Classification: Internal Status: Draft

WAG Mechanisms at macroscopic/ field level

Presentation at FORCE WAG Seminar Stavanger, 18 Mar 2009

Anders GjesdalLeading Advisor Drainage Strategy, StatoilHydro

2

Outline

• Introduction

• Sweep

• WAG in well pairs

• WAG at field level

• Concluding remarks

3

IntroductionTo make WAG work at all levels• Levels

– Microscopic core level

– Macroscopic at well pair level

– Macroscopic in the reservoir

– Macroscopic at the field level

– (Macroscopic at area level )

• WAG mechanisms has to function at all levels to be successful

• Gas management – constraints

• WAG development - Producers and Injectors

• Injection planning and prioritisation

• Surveillance

C-18 A

C-32 A

C-22

A-13 A

9-9

A-16 AT2A-2

C-11

C-11 A

C-13

C-23 B

C-31C-31

C-33

C-34C-39

C-40

C-41

C-41 T2

C-42 A

C-7

C-8

C-42 A

9-3

A-11

A-6 AT2

C-12

C-25 T2

C-35

C-42

C-9

C-30 A

C-15

C-16

C-17

C-20

C-21

C-23

C-23 A

C-23 T2C-26

C-28C-32 C-36

C-38

C-30 A

C-19 BT2

C-40 AT2

C-1 B

06

32

2 3 6 0

23

70

2

3 7 0

23

7

0

23

80

23

80

23

80

23

90

23

90

23

90

24

00

24

10

41

0

24

20

24

20

24

30

24

30

24

40

24

50

24

60

2

24

702

48

0

24

90

25

00

21

0

25

20

0

0

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2

23

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2 3

70

2 37

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2 3 8 0

2 3

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90

2 3 9 0

23 9 0

2 40 0

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2 41 0

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2 4 2 0

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2 4 8 0

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90

02

25

00

5

25

20

East flank potential (attic oil)

Main Field Potential Microscopic: Reduction in SorMacroscopic: Roof and attic oil

Attic oil

4

Introduction – Key is Sweep

•

• Gas displacement often gives a better microscopic sweep compared to water. Sorg is often lower than Sorw , particularly at miscible conditions

• Fraction of the reservoir volume contacted by gas limits the impact of improved microscopic sweep.

With good reservoir quality and long well distance often found offshore Norway this is often the case.

• At field level focus is turned towards increasing the volumetric sweep

– Key factors influencing volumetric sweep.

• Gravity

• Mobility ratio

• Heterogeneity of the reservoir

• Reservoir thickness and vertical communication kv/kh

• Geometry, Structure, top perforations, spill points

• Available gas

• Available gas capacities

• Injection schedule and rates

• Number of producers and injectors – Well location and distance

cMicroscopiVolumetric EEEfficiencySweep _

Man

agea

ble

5

Effect of kv/kh, effect of horizontal restrictions

• Typically we anticipate that only 10-20% of the reservoir is gas contacted between well pairs

• Horizontal barriers tends to increase sweep

• At kv/kh 0.01 we see that the gas contacted volume increases noticeably

• The limited gas sweep makes sweep of the attics and geometry very important for the WAG mechanism

6

WAG mechanisms in well pair

• Attic Volumes andUpper part of stratigraphy

• Gas lift

– Free gas back-produced provides additional well hydraulic potential.

• Voidage

– Gas contributes to pressure maintenance, but voidage replacement is often reduced in gas injection periods

• Lower part of stratigraphy (up-dip wag)

• Pattern injection to increase sweep (not applied offshore Norway)

Roof oil

WAG

OP

Gasmovement

"WAG Attic oil"

Tarbert Fm.

WAG - Water Alternating Gas Injection

7

WAG at a reservoir or field level

• How can we get the most out of our WAG kit?

• Maximise injection effectiveness.

• Move the WAG kit around to new areas or flooding units?

• Keep the kit active

– Avoid excessive gas re-cycling, capacity utilization.

– Ensure back-production of gas, avoid “stranded” gas. (Ensure injection and producer timing)

• When to move?: Re-cycling ratios are a good indication on the gas (and water) injection efficiency

8

Multidisciplinary WAG Surveillance Team

Evaluate: 

• Optimizing of the gas utilization

• The effectiveness of the WAG process

•  Interpretation of the field performance

•  Tracer injection, planning and evaluation

•  Data acquisition, planning and evaluation

C-PlatformWAG

Surveillance Team

A-Platform

B-Platform

Reservoir Management Team

9

WAG response in B-5

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

jan.

97

mai

.97

sep.

97

jan.

98

mai

.98

sep.

98

jan.

99

mai

.99

sep.

99

jan.

00

mai

.00

sep.

00

jan.

01

mai

.01

sep.

01

jan.

02

mai

.02

sep.

02

jan.

03

mai

.03

sep.

03

jan.

04

mai

.04

sep.

04

jan.

05

WA

G in

cr. o

il (S

m3/

cd)

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

Cum

. oil

(mill.

Sm

3) /

Gas

inj.

(mill.

Sm

3/cd

)Effect of 3 WAG cycle Effect of 2 WAG cycle

Effect of 1 WAG cycle Gas Injected MSm3/d

C-5 Decline

0

10

20

30

40

50

60

70

80

90

100

Cumulative oil production Sm3

0

1 000

2 000

3 000

4 000

5 000

Oil rate (S

m³/d

)

oil rate

Operasjoner

wct

Stengte nederste del av L11 samt L12 i horsten i mai 03

K-3 H gass 22.09.03

K-6 H gass 23.01.04

K-3 H gass 07.06.04

Begge på gass 27.07.04

C-18 A

C-32 A

C-22

A-13 A

9-9

A-16 AT2A-2

C-11

C-11 A

C-13

C-23 B

C-31C-31

C-33

C-34C-39

C-40

C-41

C-41 T2

C-42 A

C-7

C-8

C-42 A

9-3

A-11

A-6 AT2

C-12

C-25 T2

C-35

C-42

C-9

C-30 A

C-15

C-16

C-17

C-20

C-21

C-23

C-23 A

C-23 T2C-26

C-28C-32 C-36

C-38

C-30 A

C-19 BT2

C-40 AT2

C-1 B

06

32

2 3 6 0

23

70

2

3 7 0

23

7

0

23

80

23

80

23

80

23

90

23

90

23

90

24

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410

24

20

24

20

24

30

24

30

24

40

24

50

24

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2

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702

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25

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20

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2 3

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2 40 0

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2 41 0

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2 4 3 0

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2 4 4

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05

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2 4

60

24

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2 4 8 0

08

42

09

42

24

90

02

25

00

5

25

20

East flank potential (attic oil)

Main Field Potential Microscopic: Reduction in SorMacroscopic: Roof and attic oil

Attic oil

0

100

200

300

400

500

600

700

800

900

1 000

jan

.98

ap

r.9

8

jul.9

8

okt

.98

jan

.99

ap

r.9

9

jul.9

9

okt

.99

jan

.00

ap

r.0

0

jul.0

0

okt

.00

jan

.01

ap

r.0

1

jul.0

1

okt

.01

jan

.02

ap

r.0

2

jul.0

2

okt

.02

jan

.03

ap

r.0

3

jul.0

3

okt

.03

jan

.04

ap

r.0

4

jul.0

4

okt

.04

0

10

20

30

40

50

60

70

80

90

100

Oil Rate Sm3/d Water flooded oil rate Sm3/d Incremental Oil Rate Sm3/ d

WHP BAR Water Cut % GOR

WAG response:

•Increasing WHP

•Increasing oil rate

•Increasing GOR

•Decreasing WCT

4D Seismic

Saturation logs

Observe well performance

Tracers

Estimate incremental reserves

Monitor gas injection efficiency

Monitoring each WAG injector and associated producers

10

1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12A-1

A-19 N/T N/T N/TA-14 A R R R R R R R RA-42 A R R R R RA-36 A

B-9

B-25

B-30 A N/T N/T N/T N/T N/T N/T N/T N/T B-5

B-14 C EF EF EF EF EF EF EF EF EF EF EF EFB-4 A

B-26 A R R R R R R R RB-18 A EF EF EF EF EF EF EF EF EF EF EF EF EF

C-9 T/N T/N T/N T/N T/NC-35

C-10 A T T T T TC-1 B

C-30 A

C-4 B EF EF EF EF EF EF EF EF EF EF EF EF EF EFC-2 T/N T/N T/N T/N T/N T/N T/N T/N T/N T/N T/N

2006 2007

433,000 434,000 435,000 436,000 437 ,000 438,000 439,000 440,000 441,000 442,000 443,000 444 ,000

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B-1

B-10

B-11B-14

B-15

B-2 AT2B-2 T3

B-2 T5X

B-22

B-23

B-25

B-26

B-30

B-35

B-4

B-40

B-41

B-42B-42

B-5

B-9

9-1

9-3

9-4

9-9

A-1

A-11

A-14

A-15

A-19

A-22

A-23 A

A-25

A-26

A-30 A-31

A-32

A-35A-35 AA-35 AT2

A-36

A-4

A-6

A-6 AT2

A-9

C-1

C-12

C-14

C-19

C -25 T2

C-30

C-35

C -37 T2

C-4

C-42

C -9

24-1

24-4

C-5

B-36

C -30 A

A-14 A

B-6 B

12-1

12-2

12-5

B-10 A

B-12 T2

B-13

B-14 A

B-16B-16 AB-16 AT2

B-16 BB-16 BT2

B-17

B-18

B-19

B-2 B

B-2 B

B-2 B

B-2 BT2

B-20 B-21

B-22 A

B-23 A

B-23 A

B-23 AT2

B-23 AT2

B-24

B-24 A

B-27 T2

B-28

B-28 A

B-28 B

B-28 C

B-29 T2

B-3

B-31

B-32B-33

B-33B-33

B-33

B-34

B-35 A

B-36

B-36

B-39

B-39 AB-39 BB-39 BT2

B-41 A

B-6B-6 AB-7

B-8

9-9

A-10

A-11 AA-11 BA-12

A-13

A-15 A

A-16

A-16 AT2

A-17

A-18

A-2A-2 A

A-20 AA-23

A-24A-25 AA-25 T2A-25 T3

A-27 A

A-29

A-3A-3 A

A-31 A

A-32 A

A-33

A-34

A-34 AA-34 AT3

A-37

A-37 A

A-38A-38 A

A-39

A-40 AA-40 AT2A-40 AT3

A-41

A-41 AA-41 AT2 A-41 AT2

A-42

A-7 A-8A-8 A

A-8 B

C -1 A

C-11

C -11 A

C -12 A

C-12 B T2

C-13

C -23 B

C-31

C-33

C-34C-39

C-39

C-39

C-40

C-41C -41 T3

C -41 T3

C -42 A

C -5 AC -4 A

C-6

C-7

C-8

12-5

12-4

B-35A

B-1 A

B-1 B

B-6 B

B-11 AB-12 T2

B-37

B-38 A

A-7 A

A-11 AT2A-11 AT3

A-13 A

A-15 BA-17 A

A-18 A

A-20

A-22 A T2

A-26 A

A-27 B

A-28

A-40

C -1 B

C-10 A

C-10

C-15

C-16C-17C -17

C-18

C -18 T4 C-19 A T2

C -18 A

C -19 B

C-20

C-21

C-22

C -23 A

C -23 T2C-26C -26 A

C-28

C -29 T4

C-32

C -32 A

C-36

C -37 A

C-38

C -40 A

C -42 AC -42 A

C -42 A

C-42 A

C-42 A

B-19 AB-19 AT2

B-21 B

A-15 AA-15 A

A-42 A

A-8 C

A-7 B

A-23 B

B-11 B

B-2 C

B-36 A

A-40 B

A-7 C

A-31 AT2

A-31 AT2

A-31 AT2

A-27

A-27

A-13 B

A-30 AT2A-36 A

A-37 B

B-3 A

B-4 A

B-15 A

B-40 BB-40 C

B-14 B

B-14 C

C -19 C

C -27 A

C -34 A

C -38 A

C -40 B

C -11 B

C-15 AT2C-19 B T2

C-40 A T2

433,000 434,000 435,000 436,000 437 ,000 438,000 439,000 440,000 441,000 442,000 443,000 444 ,000

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K ILOM ETER S0 1 2 KILOM ETERSTop Reservoir Depth Structure M ap

Statfjord F ie ld

C-9

A-19

C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2A-1

A-36 A

B-9

B-25

B-30A

C-35

B-2B

B-11A

B-22A

B-32

B-6B

B-10A B-31

C-6

C-24

C-10A

Active WAG injector

Future WAG injector

Upper BrentReservoir

C-2

B-5 ?

A-28

A-37BA-20A

A-22A

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B-1

B-10

B-11B-14

B-15

B-2 AT2B-2 T3

B-2 T5X

B-22

B-23

B-25

B-26

B-30

B-35

B-4

B-40

B-41

B-42B-42

B-5

B-9

9-1

9-3

9-4

9-9

A-1

A-11

A-14

A-15

A-19

A-22

A-23 A

A-25

A-26

A-30 A-31

A-32

A-35A-35 AA-35 AT2

A-36

A-4

A-6

A-6 AT2

A-9

C-1

C-12

C-14

C-19

C -25 T2

C-30

C-35

C -37 T2

C-4

C-42

C -9

24-1

24-4

C-5

B-36

C -30 A

A-14 A

B-6 B

12-1

12-2

12-5

B-10 A

B-12 T2

B-13

B-14 A

B-16B-16 AB-16 AT2

B-16 BB-16 BT2

B-17

B-18

B-19

B-2 B

B-2 B

B-2 B

B-2 BT2

B-20 B-21

B-22 A

B-23 A

B-23 A

B-23 AT2

B-23 AT2

B-24

B-24 A

B-27 T2

B-28

B-28 A

B-28 B

B-28 C

B-29 T2

B-3

B-31

B-32B-33

B-33B-33

B-33

B-34

B-35 A

B-36

B-36

B-39

B-39 AB-39 BB-39 BT2

B-41 A

B-6B-6 AB-7

B-8

9-9

A-10

A-11 AA-11 BA-12

A-13

A-15 A

A-16

A-16 AT2

A-17

A-18

A-2A-2 A

A-20 AA-23

A-24A-25 AA-25 T2A-25 T3

A-27 A

A-29

A-3A-3 A

A-31 A

A-32 A

A-33

A-34

A-34 AA-34 AT3

A-37

A-37 A

A-38A-38 A

A-39

A-40 AA-40 AT2A-40 AT3

A-41

A-41 AA-41 AT2 A-41 AT2

A-42

A-7 A-8A-8 A

A-8 B

C -1 A

C-11

C -11 A

C -12 A

C-12 B T2

C-13

C -23 B

C-31

C-33

C-34C-39

C-39

C-39

C-40

C-41C -41 T3

C -41 T3

C -42 A

C -5 AC -4 A

C-6

C-7

C-8

12-5

12-4

B-35A

B-1 A

B-1 B

B-6 B

B-11 AB-12 T2

B-37

B-38 A

A-7 A

A-11 AT2A-11 AT3

A-13 A

A-15 BA-17 A

A-18 A

A-20

A-22 A T2

A-26 A

A-27 B

A-28

A-40

C -1 B

C-10 A

C-10

C-15

C-16C-17C -17

C-18

C -18 T4 C-19 A T2

C -18 A

C -19 B

C-20

C-21

C-22

C -23 A

C -23 T2C-26C -26 A

C-28

C -29 T4

C-32

C -32 A

C-36

C -37 A

C-38

C -40 A

C -42 AC -42 A

C -42 A

C-42 A

C-42 A

B-19 AB-19 AT2

B-21 B

A-15 AA-15 A

A-42 A

A-8 C

A-7 B

A-23 B

B-11 B

B-2 C

B-36 A

A-40 B

A-7 C

A-31 AT2

A-31 AT2

A-31 AT2

A-27

A-27

A-13 B

A-30 AT2A-36 A

A-37 B

B-3 A

B-4 A

B-15 A

B-40 BB-40 C

B-14 B

B-14 C

C -19 C

C -27 A

C -34 A

C -38 A

C -40 B

C -11 B

C-15 AT2C-19 B T2

C-40 A T2

433,000 434,000 435,000 436,000 437 ,000 438,000 439,000 440,000 441,000 442,000 443,000 444 ,000

6,8

01

,00

06

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6,7

99

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06

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6,7

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06

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6,0

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6,7

95

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06

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4,0

00

6,7

93

,00

06

,79

2,0

00

6,7

91

,00

06

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0,0

00

6,7

89

,00

06

,78

8,0

00

6,7

87

,00

06

,78

6,0

00

6,7

85

,00

06

,78

4,0

00

444 ,000443,000442,000441,000440,000439,000438,000437 ,000436,000435,000434,000433,000

6,7

84

,00

06

,78

5,0

00

6,7

86

,00

06

,78

7,0

00

6,7

88

,00

06

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00

6,7

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06

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6,7

92

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06

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3,0

00

6,7

94

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06

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6,7

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6,7

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433,000 434,000 435,000 436,000 437 ,000 438,000 439,000 440,000 441,000 442,000 443,000 444 ,000

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06

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06

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06

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06

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06

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06

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06

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K ILOM ETER S0 1 2 KILOM ETERSTop Reservoir Depth Structure M ap

Statfjord F ie ld

C-9

A-19

C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

C-26C-26

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

C-39

C-27 A

C-26 A

C-16

C-31

C-36

A-15 B

A-6 AT2

A-15 B

A-6 AT2A-1

A-36 A

B-9

B-25

B-30A

C-35

B-2B

B-11A

B-22A

B-32

B-6B

B-10A B-31

B-2B

B-11A

B-22A

B-32

B-6B

B-10A B-31

C-6

C-24

C-6

C-24

C-10A

Active WAG injector

Future WAG injector

Upper BrentReservoir

C-2

B-5 ?

A-28

A-37BA-20A

A-22A

A-28

A-37BA-20A

A-22A

0

200

400

600

800

1000

1200

1400

1600

C-2

C-9

C-1

0 A

C-3

5

A-1

9

A-1

B-9

B-2

5

C-1

B

C-4

B

C-3

0 A

A-4

2 A

A-3

6 A

A-1

4 A

B-5

B-2

6 A

B-4

A

B-3

0 A

B-1

8 A

B-1

4 C

Ga

s v

olu

me

(m

ill. S

m3

)

GC #3

GC #2

GC #1

C-18 A

C-32 A

C-22

A-13 A

9-9

A-16 AT2A-2

C-11

C-11 A

C-13

C-23 B

C-31C-31

C-33

C-34C-39

C-40

C-41

C-41 T2

C-42 A

C-7

C-8

C-42 A

9-3

A-11

A-6 AT2

C-12

C-25 T2

C-35

C-42

C-9

C-30 A

C-15

C-16

C-17

C-20

C-21

C-23

C-23 A

C-23 T2C-26

C-28C-32 C-36

C-38

C-30 A

C-19 BT2

C-40 AT2

C-1 B

06

32

2 3 6 0

23

70

2

3 7 0

23

7

0

23

80

23

80

23

80

23

90

23

90

23

90

24

00

24

10

41

0

24

20

24

20

24

30

24

30

24

40

24

50

24

60

2

24

702

48

0

24

90

25

00

21

0

25

20

0

0

063

2

23

70

2 3

70

2 37

0

2 3 8 0

2 3

80

90

2 3 9 0

23 9 0

2 40 0

00

42

2 41 0

01

42

2 4 2 0

24

20

0 24

2

0242

24

30

243 0

2 4 3 0

40

2 4 4

0

24

40

24

50

05

42

05

42

2 4

60

24

70

2 4 8 0

08

42

09

42

24

90

02

25

00

5

25

20

East flank potential (attic oil)

Main Field Potential Microscopic: Reduction in SorMacroscopic: Roof and attic oil

Attic oil

Identify and map potential WAG oil Identify injection points and associated producers

Plan and prioritize gas injectionMonitor gas injection efficiency

Prognosis for back-production

Monitoring at field level

Gas Injection vs. Backproduction

0

1

2

3

4

5

6

7

8

9

10

jan

.97

jul.9

7

jan

.98

jul.9

8

jan

.99

jul.9

9

jan

.00

jul.0

0

jan

.01

jul.0

1

jan

.02

jul.0

2

jan

.03

jul.0

3

jan

.04

jul.0

4

jan

.05

jul.0

5

jan

.06

Ga

s R

ate

- M

Sm

3/c

d

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Cu

m. G

as

Vo

lum

es

- G

Sm

3

Injected Gas Rate

Cum. Injected Gas

Cum. Backproduced Gas

Backproduced Gas Rate

11

Typical WAG behaviour

• Volumetric gas sweep often low.

• Gas breakthrough varies from a few months to 1-2 years.

• Slug size varies from 200 MSm3 to 1-2 GSm3

• Typical gain is 1 Sm³ of oil per 500-1500 Sm³ of gas injected

• Typical back-production of gas is 40-65%

• Higher retained gas typically yields more incremental oil

• When attics have been filled, re-cycling rate increases and gas injection efficiently drops.

• Gas moves significantly faster than water

12

Concluding remarks

• WAG has successfully contributed with substantial IOR volumes

• Drainage of attics is the most important and most efficient mechanism

• Try to identify attics: Use 4D seismic processing and detailed geological studies to target extra oil recovery

• Move the WAG into new areas

• Re-cycling ratios are a good indication on the gas (and water) injection efficiency

• Availability of WAG injectors important to ensure gas is injected where it gives the highest efficiency

• Gas tracer velocity can give information on gas storage, reservoir communication

• 4D seismic gives important information on gas movement

• Gas movement and the corresponding incremental oil seem to depend on:

– Structural complexity and geometry

– Formation – vertical communication

– Production well coverage

– Distance between WAG injector and production wells

• Each WAG injector has its own characteristics in terms of response time and behaviour of WAG producers

• KEY to success is: Surveillance and good planning