1 Petroleum Engineering 406 Floating Drilling Lesson 11a Motion Compensation

2 Lesson 6 - Motion Compensation  Reentry  Tensioners  Heave Compensators  Passive Motion Compensation  Active and Semiactive Systems

3 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)

4 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

5 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?

6 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...

7 Pneumatic Riser Tensioning System

8 Pneumatic/Hydraulic Heave Compensation System  Pneumatic/Hydraulic Tensioners:  Take up much less room  Facilitate changing the tension by changing the air pressure  Can be used for the marine riser, the guidelines and the drill string

9 Pneumatic/Hydraulic Heave Compensation System  Passive Systems are the most popular  Require essentially no energy input  Use an “air spring” with a variable spring constant  Can keep the tension within ~ 15% or even less.

10 Pneumatic/Hydraulic Heave Compensation System  Active Systems  Require external energy through each load cycle  Provides a highly consistent force  But -- Has a high initial cost  Has a high operating cost

11 Lower sheaves are attached to the cylinder (and vessel), upper sheaves are attached to the piston rod 20 ft 5 ft 1,500 psig WP Typical Tensioner