Acoustics – Geophysical or subsurface exploration – Seismic wave generation
Patent
1994-03-04
1995-12-12
Eldred, J. Woodrow
Acoustics
Geophysical or subsurface exploration
Seismic wave generation
367144, G01V 104
Patent
active
054751888
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for securing two or more seismic energy sources at fixed relative positions during firing of the sources, by placing them in a rigid framework consisting of end frames and intermediate longitudinal bars. The seismic energy sources are preferably of the airgun type.
In seismic surveys at sea the seismic signals are transmitted from energy sources which are normally arranged in groups. In order to increase the effect from energy sources these may also be arranged in sets, with several seismic energy sources or airguns being suspended in a frame-like arrangement, a so-called "cluster".
In an article in the periodical Geophysics, Vol. 44, no. 5 (May 1979), pages 865-879, there is a description of an arrangement of airguns in a group or "cluster" where the guns are secured in the frame at predetermined intervals, thus enabling them to be fired while in a state of constant geometry and without this geometry being altered by or after the firing. Such an assembly of airguns in a framework offers a number of advantages when conducting seismic surveys, but is a technique which has been known for some time and which does not constitute any part of the present invention.
In U.S. Pat. No. 4,719,987 (corresponding to Norwegian patent application no. 85 2459) an embodiment is illustrated for suspension of seismic energy sources in groups, where the energy sources are kept at fixed relative positions by means of a chain device which is attached to the sources by means of sleeves. However, during firing these energy sources will be able to move in relation to one another and it will not be possible to obtain 100% accurate positioning.
Furthermore, in NO patent no. 165 857 there is a description of a securing device for seismic energy sources in a framework, where the energy sources or airguns are fastened in a frame and secured in a shock-absorbing rubber packing. Although it is true that in this construction the airguns are secured at defined intervals, the device requires a relatively large amount of space and every frame is constructed for a special gun type, or the securing device has to be adpated to suit the respective gun types.
The object of the present invention is to provide a new device for securing two or more seismic energy sources at relative positions during firing of the source, which device, while forming a completely rigid framework for the seismic energy sources, should at the same time be as simple as possible, so that it is easy to stow away when not in use and also easy to assemble. A further object of the invention is to provide a rigid framework of a type which does not cause any bouncing or shifting of the guns in relation to one another, and which can be used for guns of different sizes so that it is only necessary to keep one single type of device in store.
In U.S. Pat. No. 4,970,046 it is also described a system for positioning of airguns. According to this U.S. patent the air guns are held in position and spaced from each other by means of single rod elements comprising shock absorbers, connecting means and clamps. The frame according to the U.S. patent is in reality a system in which a plurality of rod elements are provided between air guns in order to maintain the space between them. The system is time consuming in building up an air gun configuration and the rod elements will also have a certain influence on the pulses from the air guns.
Further examples on frames and fastening means for connecting air guns are shown in the U.S. Pat. Nos. 4,721,180, 4,858,205 and the European Patent Application 0368472.
Yet another object of the invention is to supply a device which is designed in such a way that the frame does not obstruct the positioning of the guns in any way, so that the transmitted sound pulses are in no way affected by the framework.
These objects are achieved by a device of the type described in the introduction, which is characterized by the features in the claims presented.
In the design of the frame in accordance with the invention all the above-ment
REFERENCES:
patent: 4721180 (1988-01-01), Haughland et al.
patent: 4858205 (1989-08-01), Harrison
patent: 4970046 (1990-11-01), Dolengowski
patent: 5051966 (1991-09-01), Gjestrum et al.
Cappelen Hans
Elholm Tor
Sarbotten Ayvind
Vatne Odd O.
Eldred J. Woodrow
Geco A.S.
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