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Petroleum Engineering 406Floating Drilling

Lesson 11a Motion Compensation

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Lesson 6 - Motion Compensation

ReentryTensioners Heave Compensators Passive Motion Compensation Active and Semiactive Systems

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Re-entry

It is possible to re-enter a borehole without using guidelines!

1. Use land-based navigation equipment to get the vessel in the vicinity of the well

or better still: Use GPS (Global Positioning System)

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Re-entry, cont’d

2. Lower reentry string to a safe distance above the wellhead

3. Use position location equipment to complete the job:

(i) Television camera

(ii) Acoustic device - pinger or transponder (iii) ROV - Remote Operated Vehicle

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Heave Compensation

How do you maintain a constant tension on the marine riser - when the vessel

heaves?

How do you maintain a constant weight on the bit - when the vessel heaves?

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Deadweight Riser Tensioning System

Dead Weight(~constant

tension)

Dead Weight

Slip Joint

Marine Riser

Early design - OK up to 100,000 lbf. Attached to lower half of telescoping joint. Adds weight & is bulky...

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Pneumatic Riser Tensioning System

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Pneumatic/Hydraulic Heave Compensation System

Pneumatic/Hydraulic Tensioners:

Take up much less roomFacilitate changing the tension by changing the air pressureCan be used for the marine riser,

the guidelines and the drill string

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Pneumatic/Hydraulic Heave Compensation System

Passive Systems are the most popularRequire essentially no energy inputUse an “air spring” with a variable spring constantCan keep the tension within ~ 15%

or even less.

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Pneumatic/Hydraulic Heave Compensation System

Active SystemsRequire external energy through each load cycleProvides a highly consistent forceBut -- Has a high initial costHas a high operating cost

11Lower sheaves are attached to the cylinder (and vessel), upper sheaves are attached to the piston rod

20 ft

5 ft1,500 psig WP

TypicalTensioner