1. Petroleum Engineering 626 Offshore Drilling Lesson 6C Motion Compensation

2. Lesson 6C - Motion Compensation
Bumper Subs
T = H - wd
Buoyant Riser
Jackup Rig

3. 1. Always run the bumper subs at the neutral point in the string.
Fit into the drill collar string, but do not have the ruggedness of drill collars. To obtain a reasonable operating life from bumper subs, action has to be taken on the following points of concern:
1. Always run the bumper subs at the neutral point in the string.

4. Bumper Subs, cont’d
2. Bumper subs are designed to stroke, and if operated at a single position, they will wear at that position.
3. Running the subs in tension minimizes the area through which the torque will be transmitted, and will cause excessive wear and fatigue.

5. Bumper Subs
4. Running the joint in compression increases torque reversals and fatigue in the tool. It also increases “bit chatter” and instantaneous peak torque, causing unnecessary wear to the tool and the string. This is the fault of the operation, not the sub.

6. Bumper Subs
5. From items 3 and 4 above, it is evident that once the string has been run, the weight on the bit is fixed. This weight should not be changed until the string has been pulled and the number of drill collars below the bumper sub changed.

7. Bumper Subs
6.Do not separate the bumper subs in a drillstring for heavy drilling operations.
7.Special care and maintenance are required to obtain a reasonable operating life.
*Remember: bumper subs fit into the same part of the drillstring where drill collars and stabilizers have been destroyed. This is a severe test of workmanship &maintenance.

8. Unbalanced
Bumper
Subs

9. Buoyant Riser Module

10. Then lower legs to seafloor
Cantilever Jackup Rig
Float out to location
Then lower legs to seafloor
Then jack up

11. Jackup Rig
Side View

12. Jackup Rig
Deck Plan