Further Development of Skua, a Mature Triassic HPHT Field ... S… · • Skua is a mature HPHT oil field in the Central North Sea whose one d evelopment well was characterised by

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Further Development of Skua, a Mature Triassic HPHT Field in the Central North Sea

Presenter:

Fiona Fairhurst

Production Geologist, Shell UK Ltd.

Co-Authors:

Tom McKie, Sedimentologist

Louis Sturgess, Geophysicist

Acknowledgments:

Thanks to ExxonMobil, our field partner, for giving permission to present at Devex.


ETAP Fields

M IRREN

1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E 57 o 30’N

57 o 20’N

57 o 10’N

57 o 00’N 1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E

30’N

20’N

10’N

00’N

ETAP Satellites

Other Discoveries

FIDDICH

0 10 km

Oil Pipeline

Gas Pipeline

M ADOES

ETAP Fields

Other F ields

W OOD

M ontrose

Arbroath

Arkwright

M onan M ungo

Lom ond

M erganser Gannet A

Gannet D

Selkirk

Turnstone

Seagull

Egret

Heron Scoter

Erskine

Shearwater

Elgin Banff

Gannet G

M achar

Skua

Phyllis

M illburn

M arnock M IRREN

1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E 57 o 30’N

57 o 20’N

57 o 10’N

57 o 00’N 1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E

30’N

20’N

10’N

00’N

ETAP Satellites

Other Discoveries

FIDDICH

0 10 km

Oil Pipeline

Gas Pipeline

M ADOES

ETAP Fields

Other F ields

W OOD

M ontrose

Arbroath

Arkwright

M onan M ungo

Lom ond

M erganser Gannet A

Gannet D

Selkirk

Turnstone

Seagull

Egret

Heron Scoter

Erskine

Shearwater

Elgin Banff

Gannet G

M achar

Skua

Phyllis

M illburn

M arnock M IRREN

1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E 1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E 57 o 30’N

57 o 20’N

57 o 10’N

57 o 00’N

57 o 30’N

57 o 20’N

57 o 10’N

57 o 00’N 1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E 1 o 00’E 1 o 24’E 1 o 48’E 2 o 12’E

30’N

20’N

10’N

00’N

30’N

20’N

10’N

00’N

ETAP Satellites

Other Discoveries

FIDDICH

0 10 km

0 10 km

Oil Pipeline

Gas Pipeline

M adoes

ETAP Fields

Other F ields

W OOD

M ontrose

Arbroath

Arkwright

M onan M ungo

Lom ond

M erganser Gannet A

Gannet D

Selkirk

Turnstone

Seagull

Egret

Heron Scoter

Erskine

Shearwater

Elgin Banff

Gannet G

M achar

Skua

Phyllis

M illburn

M arnock


Heron Cluster Sub-Sea Infrastructure


Cluster Summary

• Cluster has produced ~100MMbbl of light oil since 1998

• Triassic Skagerrak reservoirs, depths up to 15,000ft.

• High Pressure High Temperature Fields (12350psi, 350ºF).

• Oil production is declining – depletion drive mechanism.

• Potential scope to drill and increase recovery?


Outline

• Regional Geological Picture

• Skua Field

• Development History

• Opportunities

• Uncertainties

• Ongoing work

• Concluding Remarks


Stratigraphy

The Triassic Skagerrak Fm is equivalent to the Judy Sandstone Mbr.

1000ft


Regional Geology - The Skagerrak Reservoir over ETAP

PlayaPalustrine SplayFluvial

γ ∆ tN/D

Playa

Palustrine

Term inal splay

Fluvial

Lacustrine

22/29-1S1

Upper Lower

50km0.5km

Neales River and Terminal Fan, Lake Eyre, Australia


Structural FrameworkLine of section

EW


Lark shales, Sele, Balder and Forties

Smith Bank Shale

Basement (Permian)

ChalkJurassic

E

BCUBCU

Top Marnock Shale

Top Marnock Shale

Skaggerak Sands10-14º dip

W

Structural FrameworkLine of section

Zechstein Salt


Skua Field

OWC @ 12075ft (RFT data)

Blocks: All & Subcycles: All

0

5,000

10,000

15,000

20,000

25,000

Jan-0

2

Jan-0

3

Jan-0

4

Jan-0

5

Jan-0

6

Jan-0

7

Rate

s (plb

l/cd) C

um (bl*

E3)

Oil Rate Water Rate BSW (frac) Cum Oil Cum Wat Cum Gross

Jan-0

8

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

BSW (frac)

SKUAS01S1 Oil & Water Production Profiles

SKS01S1B-7

B-9

1km

• SKS01S1 came on at ~16000bbl/d• Initial reservoir pressure of 9350psi.• Rapid pressure decline to ~5500psi in mid 2003.• By mid 2004 became sub hydrostatic.• Post 2004 well intervention, 4350psi recorded at wellhead & high (~50%) highly saline water production.• Well shut-in in late 2004 and remains so.

• Estimated oil in place volume: ~115MMstb• Produced Oil = 9.6MMstb• Current Recovery Factor ~ 8%

Top Skagerrak Reservoir Structure Time Map


1

2

3

1. Attic Volume2. Northern infill target3. Southern Infill target

4D RMS amplitude signal extracted between BCU + 10ms and +80ms

Opportunities on Skua

0.5km


1. Attic Opportunity – 3D Structure Interpretation

Line of sectionW E

SKS01S1OWC @ 12075ft

Top Triassic

BCU

Top Marnock Sh


1. Attic Opportunity – 4D Interpretation

Water flowing through higher perm units into well…?

Stratigraphic or structural reasons?

EW

Line of section

Middle Shale

Heron Shale

Unpenetrated flank stratigraphy… Potential oil bearing Joanne sands?

BCU – Top Triassic surface

ATTIC VOLUME

ATTIC VOLUME?

OOWC in Lower Skagerrak?

OOWC

OWC


Potential Down-flank Opportunity

SKS01

22/24B-9

OWC

Amplitude pattern follows subcroppingpattern of Skagerrak sand-shale packages.

Observed Acoustic Impedence contrasts can be explained by shales vs oil bearing (rather than water) sands.

0.8km

22/24B-7

SKS01S1 Heron Shale

Amplitude map of post cursor amplitudes from BCU (Top reservoir).

Middle Shale


2 & 3. Infill Opportunities

3

1. Attic Volume2. Northern infill target3. Southern Infill target

4D RMS amplitude signal

0.5km

2


Is signal across fault real? Does this correspond to production from northern

block?

NS

2. North/South Infill Targets - 4D Section

Line of section

North TARGETSouth

TARGET

Likely sealing

Partial sealing


Northern Flank Uncertainty

Line of section

NS

Skua

S01S1

2 Concepts : 1) Fault Seal (orange) and 2) Dip Closure (green) in the saddle area

Marnock

Volume gained in Fault Seal / Lost in Dip Closure – 11*106m3 (~3MMstb STOIIP)Volume lost in Fault Seal / Gained in Dip Closure – 6*106m3 (1-2MMstb STOIIP)

12075ft OWC

11739ft GWC

North TARGET


Ongoing Work

• 4D reprocessing to better image possible depletion signal in North Block.

• Improvements to reservoir static/dynamic modelling.

• Geomechanical study to address pressure depletion estimates, stress arching.

• Well engineering studies to establish the drillability of partially depleted HPHT Skagerrak reservoirs.

• Production chemistry / Production Technology to assess the need for down-hole wash water injection and fully understand what happened to the SKS01S1 well.

• Facilities engineers to address the feasibility of gas lift installation.


Concluding Remarks

•• SkuaSkua is a mature HPHT oil field in the Central North Sea whose one dis a mature HPHT oil field in the Central North Sea whose one development well evelopment well was characterised by a high initial production rate (~16,000bbl/was characterised by a high initial production rate (~16,000bbl/d).d).

•• The well saw a rapid, high produced water cut in late 2004 and wThe well saw a rapid, high produced water cut in late 2004 and was shutas shut--in.in.

•• Ongoing studies show several possible opportunities exist to incOngoing studies show several possible opportunities exist to increase field recovery.rease field recovery.

•• But, realising these opportunities presents many major subsurfacBut, realising these opportunities presents many major subsurface and engineering e and engineering challenges.challenges.


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Documents

Further Development of Skua, a Mature Triassic HPHT Field ... S… · • Skua is a mature HPHT oil field in the Central North Sea whose one d evelopment well was characterised by