JPH0820438B2 - Nondestructive measurement method of physical properties of formation using acoustic wave - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive measurement method using acoustic waves of physical properties of a stratum, and is particularly suitable for use in soil investigation for planning and designing civil works and foundation works. The purpose is to obtain cross-sectional distributions such as porosity, water permeability, sediment changes, and shear deformation rate and shear force in the seabed sedimentary layer. More specifically, the present invention relates to the use of pseudo-random binary sequence code driven acoustic transfer in a liquid infiltrated sedimentary layer.

[0002]

2. Description of the Related Art "Synthetic Seismograms for Mar"
ine Sediments and Determination of Porosity an
d Permerbility (synthetic seismic record of seafloor sediments and determination of porosity and permeability) "(Geophysics, Volume 53,
No. 8 (August 1988, pp. 1056-1057), the inventor has published a numerical simulation of vertical seismic profiles of submarine sediments. The vertical seismic profile of the form cited in this paper is very useful for exploration of alluvial deposits, geotechnical problem solving, and construction of underwater structure projects. In a typical vertical seismic profile, high power electrical seismic sources have been used to study submarine sediments. The frequency range that can be used in such studies has been found to be approximately 100 Hz to 200 Hz, which can lead to transmission distances in seabed sediments of up to 1000 m or more.

In the series of tests described in the above article, a single exploration hole was used in which the source of seismic energy and the receiver were both placed in the same exploration hole to obtain a vertical seismic profile. Was trying to get. As reported in detail in the above paper, very interesting results were obtained even under such arrangement conditions.

As described in the above paper, by using the vertical seismic profile, theoretically and practically valid results can be obtained. Using the Biot's theory and the results obtained by the vertical seismic profile method to calculate the spectral ratio for the synthetic example,
It is possible to determine the porosity and permeability of the seabed sedimentary layer.
However, it has been desired to more accurately determine the physical properties of the sedimentary layer, and in particular to obtain an accurate cross-sectional distribution of changes in porosity, water permeability and sediment.

"Measurements of Acoustic Wave
Velocities and Attenuation in Marine
Sediments (Measurement of acoustic wave velocity and attenuation in seafloor sediments) "(Turgut and Yamamoto, J. Acoust.
Soc. Am. 87 (6), June 1990), a nondestructive method for measuring the physical properties of a deposited layer is discussed (see Japanese Patent Application No. 2-333477). This method is especially applied to seabed sedimentary layers and is useful for obtaining cross-sectional distributions of porosity and permeability values. This method
In addition, the change of the deposited material, the shear deformation rate and the shear force will be clarified. In this method, velocity measurements are obtained by propagating the seismic energy signal directly from the source to the receiver by direct interhole tomography. This method provides much greater accuracy and clarity than ever without the use of conventional inter-hole measurement techniques. Seismic energy is applied between two or more vertically spaced wells that are spaced apart from each other.

[0006]

However, there is a difficulty in using such a technique in a noisy environment such as an iron foundry. There was a limit to the distance that I could separate. Furthermore, there are problems when using such measurement techniques at high frequencies.

That is, the conventional oscillation sources are explosives, heavy drops,
Since it is a tapping, etc., and it is not a regular wave, it is difficult to distinguish it from ambient noise and noise with the conventional acoustic wave. In particular, the attenuation of oscillating acoustic waves in soil was remarkable, and it was impossible to measure over a long distance of 10 m or more.

Therefore, the present invention can obtain an accurate cross-sectional distribution of the values of porosity and water permeability and changes thereof, even when it is carried out in a noisy environment, and thus, it is possible to obtain accurate values. It is an object of the present invention to provide a new, highly accurate, non-destructive measurement method using acoustic waves of physical properties of the formation, which can obtain clear measurement results.

Another object of the invention is to implement the method between cross-section surveying holes that are very far apart, such as for distances of one mile (1.6 km) or more.

Still another object of the present invention is to provide a new and highly accurate nondestructive measuring method at a high frequency which has been impossible up to now.

Another object of the present invention is to accurately evaluate porosity and water permeability by high-frequency acoustic tomography.

Still another object of the present invention is to provide a new method for determining the permeability distribution of a formation quickly and accurately.

Other important objects and effects of the present invention will become more apparent by the following specification and drawings.

[0014]

The present invention provides a nondestructive measurement method using acoustic waves of physical properties of a formation, which extends from the surface of the formation to at least a predetermined depth and has an inlet.
Forming at least a pair of probe holes separated from each other by a predetermined distance, arranging a receiver at a known position of the probe hole, and simulating a position of the receiver in another one of the probe holes at a position known with respect to the receiver. Arranging an oscillation source of random code vibration energy, exciting the oscillation source according to the pseudo-random code to propagate vibration energy from the oscillation source to the receiver, and from the position of the oscillation source to the position of the receiver. The object has been achieved by measuring the pseudo-random code seismic wave characteristics of the vibration energy in a path extending toward.

Further, the oscillator source is moved with respect to the receiver and the oscillator source is re-excited to further measure the pseudo-random code seismic properties in a new path extending towards the receiver. It is a thing.

Further, at least a pair of search holes separated from each other by a predetermined distance are formed, and a large number of receivers are arranged at known positions in at least one of the search holes. A source of quasi-random code seismic energy at a known location with respect to the receiver in one of, and exciting the oscillating source according to the pseudo-random code to oscillate energy from the source to the receiver. Is achieved by measuring and storing pseudo random code seismic wave characteristics of the vibration energy in a number of paths extending from the position of the oscillation source toward the position of the receiver. .

Further, at least a pair of exploration holes extending from the surface of the formation to at least a predetermined depth and having inlets and separated from each other by a predetermined distance are formed, and a predetermined known shape substantially along the formation surface between the exploration holes is formed. , A plurality of receivers are spaced apart from each other, and a plurality of receivers are spaced apart from each other at a known location within at least one of the exploration holes An oscillating source of pseudo-random code vibration energy is disposed at a known position in the inside of the device, and the oscillating source is excited according to the pseudo-random code to propagate the oscillating energy from the oscillating source to the receiver. , Measuring a pseudo-random code seismic wave characteristic of the seismic energy in a number of paths extending from the position of the oscillation source toward the position of the receiver, and setting the oscillation source to the receiver. Dynamic and, again exciting the emitting vibration source, by further measuring the pseudo-random code seismic properties in a new multiple paths extending toward the receiver, is obtained by achieving the above object.

Further, the oscillation source of the vibration energy is a piezoelectric ceramic converter.

Further, the exploration holes are substantially parallel to each other.

Further, the receivers are arranged at substantially equal intervals.

Further, in measuring the seismic wave characteristic, the characteristic attenuation and velocity of the propagating vibration energy are measured.

Further, the measured seismic wave characteristics include a frequency characteristic of longitudinal wave velocity and a frequency characteristic of intrinsic damping.

Further, the frequency of the pseudo random signal is changed.

Further, the carrier frequency of the pseudo random code is changed at about 1, 2, 4, 8, and 10 kHz.

Also, each of the above-mentioned exploration holes is approximately 70-200 m
It's separated.

[0026]

As a result of the inventor's research, a pseudo random binary sequence (Pseude-Random Binary Sequence;
(Hereinafter referred to as PRBS), using an electromagnetic acoustic system using a regular-wave pseudo-noise source, direct propagation hole tomography propagates the seismic energy signal directly from the source to the receiver, It has been found that measuring the properties is very important. A pseudo-random binary sequence has a repeating sequence with a predetermined irregular pattern, for example, as shown in FIG.
It is an irregularly shaped multilevel signal. This repetitive sequence is also called a carrier signal.

Using such a pseudo-random binary sequence when operating the inter-hole placement in the formation,
Efficient and accurate operation is possible even in noisy environments where engine noise and other extraneous interference are present, allowing the experimenter to be very sensitive, such as 600 feet (960 m) or more than a mile. Sending his cross-hole signal over large distances will also give excellent results.

That is, as shown in a measurement example in a steel mill in FIG. 2, even if noises and noises due to pile driving, running of heavy machinery, etc. and PRBS code signals are mixed in the received acoustic waves, the PRBS code is mixed. By correlating with, it can be distinguished from other noises, and the time from oscillation to reception can be measured.

The use of PRBS allows excellent operation even at very high frequencies. The oscillation source of the PRBS energy is a piezoelectric ceramic converter that has been used up to now, or a hydrophone (Hydroph) as a receiver.
One, which produces a single-level regular wave when placed at a known location in another well, away from the well containing the hydrophone, is called a Sparker. Much different and better.

Therefore, according to the present invention, by forming at least a pair of exploration holes having inlets and arranged at a large distance from each other, the physical properties of the formation for obtaining the cross-sectional distribution analysis result are formed. A nondestructive measurement method using a characteristic acoustic wave can be obtained. The exploration hole extends from the surface of the stratum to at least a known depth, and is located at a predetermined position in the exploration hole and possibly along the surface of the stratum at a distance from each other such as a hydrophone or geophone (geohone). Multiple receivers, such as a receiver). A noise source in the form of a pseudo-random binarity sequence oscillator is
Located in a known location with respect to the receiver in another probe hole and excited to propagate seismic energy from the energy source to all receivers. When measuring the characteristics and paths of seismic waves directly propagated from the oscillation source to the receiver for a number of paths extending from the position of the oscillation source to the position of the receiver, an important measurement relates to the characteristics of the stratum. Furthermore, by moving the oscillator to another known position in the oscillator probe hole and exciting the oscillator again, measurements can be made on a number of new paths extending towards the receiver. By combining the results of such a series of measurements, it is possible to obtain accurate and reliable cross-sectional values and changes of the deposit. The results obtained by directly propagating and receiving the PRBS signal give much more reliable results than previously available.

According to the present invention, by directly measuring the velocity using the attenuation of the PRBS acoustic wave, it is possible to obtain a highly reliable porosity and water permeability over a long distance, and to obtain a more accurate water permeability value. Being able to do is very important. This is very important when solving groundwater related problems such as oil exploration. The porosity measurement according to the invention is intriguingly useful in the case of petroleum exploration. This is because most of the oil is absorbed in the pores of the sedimentary layer and normally only a small percentage of the oil reserves can be found. The method of the present invention can be used to accurately predict where the porosity is the smallest, i.e. where there is a high probability that there is unabsorbed free oil in the porosity of the sedimentary layer, and therefore the permeability. Based on the distribution, suitable locations for oil exploration and extraction can be indicated.

In the present invention, instead of utilizing a vertical seismic profile having only a single exploration hole with the energy source and receiver located in the same exploration hole, as already explained, It is important to utilize holes to measure the propagation from one exploration hole to another. Here, this new PRBS technology is shortened,
It is called "PRBS inter-hole tomography". This method has been found to be very effective in checking the permeability profile of the ground.

In one embodiment of the present invention, a piezoelectric acoustic element is used as an oscillation source, and the PRBS carrier frequency is changed by 1, 2, 4, 8 and 10 KHz, so that the acoustic propagation from the piezoelectric oscillation source is caused. Utilizing, as a receiver, a hydrophone arranged to extend downward along the surface of the deposited layer and in an independent exploration hole apart from the exploration hole including the piezoelectric oscillation source. You can carry out experiments. Additional experiments are performed in the same way by changing the location of the source within the borehole.

As an example, the spaced apart exploration holes may extend substantially vertically into the deposit. These exploration holes can be arranged at a distance of, for example, about 70-200 m from each other, and direct propagation is performed from the oscillation source to all hydrophones, so that longitudinal waves between the exploration holes are provided. The signal from each hydrophone can be measured via an amplifier and / or a recorder, so as to measure the (compressed wave) velocity and the intrinsic damping. Intrinsic attenuation measurements can be made using the spectral ratio method, and longitudinal wave velocity and intrinsic attenuation can be easily calculated from the phase spectrum and transfer function.

That is, according to the theory of Biot, the longitudinal wave velocity V and the intrinsic damping Q ^-1 are expressed by the following equations.

V = V0 + [(R2-R1) f × 360 °] / θ (1) Q- ¹ = [V / {πf (R2-R1)}] {ln (R1 / R2) + ln ( A1 / A2)} (2)

Here, V0 is the longitudinal wave velocity at the reference frequency ω0, R1 and R2 are the distances from the oscillation source to the two receivers, f is the oscillation frequency, θ is the phase angle, and A1 / A2 is 2
It is the amplitude ratio of two signals.

In this way, inter-hole tomography according to the present invention is used to check for spatial disparities.

Therefore, it has been found that in the present invention, acoustic pulse propagation is carried out in the deposited material, and in particular, it exhibits a propagating longitudinal wave velocity including a specific frequency range where the intrinsic attenuation is maximum. Porosity and permeability are easily estimated from longitudinal wave velocity and intrinsic damping by using the Biot theory. The details are all in our "Mea
surements of acoustic wave velocities and atten
uation in marine sediments (Measurement of acoustic wave velocity and attenuation in seafloor sediments) "J. Acoust. Soc. Am., V
ol. 87, No. 6 (June 1990), 2376-23.
The detailed description is omitted because it is described in detail on page 83.

By using a piezoelectric acoustic transducer equipped with a PRBS generator for the inter-probe tomography, not only longitudinal waves but also transverse waves are generated. Therefore, from the knowledge of the shear wave velocity, the shear wave velocity distribution within the deposit shape can also be accurately measured, and thus the shear deformation rate and shear force of the deposit can also be determined. These are important for the purpose of constructing structures and for accurately determining and knowing the presence of hydrocarbons such as oil and gas.

The shear wave velocity value directly determines the shear deformation rate and the shear strength value of the deposit. Knowing the value of the transverse wave velocity in addition to the value of the longitudinal wave velocity can provide important information about the presence or absence of hydrocarbons such as oil and gas within the deposit geometry.

[0042]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 3 shows a PR arranged in the probe hole 11 used as an energy propagation source for acoustic tomography measurement.
1 shows a BS oscillation source 10. The exploration hole 11 can be made of, for example, a plastic casing having a diameter of 5 inches (12.7 cm). Reference numeral 12 denotes a number of hydrophones arranged at intervals along the surface of the sedimentary layer, and reference numeral 13 is arranged at intervals in the longitudinal direction in the exploration holes 14 extending in the longitudinal direction. It shows a number of hydrophones. The exploration holes 14 and 11 are, as shown, separated from each other by a distance of, for example, 70-200 m or more.
It has a depth of m and is parallel to each other. Therefore, the measurements are preferably made simultaneously over a wide range of different angles with respect to the wave energy propagated by the oscillator source. All such measurements are based on direct propagation from the PRBS source 10 to the receiver hydrophones 12, 13 without the need for echoes or other phenomena in the deposited layer.

The oscillation source is powered by the PRBS code generator 21 and the power amplifier 20, and the received signal is amplified by the amplifier 23 and recorded by the recorder 22.

After placing the oscillator 10 at the position 10 'in the figure and making a number of measurements, the oscillator is lowered to another position 10''and the measurement process is repeated. Hydrophone 12,
Still other measurements are made at various other locations within the source probe hole without moving any of the 13.

In one embodiment of the present invention, the main equipment used to generate and measure the PRBS signal is the oscillator source, hydrophone array, signal amplifier and filter, P
RBS generator, frequency synthesizer, power amplifier, function generator, data acquisition box, A / B switch box, DC power supply and computer. This device is shown in FIG. 4 and will be described in more detail below.

A frequency synthesizer, generally designated 30, generates a carrier wave of constant amplitude, frequency and phase that can be modulated. Modulation, as used herein, is caused by a PRBS generator, resulting in a controlled change in frequency, phase and / or amplitude of the carrier wave. It can take any frequency to propagate the signal wave. Frequency synthesizer 30 receives power from line 54.

The frequency synthesizer is connected through line 57 to a pseudo random binary sequence (PRBS) code generator (PRBS C), generally indicated at 32.
odeGenerator). The PRBS code generator 32 receives power over line 56. This P
The RBS code generator 32 may be, for example, 2 ¹² or 4096.
Generate a pseudo-random binary sequence up to bit in length. The output signal from this generator can be modulated by an amplitude, phase or pulse modulator. The frequency of the output code of the PRBS code generator 32 is, for example, 1/64 of the frequency generated by the frequency synthesizer 30.

The PRBS code generator 32 has a line 58.
Through a variable output switching power amplifier (Power Amplifier), generally designated 34. The power amplifier 34 can have any maximum power output and maximum voltage output. In a convenient example,
They are 4k VA and 1400 volts respectively. To get the maximum voltage at the output, the input to the power amplifier 34 is
It should be limited to + -1.0 volts, for example, via lines 66 and 68. The power amplifier 34 is connected to the ground through the line 64. The power amplifier 34 withstands all types of short circuits and excessive inputs. The frequency response of power amplifier 34 is preferably substantially flat between 700 Hz and 20 kHz.

A piezoelectric acoustic transducer (Source), shown generally at 36, is connected through line 70 to a power amplifier, shown generally at 34. Piezoelectric transducer 3
6 generates a voltage which is an electric signal. The piezoelectric acoustic transducer produces an acoustic wave. The piezoelectric acoustic transducer 36 has, for example, a built-in quadruple voltage transformer. Therefore, the voltage delivered to the piezo-acoustic transducer 36 should preferably be limited to about 1/4 of the maximum voltage rating of the piezo-acoustic transducer 36.

To produce a Hydrophone Array, generally designated 38, for example, 2
Four hydrophones are arranged in a fixed pattern. The hydrophone array 38 is, for example, a 24-element array filled with oil. The hydrophone is an electroacoustic transducer that responds to water-borne sound waves and produces essentially equivalent electrical waves. Each hydrophone is capable of sensing low signals with a frequency of 1.0 Hz or less. 1 generally designated by 40
2 volt DC power supply (12 Volt DC Supply)
The hydrophone array 38 is powered through line 72.

Cables, generally designated 74 and 76, connect the hydrophone array 38 to an A / B switch box, generally designated 42. For example, 12 hydrophones are connected to the terminal A, and the remaining 12 hydrophones are connected to the terminal B.

Numeral 84, preferably RS
A cable, such as a 232 cable, connects the A / B switch box to a custom signal amplification filter, indicated generally at 44 (Signal Amplifier Filter).
The signal amplification filter 44 is connected to the ground through the line 90. The signal amplification filter 44 is connected to a low voltage such as 15 volts through line 86 and -15 volts through line 88. The signal amplification filter 44 is preferably a variable gain, a differential input, an output signal amplifier in which one of the circuits is grounded, or the like. The input differential signal is preferably 30 dB high pass in the vicinity of 500 Hz. This signal is then preferably, for example, 1, 2, 5, 10, 20, 50, 100, 20.
It is amplified by any of the gains of 0, 500, 1000 and 2000. This special amplifier 44 is, for example,
Two channels can be simultaneously amplified by the above gain. However, other amplifiers capable of amplifying more than 12 channels or less can also be used. A manual switch, generally indicated at 52, is a signal amplification filter 44.
It is connected to the.

Numeral 92, preferably RS
A cable, which is a 232C cable, connects the signal amplification filter 44 to a data acquisition box, generally indicated at 46. The PRBS code generator 32 is also connected to the data acquisition box 46 via line 60. In addition, the PRBS code generator 32 is connected through a line 62 to a function generator, generally designated 50.
or)), which in turn is connected to the data acquisition box 46 via line 63. The data acquisition box 46 preferably acts as a connection box and P
The RBS generator 32 and the signal amplification filter 44 are connected to a cable, generally designated 96, which is preferably a flat cable, which cable 96 then
Like a 33MHz IBM compatible computer,
It is connected to a multi-channel analog / digital (A / D) board built into a computer (Computer), generally designated 48, with enormous storage capacity.
The A / D board can have 16 channels, but can have more or less. This A / D
The board preferably receives the sense signal from the hydrophone on channels 1-12, the output signal of the PRBS generator on channel 13 and the external clock on channel 15.

The frequency synthesizer 30 supplies the carrier frequency required for digital operation in the PRBS code generator 32. The PRBS code generator modulates a carrier wave and transmits a pseudo random binary sequence signal wave. The power amplifier 34 amplifies this signal wave. The piezoelectric converter 36 transmits the amplified signal wave.

The hydrophone array 38 senses a pseudo-random binary sequence signal wave. The hydrophone array 38 can include 24 hydrophones each. The signal wave sensed by the twelve hydrophones is preferably the terminal A of the A / B switch box 42.
Conveyed to. Signal waves sensed by the other twelve hydrophones are preferably transmitted to the terminal B of the A / B switch box 42. The switch 52 attached to the signal amplification filter 44 is
Depending on the position of the switch 52, the sensed signal wave is received from the terminal A or the terminal B. The signal amplification filter 44 amplifies and filters the signal wave sensed by each hydrophone and outputs this information to the data acquisition box 46. The data acquisition box 46 also receives the external clock signal and the original pseudo-random binary sequence signal from the PRBS generator 32. The data acquisition box 46 also receives input from the function generator 50. The data acquisition box 46 sends this information to a multi-channel analog / digital (A /
D) Tell the board.

For the best operation of this device, the frequency rate generated by the PRBS code generator 32 is preferably in the range of four times the oscillator source frequency. The higher the computer sampling rate of the A / D board, the fewer hydrophones can be measured simultaneously. This is because the input rate on the A / D board must scan equal to the number of channels times the sampling rate. Preferably 1
There is one channel for each hydrophone. This means that if only 4 hydrophones can be sampled at a time, the computer preferably has the first 4 hydrophones, then the second 4 hydrophones, and then the third 4 hydrophones. Sampling or recording the sensing data from the hydrophone. The computer can always repeat this sampling.

Averaging is a process of taking in multiple sequence lengths such as PRBS signals and stacking them on top of each other to reduce noise and emphasize signals. If averaging is not always necessary, the computer's internal clock is
Used to record sensing data.

External clocks from the computer 48, the function generator 50 and the PRBS code generator 32 work together to perform the averaging. P
An external clock from the RBS code generator synchronizes the sense signal with the PRBS signal. PRBS for averaging
The external clock from the generator should be used so that there is no drift between the source signal and the signal measured by the hydrophone. The function generator 50 tells the computer when the pseudo-random binary sequence is complete. When a specified number of binary sequences are sensed, these sequences are stacked on top of the differences to reduce noise and enhance the signal. The frequency rate of the PRBS generator, which is four times the source frequency, is divided using the function generator to match the input frequency. For example, 1 kHz
Then, the frequency of the external clock is 4 kHz, 8 kHz
To measure one channel at a sampling rate of z, this signal is
Divided into 4 cycles. Therefore, the input rate applied to the external clock channel of the A / D board is 56 kHz.
becomes z. A square pulse coming from channel 15 of the A / D board indicates that the external clock is in use.

The data acquisition program stored in the memory of the computer uses an external or internal clock to read the sensing signal from the hydrophone, store the sensing signal in the memory, and perform calculations such as averaging. .

Function generator 50, PRBS
A computer 48 equipped with a code generator 32 and a suitable data acquisition program work together to correlate the oscillating source signal with the measured signal and to perform the averaging process. The output of this correlation can be seen in a series of times for one of each hydrophone at one particular source position. From this, transverse wave velocity, longitudinal wave velocity, shear force, porosity,
Water permeability and standard penetration can be determined. The standard penetration is
It is defined by the number of times the pipe must be struck to penetrate.

In accordance with one embodiment of the present invention, inter-probe measurements were made using two deep exploration holes 60m deep. The piezo-acoustic transducer 36 was placed in one probe hole and the hydrophone array 38 was placed in the other probe hole.
The distance between the exploration holes was 66.21 m. A PRBS code with a sequence length of 4095 was used to excite a 170 dB source with a carrier frequency of 3 kHz. The average of 4 measurements was taken. The computer sampling rate was 12 kHz. The first sensed data was as shown in the time course graphs of FIGS. These graphs show the time when the signal first arrived at the hydrophone array 38.
Using a computer program of the time-of-flight inversion method, we were able to create a longitudinal wave velocity tomograph. Assuming a general joint stress rate, the porosity, shear wave velocity, shear force and SPT (standard penetration force) hit count can be determined from the longitudinal wave velocity profile and a tomograph can be made from it. Finally, the water permeability and particle size are two different P
It could be evaluated from the longitudinal wave velocity tomography measured at the RBS carrier frequency.

The processing and interpretation of sediment data has both qualitative and quantitative properties. The quality of sediment data processing is measured by how well the processing data is interpreted. The time graphs shown in Figures 5 and 6 receive results of very good nature. In this example,
Using the embodiment of the invention shown in FIG.
The 8 included an A / D board capable of receiving data from 12 hydrophones. If the A / D board was able to receive 24 channels, A / D
B switch box 42 and switch 52 would not have been needed.

In this example, using the embodiment shown in FIG. 4, a 170 dB oscillation source was used. If the source dB is large, it will be possible to obtain high quality measurements between the probe holes 1.0 miles apart.

Further, in the experiment, four times of averaging were performed. However, any number of averagings can be performed when utilizing the present invention.

Although the present invention has been described with reference to certain specific embodiments, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. For example, more holes can be used for inter-hole tomography according to the present invention. Also, if the respective positions are known, many relative positional relationships and variations of the positions between the PRBS oscillator source and the receiver can be used. Furthermore, various theories and relational expressions have been used to determine and calculate properties such as porosity, water permeability, water permeability profile, shear deformation rate and shear force. Located in the hole, the PR
Single or multiple receivers are located in a separate exploration hole away from the BS oscillator, the PRBS oscillator is excited and seismic energy is propagated towards the receiver, measured between the PRBS oscillator and the receiver It is also possible to use other analytical methods, as long as they are based on the results of the method according to the invention, such as is carried out directly.

[0067]

As described above, according to the present invention, the pseudo random binary sequence code is used for the oscillating acoustic wave so as to distinguish it from other noises by the correlation. Even in a noisy place, the non-destructive measurement of the formation is possible, and the measurable distance per time is several hundred meters, and the accuracy is remarkably improved.

According to the experiment conducted by the inventor, it was actually confirmed that it is possible to measure up to 220 m span in a noisy place where a pile driver or a bulldozer runs in a steel mill.

[Brief description of drawings]

FIG. 1 is a time chart showing an example of a pseudo random binary sequence code signal used in the present invention.

FIG. 2 is a diagram showing an example of an acoustic wave after having been correlated with an acoustic wave that is also received.

FIG. 3 is a cross-sectional view showing a vertical cross-section of a deposited layer to illustrate one embodiment of the present invention, including an oscillator source and receiver arrangement for acoustic tomography.

FIG. 4 is a block diagram showing an apparatus used in an embodiment of the present invention.

FIG. 5 is a diagram showing initial data sensed by a hydrophone.

FIG. 6 is a diagram showing an example of initial data detected by another hydrophone.

[Explanation of symbols]

10 ... PRBS oscillator 11, 14 ... Exploration hole 12, 13 ... Hydrophone 21, 32 ... PRBS code generator (PRBS Code)
(Generator) 30 ... Frequency Synthesizer (Frequency Synthesize)
r) 36 ... Piezoelectric acoustic transducer (Source) 38 ... Hydrophone Array 44 ... Signal amplification filter (Signal Amplifier Filter)
r) 46 ... Data acquisition box (Data Acquisition Bo)
x) 48 ... Computer (Computer) 50 ... Function Generator (Function Generator)
or)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G01V 1/36 9406-2G 1/40 9406-2G (56) Reference JP-A-4-198794 ( JP, A) JP 60-108750 (JP, A) JP 57-173776 (JP, A)

Claims (12)

[Claims] 1. At least a pair of exploration holes extending from the surface of the stratum to at least a predetermined depth and having inlets and separated from each other by a predetermined distance, and arranging a receiver at a known position of the exploration holes, Arranging a source of pseudo-random code seismic energy at a known location with respect to the receiver in another one of the exploration holes and exciting the source according to the pseudo-random code;
A stratum characterized by propagating seismic energy from the oscillation source to the receiver, and measuring a pseudo-random code seismic wave characteristic of the seismic energy in a path extending from the position of the oscillation source to the position of the receiver. Nondestructive measurement method using acoustic waves of physical properties of. 2. The pseudo random code seismic wave characteristic according to claim 1, further comprising moving the oscillation source with respect to the receiver, re-exciting the oscillation source, and extending in a new path toward the receiver. A non-destructive measurement method using acoustic waves of physical properties of the formation, which is characterized by further measuring. 3. At least a pair of probe holes which are separated from each other by a predetermined distance, and a plurality of receivers are spaced apart from each other at known positions in at least one probe hole. A source of pseudo-random code seismic energy at a known location with respect to the receiver in one of the
Propagating seismic energy from the oscillation source to the receiver, measuring and storing pseudo random code seismic wave characteristics of the seismic energy in a number of paths extending from the position of the oscillation source toward the position of the receiver. Nondestructive measurement method using acoustic waves for physical properties of formations characterized by. 4. A predetermined known structure which extends from the surface of the formation to at least a predetermined depth and which has at least a pair of exploration holes having inlets and separated from each other by a predetermined distance, and which is substantially along the stratum surface between the exploration holes. , A plurality of receivers spaced apart from each other, and a plurality of receivers spaced apart from each other at a known location within at least one of the probe holes, Inside, at a known position with respect to the receiver, placing an oscillating source of pseudo-random code seismic energy, exciting the oscillating source according to the pseudo-random code,
Propagating seismic energy from the oscillation source to the receiver, measuring pseudo random code seismic wave characteristics of the seismic energy in a number of paths extending from the position of the oscillation source to the position of the receiver, the oscillation source To the receiver and re-exciting the source to further measure the pseudo-random code seismic properties in a number of new paths extending towards the receiver. Non-destructive measurement method using acoustic waves of. 5. The non-destructive measurement method according to claim 4, wherein the oscillation source of the vibration energy is a piezoelectric ceramic converter. 6. The non-destructive measurement method according to claim 4, wherein the exploration holes are substantially parallel to each other, using acoustic waves of physical properties of the formation. 7. The nondestructive measurement method according to claim 4, wherein the receivers are arranged at substantially equal intervals, using acoustic waves of physical properties of the formation. 8. The nondestructive measurement method using acoustic waves of physical characteristics of a stratum according to claim 4, wherein the characteristic attenuation and velocity of propagating vibration energy are measured when the seismic wave characteristics are measured. 9. The non-destructive use of acoustic waves of physical properties of a stratum according to claim 4, wherein the measured seismic wave characteristics include frequency characteristics of longitudinal wave velocity and period number characteristics of intrinsic damping. Measuring method. 10. The non-destructive measurement method according to claim 4, wherein the frequency of the pseudo-random signal is changed, and the physical characteristics of the formation are acoustic waves. 11. The carrier frequency of the pseudo-random code according to claim 10, wherein the carrier frequencies are approximately 1, 2, 4, 8 and 1.
A non-destructive measurement method using acoustic waves of the physical properties of the formation, which is characterized by changing at 0 kHz. 12. The non-destructive measurement method according to claim 4, wherein the exploration holes are separated from each other by approximately 70 to 200 m.