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Gas and WAG Injection in the Varg

field – A Successful IOR Story

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‘Increased Oil Recovery from a Mature Oil Field by

Gas Injection’

B. Matre* (Repsol Norge as), J. Rasmussen (Repsol Norge as), K.

Hettervik (Orec) & D. Hongbua (University of Stavanger)

-18th EAGE European Synposium on Improved Oil Recvery. Dresden

Germany 14-16th of April 2015

-20th SPE Improved Oil Recovery Conference Tulsa Ok, USA 11-13th of

April 2016

Recycled Material

Based on presentations from 2015 and 2016:

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Outline

1. The Varg Field – A brief introduction

2. A-10 A- A-07 C Well pair •Water injection

•Gas injection

•IOR and possible mechanisms

•Gas re-production

3. A-01 B •Huff’n Puff

4. Conclusion

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Varg Field

Located 200 km West of Stavanger

First Oil 1998

16 slot WHP- Dry Trees

• Not normally manned platform

FPSO WI/GI/2 Separators/2 Flow lines

FPSO owned and operated by TK

Jurassic Sandstone, ‘Darcy sand’, but

also moderate reservoir quality

Light Oil, 35oAPI, undersaturated

Pb=180-220 bar

Stoiip > 300 mmstb; produced oil 102.9

mmstb. RF varies by segment; +60%-

25%

Multiple OWC 2845-3018 m TVD SS,

Multiple compartments, Faulted.

Significant events 2014

• Gas Export

• New Seismic

Talisman (Now Repsol) Operator from

2005

• Partners Petoro as and Det norske AS

(Aker BP)

CoP 2nd of June 2016

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Varg Production

• Production levels re-established as new segments are put on production

• Importance of Wag in late life

A-10 A

A-10 A WAG

Mainly South Seg

NW and W Seg

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Production Well Behaviour Varg

Fair reserves estimate from extrapolation

Rate vs. Cum Reserves slightly under-predicts

WOR vs Cum reserves slightly over-predicts

The two methods in combination gives a fair reserves estimate.

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A-10 A- A-07 C Well pair

Excellent reservoir properties and connectivity

between wells

Segment is not influenced by other active wells Large faults to the West, Different OWC in the North,

Reservoir pinches out to the East

3D view

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Implementation of WAG

Gas available from secondary gas cap and solution gas; gas production from A-08 A

Gas compressor available

Total Investment; About 1 MNOK to connect A-7 C to gas line

For every gas/water cycle need one to two shifts to alter A07 C to water/gas injection

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A-10 A Production Plot

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IOR Oil from A-10A

• Exponential decline may overestimate IOR oil

• WOR-method- Difficult to find baseline as wct is only 25%

• At least 2 mmbl IOR oil

• (Plot also shows importance of the injector.)

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WAG Saturation Development

1.12.2012

1.06.2012

Sgas

Swat

Soil

Simulation model:

Grid sizes: x15-25m, y ~25m, z 1-2m

Active grid cells ~120 000

Permeability 50-1000 mD

STOOIP in WAG area ~ 30 mill. bbl

• Oil recovered by gas/water, gas recovered

by water.

• Improved sweep is main recovery

mechanism for IOR

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Simulation Results from A-10 A - A-07C

Simulation of A-07C w/wo gas injection

IOR oil 2.6 mmbbl

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Gas Use and Production

11.9 bcf of gas injected

13.7 bcf of gas produced since start of

gas injection

But some of that gas would have been

produced during normal water injection

operation

Considering only ‘excess gas’ (gas at

GOR above solution GOR); 9.6 bcf is re-

produced (81%)

Adding the solution gas from the IOR oil

(2.6), 11.1 bcf (94%) is reproduced. =>

Net lost gas volume to IOR is low.

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IWAG IOR Mechanisms

Microscopic displacement

Lower Sorg than Sorw IOR appeared before reaching Sorw

Increased Kro (at given Saturation) Slow process, observation is rapid increase in production

Reduced krw with gas present Unlikely, parameter not very sensitive to history matching.

PVT Oil swelling for undersaturated oil

Possible, but history match do not show sensitivity to ‘turning off PVT’

Lower oil viscosity Possible, but history match don not show sensitivity to ‘turning off PVT’

Sweep Displacement of attic oil

Possible, but not a significant attic volume

Displacement of roof oil Possible

‘WAG ‘ mixing zone Possible

Better zonal displacement in ‘fining upwards sequences’ Possible

Production issues Better lift performance

Not likely : Deep gas lift installed production was not limited by lift performance in gas or

water cycles

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Gas Injection in A-01B

• Have drilled ~24 m MD of oil filled sand (~12

m TVD)

• Found water in the lower poorer quality part

of the well

• High porosity, indicating high permeability

(~500 md)

• Failed to cement well, i.e.no zonal isolation ,

acts like open hole

• Well came in with up to ~5000 boe/d, but

rapidly declined down to ~1500 boe /d and

then died due to lack of pressure support

combined with a WCT around 60%.

• Failed to establish pressure communication

to A-13 or any other injectors.

• What to do ?

15/12-A-1 B

Dra

up

ne

11

4R

Z1

7R

Z2

25

RZ

39

7

Tops

TO

PS

_R

ES

.TO

PS

GR/CAL

BEST.GR_1

GAPI0 150

best.ucav

IN0 10

Resistivity

BEST.HRD_1

OHMM0.2 2000

BEST.HRM_1

OHMM0.2 2000

Density/Neutron

BEST.ROBB_1

G/C31.95 2.95

BEST.DRHB_1

G/C3-0.25 0.25

BEST.TNPH_1

G/C30.45 -0.15

Volumetrics

BEST.VSH_1

V/V0 1

BEST.PHIE_1

V/V1 0

BEST.VOL_UWAT_1

V/V1 0

3850

3860

3870

3880

3890

3900

3910

3920

3930

3940

3950

3960

3970

Depth

DEPTHMETRES

2779

2780

2781

2782

2783

2784

2785

2786

2787

2788

2789

2790

2791

2792

2793

2794

2795

2796

2797

2798

2799

2800

2801

2802

2803

2804

2805

2806

2807

2808

2809

2810

2811

2812

2813

2814

2815

2816

2817

2818

2819

2820

2821

2822

2823

2824

2825

2826

2827

2828

2829

2830

2831

2832

2833

2834

2835

2836

2837

Depth

TVDSSMETRES

Porosity

BEST.PHIT_1

V/V0.5 0

BEST.PHIE_1

V/V0.5 0

Permeability

BEST.KLOG_1

MD0.2 2000

FM_PRESS.MOBILITY_1

MD/CP0.2 2000

Saturation

BEST.FTEMP_1

DEGC100 150

perf.perf

B/E0 20

BEST.SWE_1

V/V1 0

BE

ST

.PA

Y_

1

BE

ST

.SA

ND

_1

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Gas injection in A-01 B using the Gas Lift System

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Motivation for Gas Injection ?

Reduce krw selectively. • Gas will be dissolved faster back into

oil

Displace attic oil • Seismic indicates sand up-dip of A-01B

Deeper Gas Lift • GLV at 1770 m TVD, Perf at 2800 m

TVD

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Production Results after ‘Huff’n Puff’

1. Inject Gas ‘slugs’ of 1 MSm3 of gas, typically 1-2 weeks

2. Rest – to allow for segregation and displacing attic oil

3. Produce , initially gas, then oil

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Conclusions

Gas injection has significantly increased late life production and reserves for the Varg Field. 3

different methods have been used to estimate incremental oil from WAG, all showing

significant benefit.

The Varg Gas injection is an example showing that IOR can be very attractive economically

with short payback time, low additional investments and most of the injected gas re-produced.

The most important recovery mechanism for IOR by WAG in A-07 C – A-10 is improved

vertical sweep.

Operational flexibility is key for successful WAG. GOR and WOR have been managed by

adjusting WAG Cycle length to production responses.

Huff ‘n Puff with hydrocarbon gas has been implemented in well A-01 B and has to date

produced about 0.13 mmstb of incremental oil. Huff’n Puff has proven to be an innovative

method for getting some gas injection benefits without a gas injector.

Gas IOR can be economical even when competing with gas export.

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Acknowledgements

• We would like to thank the Varg Partners for permission to publish the paper.

Slide 21

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Thank you

© Compañía. Dirección que ha elaborado el documento. Fecha completa.

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Questions?

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Don’t Forget the Prize!!

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Varg Production 1.1.2012 –

Dominated by A-10 A and A-05 A

25

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A-10 A Scale issues

‘THE CHALLENGE OF SCALE CONTROL IN A LATE

LIFE HIGH SALINITY, HIGH TEMPERATURE FIELD’

Myles Jordan (Nalco Energy Services Ltd), Eyvind Sorhaug (Talisman

Energy Norge AS) and David Marlow (Nalco Energy Service AS).

Presented at 22nd International Oilfield Chemistry Symposium 18th-21st

of March2012

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Varg Map

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Oil field south of Sleipner Øst in the central part of the North Sea. The water depth in the area is 84 metres. The field has been developed with the production vessel, “Petrojarl Varg”, which has integrated oil storage connected to the wellhead facility Varg A. 1984: Discovered by Den norske stats oljeselskap (Statoil) 1996: PDO approved (Operator: Saga Petroleum)

1998: First Production 2001: 1st cessation plan approved 2005: Talisman operatorship 2010: Production License 038 extended to 2021

Varg Field Introduction

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A-10 A Production

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1.09.2011

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1.12.2011

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1.12.2011

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1.01.2012

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1.02.2012

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1.03.2012

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Varg PVT input

Rs=101.8

Rs=117.8

Rs=149.5

Rs=86.1

A-10A

P (@WAG) = ~ 250 bar

GOR 100 Sm3/Sm3

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A-07C and A-10A pressure

communication

Inn med trykk-kommunikajsonssplott, se A-10A welltest A-07/A-10 pressure communication

y = 0.3845x - 15499

163.3

163.4

163.5

163.6

163.7

163.8

163.9

164

164.1

164.2

164.3

05-Jul-11

12:00:00

06-Jul-11

00:00:00

06-Jul-11

12:00:00

07-Jul-11

00:00:00

07-Jul-11

12:00:00

08-Jul-11

00:00:00

08-Jul-11

12:00:00

date

Gau

gep

ressu

re A

-10A

, b

ar

A-07 put on injection 07.07.2011