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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