Acoustics – Geophysical or subsurface exploration – Well logging
Patent
1993-07-08
1995-05-16
Lobo, Ian J.
Acoustics
Geophysical or subsurface exploration
Well logging
181121, 175 1, G01V 102, G01V 1147, G01V 140
Patent
active
054162815
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a wave source provided in a bore hole, and more particularly to a high-output inside bore hole wave source for generating elastic waves in the wall of a bore hole by dropping a deadweight onto a laminate of a plurality of alternately piled resilient members and plate members so as to deform the resilient members. This wave source is effectively applied to a velocity logging system used in a water-holding bore hole, and to the tomography for three-dimensionally analyzing the wave characteristics of a wide-range of ground.
BACKGROUND OF THE INVENTION
The wave characteristics of the ground formation constitute important basic data for the antiseismic designing of various kinds of buildings and and various kinds of structures formed by civil engineering. In order to investigate the elastic properties of the underground, a PS (P waves and S waves) velocity logging system for directly measuring the propagation of an elastic wave (P wave and S wave) in a bore hole made in the ground is used. The velocity logging is a technique for determining, on the basis of a waveform record, the arrival time of the elastic waves sent out from a wave source to a wave receiver.
Various types of bore hole wave sources have heretofore been developed. Typical examples of bore hole wave sources are disclosed in Japanese Patent Publication Nos. 58-52191/1983, 61-43669/1986, 62-14791/1987 and 62-14792/1987, and U.S. Pat. No. 4,383,591. All of these apparatuses consist basically of a structure provided with a movable member (hammer) which can be moved freely in the direction perpendicular to the axis of a bore hole, and a mechanism for driving the movable member. Such a wave source is set in a water-holding bore hole, and a vibratory force is exerted on a wall surface of the bore hole in a direction perpendicular to the axis of the bore hole by momentarily driving the movable member. The driving mechanism in use usually consists of an electromagnetic solenoid.
However, the conventional electromagnetic hammer type bore hole wave source is driven by an electromagnetic solenoid, and the diameter of the bore hole is comparatively small in general. Therefore, since the outer diameter of the wave source cannot be increased, there is a limit to the magnitude of a vibratory force which can be generated, and the range of application of the wave source is restricted. This wave source is effectively used, for example, in the case where PS wave logging operations are carried out at various depths with a series of probes, in each of which a wave source and a wave receiver are incorporated, inserted in a bore hole without being fixed to a wall surface of the bore hole. However, it is difficult to apply this wave source which has only a limited range of wave propagation to the case where inter-bore hole velocity measurement using two bore holes is conducted.
In recent years, the tomographic techniques for measuring the velocity of elastic waves between two bore holes, and three-dimensionally expressing (tomographically imaging) the wave characteristics over a wide range of underground by using computer-aided data processing techniques have been introduced. According to these techniques, a wave source is set in a wave generating bore hole, one of two bore holes, and multiple connected wave receivers are inserted in a wave receiving bore hole, the other of the two bore holes. The velocity of elastic waves is then measured with the wave source setting position (depth) varied, and the wave generating bore hole and wave receiving bore hole are interchanged with each other. However, when the above-mentioned conventional electromagnetic hammer type bore hole wave source is used, a signal can travel an inter-bore hole distance of only up to 10 m. Consequently, it becomes necessary to make a larger number of bore holes, and the conventional wave source encounters difficulties in practical use.
There is an explosive as a known wave source having a large vibratory force. When an explosive is used, elas
REFERENCES:
patent: 4252210 (1981-02-01), Sodich
patent: 4383591 (1983-05-01), Ogura
patent: 4648478 (1987-03-01), Dedole et al.
patent: 4671379 (1987-06-01), Kennedy et al.
patent: 4773501 (1988-09-01), Dedole et al.
patent: 4796723 (1989-01-01), Laurent et al.
Lobo Ian J.
Oyo Corporation
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