Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2001-06-15
2004-02-10
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C367S020000
Reexamination Certificate
active
06691038
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for controlling sea borne seismic data acquisition systems comprising an array of streamers, and in particular to the relative vertical and horizontal positioning of seismic streamers forming a seismic array towed behind a sea borne towing vessel.
DESCRIPTION OF THE RELATED ART
The related art discloses a wide variety of towed marine seismic tracking and positioning systems and methods typically comprising one or more seismic streamers and/or one or more seismic sources. Some these seismic tracking and positioning systems and methods utilize a main or host vessel and/or other-associated unmanned vessels or vehicles to tow the seismic array. Typically towing is controlled or guided by a central control system. The known marine seismic tow tracking and positioning systems and methods are comprised of apparatuses such as seismic hydrophone streamers and attached floats, paravanes, and/or buoyant members. Typically each streamer and control apparatus is connected to the host vessel by a line, cable or tether. Considerable towing power is required of a host vessel to tow existing seismic streamer systems, cables and interconnecting sensing devices. A typical host vessel is capable of towing a plurality of tow vessels and/or carrying a plurality of seismic streamers or arrays and associated support apparatus on the vessel's deck awaiting deployment.
One such tracking and positioning system for positioning and control of marine seismic streamers is taught in the international application published under the Patent Cooperation Treaty (PCT), International Publication Number WO 00/20895, international publication date Apr. 13, 2000. A marine seismic system with independently power tow vehicles is taught by U.S. Pat. No. 6,028,817. A control device for controlling the position of a marine seismic streamer is taught in the international application published under the Patent Cooperation Treaty (PCT), International Publication Number WO 98/28636, international publication date Jul. 2, 1998.
With known seismic cable tracking and positioning systems, the location and spacing of system components is limited by the type, size, and length of cables used and by the characteristics of the towing vehicles and other control devices utilized by the known seismic tracking and positioning systems. Typically, the plurality of towed seismic streamers form an array which is towed behind the host vessel. Typically, changing the configuration of such a towed streamer array, comprised of known components is a complex, cumbersome, time-consuming operation and can often become somewhat unwieldy. Moreover, the spatial and temporal positioning capability of known towing and tracking and positioning systems is limited.
There is no known seismic tracking and positioning system that enables independent and relative positioning of individual seismic streamer array elements, for example “birds”, seismic streamers, comprising sensors, sources and depth and position controls, for example to configure, manipulate and/or maintain a desired geometry of and within a towed seismic streamer array. There is also no known seismic tracking and positioning system that enables relative positioning and manipulation of an entire seismic streamer array. There is also no known tracking and positioning system that enables specification of a plurality of diverse acquisition and ancillary non-acquisition array geometries that facilitates run-time maintenance, retrieval and deployment of a towed seismic array. Moreover, there is no known seismic tracking and positioning system that tracks the geometry of the seismic streamer array and the relative positions of the individual streamers comprising array elements with respect to time and with respect to the earth's latitude and longitude so that towed seismic array data acquisition runs are repeatable, thereby enabling acquisition of four-dimensional geophysical data (x, y, z, time).
Thus, there is a need for a seismic acquisition tracking and positioning system that overcomes the above-mentioned shortcomings of known seismic data acquisition tracking and positioning systems. There has been a long-felt need for an efficient and effective towed marine seismic tracking and positioning system having system components that are easily and reliably tracked, controlled and positioned. There has also been a long-felt need for seismic data acquisition towing, tracking and positioning systems to provide sufficient positioning flexibility to enable efficient, accurate, and repeatable control of the relative and absolute horizontal and vertical positions of towed arrays and the streamers, sensors and sources within a towed array during seismic data acquisition.
SUMMARY OF THE INVENTION
The present position invention provides a method and apparatus for an active tracking and positioning system for a towed seismic streamer array. The present invention recognizes and addresses the previously mentioned shortcomings, problems and long-felt needs associated with known towed seismic tracking and positioning systems. The present invention provides a solution to the aforementioned problems and provides satisfactory meeting of those needs in its various embodiments and equivalents thereof.
The active tracking and positioning system of the present invention provides a method and apparatus that enables relative positional control of any number of towed seismic streamers. The present invention controls streamer positions horizontally and vertically using active control units positioned on each streamer within the seismic array. The three component (x, y, z) position of each streamer element, relative to the vessel, relative to each other and relative Earth coordinate latitude and longitude is controlled, tracked and stored with respect to time during each seismic data acquisition run. This stored data is referred to as legacy data. Environmental factors (wind speed, currents, temperature, salinity, etc), and maneuverability data for the streamers and geometry of the towed array (cable diameter, array type, deployed configuration, vessel type, device type, etc.) for the seismic data acquisition run are also sensed with respect to time and stored as legacy data. The acquisition of legacy data enables repetition of seismic data acquisition runs.
The present invention provides active streamer positioning devices (ASPDs) as control elements, which are installed on individual streamers comprising an array, alternatively at the diverter position, streamer head, along the length of the streamer or at the tail of the streamer. One or more ASPD is employed on each seismic array. The active control elements are also installed at the head tow point of an array, at the head or tail of one or more streamers comprising an array, and/or along any streamer comprising an element of an array. The control elements attached at the streamer head are alternatively detachably connected to the front of the array to facilitate detachment and removal of a single streamer element from the array during a data acquisition run.
The apparatus and method of the present invention enables a seismic array to be maneuvered as the towing vessel maintains it desired course or as the towing vessel maneuvers to assist in the repositioning of the array during a seismic data acquisition run. The present invention may alternatively employ methods such as force vectoring, active wings, or other known means of changing the spatial or temporal, that is the vertical or z-depth position of the streamer elements comprising the array. In addition to enabling change in the spatial and temporal positions of individual array elements, the tracking and positioning system enables maintenance of specific array position and geometry in the presence of variable environmental factors. In this mode, the control system of the present invention adjusts the lifting force of the streamer to accommodate variations in the tide, real-time current velocity and direction, water depth,
Barlow John
Madan Mossman & Sriram P.C.
Taylor Victor J.
WesternGeco L.L.C.
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