Paper No.: SPE-202360-MS

SPE-202360-MS • Probabilistic Assessment of Pressure Depletion and Inflation and its Impact on the Drilling Sequence for the Sangomar Field, Senegal • L. Gavin & P. Jagtenberg

Paper No.: SPE-202360-MSPaper Title: Probabilistic Assessment of Pressure Depletion and Inflation and its Impact on the Drilling Sequence for the Sangomar Field, Senegal

Lisa Gavin & Pieter Jagtenberg, Woodside Energy

1


2

S540

S520

S480S460

Gas Oil Water

Location and Field Overview

Field Location

Reservoirs

Schematic Subsea Layout

SANGOMAR DEVELOPMENT, SENEGAL


Drilling Sequence DriversSANGOMAR DEVELOPMENT, SENEGAL

Subsurface uncertainty

Well execution learning

Water injector learnings

Borehole stability

Rig movesProduction attainment

Rig services & equipment

Material procurement


Safe Mud Window Depends on Near Wellbore Reservoir Pressure

Reservoir pressure (psi)

Equi

v. m

ud w

eigh

t (SG

)BHS min. mud weight

SG=1.0

Pri

Intact shale fracturing

Max. ‘safe’ depletion


Safe Mud Window is Well Dependent

σ3

σ2

Well azimuthImpacts horizontal stresses

acting on wellbore

Well length & casing designDrive friction and ECD

WE

Depth seabed vs. reservoir Drives formation stresses

P

Depletion & InflationImpacts pore

pressure and stresses in post-RFSU wells


S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament

S520 Reservoir Models & ClusteringSANGOMAR DEVELOPMENT, SENEGAL

Simulation ScenariosDevelopment

• x6 oil producers

• x6 water injectors


S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament





• x9 static models – facies & structure

• x2 Gas cap – y /n

• x2 SCAL – base and fast water


S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament




• x2 Karst lineament transmissibility






S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament





• x3 Channel transmissibility






S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament





• x3 Channel transmissibility


Simulation Scenarios

= 216 models = 20 modelsK medoid clustering

Development




S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament

Clustering Inputs


SANGOMAR DEVELOPMENT, SENEGAL

Cumulative oil, gas & water at 3,

5 & 25 yrs

Present value of oil at 25 yrs

Maximum oil rate

Oil plateau duration

Recovery factor at 25 yrs

Medoids assessed on cumulative distribution for all input variables

S520 Reservoir Models & Clustering


S520 (m)

C.I. = 25 m

Oil producer

Water injector

Channel

Karst Lineament



Clustering Visualisation


Reservoir Simulation ResultsSANGOMAR DEVELOPMENT, SENEGAL

Active Water Producer

Active Oil Injector

Planned Water Injector

Well of Interest

DepletionProduction

InflationInjection

ΔPressure (psi)

125010007505002500-250-500-750-1000-1250

Different modelsSame timestep, well sequence and production ramp up

Model A Model B

2500m


100300400500600800

0

50

Integrating borehole stability & simulation resultsSANGOMAR DEVELOPMENT, SENEGAL

Depletion (psi)

Simulation Max amount of depletion

Chance of natural fractures reactivating (if present)

Pie chart proportion = probability of that depletion being encountered

Simulation range of outcomes

Natural fractures reactivate (if present)

due to depletion

Borehole stability allowable depletion


100300400500600800

0

50

Integrating borehole stability & simulation resultsSANGOMAR DEVELOPMENT, SENEGAL

Depletion (psi)

The picture can't be displayed.



Simulation Max amount of depletion

Chance of natural fractures reactivating (if present)

Pie chart proportion = probability of that depletion being encountered

Simulation range of outcomes

Natural fractures reactivate (if present)

due to depletion

Borehole stability allowable depletion


Well Sequence ImpactSANGOMAR DEVELOPMENT, SENEGAL Order Allowable

depletionBHS / MW / depletion

issues

Updated order

Allowable depletion

BHS / MW / depletion residual issues and mitigations

First Oil Window

1 1

2 2

3 3

4 10Accelerate ‘vulnerable’ S500

producer wells, to be completed before RFSU

Spread early production between north and south of the field

5 5

6 19

7 7

8 13

9 11

First Oil

10 18

11 9

12 14 Accelerate northern water injector

13 9

14 Wells exposed to potentially

severe depletion

12 Wells exposed to depletion risk, to be managed by better balanced

offtake and water injection. The two residual ‘vulnerable’ wells may be accelerated if higher mud weights confirmed to be required

15 15

16 17

17 8

18 4

Alternating producer-injector wells to manage depletion risk

19 22

20 20


severe depletion

21

22 19

23 22

A

A

A. Wells exposed to potentially severe depletion


Well Sequence ImpactSANGOMAR DEVELOPMENT, SENEGAL Order Allowable

depletionBHS / MW / depletion

issues

Updated order

Allowable depletion

BHS / MW / depletion residual issues and mitigations

First Oil Window

1 1

2 2

3 3

4 10Accelerate ‘vulnerable’ S500

producer wells, to be completed before RFSU

Spread early production between north and south of the field

5 5

6 19

7 7

8 13

9 11

First Oil

10 18

11 9

12 14 Accelerate northern water injector

13 9


severe depletion

12 Wells exposed to depletion risk, to be managed by better balanced

offtake and water injection. The two residual ‘vulnerable’ wells may be accelerated if higher mud weights confirmed to be required

15 15

16 17

17 8

18 4

Alternating producer-injector wells to manage depletion risk

19 22

20 20


severe depletion

21

22 19

23 22

A

A

A. Wells exposed to potentially severe depletion

B. Spread early production between north and south of field

C. Accelerate northern water injector

D. Alternating producer-injector wells to manage depletion risk

B

C

D

E

S500 Producer

Gas Injector

S400 Water Injector

S500 Water Injector

S400 Producer

Well typeTheoretical allowable depletion

0 psi

up to 50 psi

50-100 psi

>100 psi


ConclusionsSANGOMAR DEVELOPMENT, SENEGAL

• Many factors need to be taken into consideration when designing a well drilling sequence

• Pressure inflation and depletion impacts mud weight windows

• Borehole stability assessment defines mud weight windows

• Probabilistic simulation determines potential pressure changes in reservoir

• Combining borehole stability & simulation results identifies wells at risk

• Well sequence updated to mitigate drillability risk while still protecting production attainment


AcknowledgementsSANGOMAR DEVELOPMENT, SENEGAL

• Woodside Energy & our RSSD Joint Venture (JV) partners Capricorn Senegal Limited (Cairn), La Societe Des Petroles Du Senegal (Petrosen) & Far Senegal RSSD SA (FAR) for permission to share the work

• Jurgen Streit, Samantha Prior & the Woodside Geomechanics team

• Clinton Di Labio & the Woodside Sangomar Drilling and Completions team

• Mohammad Zafari for guidance on reservoir simulation models and workflows

• Madeline Hardy with the Woodside Data Science and Subsurface Technology Teams in collaboration with SCERF (Stanford Centre for Earth Resource Forecasting) for creating the EMVAT tool used for clustering

• Numerous other Woodside colleagues and JV partners who contributed to building the subsurface models, had helpful conversations with us on this topic & reviewed this paper

Paper No.: SPE-202360-MS

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