1 Petroleum Engineering 406 Floating Drilling Lesson 11b Motion Compensation

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

3 Motion Compensator Principles of Operation Purpose: Keep bit on bottom with low bit weight change Air pressure can support entire weight of drillstring. e.g. 200, ,000 = 160,000lbf. Reduce air press.

4 Heave Compensation for Bit We can compensate at Crown Block or at Travelling Block Example: Keep bit weight within 30% of average value. Hook load = 200,000 lbf. Avg. bit wt. = 40,000 lbf Bit Weight must be kept within 0.3 * 40k = 12k lbf. i.e. keep Hook load within 12/200 * 100% = 6% !! How is that possible? Larger air tanks!

Rucker Heave Compensator Dual Pistons - on the travelling block Large air cylinders below deck Flexible hoses

6 Figure 7-9 Vetco dual piston Heave Compensator L.P. hydraulic fluid throttled for damping Piston balancing may be problem

7 Western Gear Heave Compensator Figure 7-10 Split travelling block Hydraulically operated pistons can be locked in any position with remotely operated valves. Air operated units must be mechanically locked in position because of compressible fluid in cylinders. Single Piston Rod

8 Crown Block Heave Compensator AIR STORAGE