9th European Gas Well DeliquificationConference & Exhibition

Hampshire Hotel – Plaza Groningen The Netherlands, September 22-24, 2014

Evaluating 10 years of Foam Assisted Lift

Kees Veeken and Gert de Vries

NAM-Shell – Assen

2

Contents

• Intro

• Scope

• Results

• Conclusions & Recommendations

3

NAM Onshore (excluding Groningen)

• Gas fields ~100

• Gas wells ~300

– Production ~20e6 Sm3/d (700 MMscf/d)

– Liquid loading ~150

• Foam assisted lift 2003+

• Review 10 years foam assisted lift (FAL)

– Batch foam ~1000 jobs in ~150 wells

– Continuous foam ~100 cap string years in ~30 wells plus trial only in ~20 wells

4

FAL Performance Review

• Establish success rate of batch and continuous foam

• Quantify reduction of critical rate achieved with foam

• Investigate dependency of foam performance on reservoir, well and foam application parameters

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Parameters

• Reservoir

– Water to gas ratio (WGR), condensate to gas ratio (CGR), condendate to water ratio (CGR/WGR), H2S content

• Well

– Tubing ID, liner ID & length, depth of foam injection relative to producing interval, deviation at injection point, corrosion inhibition

• Foam*

– Batch: frequency, volume

– Continuous: injection rate

* Foam chemical selection is not covered in this review

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Batch Foam Performance

• 45 wells, 939 jobs, average 47 days between jobs

– Bullheaded total 46.6 m3 foam resulting in total 236e6 Sm3 (8.3 Bscf) incremental gas production: 5.1e3 Sm3 (180 Mscf) per liter foam, 252e3 Sm3 (8900 Mscf) per batch job

– 103e6 Sm3 (3.6 Bscf) out of 236e6 Sm3 (8.3 Bscf) associated with kicking off shut-in wells producing formation water or receiving batch corrosion inhibitor or fresh water soak treatments

• No gains in 24 out of 45 wells (53%)

• If it works it works well!

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Batch Foam Success

GGT1-FR-31

74222

Nm3/d

KOL1-PR-1

19.243

BARG

KOL-100 Outlet KOL-100

15/11/2011 00:00:0018/10/2011 00:00:00 28.00 days

KOL-01

0

20000

30000

40000

50000

60000

70000

80000

1.E+05

0

10

15

20

25

30

35

40

50

Batch foam job enables kick-off after800 L corrosion inhibitor batch job every 2 weeks

hence safeguards ~75e3 Sm3/d (2600 Mscf/d)

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Continuous Foam Performance

• 32 wells, 96 cap string years

– Injected total 657 m3 foam resulting in total 808e6 Sm3 (28.5 Bscf) incremental gas production: 1.2e3 Sm3 (42 Mscf) per liter foam, 25e6 Sm3 (0.9 Bscf) gain per well, 8.4e6 Sm3 (0.3 Bscf) per foam-year

• No or insufficient gains in 14 out of 52 wells (27%)

– Most can be explained by non-foam related factors such as wells that were still producing stable or wells where inflow suffered from water breakthrough in the mean time

• Unexplained non-performance in 2 out of 52 wells (4%)

• It works well!

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Continuous Foam Success

Continuous foam safeguards ~230e3 Sm3/d (8100 Mscf/d)

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Reduction of Critical Rate

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Sta

ble

Ra

te w

ith

Fo

am

/ M

inim

um

Ra

te

No

Limit

Minimum-average-maximum = 30%-50%-70%

No Limit

Limit

0

5

10

15

20

25

30

35

40

45

50

1 10 100 1000 10000

Ga

in (e

6 S

m3

/yr)

Water-Gas Ratio (m3/e6Sm3)

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Water-Gas Ratio (Continuous Foam)

No clear trend i.e.No clear dependency on WGR

1 m3/e6Sm3 = 0.18 bbl/MMscf

0

5

10

15

20

25

30

35

40

45

50

0.1 1 10 100

Ga

in (e

6 S

m3/y

r)

Condensate-Gas Ratio (m3/e6Sm3)

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Condensate-Gas Ratio (Continuous Foam)

No clear trend i.e.No clear dependency on CGR

1 m3/e6Sm3 = 0.18 bbl/MMscf

0

5

10

15

20

25

30

35

40

45

50

0.001 0.010 0.100 1.000 10.000

Ga

in (e

6 S

m3/y

r)

CGR/WGR=CWR (-)

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Condensate-Water Ratio (Continuous Foam)

No clear CWR limitFoam effective at least up to CWR=1

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6 7 8

Ga

in (e

6 S

m3

/yr)

Tubing ID (in.)

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Tubing Size (Continuous Foam)

Larger gain for larger IDdue to larger capacity!

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140

Ga

in (e

6 S

m3/y

r)

LinerLength*(LinerID-TubingID)/TubingID (m)

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Liner Geometry (Continuous Foam)

Long large liners do not limit foam application

0

5

10

15

20

25

30

35

40

45

50

-20% 0% 20% 40% 60% 80% 100% 120%

Ga

in (e

6 S

m3/y

r)

Foam Injection Position Relative to Perforations

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Capillary String Injection Point

0% = Top, 100% = BottomDefault injection at top is OK

N.B. intervals are typically 100 m TV

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Ga

in (e

6 S

m3

/yr)

Deviation at Injection Point (deg)

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Wellbore Deviation @ Injection Point

Well deviation does not limit foam application

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Batch Foam Frequency

• Maximum 1x per week, average 1x per 7 weeks

• Assuming each foam batch lifts all liquid, optimum frequency depends on liquid produced (Q*WGR), tubing size (ID) and drawdown (DD) as following

– F ~ Q*WGR/(ID2*DD)

• Calculated optimum frequency is usually more than 1x per week, hence increase frequency as far as practical

– 3x per week is maximum frequency before continuous foam becomes more cost effective

0

100

200

300

400

500

600

700

800

0 50 100 150

Mo

nth

ly G

as

Pro

du

ctio

n (

e3

Sm

3)

Monthly Foam Consumption (L)

Gain proportional to25 L batch foam frequency

(1x-5x per month)

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Batch Foam Volume

• Minimum 25 L, average 50 L, maximum 100 L

• Assuming foam volume represents 1% of liquid volume in wellbore, optimum volume depends on tubing size (ID) and drawdown (DD) as following

– V ~ ID2*DD

• Calculated optimum volume varies between 1 and 100 L, hence reduce as far as practical

– However, more foam may be required, see below

• Success rate 53%

– Due to inefficient mixing and agitation, and due to liquid stored near-wellbore that rushes into wellbore during kick-off

• Apply rocking and/or gurgling

• Apply multiple, larger and/or more frequent batches

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Batch & Continuous Foam Success

Theory: batch period 5 days, batch volume 1 LActual: batch period 7 days, batch volume 50 L

Gas R

ate

(e3 S

m3/d

), F

oam

Volu

me (

L),

Foam

Rate

(L/d

)

FT

HP, F

BH

P (

bar)

0

50

100

150

200

0 10 20 30 40 50 60 70

Ga

s R

ate

(e

3 S

m3

/d)

Foam Injection Rate (L/d)

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Foam Concentration

50 L/d = 20,000 ppm

0

50

100

150

200

250

0 50 100 150 200 250

Ga

s R

ate

(e

3 S

m3/d

)

Foam Injection Rate (L/d)

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Foam Concentration

100 L/d = 650 ppm

0

5

10

15

20

25

30

35

40

45

50

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000

Ga

in (e

6 S

m3

/yr)

Foam Concentration (ppm)

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Foam Concentration

Best results achieved below 1000 ppm

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Continuous Foam Injection Rate

• Field data indicates that foam injection rate is often (much) too high, confirmed by observation that batch foam generates 4x as much gas per liter than continuous foam: 5.1e3 Sm3 (180 Mscf) Vs 1.2e3 Sm3 (42 Mscf)

• Reduce foam injection rate as far as practical

– Optimum foam injection rate will increase as gas rate decreases further below critical rate

• Success rate 73%

– Most failures are not directly related to foam, success rate of 3 out of 4 may be as good as it gets!

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Conclusions & Recommendations [1]

• Reservoir parameters

– High WGR (up to 2000 m3/e6Sm3), high CGR (up to 100 m3/e6Sm3), high CWR (up to 1) and H2S (up to 4000 ppm) do not rule out foam

• Well parameters

– Larger tubing ID increases gains, related to larger capacity

– Long large liner, deviation (up to 60 deg) and corrosion inhibition do not rule out foam

– No reason exists to inject below top reservoir (up to 100 m TV interval)

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Conclusions & Recommendations [2]

• Batch foam

– Frequency has been too low and should be increased

– Volume has been too high and could be decreased

– Economic alternative to continuous foam (up to 3x per week)

– Success rate has been modest (53%) and could be increased by rocking or gurgling to promote mixing and agitation

• Continuous foam

– Actually observed reduction of critical rate supports use of 30%-50%-70% reduction for candidate screening

– Injection rates have been too high (up to 10x) and should be decreased

– Success rate has been reasonable (73%), no significant increase is expected from changing foam parameters