Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Offshore prospecting
Patent
1992-04-27
1993-11-23
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Offshore prospecting
367154, G01V 138
Patent
active
052650669
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a marine seismic sea-bed cable and a method for the execution of marine exploration of the kind indicated in the introduction to the main claims. Generally, the invention concerns seismic exploration of the substratum at sea, where pressure waves and shear waves from the substratum are measured in response to the release of pressure and shear energy.
BACKGROUND ART
Marine seismic explorations are usually carried out by a seismic cable provided with several hydrophones being towed at a certain depth. Pressure waves can be released near the cable in several ways. This usually takes place by means of air guns. The pressure wave energy moves downwards through the substratum, but parts of the pressure waves are reflected from areas where there are acoustic impedance characteristics in the substratum. Hydrophones register the reflected pressure waves in the water and transform this information to electric signals which are received and processed on the seismic ship which tows the cable. Using this method, only reflected or converted shear to pressure energy is recorded. However, it is known that down in the substratum both pressure waves and shear waves are reflected. The shear waves do not travel in water and therefore cannot be detected by a hydrophone cable.
In U.S. Pat. No. 4,725,990, a marine shear cable is suggested, which is dragged along the seabed and which is provided with geophones. The cable is supposed to detect shear forces, but it has several disadvantages and weaknesses. During employment it will firstly be problematic classifying pressure waves which are reflected from the sea's surface. Secondly, all of the components are enclosed in a sleeve, which causes blows against the cable to travel to the geophones. Nor will the geophones achieve the desired contact with the sea bed. Furthermore, only one-component data is measured.
DISCLOSURE OF INVENTION
The aim of the present invention is to provide a new and improved cable for measurement of both shear waves and pressure waves.
The new and distinctive characteristics of the invention are described in the characterizing part of the main claims. Further advantageous characteristics are disclosed in the dependent claims.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be more closely described in the following, with reference to the accompanying drawings where:
FIG. 1 illustrates usage of a sea-bed cable during the carrying out of a seismic exploration according to the invention. FIG. 1A is a detailed view of the circled portion in FIG. 1.
FIG. 2 illustrates execution of a seismic exploration.
FIG. 3 shows an exploded overall view of the sphere of a geophone cable.
FIG. 4 shows a sketch of middle and lower ball part.
FIG. 5 shows a drawing of the clamping parts of the sphere.
FIG. 6 shows a drawing of upper sphere part.
FIG. 7 shows a section through middle geophone ball part.
FIG. 8 shows the sphere equipped with fins.
MODES FOR CARRYING OUT THE INVENTION
In FIG. 1 an underwater vessel 1 is shown, which tows a seismic cable 2 along the sea-bed 3 for seismic exploration of the substratum beneath the sea-bed. Such a cable will be rather long, often 2-3 kilometers. According to the embodiment of the invention shown in FIG. 1A, the seismic cable 2 comprises two parallel cables; a lower geophone cable 4 and an upper hydrophone cable 5. The geophone cable 4 is towed along the bed 3 with which it is to have optimum contact, whilst the hydrophone cable 5 floats at a predetermined distance above the geophone cable 4. Cable spheres 6 containing geophones are plated along the geophone cable 4 at constant intervals. The cable spheres 6 will be relatively heavy and make good contact with the bed.
In the area above each cable sphere on the geophone cable 4, a hydrophone element 7 will be placed on the hydrophone cable 5, the purpose of which will be described later. The hydrophone cable 5 is moreover of a type which is well known and commercially available. Hydrophones can also be arranged in simple flo
REFERENCES:
patent: 3713085 (1973-01-01), Laurent et al.
patent: 3939464 (1976-02-01), Svenson
patent: 3987404 (1976-10-01), Woodruff
patent: 4323988 (1982-04-01), Will et al.
patent: 4500980 (1985-02-01), Copeland
patent: 4725990 (1988-02-01), Zibilich, Jr.
patent: 4870625 (1989-09-01), Young
patent: 4920523 (1990-04-01), Kruka et al.
patent: 4953136 (1990-08-01), Kamata et al.
Berg Eivind
Svenning Bjornar
Den Norske Stats Oljeselskap A.S
Lobo Ian J.
LandOfFree
Seismic cable does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Seismic cable, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Seismic cable will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1855140