate TotalVolume

Evaluate Flash

Calculate Volume ofCondensate

Calculate Volume of

Gas

Flash to SC


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z (liquid)z(vapor)

z(2 phase)

P/ z = 4055 -1.0578e-05 Gp (Correct two-phase z)

P/ z = 4055 -8.1097e-06 Gp (z = z liquid)

P/ z = 4055-1.6219e-05

What's the "two-phase" z-factor?

From the EOS (Equation of state ) will have three roots. The largest Vcorresponds to the vapor and the smallest to the liquid.

VL=nlzl RT

P

Vv =nvzv RT

P

PVvRT

= zv= f (P, T, yi's)

PVLRT

= zl = f (P, T, xi's)

z2= nvn zv + nln zl z2 = PVini-npRT

or

5e+84e+83e+82e+81e+80e+00

1000

2000

3000

4000

5000

Gp

P/z

2

Gp (z = z vapor)

Estimation of Reserves: Simpson's Condensate Field

z (liquid)z(vapor)

z(2 phase)


P/ z = 4055 -8.1097e-06 Gp (z = z liquid)

P/ z = 4055-1.6219e-05



VL=nlzl RT

P

Vv =nvzv RT

P

PVvRT


PVLRT

= zl = f (P, T, xi's)


or

5e+84e+83e+82e+81e+80e+00

1000

2000

3000

4000

5000

z (liquid)z(vapor)

z(2 phase)


P/ z = 4055 -8.1097e-06 Gp (z = z liquid)

P/ z = 4055-1.6219e-05



VL=nlzl RT

P

Vv =nvzv RT

P

PVvRT


PVLRT

= zl = f (P, T, xi's)


or

5e+84e+83e+82e+81e+80e+00

1000

2000

3000

4000

5000

Gp

P/z

2

Gp (z = z vapor)

Estimation of Reserves: Simpson's Condensate Field

Differences in the

estimation of

reserves using

three different

compressibility

factors


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CVD for Near Critical Fluids

For every pressure depletion stage PVT

simulators provide

Moles produced (gas or liquid, or both)

Z factors (gas, liquid, 2-phase)

Gas & liquid

Compositions

DensitiesViscosities

Interfacial tensions


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Examples from PVTi

Output file with PVT calculations has

extension *.mes . Only portions shown here

CVD for a volatile oil at 176 oFSome experimental data provided

CVD for a Gas condensate at 250 oF

No experimental data given
http://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDgascon250.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txthttp://localhost/var/www/apps/conversion/tmp/scratch_2/L11-CVDoil176.txt


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CVD for Near Critical Fluids

For every pressure depletion stage

MOST simulators DO NOT PROVIDE

How moles produced separate at surface

Gas produced in MSCF

Oil Produced in STB


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Need to Complete Evaluation

nt, Pav, T

Oil Volume (STB),

no, Psu rface,

Tsurface

Gas Volume (MSCF),

ng, Psurf ace, Tsu rface


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What do we get with this?

A good estimate of the potential of your

reservoir

Could design separator stages to

obtain more liquid

Estimates of recovery factors for oil &

gas as a function of average reservoir

pressure


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Learning Objectives

Understand the production mechanismsfor a gas condensate or a volatile oil(Constant Volume Depletion, CVD)

Interpret the results of a simulated CVDtest from a commercial simulator

Determine oil and gas recoveries


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Worked Out Example:

Simulation of a ConstantVolume Depletion (CVD) Test

for a Gas Condensate or a

Volatile Oil Using an EOS


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Numerical Example of a CVD

Data required for the EOS for this

calculation include

initial fluid compositions

reservoir temperature

initial pressure and pressure depletion stage

When calibrating the EOS, given a certain

reservoir size need to match productiondata (Gp and Np)


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Component Mole %

C1 75.2

C2 7.7

C3 4.4C4 3.1

C5 2.2

C6 2.3

C7 2.099C8 1.235

C9 0.727

C10+

1.039

Initial gascondensate

composition

CVD Example


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Summary Results Gas

Condensate CVD at T=195F

CVD Results Z - Factor Gas Viscosity

P(psi)100

d

l

V

V100

t

p

n

n100

t

p

n

nz

g

z2

)( cPg

m

2,960 0 0 0 0.779 0.030

2,500 14.02 14.4 14.4 0.799 0.769 0.023

2,000 14.42 16.6 31.0 0.825 0.763 0.019

1,500 12.96 16.7 47.7 0.855 0.755 0.0161,000 11.09 16.5 64.2 0.891 0.735 0.015

500 8.93 16.0 80.2 0.933 0.665 0.013


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Gas produced properties for each

depletion stage (T = 195o

F )P (psi) 2,960 2,500 2,000 1,500 1,000 500Mole% 100 85.197 83.176 82.484 81.745 80.627

~Vv(f t/mol) 1.848 2.246 2.897 4.005 6.259 13.103

V

V

v

t

% 100 88.1 88.6 90.5 92.9 95.8

rg(lb/f t) 14.881 10.924 7.949 5.574 3.557 1.783

Zg 0.7787 0.7994 0.8249 0.8553 0.891 0.9327

mg

(cP) 0.0303 0.0226 0.0186 0.0162 0.0146 0.0135

Mwg 27.50 24.54 23.03 22.33 22.26 23.36


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Produced Gas Compositions after each

depletion stage at 195F to flash at

standard conditions

P (psi) 2,960 2,500 2,000 1,500 1,000 500

C1 75.2 78.84 80.695 81.403 81.021 78.595

C2 7.7 7.65 7.697 7.834 8.071 8.406C3 4.4 4.153 4.062 4.105 4.322 4.857

C4 3.1 2.743 2.56 2.518 2.664 3.244

C5 2.2 1.806 1.576 1.471 1.516 1.943

C6 2.3 1.731 1.386 1.194 1.159 1.485

C7

2.099 1.45 1.057 0.832 0.745 0.914C8 1.235 0.782 0.521 0.376 0.313 0.364

C9 0.727 0.41 0.242 0.157 0.118 0.126

C10+

1.039 0.435 0.203 0.11 0.071 0.067MwC10

+153.8 147.7 144.7 142.9 141.6 140.7


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CVD ExampleOutput needed

From the EOS information we can

calculate the following terms:

Initial Gross Gas in Place (MSCF/ac-ft)Initial Residue Gas in Place (MSCF/ac-

ft)

Initial Oil in Place (STB/ac-ft)

Increments of Gross Gas Production

(MSCF/ac-ft)


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Cumulative gross gas production(MSCF/ac-ft

Residue gas in each increment

(MSCF/ac-ftCumulative residue gas in eachpressure stage (MSCF/ac-ft

Liquid produced in each pressure stage

(STB/ac-ftCumulative liquid produced in eachpressure stage (STB/ac-ft)


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Average Gross Gas-Oil-Ratio in Each

Pressure Stage (SCF/bbl)

Average Residue Gas-Oil-Ratio in

Pressure Stage(SCF/bbl)Cumulative Gross Gas Recovery

Percentage

Cumulative Residue Gas RecoveryPercentage

Cumulative Liquid Recovered Percentage


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These terms will be described as we

move along

Quantities will be evaluated per acre

foot of net bulk reservoir rock.


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CVD ExampleSolution

The hydrocarbon pore volume per acre

foot is

f tac

f t

,..,V

S,V

HC

iwHC

3

534625012056043

156043


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CVD ExampleSolution

Step 1:

Calculate the initial number of moles

(nt) based upon the hydrocarbonpore space per acre foot. Then,

evaluate the number of moles and

cumulative number of moles

produced at each pressure stage.


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Using VHC as a base volume.

The number of moles contained in this

hydrocarbon pore volume is

CVD ExampleSolution

R

RRt

HCP

RTZnV

RR

RHC

tRTZ

PVn

ftac

molelb.,

..

,,

RTZ

PVn

RR

RHC

t 585323

65573107790

96025346


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CVD ExampleSolution

The number of moles produced at P

=2,500 psia (1stdepletion stage is)

f tac

molelb..,.nfn

tpp 6919508582953231440


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CVD ExampleSolution

Step 2:

Calculate the Initial Gross Gas in

Place per ac-ft, then evaluate theincrements of Gross Gas Production

(MSCF/ac-ft) and Cumulative Gross

Gas Production (MSCF/ac-ft)

produced after each pressure stage.


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CVD ExampleSolution

The Initial Gross Gas in Place

expressed in MMSCF/ac-ft is

714

520731058295323

.

..,

P

RTnG

SC

SCt


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CVD ExampleSolution

Note that the standard molar volume

of an ideal gas has been taken as

520 R (60 F) and 14.7 psia.

mollb/SCF..

.

P

RTV~

SC

SC

sc 5643379

714

5207310

f tac

MSCF,

feetac

SCF,,G 34118433401


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CVD ExampleSolution

The Gross Gas Production at each

pressure stage is evaluated as

where fpis the fraction of molesproduced (see summary table)

GfGpp


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CVD ExampleSolution

At P = 2,500 psia

Proceed with all the other pressures

and fill the corresponding columnsin the following table:

f tac

MSCF

.,.GfG pp 0819334111440


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CVD ExampleSolution

P(psi) np np Gp Gp GRP GRP NpNp GOR

2960 0 0 0

2500 508.69 508.69 193.08 193.08

20001500

1000

500

Here is the tricky part


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CVD ExampleSolution

Step 3:

Evaluate the Initial Residue Gas inplace (MSCF/ac-ft) and the Initial Oilin Place (STB/ac-ft).

Note that these terms are usually expressed indifferent units!

NGGR


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CVD ExampleSolution

To evaluate these quantities we need

to flash the initial number of moles

with initial gas composition tostandard conditions.

Fl h lt f d t


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Flash results of gas condensate

initial composition

to 14.7 psia and 60oFProperty Total Vapor Liquid

Mole% 100 94.983 5.017

V~ (ft/mol) 358.755 377.573 2.503

r (lb/ft) 0.077 0.061 43.706

Z 0.9458 0.9954 0.0066m(cP) 0.0103 0.5083Mw 27.5 23.18 109.4


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Gas and liquid Compositions from

flashing initial mixture to 14.7 psia and

60oF

Component Initial Vapor LiquidC1 75.2 79.147 0.47C2 7.7 8.09 0.31

C3 4.4 4.596 0.688C4 3.1 3.168 1.812C5 2.2 2.081 4.446C6 2.3 1.728 13.123

C7

2.099 0.86 25.56C8 1.235 0.258 19.741C9 0.727 0.056 13.428

C10+

1.039 0.015 20.423MwC10

+153.8 137.5 154


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CVD ExampleSolution

the Initial Residue Gas per acre-feet

is:

f tac

MSCF.,,.GfG

vR 7227313411949830


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CVD ExampleSolution

and the Initial Liquid in Place is

f tac

SCF.N

..,.V~nfNotl

6059443

503258295323050170

f tac

STB.

.

.N 0178796145

6059443


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CVD ExampleSolution

Step 4: Evaluate the following properties

Residue Gas produced (GRP) in each pressure

stage (MSCF/ac-ft)

Cumulative Residue Gas in each pressure

stage(MSCF/ac-ft)

Liquid produced (Np

)

in each pressure stage

(STB/ac-ft)

Cumulative Liquid Produced in each pressure

stage (STB/ac-ft)


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CVD ExampleSolution

This requires flashing the number of

moles of gas produced in each

depletion stage to standardconditions

Next see an example at 2,500 psi,


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Flash results to 14.7 psia and 60 oF from

the gas produced at P = 2,500 psia

Property Total Vapor Liquid

Mole% 100 97.534 2.466

V~ (ft/mol) 368.436 377.687 2.553

r (lb/ft) 0.067 0.059 44.209

Z 0.9714 0.9957 0.0067

m(cP) 0.0104 0.5396

Mw 24.68 22.45 112.88


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Compositions

of the gas and

the liquidobtained from

flashing the gas

produced at

2,500 psia

Component Total Vapor Liquid

C1 78.84 80.821 0.477

C2 7.65 7.836 0.3C3 4.153 4.242 0.634

C4 2.743 2.772 1.584

C5 1.806 1.757 3.753

C6 1.731 1.489 11.306

C7 1.266 0.741 22.039

C8 0.745 0.26 19.936

C9

0.439 0.064 15.27C10

+

0.627 0.018 24.701

MwC10+

153.8 137.5 154.3


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CVD ExampleSolution

The residue gas and the liquid produced

are evaluated as

Example at P = 2,500 psia

pvRP GfG oplp V~nfN


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CVD ExampleSolution

The residue gas

pvRP GfG

f tac

MSCFG

RP3196.188081.19397534.0

at P = 2,500 psia is


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CVD ExampleSolution

The liquid produced

oplp V~

nfN

f tac

SCFN

p0256.3255

3

.269.50802466.0

f tac

STBN

p -== 7046.5

614.5

0256.32

at P = 2,500 psia is


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CVD ExampleSolution

Cumulative values are obtained just

by adding the results obtained from

each stageYou will have an exercise of this

nature using an output from a

simulator


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CVD ExampleSolution

Step 5:

Evaluate the following

Average Gross Gas-Oil-Ratio in Each Pressure

Stage (SCF/STB)Average Residue Gas-Oil-Ratio in PressureStage(SCF/STB)

Gross Gas and Cumulative Gross Gas

Recovery PercentageResidue Gas and Cumulative Residue GasRecovery Percentage

Liquid Recovery and Cumulative LiquidRecovery Percentage


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CVD ExampleSolution

The Average Gross Gas-Oil-Ratio,

and the Average Residue Gas-Oil-

Ratio in Each Pressure Stage(SCF/STB) are evaluated as

p

p

N

G

GOR pRP

R N

GGOR


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CVD ExampleSolution

The Gross Gas and Residue Gas

Recovery Percentages are

The liquid recovery in each stage is

100G

GpGross

100

R

RP

GGGresid

100N

NNrec

p


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CVD ExampleSolution

for example at P = 2,500 psia

STB

SCF.,

.

.,GOR 5584633

70465

0081193

STB

SCF.,

.

.,GOR

R 901133

70465

6319188

7814100

722731

3196188.

.,

.Gresid


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CVD ExampleSolution

for example at P = 2,500 psia

STB

SCF.,

.

.,GOR

R 901133

70465

6319188

4141003411

081193.

,

.Gross

227100

017879

70465.

.

.Nrec


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CVD ExampleSolution

Steps 1 to 5 are repeated for all the

depletion pressures, and the

cumulative values are calculated

From a CVD simulated test

properties of the liquid remaining inthe reservoir are also reported.

These can be used for gas cycling

projects.

Properties of the liquid (oil) remaining in


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Properties of the liquid (oil) remaining in

the reservoir at 195oF after every

depletion stage (Condensate Good

Money).P (ps i) 2,960 2,500 2,000 1,500 1,000 500

Mole% 100 14.803 16.824 17.516 18.255 19.373

~

Vo(f t/mo l)1.848 1.75 1.852 1.982 2.149 2.381

V

Vl

t

% 100 11.9 11.4 9.5 7.1 4.2

ro(lb /f t) 14.881 25.476 28.402 31.069 33.657 36.364

Zo 0.7787 0.6229 0.5273 0.4232 0.3059 0.1695

mo (cP) 0.0303 0.0718 0.092 0.1158 0.1462 0.1891

Mwo 27.50 44.59 52.6 61.57 72.32 86.57


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Overall Composition changes

with pressure at 195oF

P (psi) 2,960 2,500 2,000 1,500 1,000 500

C1 75.2 75.2 74.586 73.118 70.465 65.611

C2 7.7 7.7 7.709 7.711 7.672 7.488

C3 4.4 4.4 4.442 4.533 4.67 4.83C4 3.1 3.1 3.16 3.304 3.556 3.967

C5 2.2 2.2 2.267 2.432 2.74 3.303

C6 2.3 2.3 2.396 2.639 3.101 3.994

C7 2.099 2.099 2.208 2.485 3.014 4.058

C8 1.235 1.235 1.312 1.501 1.862 2.574

C9 0.727 0.727 0.78 0.909 1.151 1.625

C10+

1.039 1.039 1.141 1.366 1.769 2.55

MwC10+

153.8 153.8 154.2 154.5 154.7 154.9


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CVD ExerciseUse PVTi

Use file provided VOLCON1.pvi

Evaluate two CVDs one at T = 220oF and at

T=260oF (volatile, condensate)

Use pressure stages of 500 psia and finalpressure of 1000 psia

Save gas compositions of every depletion

stage

Calculate the cumulative oil and gas

produced for each case and
http://localhost/var/www/apps/conversion/tmp/scratch_2/11.VOLCON1.PVIhttp://localhost/var/www/apps/conversion/tmp/scratch_2/11.VOLCON1.PVI


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CVD ExerciseUse PVTi

Cumulative Gross Gas Production(MSCF/ac-ft)

Residue Gas in Each Increment(MSCF/ac-ft)

Cumulative Residue Gas in Each PressureStage (MSCF/ac-ft

Liquid Produced in Each Pressure Stage

(STB/ac-ftCumulative Liquid Produced in EachPressure Stage(STB/ac-ft)

Properties of the gas produced


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Properties of the gas produced

at 195 oF for each depletion

stageP (psi) 2,960 2,500 2,000 1,500 1,000 500Mole% 100 85.197 83.176 82.484 81.745 80.627

~Vv

(f t/mol) 1.848 2.246 2.897 4.005 6.259 13.103

V

V

v

t

% 100 88.1 88.6 90.5 92.9 95.8

rg

(lb/f t) 14.881 10.924 7.949 5.574 3.557 1.783

Zg 0.7787 0.7994 0.8249 0.8553 0.891 0.9327mg

(cP) 0.0303 0.0226 0.0186 0.0162 0.0146 0.0135

Mwg 27.50 24.54 23.03 22.33 22.26 23.36

Produced Gas Compositions after each


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p

depletion stage at 165F used to perform

the flash calculations at standard

conditionsP (psi) 2,960 2,500 2,000 1,500 1,000 500

C1 75.2 78.84 80.695 81.403 81.021 78.595

C2 7.7 7.65 7.697 7.834 8.071 8.406

C3 4.4 4.153 4.062 4.105 4.322 4.857C4 3.1 2.743 2.56 2.518 2.664 3.244

C5 2.2 1.806 1.576 1.471 1.516 1.943

C6 2.3 1.731 1.386 1.194 1.159 1.485

C7 2.099 1.45 1.057 0.832 0.745 0.914

C8 1.235 0.782 0.521 0.376 0.313 0.364C9 0.727 0.41 0.242 0.157 0.118 0.126

C10+

1.039 0.435 0.203 0.11 0.071 0.067MwC10

+153.8 147.7 144.7 142.9 141.6 140.7

l11-evaluating production performancecvd

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