Marine seismic surveying in icy or obstructed waters

Abstract

A skeg mounts from the stern of a towing vessel and extends below the waterline. A channel in the skeg protects cables for steamers and a source of a seismic system deployed from the vessel. Tow points on the skeg lie below the water's surface and connect to towlines to support the steamers and source. A floatation device supports the source and tows below the water's surface to avoid ice floes. The streamers can have vehicles deployed thereon for controlling a position on the streamer. To facilitate locating the streamers, these vehicles on the streamers can be brought to the surface when clear of ice floes so that GPS readings can be obtained and communicated to a control system. After obtaining readings, the vehicles can be floated back under the surface. Deploying, using, and retrieving the system accounts for ice at the surface in icy regions. In addition, handling the seismic record can account for noise generated by ice impact events.

1 . (canceled) 
     
     
         2 . A marine seismic surveying apparatus for a vessel in water having an obstructed surface, the apparatus comprising:
 at least one streamer towed from the vessel below the obstructed surface of the water and detecting seismic energy;   at least one first controllable device disposed on the at least one streamer, the at least one controllable device having a vertical position controllable in the water relative to the obstructed surface,   a global positioning system receiver associated with the at least one first controllable device and obtaining first location information at least intermittently when positioned at least near the obstructed surface of the water;   an inertial navigation system associated with the at least one first controllable device and reckoning second location information of the at least one controllable device in the water in place of the first location information obtained with the receiver; and   at least one control system in communication with the receiver and the inertial navigation system and using the first and second location information to locate the at least one streamer.   
     
     
         3 . The apparatus of  claim 2 , further comprising at least one detector associated with the at least one first controllable device, the at least one detector detecting for an obstruction at the obstructed surface of the water and generating a detector signal in response thereto. 
     
     
         4 . The apparatus of  claim 3 , wherein the at least one detector comprises a sonar, an ice profiler, an optical sensor, a multi-beam fathometer, a camera, a sonar detecting when ice of a particular thickness is present at the obstructed surface, an optical sensor determining available light at the obstructed surface, or a digital camera feeding video or images along the at least one streamer to the vessel. 
     
     
         5 . The apparatus of  claim 3 , wherein the at least one control system receives the detector signal, the at least one control system signaling, in response to a detected absence of the obstruction at the obstructed surface, the at least at least one first controllable device to position the receiver at least near the obstructed surface and determining, from the first information of the receiver, a fixed location of the at least one controllable device to locate the at least one streamer. 
     
     
         6 . The apparatus of  claim 3 , wherein the at least one control system receives the detector signal, the at least one control system signaling, in response to a detected presence of the obstruction at the obstructed surface, the at least one controllable device to position the receiver below the obstructed surface and using the second information from inertial navigation system in conjunction with the fixed location to dead reckon an ongoing position of the at least one first controllable device to locate the at least one streamer. 
     
     
         7 . The apparatus of  claim 2 , wherein the at least one first controllable device operated in a first condition tows below the obstructed surface of the water and operated in a second condition tows at the obstructed surface of the water; and wherein the receiver is disposed on the at least one first controllable device and obtains the first information when the at least one first controllable device operated in the second condition positions the receiver at the obstructed surface of the water. 
     
     
         8 . The apparatus of  claim 2 , wherein the receiver deploys from the at least one first controllable device to the obstructed surface of the water to obtain the first information. 
     
     
         9 . The apparatus of  claim 2 , wherein the at least one first controllable device comprises one or more of a fin, a fillable bladder, and a shiftable mass to vertically control the at least one first controllable device in the water. 
     
     
         10 . The apparatus of  claim 2 , wherein the at least one first controllable device comprises a vehicle disposed on a distal end of the at least one streamer and being laterally and vertically controllable in the water. 
     
     
         11 . The apparatus of  claim 2 , further comprising at least one second controllable device disposed on the at least one streamer and being at least laterally controllable in the water. 
     
     
         12 . The apparatus of  claim 2 , further comprising an element producing controllable drag on the at least one streamer. 
     
     
         13 . The apparatus of  claim 2 , wherein the at least one control system dead reckons a first position of the at least one first controllable device based on the first and second information. 
     
     
         14 . The apparatus of  claim 13 , further comprising at least one location device disposed on the at least one streamer and obtaining third location information, the at least one control system determining a second position of a seismic signal detector on the at least one streamer based the first position and the third location information. 
     
     
         15 . The apparatus of  claim 14 , wherein the at least one location device comprises at least one compass obtaining at least one compass heading as the third location information of the at least one streamer. 
     
     
         16 . The apparatus of  claim 14 , wherein the at least one location device comprises at least one acoustic sensor obtaining acoustic cross-bracing as the third location information of the at least one streamer. 
     
     
         17 . The apparatus of  claim 2 , further comprising:
 at least one source towed from the vessel below the obstructed surface of the water and generating a seismic source signal; and   a submersible flotation device being towed below the obstructed surface of the water and supporting the at least one source at a level in the water.   
     
     
         18 . A marine seismic survey system for use with at least one vessel having a hull, the system comprising:
 a first sensor acoustically coupled to the hull of the at least one vessel and detecting impact information indicative of ice impacts against the hull;   a location device disposed on the at least one vessel and obtaining location information associated with the seismic survey system;   a source towable in water behind the at least one vessel and generating a seismic source signal;   at least one second sensor towable in the water behind the at least one vessel and detecting seismic energy;   at least one recorder operatively coupled to the first sensor and the location device and recording first information, the first information including the impact information, first of the location information, and first time information for the ice impacts against the hull, the at least one recorder operatively coupled to the at least one second sensor and the location device and recording second information, the second information including the detected seismic energy, second of the location information, and second time information for the detections of the seismic energy; and   at least one processor in communication with the at least one recorder, the at least one processor configured to process the second information in light of the first information and configured to produce a seismic record from the processing.   
     
     
         19 . A marine seismic survey method, comprising:
 detecting an ice impact event against a hull of at least one vessel;   recording impact information of the detected ice impact event associated with first location information and first time information for the detected ice impact event;   generating a seismic source signal with a source towed behind the at least one vessel;   detecting seismic energy with at least one sensor towed behind the at least one vessel;   recording seismic information of the detected seismic energy associated with second location information and second time information for the detected seismic energy; and   producing a seismic record by processing the seismic information in light of the impact information.   
     
     
         20 . The method of  claim 19 , wherein processing the seismic information in light of the impact information comprises filtering out the detected ice impact event from the seismic record. 
     
     
         21 . The method of  claim 19 , wherein processing the seismic information in light of the impact information comprises:
 isolating the detected ice impact event from the seismic record; and   using the isolated ice impact event as a source of seismic energy in the detected seismic energy.