Flywheel-based energy storage on a heave-compensating drawworks

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#FIG. 1 is a diagrammatic illustration of the system and process of the present invention.

#FIG. 2 is a block diagram showing the processing of energy in accordance with the present invention.

#FIG. 3 is an illustration showing the use of the AC motors in association with the winch drum and the flywheel.

#Referring to FIG. 1, there is shown a drilling ship 10 as illustrated as floating on a body of water 12. The drilling ship 10 is utilized in association with heave-compensating drawworks 14. As can be seen, a derrick 16 extends upwardly from the deck 18 of ship 10. A sheave assembly 20 is positioned at the top of the derrick 16. The sheave assembly 20 supports a wire rope 22 extending thereover. Wire rope 22 extends downwardly so as to support a hook load 24 at an end of the wire rope 22. The hook load 24 is configured so as to support the drill string 26. It can be seen that the drill string 26 extends to the floor 18 of the ship 10 and downwardly through the body of water 12. Ultimately, the drill string 26 will have a bit on the end opposite the hook load 24 which is used for the drilling activities. It is important to note that the weight supported by the hook load 24 and by the wire rope 22 is extremely heavy. A winch drum 28 is connected to the opposite end of the wire rope 22 and supported on the deck 18 of the ship 10. The winch drum 28 is used for paying in and paying out the wire rope 22 in relation to the desired movement of the drill string 26 or the desired weight-on-bit at the end of the drill string 26.

#Since the water 12 will have wave action thereon, the ship 10 will tend to follow this wave action and heave upwardly and downwardly. Since it is desired to maintain a relatively constant weight-on-bit in association with the drilling activities of the drill string 26, the sheave assembly 20 and the associated wire rope 22 will need to raise and lower in relation to the wave motion of the water 12. When a wave is encountered and a ship elevates by reaching the crest of the wave, then the sheave assembly 20 and the associated wire rope 22 should be payed out by the winch drum 28 so as to maintain the drill string 26 at a constant position. On the other hand, when the ship 10 encounters a trough of the wave of water 12, it will be necessary for the winch drum 28 to rotate to draw in the wire rope 22 and to raise the sheave assembly 20 in order to maintain this proper position of the drill string 26. The hook load 24 can also be used for the lowering of the drill string 26 prior to drilling. Under these circumstances, the winch drum 28 will pay out the wire rope 22 so as to properly lower the hook load 24 for the purposes of lowering the drill string 26 to a desired underwater location.

#In the prior art, when the drill string 26 is lowered to its underwater location, the winch drum 28 would need to be braked so as to prevent undesired inertia. As such, the maximum speed of lowering of the drill string 26 was precisely controlled. It was not possible to achieve the maximum lowering rate because of the concern for the motor inertia and the need for braking.