Marine seismic cable handler
AssigneeWestern Geophysical Company of America
InventorsBen B. Thigpen, Joel J. Hebert
Life of this patent
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Abstract
A hydraulically-powered yo-yo reel for handling a marine seismic cable in shallow water. At the beginning of a recording episode, a partially reeled-in seismic cable is released to drift to a standstill behind a ship. Data are recorded. The cable is then accelerated to match the ships's velocity. Following the initial acceleration, the cable is superaccelerated as it is partially reeled in. A microprocessor adjusts a dwell time between recording episodes to compensate for small variations in the ship's velocity.
Claims6
An improved dual-purpose cable handler for manipulating a seismic-signal detector streamer cable towed through a body of water by a ship sailing at a desired base velocity, the ship including a sound source for generating seismic impulses and a recorder for processing seismic signals received by the detector streamer cable during a recording cycle, the improvement comprising:
- means for operating the cable handler in an intermittent towing mode including:
- a. means for decelerating said detector streamer cable substantially to a standstill;
- b. means for initiating a recording cycle;
- c. means for accelerating said detector streamer cable, at the end of the recording cycle, to match the ship's velocity;
- d. means for establishing a cable reel-in cycle;
- e. means for decelerating said detector streamer cable upon completion of the reel-in cycle;
- means for time-sequencing the operations of means a. through e. during a recording episode;
- and
- means for applying, between successive recording episodes, a vernier compensation for small velocity variations relative to a desired base velocity.
A method for manipulating a marine seismic-detector streamer cable, towed behind a ship at a desired base velocity, during successive recording episodes, comprising the steps of:
- decelerating said cable substantially to a standstill;
- recording seismic data;
- accelerating said seismic cable to match the ship's velocity;
- superaccelerating said seismic cable relative to the water;
- decelerating said seismic cable to match the ship's velocity;
- and
- interposing a desired dwell time between successive recording episodes to furnish a vernier compensation for small changes in the ship's velocity relative to the base velocity.
An improved cable handler for manipulating, during a recording episode, a marine seismic detector cable towed behind a ship at a desired base velocity, the ship including means for generating a seismic impulse and means for recording seismic signals during a recording cycle, the improvement comprising:
- a reversible, hydraulically powered cable reel and a tow line for coupling the streamer cable to said reel;
- a hydraulic control circuit for selectively programming the reel to operate in a reel-in mode, a positive reel-out mode, a free-wheeling mode and a lock-reel mode;
- a microprocessor, interconnected with the hydraulic control circuit, the seismic impulse generating means and the seismic signal recording means, for establishing a recording episode by sequentially setting the cable reel to the free-wheeling mode to decelerate the detector cable, initiating a recording cycle, setting the cable reel to the lock-reel mode to accelerate the detector cable, setting the cable reel to the reel-in mode to superaccelerate the detector cable, and setting the cable reel to the lock-reel mode to decelerate and stabilize the detector cable;
- and
- an automated navigation system coupled to the microprocessor for interposing a desired dwell time between the end of a first recording episode and the beginning of another recording episode to provide vernier compensation for small variations in the ship's velocity relative to the base velocity.
Dependencies are inferred from the claim text.