Classification: Internal Status: Draft

A Microbial EOR Pilot in the Gullfaks Field

Rune Instefjord, Ole Tørnqvist and Petter Eltvik

2

Content

• Introduction to the Gullfaks field

• What is MEOR?

• Selection of pilot area

• Equipment

• Implementation of the pilot

• Results

• Conclusions

3

Key data for GF main field

• Discovered: 1978

• Start production: 1986

• STOOIP: 599 MSm³

• Base oil reserves: 358 MSm3

• Produced to date: 336 MSm3

• Daily production: 15 kSm3

• Average water cut: 84 %

• Expected recovery: 60 %

– Recovery pr. 2007: 56%

– Recovery of base res: 94%

• Initial pressure/temperature: 310-320 bar/

71 oC at 1850 m TVD MHN

• Bubble point pressure: ~200-240 bar at

1850 m TVD MHN

• GOR: ~ 100 Sm³/Sm³

• Oil viscosity: ~ 0.5 – 1 cp

4Reservoir Quality

• Reservoirs: Brent, Cook, Statfjord & Lunde

• Very faulted and eroded, with contrasting layers

• Dip up to 12 o in the western part.

• Weak formations

• Porosity (Brent): 30-35 %

• Permeability (Brent): 10 D – 10 mD

5

Drainage strategy

• Aquifer support

• Water injection

• Reservoir pressure over bubble point

• WAG

6

MEOR Principles – reservoir effects

• Cultivate bacteria which lives on the contact (pore scale) between water and oil near the injector.

• The bacteria reduces the surface tension between oil and water and thereby activates oil.

• Already done this process for many years, before start on nitrat injection. (which we have done

for many years due to souring). Drawback: H2S

BACTERIA + OIL + N + P + O2

MOBILISED RESIDUAL OIL ENHANCED SWEEP EFFICIENCY

RED

UC

ED

INTE

RFA

CIA

L

TENSIO

N

RED

UCED

WATER

PERM

EABILITY

7

What is needed for the MEOR pilot

• Nitrate (already injecting du to H2S control).

• Phosphate.

• Air (we remove oxygen from injected seawater due to corrosion of tubing.)

• Equipment :

– Storage tank.

– Chemical pump for nitrate/phosphate.

– Air compressor.

– Air storage.

– Pipes and valves.

Chemical-pump

8

Principle drawing

Water injection-manifold

Well A-41

05-KB01B

42-PF36

42-TB21A

WING

05-KB01A

Water injection-manifold

FE

117

FE

050A

FE

651

14-HV119

14-HV626

FE

050B

P

SUM

Air storage05-XV004 05-FV003

FIC

003

FE

003

PIT

005

PIT

015

Water injection

Chemical injection

Air injection

9

Selection of a good pilot candidate

• An area with steady-state conditions, as little as possible influence from other wells or areas. It is very important to know that the effects we are measuring

is from MEOR and not from ‘something else’.

• The injector should, with advantage, be in the oil zone.

• The distance between injector and producer should not be too long due to

throughput time. To get results in a reasonable time is important.

• The injector should be at a lower level than the producer. If not, the process

will not work.

• Good reservoir understanding.

• The producer(s) should be in steady-state conditions as regards to water cut.

10

G1

G2

G3

G4

G5

G6

H1

H2

H4

H5

H6A

I1

I2A

I2C

I3B

I4I5A

I5B

U1

H3

1

1800

14

1949

3

1949

41792

81936

9

1823

A-1H

1755

A-10

1782

A-11

1925

A-12

1919

A-12(F)

1921

A-12(F)

1965

A-13

1809

A-14

1833

A-15

1965

A-161922

A-16A(F)1945

A-171778

A-17AT21788

A-18(F)2009

A-19

1869

A-19A(F)

1844

A-19A

1830

A-19AT2(F)

1846

A-19AT3

1834

A-19AT3(F)

1844

A-2AH

1753

A-20(F)

1991

A-20A2017

A-221909

A-23

1976

A-24A

1983

A-26

1888

A-3H

1785

A-30(F)1904

A-31

1896

A-32

A-32B

A-33

1880

A-341752

A-34A1752

A-34A(F)

1787

A-34A(F)

1780

A-35

1813

A-36T31745

A-38

1833

A-38(F)

1840 A-39

1765

A-39A(F)

1760

A-39A(F)1765

A-39A

1764

A-39A1761

A-41

1808

A-41A1791

A-41B

1764

A-44T4

1829

A-46T2

1904

A-5H

1810

A-6A

1796

A-7A

1904

A-81875

B-1

2001

B-101773

B-10A1765

B-111822

B-12

2130

B-14A

1964

B-15

1972

B-17

1941

B-191793B-19A

1798

B-19T21799

B-2

1842

B-20

1908

B-211890

B-22(F)

2038

B-22A(F)

2025

B-23

1800

B-24

1886

B-25

1756

B-26

2087

B-271898

B-32001

B-301841

B-31

1790

B-31

1770

B-321795

B-321787

B-33

1838

B-34

1791B-34(F)1766

B-362008

B-36AT2

1993

B-37

1772

B-38

1758

B-41767B-4A(F)

1916

B-4A(F)1979

B-5

1810

B-6(F)

1939

B-7

1774

B-7(F)

1788

B-8

2040

B-9

1996

C-10

1968

C-111791

C-12

1773

C-151818

C-17

2188

C-19(F)2004

C-191971

C-22

1800

C-231938

C-23A

1883

C-251857

C-26

1817

C-27

1835

C-27(F)

1842

C-271860

C-281777

C-3

1817

C-30

1793C-30

1783

C-311986

C-32

1857

C-33

1855

C-35

1767

C-38

1923

1972

C-38(F)

1924

C-38T2

1927

C-5

1761

C-19

1897

A

B

C

0671

1780

1780

1780

1780

00

81

00

81

1800

0081

1820

1820

1820

18

2

0

02

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04

81

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1840

184

0

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81

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1

860

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91

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40

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1940

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1940

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960

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0 1960

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0 1 2 km

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34/10 Gullfaks

Vann- og Gassflømming i øvre NER

Topp Ness-1 dybdekart

Delvis vann- og gass-flømmet

Usikker vann- og gass-

flømming

Vannflømmet

Oljefylt

Gasskappe

Usikker vannflømming

Usikker

gassflømming

Delvis vannflømmet

Delvis gassflømmet

Prospekt

Oljeprodu

sentVanninjekt

orGassinjekt

orVAG

injektor

Syklisk

prod./gassinj.Mulig

injeksjonMulig

produksjonØOU

mål

A-10A

A-13A-44T4

A-34A

A-39A

A-14

A-11

A-41B

A-36

A-40

B-7A

B-39B

B-25A-12

A-35

PCRI24C.35

B-38

PCRI23

C.28

C.11PCRI35

PCRI37

C.22C.26AT2

IXRI25

PCRI52

C-23CT2

C-25T2

B-36AT2

B-10A

B-19A

B-11

B-24

B-8

PBRH53

PBRH54

PBRH31

PBRH45

PBEG61

PBEG52

C-10

B-14A

PARH13

GFA

I1

Pilot area

GFC

GFB

11

Lower Brent, segment I1:

• Segment I1 is isolated from the rest of lower Brent. May

be an insignificant communication to Cook fm.

• Most shallow part of the field: No OWC established.

• Good reservoir understanding.

• Producers have a stabile production trend over time.

• Well defined water cut in the observation wells.

Status:

– STOOIP=10,4 M Sm³

– 4,10 M Sm³ produced from lower Brent (per 1.12.05).

– Recovery factor of 40% (per 1.12.05), expected recovery factor of 59%.

– Producers: A-36, A-40 and B-39B

– Injector: A-41B

12

Success criteria for the MEOR pilot

• Increased oil recovery (estimated to 35000 Sm³ in A-36).

• Increased pressure drop in the injector A-41B (decreased injectivity)

• Reduced seawater fraction in the producers A-36 and A-40.

• The throughput time for water should be longer.

– Tracer injected before start-up of pilot, Jan-05, gave a throughput time of 5 months. (550m between A-41B and A-36)

• Reduced water cut (at least 5% decrease)

• Reduced H2S in the producer.

A-36

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000ja

n.02

apr.0

2ju

l.02

okt.0

2ja

n.03

apr.0

3ju

l.03

okt.0

3ja

n.04

apr.0

4ju

l.04

okt.0

4ja

n.05

apr.0

5ju

l.05

okt.0

5

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

oil rate month water cut

13

Pilot implementation

• Tracer injected 27.01.05 with a breakthrough time of

5 months. New tracer injected 01.06.06.

• MEOR injection started 05.12.05. Expected pilot

duration of 1 year.

• Design injection rate A-41B: 6000 Sm³/d.

• Status A-36, 01.12.05 :

– Liquid rate / oil rate: ca. 2400 Sm³/d / 100 Sm³/d

– Water cut: 95%

– GOR: 110 - 140 Sm³/Sm³

• Status A-40, 01.12.05 :

– Liquid rate / oil rate: ca. 700 Sm³/d / 130 Sm³/d, restricted by sand

– Water cut: : 80%

– GOR: 80 - 100 Sm³/Sm³

• No effect expected in B-39B.

14

A-41, Injection data during the pilot period

0

20

40

60

80

100

120

140

01.02.2005 05.06.2005 07.10.2005 08.02.2006 12.06.2006 14.10.2006

I, S

m3

/d/b

ar

0

1000

2000

3000

4000

5000

6000

7000

8000

Inj. r

ate

, S

m3

/d

• The injection rate has been constant between 5000 and 6000 Sm³/d.

• 97% regularities on the injector.

• >90% regularities on the air injection.

• Nitrat/fosfat solvent: 0,107 l/min (independent of rate)

• Air: 98 ltr/min (regulated due to rate).

• Prosper is used to estimate the injectivity of A-41B.

• Well head pressure used in calculations.

• The Injectivity index seems to be rather constant and in the same order of magnitude after the MEOR injection as before.

• The expected reduction in injectivity due to bacterial growth has not been observed.

Water inj rate

0

1000

2000

3000

4000

5000

6000

7000

sep.

03

des.

03

mar

.04

jun.

04

sep.

04

des.

04

mar

.05

jun.

05

sep.

05

des.

05

mar

.06

jun.

06

sep.

06

des.

06

Water inj rate

15

A-36, production data during the pilot period

• The production has been stable at around

100 Sm³/d during the year.

• The water cut has been stable at around 95-

97%.

• The well has rate dependent water cut. High

total rate gives lower water cut.

• The well was restricted by sand and amount

of H2S.

• The seawater fraction has been stable in the

lower edge of 1.

A-36

0

10

20

30

40

50

60

70

80

90

100

jul. 98 jul. 99 jul. 00 jul. 01 jul. 02 jul. 03 jul. 04 jul. 05 jul. 06 jul. 07

0

0.2

0.4

0.6

0.8

1

1.2

SO4 SW AMIOR Vannkutt

A-36

0

5000

10000

15000

20000

25000

des.0

1

mar.

02

jun.0

2

sep.0

2

des.0

2

mar.

03

jun.0

3

sep.0

3

des.0

3

mar.

04

jun.0

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sep.0

4

des.0

4

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05

jun.0

5

sep.0

5

des.0

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mar.

06

jun.0

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sep.0

6

des.0

6

mar.

07

Date

Sm

³/m

nth

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

oil/mnth Wct

16

A-36, production data during the pilot period

• The H2S has stabilised during the period, no

reduction, as expected, is observed.

• In the period from start of planning the pilot to

the implementation, the H2S increased

rapidly.

• This increase gave a new uncertainty to the

pilot. The bacterial growth had been higher

than we first assumed.

• Problems with continuous production from

the well due to high H2S and capacity

restrictions on the platform.

H2S

0

100

200

300

400

500

600

700

800

900

1000

24.07.1998 06.12.1999 19.04.2001 01.09.2002 14.01.2004 28.05.2005 10.10.2006 22.02.2008

A-36 Amiorinjeksjon starter A-40

A-36

0

5000

10000

15000

20000

25000

des.0

1

mar.

02

jun.0

2

sep.0

2

des.0

2

mar.

03

jun.0

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sep.0

3

des.0

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des.0

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jun.0

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sep.0

5

des.0

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jun.0

6

sep.0

6

des.0

6

mar.

07

Date

Sm

³/m

nth

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

oil/mnth Wct

17

A-40, production data during the pilot period

• The production has been stable at around

200 - 300 Sm³/d during the year.

• Restricted by sand production and closed

down in october-06.

• The water cut has been increasing from 75%

to 90% during the period. The well follows an

usual trend for lower Brent wells.

• The seawater fraction has increased from 70

to 80%, following earlier trend.

• The H2S amount has not been influenced of

the pilot. It is at a much lower level than in A-

36.

H2S

0

100

200

300

400

500

600

700

800

900

1000

24.07.1998 06.12.1999 19.04.2001 01.09.2002 14.01.2004 28.05.2005 10.10.2006 22.02.2008

A-36 Amiorinjeksjon starter A-40

A-40

0

5000

10000

15000

20000

25000

30000

35000

40000

des.0

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mar.

02

jun.0

2

sep.0

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des.0

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mar.

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jun.0

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sep.0

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jun.0

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sep.0

4

des.0

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mar.

05

jun.0

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sep.0

5

des.0

5

mar.

06

jun.0

6

sep.0

6

Date

Sm

³/m

nth

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

oil/mnth wct

18

Results

• No changes in behaviour around the injector A-41B.

• No reduction in either water cut or seawater fraction in the producers A-36 and A-40.

They behave at the same trend as before MEOR injection.

• The tracer injected in June-06 also had a breakthrough time of 5 months.

• Stabilised H2S in A-36 may be due to MEOR.

• The temperature in A-36 has decreased with around 10 degrees during the year,

which means that a lot of water has gone trough the reservoir.

• The oil rate in the producers has not been influenced by the MEOR process.

• No increased oil recovery from the MEOR pilot.

19

Conclusions

• No increased oil recovery from the MEOR pilot.

• Possible explanations:

– Existing bio-film in the injector might have affected the establishment of a new bio-

film needed for the aerobic process. A high level of H2S was present in the area

as a result of long time water flooding. This had possibly reduced oil saturation in the area prior to MEOR pilot due to an anaerobic MEOR process.

– Water flooding in general is very effective on Gullfaks. Due to extensive water flooding, the residual oil saturation could have reached a very low value.

– Due to Etive-Rannoch override effect, the contact between injection water

containing nutrients and oxygen and remaining oil, might have been limited

causing no MEOR effect. The decrease in temperature indicates that the water

only hits a small area.