Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
1999-03-29
2001-02-13
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
Reexamination Certificate
active
06188646
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of seismic exploration and more particularly, to a hydrophone carrier in a marine seismic streamer.
BACKGROUND OF THE INVENTION
Marine seismic exploration operations commonly include towing a seismic streamer behind a vessel. The seismic streamer includes data communications channels, power conductors, one or more strength members, and a number of sound-sensitive hydrophones. To maintain a very nearly neutral buoyancy, the streamer is commonly filled with a ballast fluid, such as kerosene or oil.
As the streamer is towed through the water during seismic operations, its primary function is to receive seismic signals at the plurality of hydrophones from subsurface geological structures, convert these signals to a voltage signal, and transmit these voltage signals to a central receiving station on board the vessel. The seismic signals are very often very weak, and can be masked by noise from a variety of sources. It is therefore imperative that these sources of noise be minimized so as not to interfere with the seismic signal of interest. This means that the signal to noise ratio of the sound receiving apparatus should be as high as possible.
Large diameter fluid-filled cables have achieved excellent signal to noise characteristics, but these cables are expensive, cumbersome, heavy, and not well suited to seismic operations in heavy weather at sea. Consequently, more recent fluid-filled cables have smaller diameters, at the cost of very fine signal quality. However, these smaller diameters cables are more robust, lighter, less expensive, easier to tow and operate, and have demonstrated adequate signal quality in most operating situations.
Even the smaller diameter streamer cables have their ballast fluid contained with a thin plastic jacket, typically 3-4 mm thick. This skin is susceptible to damage during normal streamer deployment and retrieval operations, and may also be easily damaged by objects in the water, by accidental contact with other streamers, and by a number of common hazards. Other internal components of the streamer cable are also susceptible to damage during normal streamer deployment and retrieval and from hazardous operating conditions. These factors, among others, have led to the developments today in solid-filled cables. Solid-filled cables are more robust and suffer less damage from normal operations and hazard conditions.
Solid-filled streamers include groups of hydrophones spaced apart along the length of the cable. Ideally, the hydrophones would be isolated from any noise in the cable, while positioned to receive the maximum amount of the seismic signal of interest. The hydrophones along the cable are commonly mounted within a hydrophone carrier, which is an integral portion of the cable.
Thus, there is a need for a hydrophone carrier in a solid-filled seismic cable which is robust, inexpensive, and easily accessible for repairs while the towing vessel is deployed at sea. The carrier should be as strong as the rest of the cable, during all phases of operation, including steady state steaming, heavy weather (which can induce longitudinal jerks in the cable) and deployment and retrieval operations in which the cable is reeled onto a winch. The carrier should also isolate the hydrophones from noise conducted along the cable, while exposing the hydrophones to the seismic signal without damping the signal.
SUMMARY OF THE INVENTION
The present invention addresses these and other challenges of the prior art in a solid seismic streamer. One or more hydrophones is mounted within a chamber of the streamer and the chamber includes openings which permit sea water to flow into the chamber. The openings also provide for free communication of seismic signals directly onto the hydrophone elements within the chamber.
The chamber is formed by a cylindrical chamber wall, preferably made of titanium, which is formed as a top half and a bottom half which may be bolted together or otherwise joined. The chamber wall mates with a complementary annular groove in each of a pair of collars. The collars are similarly formed as a top half and a bottom half which may be bolted together or otherwise joined. The chamber is also bounded on its interior by a central member, or a covering for the central member. The central member includes the power and data communications conductors, as well as at least one strength member.
The hydrophone element is preferably formed as a pair of opposed piezoelectric elements or fiber optic sensors mounted to a common support structure. The support structure is in turn enclosed within a sealed tube which is filled with a fluid, preferably a nonorganic oil. The piezoelectric elements are electrically coupled through a stuffing tube plugging one end of the tube for connection to the central member. Other structures for the hydrophone element are equally preferred, including a free-flooding hydrophone mounting, or an optical fiber sensor.
These and other features of this invention will be apparent to those skilled in the art from a review of the following description along with the accompanying drawings.
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Craig Gary
Erath Louis
Lamance David
Luscombe John
Maples Michael
Felsman, Bradley, Vaden, Gunter & Dillon L.L.P.
Pihulic Daniel T.
Syntron Inc.
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