Device for Compensation of Wave Influenced Distance Variations on a Drill String

• US 20150129238A1
• Filed: 03/12/2013
• Published: 05/14/2015
• Est. Priority Date: 03/12/2012
• Status: Active Grant

• Current Assignee: Depro AS
• Original Assignee: Depro AS
• Inventors: Liland, Tommy Andre Hognestad, Naesgaard, Kjetil
• Granted Patent: US 9,359,836 B2
• Time in Patent Office: Days
• US Class Current: 166/367
• CPC Class Codes: E21B 17/01 Risers
• CPC Class Codes: E21B 17/07 Telescoping joints for varying drill string lengths; Shock absorbers
• CPC Class Codes: E21B 19/006 including heave compensators
• CPC Class Codes: E21B 19/09 specially adapted for drilling underwater formations from a floating support using heave compensators supporting the drill string

Abstract

Device (11) for compensation of wave induced distance variations to a drill string between a floating drill rig and a seabed-fixed installation, comprising an extendable cylinder/piston unit (12) which is arranged to be able to compensate when the load exceeds a pre-determined threshold value. The cylinder (13) of the cylinder/piston unit (12) comprises a non-compressible liquid at both sides of a piston (14) positioned substantially in the middle of the cylinder (13) and is prevented from fluid communication with the surroundings. A control valve (19) is arranged to activate the device (11) by opening for fluid communication between the cylinder (13) and a gas containing accumulator (17) when the load exceeds a predetermined threshold value. The device is characterized by being a complete, self-supported unit comprising cylinder (13), piston (14) on a piston rod (15), accumulator (17), control valve (19) and drainage tank (20).

Claims

1-8. -8. (canceled)

9. A device for compensation of wave induced distance variations to a drill string between a floating drill rig and a seabed-fixed installation, comprising an extendable cylinder/piston unit (12) configured to be able to compensate when the load exceeds a pre-determined threshold value, the cylinder/piston unit (12) including a reciprocable piston (14) within a coaxial longitudinally extending cylinder (13) with a non-compressible liquid at both longitudinal sides of a piston (14), the piston (14) positioned substantially in the longitudinal middle of the cylinder (13) and being prevented from fluid communication with the surroundings in the base position, wherein at least one control valve (19) is arranged to activate the device (11) into an activated position by opening to allow fluid communication between the cylinder (13) and a gas containing accumulator (17) when the load exceeds a pre-determined threshold value, the device (11) being a complete self-supported unit comprising cylinder (13), piston (14) on a piston rod (15), accumulator (17), control valve (19) and drainage tank (20).

10. The device (11) of claim 9, wherein each accumulator (17) in its base position is filled with gas under pressure and is provided with a control valve (19) which upon activation allows fluid flow into and out from the accumulator.

11. The device (11) of claim 9, comprising at least one drainage tank (20) that temporarily receives excess liquid from the cylinder (13) when the device is activated, and a dump valve (21) between the cylinder (13) and the drainage tank (20) arranged to open to allow communication of said excess liquid.

12. The device (11) of claim 11, wherein all liquids are non-compressible.

13. The device (11) of claim 9, wherein all liquids are non-compressible.

14. The device (11) of claim 9, wherein the cylinder/piston unit (12) in its base position has a longitudinal length and is rigid, whereby the cylinder/piston unit (12) can transmit longitudinal tensional and compressional forces without changing its length.

15. The device (11) of claim 9, wherein the control valve (19) is arranged to measure the pressure continuously and to open at a pre-determined threshold pressure, thereby activating the device (11) to allow fluid communication between the cylinder (13) and the accumulator (17), thereby allowing the length of the cylinder/piston unit (12) to be freely hanged within mechanically determined limits.

16. The device (11) of claim 9, wherein after activation the device remains in the activated position until it is manually switched back to base position.

17. The device (11) of claim 9, comprising at least two cylinder/piston units (12), at least one accumulator (17), and at least one drainage tank (20) per cylinder/piston unit (12).