JPS6214791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation source for S-wave logging used in a well containing borehole water, and more specifically, the present invention relates to an oscillation source for S-wave logging used in a well containing borehole water. This invention relates to an oscillation source that causes an oscillation force to act on a hole wall surface through water in the hole without using a mechanical mechanism.

PS logging is a method of directly measuring underground elastic wave velocities, that is, P wave (longitudinal wave) velocity and S wave (transverse wave) velocity, in a wellbore and investigating the elastic properties of the underground from these values.

In recent years, highly accurate elastic wave data deep underground has been required from fields such as earthquake engineering and resource engineering. However, as a device for measuring elastic waves deep underground, only the P-wave logging device is in widespread use. This is because P waves propagate at the fastest speed among elastic waves, so it is relatively easy to confirm, whereas S waves are caused by waves that propagate faster (mainly tube waves caused by P waves). This is because the waveform is easily visible and difficult to confirm.

On the other hand, as a method to suppress the radiation of P waves and effectively radiate S waves, the source force in one direction perpendicular to the hole axis is generated by operating the motion mechanism inside the source body. A method has also been proposed in which S-waves with excellent directivity are radiated in the direction orthogonal to the source force by applying positive and negative indirect pressure to the hole wall through the water in the hole (Unexamined Japanese Patent Publication No. Showa 54-
(See Publication No. 107401).

However, conventional methods, including this method, require some kind of mechanical mechanism, such as holding a rigid body that acts on vibration so that it can move freely in one direction, which inevitably increases the size and complexity of the device. It has the disadvantage that it not only radiates a certain amount of tube waves and P waves, which are interference waves for receiving S waves.

The purpose of the present invention is to eliminate the drawbacks of the prior art, to make the device smaller and simpler because it does not require a mechanical mechanism, and to avoid tube waves and other problems that hinder the reception of S waves. An object of the present invention is to provide an S-wave logging source that can almost completely prevent P-wave radiation.

In order to achieve this object, the present invention directly moves the water in the hole in contact with the rubber sheet by applying electromagnetic force from a coil to the magnetic fluid sealed with the rubber sheet to drive it. It is configured to apply a force to the hole wall.

Hereinafter, the present invention will be explained in detail based on the drawings.
FIG. 1 schematically shows an example of an oscillation source according to the present invention, and the basic configuration and operating principle will first be explained using it. The source is used in a borehole with borehole water. The probe 1 has a region inside thereof partitioned by a rubber sheet 2, and a magnetic fluid 3 is sealed within the region, and coil rings 4a, 4a and 4a are arranged near both ends outside the region.
4b is arranged. The rubber sheet 2 is in contact with the borehole water 5. Note that "magnetic fluid" here refers to something that has relatively strong magnetism and exhibits the behavior of a fluid, for example, a particle size of 100 Å.
A monomolecular layer of a surfactant is chemically adsorbed onto the surface of fine particles of magnetite or other ferrite, and then dispersed in water or an organic solvent.

Now, when the coil ring 4a is energized, a magnetic field is generated around it, and the magnetic fluid 3 moves in the X direction because it corresponds to the plunger of a solenoid in terms of a magnetic circuit. The mechanical motion of the magnetic fluid at this time is the fluid itself. Therefore, the borehole water 5 moves in the X direction without any volume change. In other words, it can be regarded as the same as moving the borehole water 5 directly in the X direction. This movement of the water 5 in the hole applies force to the hole wall 6 in the X direction, making it possible to radiate only the S wave in the direction of the hole axis. Note that when the coil ring 4a is no longer energized, the elasticity of the rubber sheet 2 causes the magnetic fluid 3 to return to its original state. Furthermore, when a current is passed through the coil ring 4b, the magnetic fluid 3 is driven in the opposite direction (in the -X direction), and the inversion record of the S wave can be easily obtained, so that confirmation can be made with certainty.

An embodiment of the vibration source according to the present invention is shown in FIGS. 2 and 3. A cylindrical outer case 10 is attached to the probe 1 in a direction perpendicular to its central axis, and the vibration source main body is housed inside the outer case 10 . The main body of the vibration source has a symmetrical structure, as clearly shown in FIG. A rubber sheet 2 that bulges outward at the center and is pressed through an O-ring 12, a pressing member 13 with a cylindrical flange that presses down the rubber sheet 2, and an inner magnetic yoke 14.
, coil rings 4a and 4b wound around a bobbin 15 that fits into the stepped portion of the inner magnetic yoke 14, and an outer magnetic yoke 1 that also serves as a set screw to tighten them.
It consists of 6. Note that numerals 17 and 18 are O-ring seals, respectively. A region surrounded by the rubber sheet 2 and the central non-magnetic cylindrical block 11 is filled with magnetic fluid 3. Yokes surrounding the coil rings 4a and 4b, that is, inner and outer magnetic yokes 1
4 and 16 have an open magnetic path structure, and the bulging end of the rubber sheet 2 is located near the open magnetic path. In other words, the magnetic fluid 3 sealed with the rubber sheet 2 can be considered to be similar to a plunger in a solenoid constituted by the coil rings 4a and 4b and the inner and outer magnetic yokes 14 and 16. Therefore, the coil ring 4a
If the coil ring 4b is energized, the entire magnetic fluid can be moved in the X direction, and conversely, if the coil ring 4b is energized, the entire magnetic fluid can be moved in the -X direction. When the electricity is turned off, the elasticity of the rubber sheet 2 causes the magnetic fluid 3 to return to its original position.

Such sources, along with geophones and the like, are inserted into the well water as a series of sondes. In fact, P waves, S waves
Figure 4 shows an example of application to wave logging. A weight 40 for facilitating the insertion of the sonde from below, and two stray geophones 41 and 4 each incorporating a vertical motion receiving element for P waves and a horizontal motion receiving element for S waves.
2, a filter tube 43 for blocking in-hole sound waves that interfere with the reception of S waves, and a preamplifier section 4
4. A damper 45 for preventing interference waves propagating through the sonde body, an oscillation source 46 incorporating the S-wave oscillation source according to the present invention and a separate P-wave oscillation source, and a vibration source 46 for driving the oscillation source 46. The source drivers 47 are successive in this order and are raised and lowered to a predetermined position in the borehole 10 by a winch 50 via a sheave 49. Further, a control recording device 52 and a battery 53 are installed on the ground surface.

A block diagram of the measurement system is shown in Figure 5. The transmission of signals and energy between the sonde assembly 54 and the control recording device 52 takes place by means of a logging cable 55. A measurement mode selection circuit 60 controls the vibration direction N or R and input switches 61 and 62. Power is supplied from the DC high voltage source 64 to the vibration source driver 47 . A shot pulse is applied to the vibration source driver 47 by the shot pulse generator 65, and the magnetic fluid 3 is heated to a predetermined N.
Or drive in the R direction. As a result, the water in the hole is moved without changing its volume, and only S waves can be radiated in the direction of the hole axis. For reference, the radiation pattern of S waves is shown in Figure 4. The radiated S waves are detected by stray geophones 41 and 42, amplified by a preamplifier 44, and sent to a 6-channel waveform storage device 66 on the ground, where they are temporarily stored and then sent to an 8-channel electromagnetic oscilloscope. A graph 67 is recorded on the recording paper along with time marks. The S wave can be reliably confirmed because the waveform is reversed by changing the direction of vibration (N and R). Analyzing the S wave velocity distribution etc. from these data is as follows.
Using the same method as before.

As described above, the present invention is configured so that the electromagnetic force from the coil ring acts on the magnetic fluid to drive it, and the water in the hole is directly moved through the rubber sheet to exert a force on the hole wall. Since there is no mechanical mechanism like a conventional vibration source, the device can be made smaller and simpler, and since the movable part is a magnetic fluid, it can be regarded as the same as directly moving the water in the hole, so the S wave Tube waves and P that impede reception
Wave radiation can be suppressed almost completely. That is, in order for the vibration source in the borehole water not to radiate P waves and tube waves, it is essential that there is no volume change at all due to the vibration action. However, as described in the above-mentioned Japanese Patent Application Laid-Open No. 54-107401, when a movable coil is suspended in a body and surrounded by a rubber tube, a space is formed between the coil and the body. Even though both end faces of the coil are in contact with the rubber tube before excitation, when the coil is then driven, for example, to the right, the rubber tube on the right is actively pushed and the displacement occurs, and the rubber tube on the left is displaced. Since the displacement caused by passively pulling the rubber tube part is large, a slight gap is created between the left side coil end face and the left rubber tube part facing the end face, and the volume change is reduced by that amount. The result was a nuisance. In contrast, in the vibration source of the present invention, by using a magnetic fluid as the movable body, the space equivalent to the above is eliminated, and by moving the entire body, it is possible to create an vibration source with no volume change. It can produce many excellent effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the operating principle of the vibration source according to the present invention, FIG. 2 is a sectional view showing an embodiment of the vibration source according to the present invention, FIG. 3 is a partially cutaway perspective view thereof, and FIG. The figure is an explanatory diagram showing an example of a usage state, and FIG. 5 is an explanatory diagram showing an example of a measurement system. DESCRIPTION OF SYMBOLS 1... Probe, 2... Rubber sheet, 3... Magnetic fluid, 4a, 4b... Coil ring, 5... Hole water, 6... Hole wall.

Claims (1)

[Claims] 1 It is inserted into a borehole that has borehole water, and by moving a movable body installed inside, a vibration source force is applied to the borehole wall surface in one direction perpendicular to the borehole axis through the borehole water that is in contact with it. In the S-wave vibration source to be applied,
The movable body is a rubber sheet and a magnetic fluid sealed by the rubber sheet, and an electromagnetic force is applied to the magnetic fluid by energizing an electromagnetic coil section provided near an outer end of the movable body, A driven vibration source for S-wave logging.