12

3

4

5

6 7

8

The cement that was supposed to stop oil and gas reaching the well pipe casing did not work. The report blames the type of cement used

1 The cement and valve at the bottom of the drill pipe failed to stop oil and gas bursting into the well pipe

2

Well pipe metalcasing

Oil and gas Oil and gas

Cement fills ‘annulus’ gap

Float collar(one-way valve)and shoe trackcement

Shoetrack

Well pipe

FailedFailed

What went wrong?

The BP report identifies eight key elementsin the Deepwater Horizon drilling operation - each of which could have prevented the disaster

Staff misread a key pressure test thinking high readings were an error3 Oil and gas were now pouring up the

well, but it took 40 minutes for this to be noticed

4

Once oil and gas started flooding to the surface, they were not diverted overboard but swept on to the rig

5

Riser carries oil to rig

Blowoutpreventer

Oil and gas flowing unnoticed

Failed

Oil and gas should have been directed overboard

Failed

The oil and gas ‘vented directly on to the rig’. This made an explosion was inevitable

6

Cloud of gas spreads around the rig and under the deck

Failed

The fire prevention system on the rig failed. The report says the ‘heating, ventilation and air conditioning system … transferred a gas-rich mixture into the engine rooms’. Two huge explosions followed, killing 11 crew members

7 The ‘failsafe’ blowout preventer (BOP) failed. Fire on the rig stopped it being remotely shut down, while an automated system also failed. The BOP had flat batteries in one control pod and a faulty solenoid valve in another

8

Failed

Gas ignites, destroying the rig

Key test involved filling the kill line to check pressureon the drill. Because the line was blocked, no fluids escaped - leading staff to assume everything was working correctly

Multiple cutoffdevices shouldhave shut off the flow of oil and gasautomatically

Failed

19 April 7.30pm–12.36am

20 April 4.50pm

20 April 7.55pm

20 April 9.56pm

20 April 8.50pm

20 April 9.40pm 20 April 9.49pm

Sea floor at 5,000 feet

Oil-bearing rock at 18,000 feet

SOURCE: BP DRAWINGS NOT TO SCALE

The key times

Report: ‘There were weaknesses in cement design’

Report: ‘The investigation team identified … failure’

Report: ‘Site leaders reached the incorrect view’

Report: ‘Weaknesses in the testing regime and maintenance management’

Report: ‘Rig crew did not recognise the influx’

Report: ‘This overwhelmed the … system’

Report: ‘If fluids had been diverted overboard … consequences may have been reduced’

Report: ‘The fire and gas system did not prevent … ignition’

Failed

Blowoutpreventer

Drill pipe

Deepwater Horizonrig

Riser