8/16/2019 BP - Deep Water Horizon - Gulf Mexico - Oil-cause-0507101

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WHAT HAPPENED ON THEDEEPWATER HORIZONOn April 20, Deepwater Horizon was two days away from temporarily capping the oil well it haddrilled and handing off the pumping of the oil to a production platform or pipeline. But duringthis disconnection process the rig suffered a blowout, caught fire and sank to the bottom.

Here is what went wrong:

DEEPWATERHORIZON

RISER

BOP

WELL

OIL LAYER

GULF OFMEXICO

EMMETT MAYER III AND DAN SHEA / THE TIMES-PICAYUNE

Note: Man shown for scale.BOP is located on the seafloor 5,000 feet below thesurface.

THE CEMENT FAILS

THE WAYIT ISSUPPOSEDTO WORK: SEAWATER IN THE RISER 

THE BLOWOUT

PREVENTER FAILS

Oil is 18,000feet belowthe sea floor

Well is locatedin 5,000 feetof water

In a properlycapped welltwo largecement plugsseparated by

drilling mudare in place

Thin line ofcement encasesa steel well pipe

Riser adapter

Drill bit

Until the well iscompletely plugged,the pressure froma column of thickdrilling mud keepsnatural gas and oilin the ground

DRILL PIPE

BOTTOMPLUG

TOPPLUG

3

2

3

2

1

1

DRILL PIPE ASIT DRILLS DOWNTO OIL LAYER

Mud is pumpeddown the drillpipe from the rig

The mud thenrises back tothe rig carryingshavings with it

Casing

Casing

Cement Cementplug

Drillingmud

Drillpipe

Cement

Cement

Note: Vertical height of water and sediment layers is to scale. Rig and drilling components are not. Source: Staff research

Deepwater Horizon had begun toremove the heavy column of drillingmud that is the primary means ofcontrolling pressure inside a well.

Cement is supposed to protect theoutside of the well pipe and is usedto seal off a well when needed.

PROBLEM:Either the primary or secondarycementing failed, pushing a hugecolumn of natural gas into thewell pipe.

PROBLEM:When the cement failed, thenatural gas rocketed to thesurface, as the weakened mixtureof mud and seawater did not havethe pressure necessary to holdthe gas back. The gas exploded the

rig, killing 11 men and destroyingthe rig.

PROBLEM: With only seconds to react, rigoperators fired off the shearram, but it only partiallysheared the drill pipe. A jointmay have been in the way, or

the ram was fouled by pieces ofcasing or cement from theblowout. For days, remotelyoperated robots tried to fire offthe ram manually, but failed.

Cement is pushed between the wellcasings and the sediment layers that havebeen drilled through. It protects the metalwall from gas pressure and from gasleaking up the outside of the well pipe.

Primary

When a well is to be temporarilyabandoned, two plugs are cemented inwith drilling fluid between them.Sometimes more plugs are used.

THE CEMENTING PROCESS:

The BOP stack is a 450-ton series ofvalves developed to prevent agusher if the mud control isoverwhelmed.

SHEAR RAM: The finalfail safe, it is designedto close the well bycutting through andsealing the drill pipe.But they are notdesigned to cut through

 joints where two drillpipe sections connect.

FOUR BLIND RAMS: Can withstand more

pressure thanannular valves overopen holes. Not usedwith a drill pipe inplace. Two metalblocks close on eachother, sealing thewell.

TWO ANNULAR VALVES: Closes in and seals on thedrill pipe. Or if the drillpipe is not in use, it closesthe open hole.

THE USES OF MUD:

Ú During drilling, mud is pumpeddown the riser and well to the tip ofthe drill. The mud then flows back upto rig, taking the drill shavings with it.

Ú The weight of the mud maintainswell pressure so the oil does notrise to the surface.

Ú The thickness of the mud can beadjusted to deal with a “kick,” asudden surge of gas pressure.

Secondary

Flex joint

Yellowcontrolpod

Bluecontrol

pod

Drill pipe

Wellheadconnector