Offshore drilling

Offshore, the drilling process is performed using a platform (fixed, floating, semi-submersible with an anchor or dynamic positioning system) or a drillship. The kind of system used depends on the water depth.

DRILLING IN SHALLOW WATER

In this case, the drilling system, installed on a fixed platform (compact rig or Jack Up), has the following characteristics:

> the wellhead is located on the platform

> the Blow Out Preventer is also located on the platform, between the wellhead and the drilling floor.

Land rigCompact rig

Jack-upSemi-

submersibleDP drillship

Subsea wells

Land rigCompact rig

Jack-upSemi-

submersibleDP drillship

Subsea wellsSubsea wells

Onshore drillingCompact rig

Jack-upDrillship

Jack Up commissioning

Semi- submersible

100

– 20

0 m

max

200

- 50

00 m

In the case of offshore drilling, the platform is connected to the sea bed using a tubular device (riser, flexibles, …), through which the drilling bit and the drillstring are run into the borehole and where the drilling mud circulates.

THE GRADUATE SCHOOL FOR ENERGY AND TRANSPORTATION PROFESSIONSIFP SCHOOL

DEEP OFFSHORE OR ULTRA-DEEP OFFSHORE DRILLING

In deep or ultra deep offshore locations, drilling is performed using a semi-submersible platform or a drillship. In this case, the wellhead is located at the sea bed. The BOP is installed just above it and a flexible joint connects the BOP to a tubular device, which, in turn, is connected to the platform.

Contrary to fixed p latforms, fl oating pl atforms ar e su bjected to wave movements. In the case of high waves, the tubular device is disconnected from the flexible joint and reconnected, using a robot located at the sea bed controlled remotely from the rig. Sensors surrounding the wellhead help locate the well from the surface.

Semi-submersible platforms can be anchored, or, as for drilling ships, can be equipped with lateral motors which are automatically controlled to maintain the vessel in the correct position, vertical to the wellhead.

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Semi-submersible platform

Drillship

RISER

FLEXIBLE JOINT

JOINT

BOP

WELL HEAD

CONDUCTOR PIPE

ACOUSTIC BEACON

SEA BED

Connection between the well and a floating drilling rig

SEMI-SUBMERSIBLE WITH DYNAMIC POSITIONNING SYSTEM

+ Useful link:

www.ifpenergiesnouvelles.fr/espace-decouverte/les-cles-pour-comprendre/les-

sources-d-energie/le-petrole

IFP School228-232, avenue Napoléon Bonaparte

www.ifp-school.com

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