Method and node deployer for seismic surveys

1. A method for seismic survey by autonomous seismic nodes at a sea floor, comprising:

attaching the autonomous seismic nodes to a rope, wherein each of the autonomous seismic nodes comprises a recording unit, a memory for storing seismic signals, and a power source, and wherein the autonomous seismic nodes are detachably connected to the rope;

loading the rope with the autonomous seismic nodes into a magazine so that the rope with the autonomous seismic nodes is loosely packed in the magazine essentially without supporting structure to minimize a packing volume;

loading the magazine into a node deployer;

lowering the node deployer into the sea;

towing the node deployer above the sea floor;

deploying the rope with the autonomous seismic nodes at the sea floor from the magazine by two rollers driven by a motor arranged to pull the rope out of the magazine at a speed greater than a speed of a vessel;

collecting seismic data by the autonomous seismic nodes;

retrieving the rope with the autonomous seismic nodes from the sea floor by the two rollers driven by a motor arranged to pull the rope into the magazine, wherein the two rollers are configured to move an equal distance in opposite directions to allow a node to pass between them;

detaching the autonomous seismic nodes from the rope; and

unloading seismic data from the autonomous seismic nodes.

2. The method of claim 1 , wherein attaching the autonomous seismic nodes to the rope is done on a vessel.

3. The method of claim 1 , wherein the rope is held together by rubber bands or similar to keep it together during handling and stacking in the magazine.

4. The method of claim 1 , wherein the node deployer is lowered into the sea by an active heave compensated winch.

5. The method of claim 1 , wherein deploying the rope with the autonomous seismic nodes at the sea floor is done by letting the rope run out freely.

6. The method of claim 1 , wherein deploying the rope with the autonomous seismic nodes at the sea floor is done by paying out the rope in a controlled way.

7. The method of claim 1 , wherein the autonomous seismic nodes are deployed in pre-defined positions.

8. The method of claim 1 , wherein retrieving the rope with the seismic nodes from the sea floor is done by hauling the rope into a vessel.

9. The method of claim 8 , wherein the vessel is at the sea surface.

10. The method of claim 9 , comprising:

connecting a retrieval line to the rope; and

hauling the rope into the vessel by the retrieval line.

11. The method of claim 10 , comprising:

attaching a buoyant connection device to the rope; and

connecting the retrieval line to the buoyant connection device.

12. The method of claim 11 , comprising attaching multiple spaced apart buoyant connection devices to the rope, for enabling connecting the retrieval line to the rope in multiple positions.

13. The method of claim 1 , comprising the use of a ROY Remotely Operated Vehicle (ROV).

14. The method of claim 13 , wherein the ROV grips the rope or one of the autonomous seismic nodes.

15. The method of claim 1 , comprising separating the autonomous seismic nodes from the rope after retrieving the rope with the autonomous seismic nodes from the sea floor.

16. The method of claim 1 , wherein two or more node deployers are towed by a vessel, for simultaneously deploying two or more ropes with the autonomous seismic nodes.

17. A node deployer for subsea towing above a sea floor, for deploying a rope with autonomous seismic nodes at the sea floor, comprising:

a connection device for a towing cable;

a magazine containing the rope with the autonomous seismic nodes loosely packed inside the magazine essentially without supporting structure to minimize a packing volume inside the magazine, and the autonomous seismic nodes are detachably connected to the rope, wherein the rope with the autonomous seismic nodes are configured to be deployed from the magazine by two rollers driven by a motor arranged to pull the rope out of the magazine at a speed greater than a vessel, and the magazine is removably loaded into the node deployer, and wherein the autonomous seismic nodes each comprising a recorder; and

a memory for storing seismic signals and a power source;

wherein the rollers are configured to move an equal distance in opposite directions to allow a node to pass between them.

18. The node deployer of claim 17 , wherein the node deployer comprises a frame for the magazine.

19. The node deployer of claim 17 , wherein the magazine is self-supported.

20. The node deployer of claim 17 , wherein the magazine is supported by a surrounding structure when in the node deployer.

21. The node deployer of claim 17 , wherein the node deployer is adapted to let rope run out freely when deploying the rope.

22. The node deployer of claim 17 , wherein the node deployer is adapted to pay out the rope in a controlled way when deploying the rope.

23. The node deployer of claim 17 , comprising one or more deflectors for controlling lateral movement during towing.

24. The node deployer of claim 17 , comprising one or more flaps for controlling vertical movement during towing.

25. The node deployer of claim 17 , comprising instrumentation to identify obstacles in its path.

26. The node deployer of claim 17 , comprising a control loop which steers it away from obstacles in its path.

27. The node deployer of claim 17 , wherein the rollers are biased by a spring to provide a safe grip on the rope and node.

28. The node deployer of claim 27 , wherein the magazine comprises a plurality of trays configured to be set upon each other, wherein each tray is configured to receive a length of rope connecting the autonomous seismic nodes, which rope extends through the entire magazine.

29. The node deployer of claim 28 , wherein the tray comprises a plurality of compartments, each compartment is configured to receive a coil of the rope with the associated autonomous seismic nodes.

30. The node deployer of claim 28 , wherein the tray is open at the top for facilitating loading of the autonomous seismic nodes and rope.

31. The node deployer of claim 28 , further comprising a retainer configured to provide a tension to the rope as the rope leaves the magazine.

32. The node deployer of claim 31 , wherein the retainer is a spring loaded door.