Hybrid tensioning of riser string

1. An apparatus, comprising:

a direct current (DC) power distribution bus;

an energy storage system coupled to the DC power distribution bus wherein the energy storage system comprises:

an energy storage device; and

a bi-directional power converter coupled to the energy storage device and the DC power distribution bus;

a power dissipater coupled to the DC power distribution bus;

a drilling riser;

a plurality of wires coupled to the drilling riser;

a first and second electrical tensioner coupled to the drilling riser via a first and a second wire of the plurality of wires and coupled to the power distribution bus;

a hydro-pneumatic tensioner coupled to the drilling riser via a third wire of the plurality of wires; and

a controller configured:

to distribute tension to the first and second electrical tensioners; and

to control the first and second electrical tensioners to adjust a tension of the first and second wires;

to transfer energy from the energy storage device to at least one of the first and second electrical tensioners;

to store energy from at least one of the first and second electrical tensioners in the energy storage device;

to measure tensions delivered by the hydro-pneumatic and electrical tensioners; and

to determine a tension for the first and second electrical tensioners based, in part, on the measured tensions of the hydro-pneumatic and electrical tensioners.

2. The apparatus of claim 1 , in

which the controller further determines the tension for the first and second electrical tensioners based on at least one of:

a drilling vessel heave relative position;

a drilling vessel velocity and acceleration;

a drilling riser position;

a drilling riser velocity;

a drilling riser acceleration; and

a tension measurement.

3. The apparatus of claim 1 , further comprising: a unidirectional power converter coupled to the power dissipater and the DC power distribution bus.

4. The apparatus of claim 1 , in which the controller is further configured to control the distance between a lower marine riser package and a blowout preventer by adjusting the length of the plurality of wires to compensate for vessel heave motion in an active heave compensation mode.

5. The apparatus of claim 1 , in which the controller is further configured to control the first and second electrical tensioners to apply dynamic tensions to reduce resonant conditions in the drilling riser in a vortex-induced vibration (VIV) suppression mode.

6. The apparatus of claim 1 , in which the controller is further configured to control the first and second electrical tensioners to dynamic control an upper pulling force on the drilling riser in an anti-recoil mode.

7. The apparatus of claim 1 , in which the controller is further configured to control the first and second electrical tensioners to control a relative position of the drilling riser with respect to a vessel position in water to eliminate a mass spring effect in the drilling riser during movement of the vessel from a first well center to a second different well center.

8. The apparatus of claim 1 , in which the controller is further configured to adjust the length of the first and second wires to reposition the drilling riser on a different drilling station for a dual activity drilling vessel.

9. The apparatus of claim 1 , further comprising:

a position sensor coupled to the electric tensioner and coupled to the controller;

a motion reference unit (MRU) attached to the drilling riser and coupled to the electric tensioner and coupled to the controller, in which the controller is configured to control the first and second electrical tensioners based, in part, on data received from the position sensor and the motion reference unit, in which the controller comprises:

a first controller executing an inner feedback loop; and

a second controller executing an outer feedback loop.

10. The apparatus of claim 9 , wherein the first controller is a proportional-integral-derivative (PID) controller, and wherein the second controller is a proportional-integral-derivative (PID) controller.

11. A method, comprising:

measuring a tension delivered by a tensioner;

determining a tension for a plurality of electrical tensioners based, in part, on the measured tension;

distributing the determined tension to the plurality of electrical tensioners;

controlling the plurality of electrical tensioners based, in part, on the determined tension;

transferring energy from an energy storage device to an electrical tensioner of the plurality of electrical tensioners; and

storing energy from an electrical tensioner of the plurality of electrical tensioners in an energy storage device.

12. The method of claim 11 , in which measuring a tension delivered by a tensioner comprises measuring a tension delivered by a hydro-pneumatic tensioner.

13. The method of claim 11 , in which the step of controlling the plurality of electrical tensioners comprises compensating for vessel heave motion in an active heave compensation mode.

14. The method of claim 11 , in which the step of controlling the plurality of electrical tensioners comprises reducing resonant conditions in a drilling string in a vortex-induced vibration (VIV) suppression mode.

15. The method of claim 11 , in which the step of controlling the plurality of electrical tensioners comprises dynamic controlling an upper pulling force on the drilling riser in an anti-recoil mode.

16. The method of claim 11 , further comprising harvesting wave energy by:

applying a larger tension from the plurality of electrical tensioners when a vessel is rising up; and

applying a smaller tension from the plurality of electrical tensioners when the vessel is falling down.

17. The method of claim 13 , further comprising managing energy in the energy storage device based on at least one of state of charge, power, voltage, and current.

18. The method of claim 13 , wherein determining the tension for a plurality of electrical tensioners is further based on at least one of:

the tension delivered by a hydro-pneumatic tensioner;

a total required tension of an entire system;

a total number of hydro-pneumatic tensioners in the system; and

a total number of electrical tensioners in the system.

19. An apparatus, comprising:

a direct current (DC) power distribution bus;

a drilling riser;

a plurality of wires coupled to the drilling riser;

a first and second electrical tensioner coupled to the drilling riser via a first and a second wire of the plurality of wires and coupled to the power distribution bus;

a controller configured:

to distribute tension to the first and second electrical tensioners; and

to control the first and second electrical tensioners to adjust a tension of the first and second wires;

a position sensor coupled to the electric tensioner and coupled to the controller; and

a motion reference unit (MRU) attached to the drilling riser and coupled to the electric tensioner and coupled to the controller, in which the controller is configured to control the first and second electrical tensioners based, in part, on data received from the position sensor and the motion reference unit, in which the controller comprises:

a first controller executing an inner feedback loop; and

a second controller executing an outer feedback loop.

20. The apparatus of claim 19 , further comprising:

a hydro-pneumatic tensioner coupled to the drilling riser via a third wire of the plurality of wires;

wherein the controller is further configured:

to measure tensions delivered by the hydro-pneumatic and electrical tensioners; and

to determine a tension for the first and second electrical tensioners based, in part, on the measured tensions of the hydro-pneumatic and electrical tensioners.

21. The apparatus of claim 20 , in which the controller further determines the tension for the first and second electrical tensioners based on at least one of:

a drilling vessel heave relative position;

a drilling vessel velocity and acceleration;

a drilling riser position;

a drilling riser velocity;

a drilling riser acceleration; and

a tension measurement.

22. The apparatus of claim 19 , further comprising:

an energy storage system coupled to the DC power distribution bus; and

a power dissipater coupled to the DC power distribution bus.

23. The apparatus of claim 22 , wherein the energy storage system comprises:

an energy storage device; and

a bi-directional power converter coupled to the energy storage device and the DC power distribution bus.

24. The apparatus of claim 22 , further comprising: a unidirectional power converter coupled to the power dissipater and the DC power distribution bus.

25. The apparatus of claim 19 , in which the controller is further configured to control the distance between a lower marine riser package and a blowout preventer by adjusting the length of the plurality of wires to compensate for vessel heave motion in an active heave compensation mode.

26. The apparatus of claim 19 , in which the controller is further configured to control the first and second electrical tensioners to apply dynamic tensions to reduce resonant conditions in the drilling riser in a vortex- induced vibration (VIV) suppression mode.

27. The apparatus of claim 19 , in which the controller is further configured to control the first and second electrical tensioners to dynamic control an upper pulling force on the drilling riser in an anti-recoil mode.

28. The apparatus of claim 19 , in which the controller is further configured to control the first and second electrical tensioners to control a relative position of the drilling riser with respect to a vessel position in water to eliminate a mass spring effect in the drilling riser during movement of the vessel from a first well center to a second different well center.

29. The apparatus of claim 19 , in which the controller is further configured to adjust the length of the first and second wires to reposition the drilling riser on a different drilling station for a dual activity drilling vessel.

30. The apparatus of claim 19 , wherein the first controller is a proportional-integral-derivative (PID) controller, and wherein the second controller is a proportional-integral-derivative (PID) controller.