Variable buoyancy control and recovery system for seismic data acquisition

1. A ballast module comprising:

a housing adapted for mounting coaxially over an outer jacket of a seismic cable system configured for acquiring seismic data;

a reservoir disposed within the housing, the reservoir configured to transfer a ballast medium between the reservoir and a volume defined within the outer jacket of the seismic cable system; and

a controller configured to selectively operate the reservoir to control buoyancy of the seismic cable system, wherein the buoyancy is responsive to changes in the volume based on the transfer of the ballast medium during acquisition of the seismic data by the seismic cable system.

2. The ballast module of claim 1 , further comprising an interface configured for communications between the controller and an external trim control processor, wherein the controller is configured to selectively operate the reservoir to provide real-time buoyancy and trim control along a length of the seismic cable system in response to the communications, during acquisition of the seismic data.

3. The ballast module of claim 1 , further comprising a pressure sensor in communication with a water column external to the housing, wherein the pressure sensor is responsive to depth in the water column and the controller is configured to selectively operate the reservoir based on the depth in the water column.

4. The ballast module of claim 1 , further comprising a transfer mechanism configured to transfer the ballast medium into the volume defined within the outer jacket of the seismic cable system in response to control signals from the controller.

5. The ballast module of claim 4 , wherein the housing is configured to mount in-line between two adjacent sections of the seismic cable system, wherein the transfer mechanism is configured to transfer the ballast medium into a core of one or both of the two adjacent sections.

6. The ballast module of claim 5 , further comprising an electronics module configured for data communication between the two adjacent sections during acquisition of the seismic data.

7. The ballast module of claim 5 , further comprising first and second axial couplings configured for connecting the housing in-line between the two adjacent sections of the seismic cable system.

8. The ballast module of claim 4 , wherein the transfer mechanism comprises a pump or valve configured to transfer the ballast medium between the reservoir and the volume defined in the outer jacket of the seismic cable system.

9. A seismic data acquisition system comprising:

a seismic cable configured for acquiring seismic data; and

a ballast module disposed along the seismic cable, wherein the ballast module comprises:

a housing comprising axial couplings for removably mounting the ballast module between two adjacent sections of the seismic cable;

a reservoir disposed within the housing, the reservoir containing a ballast fluid; and

a transfer mechanism coupled to the reservoir, the transfer mechanism configured to transfer the ballast fluid from the reservoir, through at least one of the axial couplings, and to a volume defined within a cable jacket of at least one of the two adjacent sections of the seismic cable,

wherein buoyancy along a length of the seismic cable is controlled by changes in the volume defined within the cable jacket, responsive to the transfer of the ballast fluid.

10. The system of claim 9 , further comprising a processor in communication with the ballast module, the processor configured to trim the buoyancy of the seismic cable along the length thereof, wherein the buoyancy of the seismic cable is responsive to selective transfer of the ballast fluid as determined by the processor.

11. The system of claim 9 , further comprising one or more interfaces configured for peer-to-peer communication of a recovery signal in the ballast module, whereby the ballast module is configured to transfer the ballast fluid to provide positive buoyancy to an adjacent section of the seismic cable.

12. The system of claim 9 , further comprising a port defined in the reservoir, the port configured for one or both of replenishing the ballast fluid or extracting the ballast fluid to an external vessel disposed outside the housing.

13. The system of claim 9 , wherein the housing is configured to mount in-line between the two adjacent sections of the seismic cable, wherein the transfer mechanism is configured to transfer the ballast fluid into a core of one or both of the two adjacent sections.

14. A method comprising:

deploying a seismic cable to a seismic medium;

acquiring seismic data with the seismic cable;

operating a ballast module to transfer a ballast medium between a reservoir of the ballast module and a cable jacket of a core of one or both of two adjacent sections of the seismic cable, wherein the reservoir is disposed within a housing of the ballast module, wherein the housing comprises axial couplings that removably mount the ballast module in-line between the two adjacent sections of the seismic cable; and

controlling a buoyancy of the seismic cable, wherein the buoyancy is responsive to the transfer of the ballast medium from the reservoir to a volume defined within the cable jacket of one or both of the two adjacent sections.

15. The method of claim 14 , wherein the volume is responsive to radial expansion or contraction of the cable jacket upon the transfer of the ballast medium.

16. The method of claim 14 , further comprising controlling trim along one or both of the two adjacent sections of the seismic cable during acquisition of the seismic data, wherein a depth of the seismic cable is maintained responsive to the buoyancy.

17. The method of claim 16 , further comprising retrieving the seismic cable to a seismic vessel and storing the seismic cable between successive acquisitions of the seismic data with the ballast module mounted in-line between the two adjacent sections.

18. The method of claim 17 , further comprising one or more of extracting the ballast medium from the reservoir before storing the seismic cable and replenishing the ballast medium in the reservoir prior to deploying the seismic cable.