subsea p&a: a step change in rig site hazard exposure ... · up subsea test tree days removed ~...

Copyright of Shell UK Limited

Subsea P&A:

A step change in rig site hazard exposure through risk-

based design and execution

Lynda Nwike

Wells Subsea Design EngineerShell UK

1October 2017

Shell

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Shell

Agenda

• Overview of A&C wells

• The Risk Based Approach to Design

• Scope removal & Optimisation from 2016 Base Case

• A&C Planning and Execution Improvements

• 2016 Plan vs 2017 Execution

• Total HSE exposure reduction & Execution times

• The bigger picture. What next?

• Q&A

October 2017 3Copyright of Shell UK Limited

Shell

A&C Well Overview

14

Shell

Atlantic and Cromarty Field Overview

▪ 3x suspended subsea production gas wells in the

Central North Sea.

▪ Project in partnership with Hess.

▪ Cameron STM -15 wellheads and horizontal trees.

▪ Horizontal trees – all operations conducted with tree

in place.

▪ Water depth ~380ft


Shell

Atlantic and Cromarty project timeline

6October 2017

2005-06• Wells drilled with Global Santa Fe 140

2010• Cessation of production for the A&C wells

2014

• Well Enhancer LWIV used to plug and lubricate all wells.

• Well content bullheaded into reservoir

• 2 x bridge plugs installed in well

• 2 x crown plugs set in SXT

2017

• Rig move survey March

• Atlantic and Cromarty PDHG Pressure check on Goldeneye April to confirm P&L plugs still holding.

• Well abandonment completed July-Aug with Ocean Patriot rig

• Subsea tree and wellhead severance planned for October


ShellCopyright of Shell UK Limited

Subsurface overview

• All wells have sidetracks in the Chalk which is predominantly

without flow potential.

• All side-tracks deemed as fully abandoned.

7

Reservoir: One NPNT hydrocarbon reservoir: Captain

Sandstone. Sub hydrostatic reservoir. Max recharge pressure

would be to a hydrostatic gradient.

Reservoir seals: Rodby and Carrack formations are the original

reservoir seal. Signs of instability when the well was drilled.

Formations would provide an additional annular seal to lateral

isolations in chalk.

Tertiary group: Water bearing sands right above the Chalk

group. No indications of abnormal pressures.

Chalks: The chalk group forms the external element for the

reservoir lateral isolation.

Shell October 2017 8

Well Status BeforeWell P&L’d with LWIV

2x plugs set:1x in liner

1x in tailpipe

Tubing cut

Hold open sleeve set

2x crown plugs set:1x in internal tree cap

1x in tubing hanger

Well Status

AfterWell P&A’d with Rig

1x barrier set:• 1x combined PWC

plug to isolate

captain reservoir set

across the Chalks

1x environmental plug:• 1x plug to cap OBM

using Perforate

Circulate Cement

technique

630pptf

OB

M

510pptf

WB

M

HSXT (no guideposts) HSXT (no guideposts)

510pptf

WB

M

Environmental plug

Combined

abandonment

barrier

Top Chalk Gp

Herring

Black Band Bed

Hidra

Rodby

Carrack

🔴 Captain

Sea

Undifferentiated

Tertiary

Lower Mackerel

Upper Mackerel

Top Chalk Gp

Herring

Black Band Bed

Hidra

Rodby

Carrack

🔴 Captain

Sea

Undifferentiated

Tertiary

Lower Mackerel

Upper Mackerel


Shell

Risk Based Approach to Design



Brent/ Subsea Experience

Competitive Scoping

Strong collaboration

between Wells and subsurface teams

Experience & lessons learnt from

other Operators

Holistic Ways of Thinking

Risk Based

Approach Cost Reduction

Lower HSE Exposure

Removal of unnecessary

scope


Shell

Scope removal and optimisation



84 total

46 total

38

11

21 days WOW/NPT

11 days WOW/NPT 4 days WOW/NPT

0

10

20

30

40

50

60

70

80

90

2016 Plan Planning Optimisations 2017 Plan Execution Optimisations 2017 Delivered

Da

ys

Time

A&C Planning & Execution Improvements

35 total



• Subsea Tree tied back to Goldeneye platform.

• Pressure gauge deep in well allowed pressure monitoring capability.

• Allowed well pressure to be measured and confirm deep set barrier integrity.

• Removed risk of having to rig up pressure containing intervention equipment

(Subsea Test Tree etc.)

• Pulled completion with crown plugs and barriers in place.

• Removed requirement to rig up e-line to pull crown plugs and install isolation

sleeve.

Removed requirement to pull crown plugs from wellhead and rig

up subsea test tree

Days removed ~ 2 days

Risks removed :

❖ Multiple lifts

❖ Working at height


Shell

Isolating the Captain Reservoir

October 2017 14

• PWC performed on all 3x wells.

• First deployment of PWC method on a subsea well for Shell UK.

• Hydrawell provided PWC service.

• Use single trip method on A1Y and A2Z wells.

• 2 trip solution required for C6Z due to lack of gun sump space to leave

guns below cement base.

• Did not displace excess cement from 800ft above base of

cement, final cement plug length ~1400ft. Reduced slops handling at

surface

Days removed ~ 5 days

Risks removed :

❖ Multiple lifts

❖ Swarf handling

❖ Swarf damage to equipment

❖ Swarf disposal

0

1

2

3

4

5

6

A1Y PWC

(actual)

A2Z PWC

(actual)

C6Z PWC

(actual)

Actual

Section mill

+ cement

Annulus remediation

timings (days)


Hydrawell’s Hydrahemera tool


Environmental Barrier

October 2017 15

• Previous subsea wells used perforating guns, sized to perforate only one or

two casing strings with mixed success.

• A&C did not need to remediate 13-3/8” annulus.

• No requirement to cap water based mud in C-annulus.

• This will be exposed to sea during wellhead recovery operations this year.

• Utilised Gator tool from Lee Energy systems.

• GATOR tool enabled large flow areas.

• No explosives were required shallow in the well.

0

1

2

3

Cut & Pull PCC with

Perf guns

A2z PCC

with Gator

Environmental Plug Clean

Times

Days

510pptf

WB

M

HSXT (no guideposts)

510pptf

WB

M

HSXT (no guideposts)

Days removed ~2 days

Risks removed :

❖ Multiple heavy lifts on deck

❖ Casing handling and transportation

❖ Rigging up & down of casing handling

equipment

PCC Strategy Cut and pull strategy


Wellhead and Subsea Tree Recovery

October 2017 16

• Wellhead severance and recovery: Rig based Vessel based.

• Subsea Xmas tree recovery: Rig based Vessel based.

• Unlocked Xmas tree from wellhead and locked dogs prior to

setting on wellhead for recovery later in year.

• Removes risk of handling tree/wellhead on rig – deck

constraints, rig ergonomics.

Days removed ~ 4.5 days

Risks removed :

❖ No handling of trees or wellheads

in moonpool area.

❖ Heavy Lift to supply vessel from rig

Shell

Plan vs Execution

2016 Base Plan

• Recover ~7000ft of completion

• Perform USIT/CBL log (A1 only)

• Set CH cement plug (Section mill & set OH plug on A2z

& C6)

• If unsuccessful, section mill 150ft window and set

plug

• Cut & pull production casing from ~2000ft

• Cut and pull intermediate casing from ~2000ft

• Set 500ft cement plug

• Cut and retrieve 20” and 30” string with MOST tool

• Pull and retrieve Wellhead

• Conduct seabed clearance scan

Total Days = 84.0days

October 2017 17

2017 Execution

• Recover ~7000ft of completion

• Perform USIT/CBL log (A1 only)

• Perforate 250ft of 9 ⅝” casing

• Wash perforated interval to remove solids and set

combined barrier cement plug across perforated

interval and in wellbore

• Perforate, circulate and cement B-annulus to isolate

OBM

• Wellhead and tree recovery to be performed on

separate campaign (~1.5days/well)

Total Rig days = 34.6days

Total Days (inc. vessel) = 39.1days

Days removed ~45days


Shell

A&C Comparative Time Review

18October 2017

0

2

4

6

8

10

12

14

16

18

20

Atlantic A1Y Atlantic A2Z Cromarty C6Z

Da

ys

Well

WOW

NPT

Clean time

Benefits of scope reduction:

• 45 days ahead of 2016 plan equates to >57,000hrs of

HSE exposure eliminated (106 POB average).

• PWC method eliminated handling of swarf in surface

circulation system and reduced deck congestion.

• Perf, circulate and cement method eliminated

handling of 48 joints of 9 ⅝” casing at surface,

shipment back onshore and disposal.

• Blending cement and expanding additive onshore

eliminated requirement for cement batch tank rig up

on the rig.

• SXT and wellheads to be recovered with vessel, no

heavy lifts from rig to supply vessel required.


Shell

The bigger picture


Shell

WHAT DOES THIS TRANSLATE

TO?



LESS…

Wo

rkin

g a

t he

igh

t

CO2 emissions

Ca

sing

ha

nd

ling

Exposure Things

Exp

osu

re t

o w

ea

the

r

Logistics

Slops handling

Heavy Lifts

Manual

Handling

Slips Trips

Falls

Sw

arf

Ha

zard

s

to go wrong

NPTWOW

……

……

……

……

……

…


Shell

FOUR HIGH EXPOSURE AREAS FOR THE FUTURE

October 2017 22

• Anchor handling

• Heavy Drilling BOPs

• Elimination of divers

• Wellhead Severance

• Necessity to understand stakeholders interests.

• Need to challenge industry norms and review the benefits vs the risks.

• Understand our wells.

• High costs vs minimal risk reduction.

• What role does new technology play?


Shell October 2017 23Copyright of Shell UK Limited

subsea p&a: a step change in rig site hazard exposure ... · up subsea test tree days removed ~...

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