Deepwater Horizon Investigation - · PDF fileHydrocarbons ignited on the Deepwater Horizon − Diversion to mud gas separator ... Blowout preventer did not seal the ... The shoe track

Deepwater Horizon Accident Investigation 1

Deepwater Horizon Investigation


Investigation Context

Terms of Reference

Investigation Team

Data and Analysis

Investigation Limitations


Well integrity was not established or failed− Annulus cement barrier did not isolate hydrocarbons

− Shoe track barriers did not isolate hydrocarbons

Hydrocarbons entered the well undetected and well control was lost− Negative pressure test was accepted although well

integrity had not been established

− Influx was not recognized until hydrocarbons were in riser

− Well control response actions failed to regain control of well

Hydrocarbons ignited on the Deepwater Horizon− Diversion to mud gas separator resulted in gas venting

onto rig

− Fire and gas system did not prevent hydrocarbon ignition

Blowout preventer did not seal the well− Blowout preventer (BOP) emergency mode did not

seal well

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2

3

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Sea Floor

Casing

Riser

BOP

Reservoir1

3

Eight Barriers Were Breached

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5

6

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6 7

8


Sea Floor

Casing

Riser

BOP

Reservoir

12.6 ppg

Bottom Wiper Plug

Mud

14.17 ppg

Cap

16.74 ppg

Foam

Cement

14.5 ppg

Shoe

Track

Spacer

14.3 ppg

6.7 ppg

Spacer

14.3 ppg

Top Wiper Plug

Bottom Wiper PlugBottom Wiper Plug

Mud

14.17 ppg

Spacer

14.3 ppg

Top Wiper PlugTop Wiper Plug

Bottom Wiper Plug

Spacer14.3 ppg

16.74 ppg

CapCement

FoamCement14.5 ppg

CementChanneling

ShoeTrack

Nitrogen Breakout

Cement is pumped down the landing string and casing into the annulus to isolate hydrocarbon

bearing sands.

Foam slurry recommended was a complex design

Risk of contamination using small volume of cement

No fluid loss additives

Incomplete pre-job cement lab testing

Foam slurry was likely unstable and resulted in nitrogen breakout

Base Oil16.7 ppg

Cement Slurry Placement

Float Collar

Tail Cement16.74 ppg

Reamer Shoe Tail Cement

Key Finding #1The annulus cement barrier did not isolate the reservoir hydrocarbons

Centralizers


Sea Floor

Casing

Riser

BOP

Reservoir

Key Finding #2The shoe track mechanical barriers did not isolate the hydrocarbons

Tail cement is displaced down the casing into the shoe track. The tail cement is

designed to prevent flow from the annulus into the casing. The float collar valves, which provide a second barrier, must close and seal to prevent flow up

the casing.

Shoe track had two types of mechanical barriers: cement in the shoe track and the double check valves in the float collar

Shoe track cement failed to act as a barrier due to contamination of the base slurry by break out of nitrogen from the foam slurry

Hydrocarbon influx was able to bypass the float collar check valves due to either:

Valves failed to convert orValves failed to seal

Flow through shoe confirmed by fluid modeling and Macondo static kill data

Float Collar

Check Valves

Flow Ports

Shoe track cement

Centralizers

Hydrocarbon Flow Path


16ppg Spacer

14.17ppg SOBM (Mud)

8.6ppg Seawater

Influx

Flow Through Shoe Track - Supporting Evidence

CasingShoe

Failure

SealAssembly

FailureYY

YY

YY

YY

YY

YY

YY

YY

NN1400 psi recorded on drill pipe during negative test at 18:30

NNStatic Kill

NNTiming for Gas Arrival to Surface

NNPressure Response from 21:31 to 21:34

NNPressure Increase from 21:08 to 21:14

NNAbility to flow from 20:58

NNRealistic Net Pay Assumption

YYMechanical Barrier Failure Mode Identified

Key Observations for FlowThrough Shoe vs. Seal

Assembly

CasingShoe

Failure

SealAssembly

Failure

YY

YY

YY

YY

YY

YY

YY

YY

NN1400 psi recorded on drill pipe during negative test at 18:30

NNStatic Kill

NNTiming for Gas Arrival to Surface

NNPressure Response from 21:31 to 21:34

NNPressure Increase from 21:08 to 21:14

NNAbility to flow from 20:58

NNRealistic Net Pay Assumption

YYMechanical Barrier Failure Mode Identified

Key Observations for FlowThrough Shoe vs. Seal

Assembly

CasingShoe

Failure

SealAssembly

Failure


Sea Floor

Shoe – 18,304’

FC – 18,115’

TOC – 17,260’

Shoe – 17,168’

KillChokeBoost

SOBM

Spacer

Seawater

Influx

SOBM

Spacer

Seawater

Influx

BOP

1400PSI

0PSI

Key Finding #3The negative pressure test was accepted although well integrity had not been established

Spacer

Sea Floor

Casing

Riser

BOP

Reservoir

Bleed volumes not recognized as a problem

Anomalous pressure on drill pipe with no flow from kill line

Test incorrectly accepted as successful

Negative testing not standardized


Flow Indications

0

200

400

600

800

1000

1200

1400

1600

1800

2000

20:4

5

20:5

0

20:5

5

21:0

0

21:0

5

21:1

0

21:1

5

21:2

0

21:2

5

21:3

0

21:3

5

Flow

Rat

e (g

pm)

0

500

1000

1500

2000

2500

3000

Pum

p Pr

essu

re (p

si)

Flow Out (calibrated)Flow In (rig pumps)DP Press (rig pumps)

Key Finding #4The influx was not recognized until hydrocarbons were in the riser

Flow indications:

#1: Drill pipe pressure increased by 100 psi, (expected decreased); ~39 bbl gain from 20:58 to 21:08

#2: Drill pipe pressure increased by 246 psi with pumps off

– Flow out does not immediately drop after shutting down pump

#3: Drill pipe pressure increased by 556 psi with pumps off; ~300 bbl gain

No well control actions taken

21:08

1,017 psi

21:31

1,200 psi

SOBM (mud)

Seawater

Influx

SOBM + seawater mix

39 bbl

300bbl

Cumulative Gain

Indication #1

Indication #2

0 bbl

Indication #3

20:52-Flow starts

Based on Real-time Data


0

500

1000

1500

2000

2500

3000

21:3

0

21:3

2

21:3

4

21:3

6

21:3

8

21:4

0

21:4

2

21:4

4

21:4

6

21:4

8

21:5

0

Drill Pipe Presssure (psi)

Pumps shut down

Discussion about “Differential Pressure”

Attempt to bleed pressure

Close Drill Pipe

Mud overflowing onto rig floor

BOP Sealing

Pressure increase due to annular activation

BOP

Key Finding #5Well control response actions failed to regain control of the well

Exp

losi

on

at

21:4

9

- Mud and water raining onto deck

- TP calls WSL, getting mud back, diverted to MGS, closed or was closing annular

- AD calls Senior TP, Well blowing out, TP is shutting it in now

Mud shoots up derrick-Diverter closed-BOP activated

First indication of well control response:49 minutes and 1000 bbls after initial influx

Influx enters riser

Annular leaking

Based on Real-time Data


Hydrocarbons were routed to the mud gas separator instead of diverting overboard

Resulted in rapid gas dispersion across the rig through the MGS vents and mud system

Key Finding #6Diversion to the mud gas separator resulted in gas venting onto the rig

When responding to a well control event the riser diverter is closed and fluids are sent to either the mud gas separator or

to the overboard diverter lines.

KillBoost

Choke

BOP

14” Diverter LinePort

Overboard 14” Diverter Line

MudSystem

Starboard Overboard

6” VacuumBreaker

IBOP

RotaryHose

Diverter

12” Vent

MGS

Bursting Disk

Starboard Overboard

OverboardCaisson

Slip Joint

Seawater

Seawater/Mud Mix

Influx

BOP Sealed at

21:47


Key Finding #7The fire and gas system did not prevent hydrocarbon ignition

Gas dispersion beyond electrically classified areas

Gas ingress into engine rooms via main deck air intakes

The on-line engines were one potential source of ignition

Aft

Fwd3D view

Aft

Aft

Gas Dispersion at 4 minutes

Fwd3D view

Section through derrick

(Upper Explosive Limit)

(Lower Explosive Limit)

Secondary protective systems are designed to reduce the potential

consequence of an event once the primary protective systems have

failed.


AMF

Key Finding #8The BOP emergency mode did not seal the well

EDS function was inoperable due to damage to MUX cables

AMF could not activate the BSR due to defects in both control pods

Auto-shear appears to have activated the BSR but did not seal the well

Potential weaknesses found in the BOP testing regime and maintenance management systems

The AMF provides an automatic means of closing the BSR without

crew intervention.

Manual Automatic ROV Intervention

EDSHP BSR Close

Emergency Methods of BOP Operation Available on DW Horizon

HOT StabAMF

Auto-shear

Damaged MUX Cable

Blue Control

Pod

Yellow Control

Pod

Damaged Hydraulic Conduit

Explosions & Fire:Loss of communicationLoss of electrical powerLoss of hydraulics


Recommendations26 Recommendations Specific to the 8 Key Findings

BP Drilling Operating Practice and Management SystemsAugment existing Engineering Technical Practices and Procedures

Further Enhance Deepwater Capability and Proficiency

Strengthen Rig Audit Action Closeout and Verification

Introduce Integrity Performance Management for Drilling and Wells Activities

Contractor and Service Provider Oversight and AssuranceReview Cementing Services

Strengthen Drilling Contractor Well Control Practices and Proficiency

Introduce more rigorous oversight of Rig Safety Critical Equipment

Review minimum requirements for BOP Configuration and Capability

Redefine BOP Minimum Criteria for Testing, Maintenance, System Modifications and Performance Reliability

BP has accepted all the recommendations and is reviewing how best to implement across its world wide operations


Well integrity was not established or failed− Annulus cement barrier did not isolate hydrocarbons

− Shoe track barriers did not isolate hydrocarbons

Hydrocarbons entered the well undetected and well control was lost− Negative pressure test was accepted although well

integrity had not been established

− Influx was not recognized until hydrocarbons were in riser

− Well control response actions failed to regain control of well

Hydrocarbons ignited on the Deepwater Horizon− Diversion to mud gas separator resulted in gas venting

onto rig

− Fire and gas system did not prevent hydrocarbon ignition

Blowout preventer did not seal the well− Blowout preventer (BOP) emergency mode did not

seal well

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Sea Floor

Casing

Riser

BOP

Reservoir1

3

Summary & Questions

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Documents

Deepwater Horizon Investigation - · PDF fileHydrocarbons ignited on the Deepwater Horizon − Diversion to mud gas separator ... Blowout preventer did not seal the ... The shoe track