Ships – Towing or pushing – Submerged object
Reexamination Certificate
1999-12-09
2001-04-17
Swinehart, Ed (Department: 3617)
Ships
Towing or pushing
Submerged object
C114S254000
Reexamination Certificate
active
06216627
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to seismic survey vessels, and is more particularly concerned with seismic survey vessels suitable for use in performing 3D marine seismic surveys covering large areas.
In order to perform a 3D marine seismic survey, a plurality of seismic streamers, each typically several thousand meters long and containing arrays of hydrophones and associated electronic equipment distributed along its length, are towed at about 5 knots behind a seismic survey vessel, which also tows one or more seismic sources, typically air guns. Acoustic signals produced by the seismic sources are directed down through the water into the earth beneath, where they are reflected from the various strata. The reflected signals are received by the hydrophones in the streamers, digitised and then transmitted to the seismic survey vessel, where they are recorded and at least partially processed with the ultimate aim of building up a representation of the earth strata in the area being surveyed.
At the present time, a typical streamer array used by the Applicant comprises a 700 meter wide array of eight evenly spaced streamers, each about 4000 meters long. The streamers are towed by their lead-ins, ie the armoured electrical cables that convey electrical power, control and data signals between the vessel and the streamers, as described in the Applicant's U.S. Pat. No. 4,798,156, and their spread is controlled and maintained by MONOWING deflectors of the kind described in the Applicant's U.S. Pat. No. 5,357,892.
An array of this relatively large size allows 3D seismic surveys of large areas to be performed very efficiently. However, because the cost of performing such surveys is so high, there is continuous pressure to improve efficiency still further.
SUMMARY OF THE INVENTION
One way of achieving this is to use even wider streamer arrays, containing even.
According to the present invention, therefore, there is provided a seismic survey vessel having a displacement monohull, and powered drum means and cooperating guide means for deploying and recovering seismic streamers over the stern of the vessel via a streamer deck disposed at a substantial height above the waterline of the vessel, wherein the drum means are mounted substantially amidships in the vessel, the streamer deck at the stern of the vessel projects laterally outwardly from the hull of the vessel on both sides of the centre line of the vessel and is wider than the remainder of the vessel, and the guide means includes guide devices distributed across substantially the whole width of the streamer deck to facilitate the lateral spreading of the streamers.
In a preferred embodiment of the invention, the streamer deck of the vessel is an upper deck (although not necessarily the uppermost deck), at a height such that when the vessel is normally docked, the deck is well above the dock.
Preferably the width of the streamer deck decreases progressively from the stern of the vessel until it becomes substantially equal to the width of the vessel amidships.
Advantageously, at least parts of the drum means are mounted in the vessel at a level lower than the streamer deck.
The vessel preferably includes a further deck below the streamer deck at the stern of the vessel, said further deck being provided with means for deploying and recovering seismic source means over the stern of the vessel.
In a particularly advantageous implementation of the invention, the guide means comprises a respective streamer handling apparatus associated with each of a plurality of the streamers, each such apparatus comprising:
a beam;
means for mounting the beam above normal head height above the streamer deck of the vessel, such that the beam extends generally longitudinally of the vessel, the mounting means including a pivotal connection to the sternmost end of the beam permitting said end to pivot about a horizontal axis extending generally transversely of the beam, and support means for lowering and raising the other end of the beam towards and away from the streamer deck; and
a respective one of said guide devices, each such guide device comprising pulley means secured to and movable along the beam.
Advantageously, the mounting means is secured to the underside of a further deck of the vessel, above the streamer deck.
Conveniently, the pulley means comprises carriage means movable along the beam, a pulley device, and means for suspending the pulley device beneath the carriage means.
Preferably, the suspension means comprises a collar which is rotatably supported on the carriage means and which is rotatable about the longitudinal axis of the beam.
Additionally, the pulley device is preferably pivotable about a horizontal axis which extends generally transversely of the beam.
The carriage means preferably includes at least one hydraulic motor arranged to move it in both directions along the beam, and is advantageously provided with hoisting means at its sternmost end.
Conveniently, the support means comprises a telescopic member which is pivotally connected at one end to the mounting means and at the other end to said other end of the beam, and is hydraulically operated.
The apparatus may further comprise downwardly projecting guidance means which is positioned at said other end of the beam and which engages and pushes down the streamer when said other end of the beam is lowered.
REFERENCES:
patent: 4313392 (1982-02-01), Guenther et al.
patent: 245957 (1987-11-01), None
Aanonsen Oyvind
Johnsen Baard
Williamson Mark Richard
Bouchard John H
Schlumberger Technology Corporation
Swinehart Ed
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