Ocean bottom seismic sensor cable system including torque-relieving swivel

Abstract

An ocean bottom cable system includes: a cable adapted to be extended from a vessel at the surface of a body of water to the bottom of a body of water. The cable includes at least one electrical conductor or at least one optical fiber. A plurality of sensor units is disposed at spaced apart locations along the cable; and at least one swivel is disposed in the cable between the vessel and at least one of the sensor units. The swivel is adapted to enable relative rotation thereby relieving torsional stress between ends of the cable coupled thereto, and is adapted to transmit axial force along the cable therethrough.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Not applicable. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] Not applicable. BACKGROUND OF INVENTION [0003] 1. Field of the Invention [0004] The invention relates generally to the field of ocean bottom cable (OBC) seismic survey systems. More specifically, the invention is related to devices for improving the efficiency of deployment and retrieval of OBCs, and for reducing damage to OBCs during deployment and retrieval. [0005] 2. Background Art [0006] Seismic surveying performed in bodies of water (marine seismic surveying), such as lakes or the ocean, includes surveying performed with ocean bottom cables. [0007] An ocean bottom cable (OBC) normally includes one or more electrical and / or optical conductors extending along the length of the cable and sensors, or sensor “units”, coupled with or disposed along the cable at spaced apart locations. The sensor units typically include one or more particle motion senso...

AI Technical Summary

Problems solved by technology

However, there is a tendency of such shallower depth OBCs to assume the shape of the winch or reel on which the OBC is wound under tension.

In such cases, the loops may cause the OBC to kink when tension is reapplied as the OBC is retrieved from the water bottom.

Kinking may damage the cable, thus necessitating expensive repair or replacement of the cable.

Frequently, such torque will result in cable loops being formed.

While such loops are by themselves not harmful, they can cause the cable to kink when the cable is retrieved from the water bottom.

Such lateral movement is another source of torque which may result in loops in the OBCs.

Just as in the case of the single OBC survey operation, when an OBC having loops therein is retrieved, the rapid application of axial stress may result in kinks in the cable as the torque along the loop cannot be quickly relieved.

Images