Process and devices for producing pressure - or shear-waves in a

Details Process and devices for producing pressure - or shear-waves in a Process and devices for producing pressure - or shear-waves in a

1986-06-06

1989-01-10

Steinberger, Brian S.

Acoustics

Geophysical or subsurface exploration

Well logging

367175, 367 75, G01V 140

Patent

active

047967242

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to processes and devices for producing pressure- or shear-waves in a solid medium by mechanical action on the walls of a bore hole.


DESCRIPTION OF THE PRIOR ART

In order to perform seismic examinations of the earth, it is necessary to produce pressure-waves, the propagation parameters of which give information about the structure of underground formations. It is customary in this connection to bore holes into the ground and to create the impulse with an explosive charge, or to use forces acting perpendicularly on the ground surface to produce corresponding waves.


OBJECTS OF THE INVENTION

Especially for finding water veins in desert areas, a very high frequency impulse in the order of one kHz is required. Suitably, a force peak in the order of approximately 30 kN is to be applied in one millisecond. Mechanical, pneumatic and hydraulic devices are not suitable for this purpose.
Electrodynamic devices, which generate an impulse parallel to the bore hole axis, are already known. However, it is especially desirable that the forces are transmitted as efficiently as possible directly into the surrounding medium.
Finally, the device for carrying out the process according to the invention must be functional in a very rough environment, namely a bore hole with a diameter of approximately 20 cm and a depth of 20 m. Thus, the device should be as simple as possible.


SUMMARY OF THE INVENTION

According to the invention this purpose is achieved in that a short-duration current is passed through a primary coil for generating a magnetic field with directly repels a secondary coil, and in that this impulse is transmitted onto the bore hole walls in a direction perpendicular to the axis of the bore hole.
Details of the process according to the invention and devices for carrying out this process are given in the dependent claims and in the description, wherein several example embodiments are discussed with reference to the drawings, wherein:


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the physical operating action of the employed effect in a first embodiment,
FIG. 2 shows schematically the physical operating action of the employed effect in a second embodiment,
FIGS. 3a, b, c show diagrams of the resulting voltages and currents,
FIG. 4 shows the functionally essential part of one embodiment for producing impulses for pressure waves, directed radially out of the bore hole axis,
FIG. 5 is a section through an arrangement for producing radial impulses,
FIG. 6a is a section through an arrangement for producing tangential impulses for shear-waves,
FIG. 6b is a section through a further arrangement for producing tangential impulses for shear-waves,
FIG. 6c is a sectional view similar to FIGS. 6a and 6b, but showing at least two short-circuited secondary coils,
FIG. 7a shows a cut open section of a bore hole casing,
FIG. 7b shows a cut open section of a bore hole casing with a secondary coil integrated into the casing for producing radially effective impulses, and
FIG. 8 is a section through a bore hole casing with a secondary coil integrated into the casing for producing tangentially effective impulses.


DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE
OF THE INVENTION
FIG. 1 shows schematically a primary coil SP and a secondary coil SS, which are arranged one behind the other on an imaginary axis O. The secondary coil SS is short-circuited and has only one turn of a winding, and is therefore in the form of a ring. The primary and secondary coils together form a transformer having a short-circuited secondary coil. If a high frequency voltage impulse according to FIG. 3a is applied to the primary coil SP from a respective source of electrical power, then a current according to FIG. 3b is produced in this primary coil SP. A counter-current is induced in the secondary coil ring SS of the transformer. The time behavior of this counter-current is shown in FIG. 3c. The secondary current I.sub.s gets larger as the coils SP and

REFERENCES:
patent: 3061037 (1962-10-01), Evans
patent: 3258741 (1966-06-01), Clark
patent: 3334328 (1967-08-01), Burg et al.
patent: 3349366 (1967-10-01), Hanff
patent: 3593255 (1971-07-01), White
patent: 4207961 (1980-06-01), Kitsunezaki
patent: 4383591 (1983-05-01), Ogura
patent: 4394754 (1983-07-01), Waters
patent: 4541081 (1985-09-01), Smith
Article entitled, "Physik", by Dr. Christian Gerthsen, Springer-Verlag, Bin, Goettinger, Heidelberg, 1960, cover page & pp. 225 & 265.

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