11

Hai Xuan Vo, Chunmei Shi and Roland N. Horne

Stanford University

April 20, 2023

Flow Behavior of Gas-Condensate Wells- the impact of composition

Flow Behavior of Gas-Condensate Wells- the impact of composition

22

Condensate blockage

• The productivity loss caused by the condensate buildup is striking, in some cases, the decline can be as high as a factor of 30, according to Whitson (2005).

• Barnum et al. (1995) reviewed data from 17 fields, and concluded that severe loss of gas recovery occurs primarily in low productivity reservoirs with a permeability-thickness below 1000 md−ft.

Gas

pro

du

ctio

n r

ate

(mcf

/mo

nth

) Well #3, Whelan field

1970 1972 1974 1976 1978 1980 1982 1984 1986 1988

Year

1,000,000

100,000

10,000

1,000

33

The composition change

• Heavy component composition in the flowing phase decreases once the reservoir pressure drops below the dew point pressure.

(A field case from KekeYa gas field, China)

Source: Yuan Shiyi, Ye Jigen and Sun Zhidao “Theory and practices in gas-condensate reservoir development”.

Year 1995 Year 1999

C1+N2 77.28 83.86 86.08

C2 7.935 7.78 9.3

C3 3.126 2.38 2.6

C4 2.505 1.52 0.65

C5+ 8.908 4.4 1.31

Well K401 @ initial reservoir condition

Well K233Composition

44(A field case from KekeYa gas field, China)Source: Yuan Shiyi, Ye Jigen and Sun Zhidao “Theory and practices in gas-condensate reservoir development”.

The composition change

• The composition of the heavier component in the flowing phase decreases once the reservoir pressure drops below the dew-

point pressure.

55

Why study composition?

• To understand the phase behavior change.

• To understand the dynamic condensate saturation build-up.Due to compositional variation and relative permeability constraints, the

condensate saturation build-up is a dynamic process and varies as a function of

time, place (distance to wellbore) and phase behavior.

• To develop optimum producing schemes.

Changing the well producing schemes can affect the liquid dropout composition

and can therefore change the degree of productivity loss.

Objectives of this study:– Verify the composition change by experiment.

– Develop optimum producing schemes for condensate recovery.

6

Project Management Plan

• Task 1.0. Project Management Plan • Task 2.0. Technology Status Assessment • Task 3.0. Technology Transfer • Task 4.0. Scoping Study • Task 5.0. Condensate Banking Study –

Numerical and Experimental (in progress)

• Task 6.0. Developing Optimal Production Strategy (third stage)

7

2009 Activities

8

Project Management Plan

• Task 1.0. Project Management Plan • Task 2.0. Technology Status Assessment • Task 3.0. Technology Transfer • Task 4.0. Scoping Study • Task 5.0. Condensate Banking Study –

Numerical and Experimental (in progress)

• Task 6.0. Developing Optimal Production Strategy (third stage)

9

2009 Achievements

• New gas chromatograph (GC)

• Core permeability measurement

• Core X-ray tomography (CT) scanning

• Experiments with old apparatus design

• Apparatus improvement

• Experiments with improved apparatus design

• Three-phase flow simulation

10

New Equipment – Gas Chromatograph (1)

• Owning a GC has provided flexibility, better accuracy and saves time.

• Need to install and calibrate the GC.

11

New Equipment – Gas Chromatograph (2)

• GC is calibrated using a gas mixture standard of C1-nC4 with composition similar to the mixture that is used for experiments.

12

Core Permeability

• Measurements are done using N2 gas

• k ~ 8.7 md

y = 13.054x + 8.7838

R2 = 0.9759

0

2

4

6

8

10

12

14

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

1/Pm (atm)

k (m

d)

Measure points

Linear (Measure points)

13

Core CT Scanning

CT number image of core filled with C1 gas

CT number image of core filled with n-C4 liquid

These will be used as “base lines” to calculate condensate saturation from CT scanning for core filled with the gas condensate.

14

Previous Apparatus Design

Tubing

Sampling ports

15

Old Design: Noncapture Experiment (1)

Observation:

• In no-flow condition, n-C4 concentration is not constant.

• n-C4 concentration in flow condition is higher than the one in no-flow condition.

Steps:

• Core is vacuumed.

• Fill core with mixture of C1-nC4 to pressure about 100 psi above dew point pressure of C1-nC4.

• Take samples in no-flow condition.

• Flow the mixture at 1000 psi differential pressure through the core and take samples in flow condition.

024

68

1012

1416

0 1 2 3 4 5 6 7 8

Port

n-C

4(%

) No-flow

Flow

Cylinder

flow

16

• Did another noncapture experiment, with different result.

• Repeatability of experiments is important for scientific study.

• Is it because the gas in the tubing is not flushed away during the flow so the next samples are contaminated by the remaining gas?

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8

Port

n-C

4(%

) No-flow

Flow

Cylinder

Old Design: Noncapture Experiment (2)

flow

17

Old Design: Capture Experiment

Observation:

• Samples taken during flow contain mainly C1

• Is it because the C1 in the tubing is not flushed away during the flow?

Steps:

• Core is vacuumed and pre-saturated with C1 at 2000 psi (about 100 psi above dew point pressure of C1-nC4).

• Flush the C1-nC4 mixture through the core at 50 psi differential pressure for 10 minutes then 1000 psi differential pressure for 3 minutes.

• Close upstream and downstream valves.

• Take samples in capture-mode.

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7

Port

n-C

4(%

)

Captureexperiment

Upstream

Downstreamr

Discharged

Original

flow

18

Old Design

• During flow the tubing might be still filled with gas from previous condition.

• Purging tubing before taking flow sample may help?

19

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8

Port

n-C

4(%

) No-flow

Flow

Cylinder

Old Design: Noncapture with Purging

• Purging tubing before taking flow sample: liquid drops out hence n-C4 concentration is even higher than the concentration from cylinder.

• Purging is not a good solution.

flow

20

Improved Apparatus Design

Fit valves on core to minimize dead volume.

Able to vacuum tubing before taking samples.

21

Improved Design: Noncapture Experiment – Noflow Condition

• Good repeatability in static conditions except ports 7/8.

• Possible that condensate liquid dropout along the core being flushed to the end. Is it because the gas mixture flowed directly in the vacuumed core without any cushion?

0

5

10

15

20

0 1 2 3 4 5 6 7 8

Port

n-C

4(%

)

Cylinder

No-flow batch 3

No-flow batch 4

No-flow batch 5

flow

22

Improved Design: Capture Experiment (1)

• Good repeatability in static condition and flowing condition

0

2

4

6

8

10

12

14

16

18

20

0 1 2 3 4 5 6 7 8

Port

n-C

4(%

)

No-flow batch 1

Flowing batch 1

Cylinder

No-flow batch 2

Flowing batch 2

Steps:

• Core is vacuumed and presaturated with C1 at 2200 psi (about 300 psi above dew point pressure of C1-nC4).

• Flush the C1-nC4 mixture through the core at 100 psi differential pressure for 10 minutes.

• Close downstream valve and take samples in noflow condition.

• Flush the C1-nC4 mixture through the core at 1000 psi differential pressure for 3 minutes.

• Close upstream and downstream valves and take samples in capture-mode.

flow

23

Improved Design: Capture Experiment (2)

• Did another experiment following the same procedure

• Good repeatability and confirm previous result.

flow

24

Three-Phase Flow Simulation (1)

• Extension of previous work (two-phase gas-oil) but now with presence of immobile water (three-phase gas-oil-water).

• Mixture of C1/n-C4 with initial molar composition = 0.85/.015.

• Sor = 0.24

• Sgr = 0

• Swi = 0.16

25

Two-phase (gas-oil): Oil saturation.

Maximum condensate accumulation reaches about 53% in one minute.

Three-phase (gas-oil-water): Oil saturation.

Maximum condensate accumulation reaches about 37% in one minute.

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60

Distance

So

t = 0.10002 min

t = 0.49998 min

t = 1 min

t = 2 min

t = 5 min

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 10 20 30 40 50 60

Distance

So

t = 0.10002 min

t = 0.49998 min

t = 1 min

t = 2 mins

t = 5 mins

Three-Phase Flow Simulation (2)

flow flow

26

Two-phase (gas-oil): total liquid (oil) saturation.

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60

Distance

To

tal

Liq

uid

Sa

tura

tio

n

t = 5 min

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60

Distance

To

tal L

iqu

is S

atu

rati

on

t = 5 mins

Three-phase (gas-oil-water): total liquid (immobile water and oil) saturation.

• The results of total liquid saturation versus distance for both cases are almost the same in the region where condensate drops out.

• Presence of immobile water has effect on the condensate dropout saturation.

Three-Phase Flow Simulation (3)

flow flow

27

Plan Forward

• Do experiments with present of immobile water.

• Conduct optimization study.

2828

Questions, suggestions and discussions

Thank you!

2929

Backup SlidesBackup Slides

• Scoping study

3030

Compositional variation models

• One-dimensional linear flow

• Where:

• Three-dimensional radial flow

2)(x

pB

t

pA

t

zii

i

cni ,1

,ln

)(p

Gz

m

mA i

ii

,

1

cn

iiGG

pn

jjjiji SxG

1

pn

j j

rjjiji

kkxm

1 ,

1

cn

iimm),ln(

m

m

pG

mB iii

2)(r

pB

t

pA

t

zii

i

cni ,1

3131

Impact of kr models on Ai and Bi

rcmrcirc kfkfk ))(1()(

rgmrgirg kfkfk ))(1()(

nf1

*)()(

Kr (IFT) models are given by:

Where:

Three kr models:

• Miscible krcm and krgm

• Immiscible krci and krgi

• Mixtures in between, kr(IFT)

3232

Impact of kr models on Ai and Bi

zC1/zC4 = 75%/25%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80 100Liquid saturation (%)

kr

krc(IFT)krg(IFT)krcikrcgikrcm(IFT)krgm(IFT)

As the miscibility decreases in the fluid, liquid phase in the mixture needs to overcome greater critical condensate saturation to become mobile. The liquid mobility is also harmed as the phase interface becomes distinct.

3333

Impact of kr models on Ai and Bi

-0.00018

-0.00016

-0.00014

-0.00012

-0.0001

-0.00008

-0.00006

-0.00004

-0.00002

0

0 500 1000 1500 2000

Pressure (psi)

AC

4 (A

co

effi

cie

nt f

or

bu

tan

e c

om

po

ne

nt)

zC4 = 0.25, Kr(IFT)

zC4 = 0.25, Kri

zC4 = 0.25, Krm

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0 500 1000 1500 2000

Pressure (psi)

Coe

ff B

for

com

pone

nt C

4

zC4 = 0.25, Kr(IFT)

zC4 = 0.25, Kri

zC4 = 0.25, Krm

Impact of kr models on AC4 Impact of kr models on Bc4

Observations:

• Relative permeability has greater impact on term BC4 than on term AC4.• Miscible behavior tends to generate greater AC4 and BC4 values, while

immiscible fluid has lower AC4 and BC4 values.

3434

Impact of fluid type on Ai and Bi

0

500

1000

1500

2000

2500

-140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180

Temperature (°F)

Pre

ss

ure

(p

sia

)

2-Phase boundary for 20% C4 Critical for 20% C42-Phase boundary for 25% C4 2-Phase boundary for 25% C4Critical for 25% C4 2-Phase boundary for 15% C4Critical for 15% C4

T=60°F

15% C4

20% C4

25% C4

• The fluid with 15% butane is a lean gas-condensate system.• The fluid with 20% butane is near critical gas-condensate.• While the fluid with 25% butane is light oil.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 500 1000 1500 2000

Pressure (psia)

Liq

uid

Vo

lum

e, %

ori

gin

al v

ol.

15% C4

20% C4

25% C4

Liquid drop at T = 60 ºF

3535

Impact of fluid type on Ai and Bi

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0 500 1000 1500 2000

Pressure (psi)

BC

4 (B

co

effi

cie

nt f

or

bu

tan

e c

om

po

ne

nt)

zC4 = 0.15

zC4 = 0.25

zC4 = 0.20

-0.0006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

0

0 500 1000 1500 2000

Pressure (psi)

AC

4 (A

co

effi

cie

nt f

or

bu

tan

e c

om

po

ne

nt)

zC4 = 0.15

zC4 = 0.25

zC4 = 0.20

Impact of fluid type on AC4 Impact of fluid type on BC4

Observations:

• Fluid type has greater impact on term AC4 than on term BC4.• The difference on AC4 decreases as the fluid pressure increases. As the

fluid pressure approaches dew-point pressure, AC4 approaches zero.

3636

Impact of pressure on Ai and Bi

• Both AC4 and BC4 decrease as the pressure drops.• AC4 value is negative and relatively small.• AC4 approaches zero as pressure approaches dewpoint pressure.• BC4 is 100 times greater than AC4 in magnitude.

• BC4 is positive at higher pressure end, and negative on the lower pressure end.

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0 500 1000 1500 2000

Pressure (psi)

BC

4 (B

co

effi

cie

nt f

or

bu

tan

e c

om

po

ne

nt)

zC4 = 0.15

zC4 = 0.25

zC4 = 0.20

-0.0006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

0

0 500 1000 1500 2000

Pressure (psi)

AC

4 (A

co

effi

cie

nt f

or

bu

tan

e c

om

po

ne

nt)

zC4 = 0.15

zC4 = 0.25

zC4 = 0.20

04CB

04CB

3737

Theoretical analysis summary

2)(r

pB

t

pA

t

zii

i

0t

p

cni ,1

1. When , or pressure approaches dewpoint pressure:

2)(r

pB

t

zi

i

,0

t

zi

,0t

ziIf

If 0iB

0iB

0r

p

t

pA

t

zi

i

,0

t

zi

,0t

zi If

If 0t

p

0t

p

2. When , or :

Near well region

0iB

(analysis for (analysis for zzii of the heavy components) of the heavy components)

Regions away from the well

zi increases as pressure decreases

zi decreases as pressure decreases

zi increases during depletion

zi decreases with pressure support