KR102412646B1 - Land seismic exploration system - Google Patents

Abstract

The present invention provides an oscillator for transmitting elastic waves while moving in a river; a plurality of receivers that receive a signal returned by the acoustic wave transmitted to the oscillator being reflected by the reflective surface, and are installed in a lower phase corresponding to the movement path of the oscillator to be spaced apart from each other; and a control unit for storing and processing information on the signal received from the receiver and the seismic wave transmitted from the oscillator.

Description

LAND SEISMIC EXPLORATION SYSTEM

The present invention relates to a land nodal-airgun seismic exploration system.

Seismic exploration is to investigate the physical characteristics of the underground stratum structure, sediments and rocks by recording the reflection or refracting of seismic waves artificially generated by the oscillator with a receiver.

Such seismic exploration is used for exploration of resources that exist underground, such as oil, natural gas, and gas hydrate, and for engineering purposes for offshore construction such as undersea pipelines and cables, undersea tunnels, undersea storage facilities, and bridges. often used

Seismic exploration is not only academic research on specific areas such as fault zones and intertidal zones, but also various civil engineering such as highways, railways, and dam construction, geothermal and mineral resource exploration, environmental impact investigations in landfills and seawater infiltration areas, and safety management of cultural properties. It is used in various fields such as application to archeology for

Ocean seismic exploration acquires data by towing an oscillator and receiver with a probe or by mounting it on the hull. Contrary to this, in land seismic exploration, an oscillator (or sound source) is installed at a specific point to perform the exploration, or a VibroCyce vehicle is used.

Basically, unlike ocean seismic exploration, land seismic exploration is subject to various limitations. A typical example is the problem of noise in life. In general, traffic noise from automobiles or trains, power line noise having a frequency band of about 60 Hz similar to the frequency of seismic sound waves, and noise from communication facilities occur in downtown areas, and these living noises interfere with land seismic exploration. Due to these problems, seismic waves generated using impulse sources (eg, gunpowder, gravitational weight, etc.) are ideal for land seismic exploration because they have a higher frequency, but there are stability problems and destruction of structures such as pavements. There are restrictions on where you can be.

Therefore, there is a need for a new seismic exploration method that can be used on land.

An object of the present invention is to provide a land nodal-airgun seismic exploration system and a signal processing method that can be used for land seismic exploration and can solve problems caused by living noise.

On the other hand, other objects not specified in the present invention will be additionally considered within the range that can be easily inferred from the following detailed description and effects thereof.

In order to achieve the above problem solving goal, a land seismic wave exploration system according to an embodiment of the present invention includes an oscillator for transmitting seismic waves while moving in a river; a plurality of receivers that receive a signal returned by the acoustic wave transmitted to the oscillator being reflected by the reflective surface, and are installed in a lower phase corresponding to the movement path of the oscillator to be spaced apart from each other; and a control unit that stores information about the signal received from the receiver and the acoustic wave transmitted from the oscillator and performs signal processing.

In an example, the oscillator may be characterized by using an air gun as a transmission sound source.

In an example, the oscillator may include a position information measurement module to store position information for transmitting an acoustic wave from the oscillator.

In an example, the control unit may perform signal processing by performing delay compensation according to a difference between the lateral line of the oscillator and the lateral line of the receiver.

In an example, the plurality of receivers may be installed to be vertically spaced apart from a movement path of the oscillator.

The land seismic exploration system according to an embodiment of the present invention installs a receiver in the river bed and generates seismic waves while moving in the river using the oscillator to perform seismic exploration, thereby minimizing the effect of living noise generated in urban areas. It can perform land seismic exploration more accurately.

Meanwhile, in a signal processing method of a land seismic wave exploration system according to another embodiment of the present invention, an oscillator is provided with a GPS to determine a location where an actual seismic signal is generated, and the oscillator is corrected to be in the same position as the receiver during signal processing. Thus, it is possible to more accurately analyze the results of land seismic surveys.

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 is a schematic configuration diagram of a land seismic wave exploration system according to an embodiment of the present invention.
2A and 2B are schematic reference diagrams for explaining that seismic exploration is performed while moving an oscillator in a river using the land seismic exploration system according to an embodiment of the present invention.
3 is a schematic flowchart for explaining the construction of a sound source collection from a lateral line design of a land seismic wave exploration system according to an embodiment of the present invention.
4 is a schematic flowchart of a signal processing method of a land seismic survey system according to another embodiment of the present invention.
5 is a result of collecting signal tones received by a receiver at a point in the land seismic wave exploration system according to an embodiment of the present invention.
6 is an amplitude spectrum of a first trace among the detection results of the land seismic wave exploration system according to an embodiment of the present invention, and shows (a) and (b) before and after section-band pass filtering.
FIG. 7 is a result of performing section band pass filtering on the result of FIG. 5 .
8 is a reference diagram for explaining a process for estimating the velocity of an acoustic wave signal.
9 is a reference diagram for explaining a prediction filter multiplication process for removing multiple reflected waves.
FIG. 10 is a result of performing predictive filter multiplication on the result of FIG. 7 .
11 is a reference diagram for explaining static time delay compensation.
12 illustrates a trace collection by extracting a signal having a constant value (eg, 130 m) between the oscillator and the receiver.
13 is a common reflection point map in which the number of folds in each receiver is measured to construct a common reflection point collection.
14 shows a speed spectrum (a), a super common reflection point collection result (b), and a speed selected from the velocity analysis result for the super common reflection point collection when a super common reflection point collection having 10 or more common reflection points is constructed. The result (c) of polymerization by correcting the vertical time difference (NMO) is shown.
15 is a schematic cross-sectional view of velocity obtained by performing velocity analysis on all super common reflection point collections of FIG. 14 .
16 is a view showing an optimal stratum cross-sectional view after static delay compensation is completed.
It is revealed that the accompanying drawings are exemplified by reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby.

Hereinafter, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described with reference to the drawings. In the description of the present invention, if it is determined that related known functions are obvious to those skilled in the art and may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

terrestrial seismic exploration system

1 is a schematic configuration diagram of a land seismic wave exploration system according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are views of a land seismic wave exploration system in a river according to an embodiment of the present invention. It is a schematic reference diagram for explaining performing seismic exploration while moving the oscillator.

Each configuration and function of the land seismic wave exploration system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3 .

The land seismic wave exploration system 100 according to an embodiment of the present invention includes an oscillator 10 , a receiver 20 , and a controller 30 , like other conventional seismic wave exploration systems. However, in the land seismic exploration system 100 of the present invention, the oscillator 10 is located in a river and the receiver 20 is located in a river bank at a position corresponding to the oscillator 10 . In particular, it was attempted to solve the problems described in the background art by installing the land seismic wave exploration system 100 according to an embodiment of the present invention in a river passing through the city center. The control unit 30 serves to adjust the moment at which the oscillator 10 transmits the acoustic wave sound source. The receiver 20 serves to record all signal tones, including reflected tones.

At the estuary of the Hyeongsan River, seismic exploration was actually performed using the land seismic exploration system 100 according to an embodiment of the present invention.

The oscillator 10 may be installed on a ship in a river, or installed in the form of being lifted by the ship. The oscillator 10 transmits an elastic wave at a predetermined distance interval or a predetermined time interval while moving in a river. In this case, the land seismic wave exploration system 100 of the present invention may use an air gun as the oscillator 10 . The air gun mainly used in marine seismic exploration plays a role in discharging high-pressure compressed air from the water and sending the energy to the inside of the strata. In marine seismic exploration, a combination of several air guns is used as a transmission sound source to reduce the bubble effect, but it is not appropriate to use a large-scale air gun as a transmission sound source in rivers. Therefore, the land seismic exploration system 100 of the present invention preferably uses a small-scale air gun in consideration of the river environment.

The oscillator 10 includes a location information measuring module capable of recording location information when transmitting an elastic wave signal, and a time information measuring module measuring time information when transmitting an elastic wave signal. A global positioning system (GPS) may be used as the location information measurement module.

In the present invention, the oscillator 10 is fixed to a small ship at a depth of about 1 m, and the oscillator 10 is transmitted at intervals of 5 m while pulling the oscillator 10 at a speed of 2.5 to 3 knots, and a total of 37 transmissions are performed. 2800LLX of Teledyne Marine was used as the air gun. Table 1 below shows the specifications of the air gun used in the present invention.

Model Longlife Airgun 2800 LLX Max. pressure 2,000 psi Manufacturer Bolt Tech. output volume 5 cubic inches to 120 cubic inches Frequency 50 to 200 Hz

The receiver 20 is installed at the bottom. As the receiver 20, a wireless receiver is used to increase the convenience of installation. The receiver 20, like the oscillator 10, includes a position information measurement module capable of recording position information, and a time information measurement module that measures time information upon reception of an acoustic wave signal.

In the present invention, 135 receivers 20 were installed at intervals of 5 m on the bottom. The receiver was installed at a distance of 10m from the river. In the receiver 20, the recording time interval of the acoustic wave signal was set to 1 ms, and the recording time for generating the sound source was set to 5 s.

Table 2 shows data acquisition parameters during actual exploration using the land seismic exploration system according to an embodiment of the present invention.

shot interval 5 m No. of shots 37 Receiver interval 5 m No. of receivers 135 airgun 50 cu inch 20 ~ 2000 Hz sampling rate 1 ms record length 5 s Near offset 122 m Far offset 793 m

2(a) and 2(b) relate to probe wave exploration performed at the estuary of the Hyeongsan River. In FIG. 2(a), the red dotted line indicates the position of the receiver 20, and the yellow dotted line indicates the position of the oscillator 10. The location is indicated, and the red arrow indicates the direction of exploration. The receiver 20 was installed to be spaced apart from each other along the river as shown in FIG. 2(b). The positions of the oscillator and receiver were recorded using GPS. After setting the probe, determine the interval between the oscillator and receiver, the type of transmitted sound source and the depth of the transmitted sound source, and determine the recording time and interval for recording the beep sound. The GPS time at the moment when the sound source is transmitted from the oscillator is recorded, and the signal sound recorded in all receivers is transmitted to the control unit 30 using a wired communication network. And the sound source collection is constructed by extracting the recorded data from the GPS time of the transmitted sound source to the predefined recording time. The process from the side line design to the sound source collection configuration is shown in FIG. 3 .

Signal processing method

In the land seismic exploration system according to the embodiment of the present invention described above, the oscillator is located in the river and the receiver is located in the river, so their positions are different from each other. In addition, the oscillator transmits an elastic wave while moving, and the receiver receives the elastic wave at a fixed position.

Accordingly, the sound source collection configuration of the land seismic wave exploration system according to an embodiment of the present invention is inevitably significantly different from the methods of conventional seismic wave exploration technologies.

Hereinafter, the signal processing method of the terrestrial seismic survey system according to an embodiment of the present invention will be described using the results of seismic survey performed at the estuary of the Hyeongsan River.

4 is a schematic flowchart of a signal processing method of a land seismic survey system according to another embodiment of the present invention.

According to another embodiment of the present invention, a signal processing method of a land seismic wave exploration system includes the steps of: transmitting an elastic wave while an oscillator of the land seismic wave exploration system moves, and receiving an original signal by listening to the receiver; section-pass filtering the original signal; removing multiple reflections from the pass-pass filtered signal; performing delay compensation according to a difference between a side line of an oscillator and a side line of a receiver with respect to a signal from which multiple reflected waves are removed; and classifying the signal according to the distance between the oscillator and the receiver with respect to the signal on which the delay compensation has been performed to configure a proximity trace collection.

FIG. 5 shows seismic waves received by 135 receivers for the first sound source as a result of collecting signal sounds received from receivers at a point in the land seismic wave exploration system according to an embodiment of the present invention. The time is the extracted data up to 5s based on the oscillation time of the oscillator. In the sound source collection for the first sound source, the distance from the oscillator to the nearest receiver is 126 m, and the distance to the furthest receiver is 596 m. For all sound source sets, the distance from the oscillator to the nearest receiver was 122 m, and the distance to the furthest receiver was 793 m.

As can be seen in FIG. 5 , in the original signal, it is possible to check the reflected wave recorded in the form of a direct wave and a multi-reflected wave whose recording time varies according to the position of the receiver. It can be seen from FIG. 5 that the reflected wave has a convex parabolic shape, which is affected by the distance between the oscillator and each receiver. Therefore, in order to obtain accurate land seismic survey results, signal processing for the results is required.

Therefore, it is necessary to perform section-band-pass filtering according to the frequency band on the original signal.

FIG. 6 shows the frequency domain by extracting the signal recorded in the first receiver among the sound sources of FIG. 5 .

It can be seen that the signal recorded on the receiver in FIG. 6(a) contains a significant portion of low-frequency components of 10 Hz or less, and that the signal is mainly distributed in the 10-30 Hz frequency band. In order to check the reflected wave signal that may be in the low frequency band, as a result of applying the section band pass filter in various frequency bands, the frequency band was determined to be 10-20-100-120 Hz, and the result is shown in FIG. 6(b). As can be seen from Fig. 6(b), it can be seen that the signal sound having the maximum amplitude at 14 Hz is recorded.

The result of applying the section band pass filtering as described above is shown in FIG. 7 . Comparing FIGS. 7 and 5 , it can be confirmed that a reflected wave that was not seen in the low frequency band appears. In particular, the main reflected wave was clearly displayed around 0.43 s during the round trip.

Since the reflected wave signal in the sound source signifies the existence of the reflection boundary, the stratum boundary can be predicted by the signal processing result.

Table 3 shows the time-distance values selected along the reflected wave hyperbola to estimate the velocity of the reflective surface corresponding to the first main reflected wave.

Rcv. No. Offset (m) Time(s) One
3
5
7
8
10
12
14
16
17
19
21
23
28
30
33
37
39
42
46
48
51
57
60
64
67
70
72
74
77
79
83
86
90
92
95
104 159
153
148
143
141
137
133
130
128
127
125
126
127
132
135
141
151
157
166
180
187
198
222
235
252
265
279
288
298
312
322
341
355
375
385
399
443 0.521683
0.501282
0.480881
0.475052
0.463395
0.454651
0.442994
0.434250
0.431336
0.431336
0.434250
0.440079
0.442994
0.448823
0.463395
0.480881
0.501282
0.518769
0.550828
0.594544
0.606202
0.655747
0.719865
0.769410
0.807298
0.851014
0.891816
0.918046
0.950105
0.996736
1.034620
1.087080
1.145370
1.194920
1.235720
1.276520
1.404760

After applying the bandpass filtering, the step of estimating the velocity of the reflective surface is performed. When the slope is obtained by converting the offset-time value of Table 3 using the t ² -x ² curve, the acoustic wave velocity at the reflective surface becomes the reciprocal of the slope square (see FIG. 8 ). Using this, the velocity of the first reflective surface is about 316 m/s. If the velocity of the first reflective surface is known, it can be estimated that the thickness of the strata up to the first reflective surface is about 28 m. In the sound source collection, it can be seen that there are the first main reflected wave at 0.43 s in the reciprocating gaze, the second reflected wave in the vicinity of 1 s in the reciprocating gaze, and then there are multiple reflected waves.

Next, a step of removing multiple reflected waves is performed. In the present invention, predictive filter deconvolution is used to remove multiple reflected waves. Predictive filter multiplication improves the signal-to-noise ratio by removing multiple reflections. The deconvolution operator length is determined as the time when the magnitude of the first amplitude corresponds to 0 by analyzing the trace autocorrelation application result (refer to FIG. 9 ). In addition, the predictive lag length is determined by checking the time between the time when the first amplitude becomes 0 as a result of the autocorrelation and the time when the second amplitude becomes 0. If it is a spike multiplication that determines equal to the sampling rate. In the signal processing process for the exploration results at the estuary of the Hyeongsan River, the length of the multiplication operator was 30 ms and the length of the prediction delay was 100 ms, and the results are shown in FIG. 10 . Comparing FIGS. 10 and 7 , it can be seen that the multi-reflected wave existing in the time period after 1 s of round-trip gaze is significantly reduced.

After the step of removing the multi-reflected wave is performed, the step of compensating for the delay of arrival according to the difference between the receiver's lateral line and the oscillator's lateral line is performed.

As can be seen from FIG. 11 , in the land seismic exploration system according to an embodiment of the present invention, the wireless receiver is installed in a river bed about 10 m away from the river, and the sound source lateral line and the receiver lateral line are not in a straight line, but are maintained close to parallel. It is necessary to compensate for the time delay according to the position difference.

In the step of performing the time delay correction, the first step is to obtain position information of the oscillator and receiver. The oscillator position (S ₁ ) and receiver position (R _n ) are stored as GPS coordinate values S ₁ (sx, sy) and r _n (gx, gy), respectively, from which the oscillator-receiver distance can be determined.

Then, the steps of calculating the distance and time from the oscillator S ₁ to the reflection point A and from the reflection point A to the receiver r _n are performed, taking into account the time taken to arrive at the recorded signal and the speed of the water. For example, the distance from the oscillator S ₁ to the reflection point A and the distance and time from the reflection point A to the first receiver r ₁ are calculated. The distance from the oscillator (S ₁ ) to the first receiver (r ₁ ) is 159 m, and the recorded arrival time of the seismic wave is 176 ms. If it is assumed that the propagation from the oscillator to the receiver is at the speed of water, the arrival time of the gaze is 106 ms, and the arrival time of the seismic wave from A to the receiver is estimated to be about 70 ms. Therefore, the distance from A to the receiver is about 10.8 m, so the seismic velocity at the bottom can be estimated to be about 154 m/s. If it is assumed that the receiver (r ₁ ) in the lower phase is located at B, which is on the lateral line of the oscillator, the arrival time of the seismic wave from the sound source (S ₁ ) to B is about 40 ms. Since the arrival time of the seismic wave from the sound source (S ₁ ) to the receiver is 176 ms, there is a difference in arrival delay time of 136 ms. Therefore, when the 136 ms acoustic wave arrival delay time is corrected for all sound source collections, the general two-dimensional acoustic wave data processing process can be applied.

After performing the time delay compensation step, a step of constructing a proximity trace collection by extracting a signal according to the distance between the oscillator and the receiver is performed.

In general, when noise removal and correction are completed through signal processing, a rough stratum structure is identified through a collection of nearest traces, and then data processing is performed. Most of the nearest trace set is composed by extracting the signal from the first listener of the sound source set.

However, in the land seismic survey system according to an embodiment of the present invention, it is very difficult to transmit while maintaining a constant position of the oscillator. Instead, in the land seismic wave exploration system according to an embodiment of the present invention, when an oscillator oscillates a seismic wave, the location and time are recorded using the GPS system.

Accordingly, in the signal processing method of the land seismic wave exploration system according to another embodiment of the present invention, unlike the prior art, a signal sound is extracted according to a distance between an oscillator and a receiver to configure a proximity trace collection. Here, the proximity trace collection was constructed by extracting the signal sound corresponding to the oscillator-receiver distance around 130 m. As can be seen from FIG. 12 , it can be seen that, unlike FIG. 10 , the reflected wave appears at a constant reciprocating gaze since the signal sounds corresponding to around 130 m are collected.

On the other hand, as shown in FIG. 13 , in the land seismic exploration system according to an embodiment of the present invention, it is difficult to maintain a constant transmission interval according to field conditions in the transmission of seismic waves from an oscillator in a river, so that a collection of common reflection points can be formed. When the number of folds appears inconsistent. A common reflection point (CRP) or a common midpoint (CMP) refers to a point at which acoustic waves transmitted from different locations are commonly reflected. As shown in FIG. 13 , the number of folds gradually increases when exploration is started, and after the maximum number of folds is configured, the number of folds gradually decreases at the end of the exploration. At this time, the maximum number of folds is 39, and a set of super common reflection points is created by targeting the collection of common reflection points (CMP 20 ~ CMP 240) that make up the number of folds of 10 or more. In the land seismic survey system according to an embodiment of the present invention, the signal strength is relatively low by using a mini air gun, but the accuracy of the seismic survey result can be further improved by creating a collection of super common reflection points.

After generating the super common reflection point collection, velocity analysis is performed as shown in FIG. 14(a). When velocity analysis is completed for all the super common reflection point collections, a velocity cross-section as shown in FIG. 15 can be obtained. 15 is obtained by performing velocity analysis for each collection of 20 common reflection points and applying interpolation.

After the velocity analysis is completed, vertical time difference correction (NMO: normal moveout) is performed using the velocity selected in velocity analysis for the super common reflection collection as shown in FIG. get a collection The reflected wave appears in the form of a hyperbola in the sound source collection, and the slope of the hyperbola varies according to the stratum velocity. Velocity analysis refers to a method of finding the slope most similar to the reflected wave hyperbola by substituting various velocities. Velocity analysis calculates the amplitude along the hyperbola and displays it as a spectrum. At this time, the maximum amplitude becomes the velocity at the stratum interface. And by applying this speed to the process of horizontally adjusting the reflected wave hyperbola, the vertical time difference correction is performed by correcting the difference between the hyperbola inclination and the horizontal line.

This process is carried out for all super common reflection sets, and polymerization results in a final stratum cross-sectional view as shown in FIG. 16 .

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

Claims (6)

an oscillator that transmits elastic waves while moving in a river; a plurality of receivers that receive a signal returned by the acoustic wave transmitted from the oscillator being reflected by the reflective surface of the stratum, and are installed to be spaced apart from each other in the lower bed corresponding to the movement path of the oscillator; and a control unit for storing and processing information about the signal received from the receiver and the seismic wave transmitted from the oscillator;
obtaining an original signal by transmitting seismic waves while an oscillator of the land seismic wave exploration system moves, and receiving the seismic waves in the receiver;
section-pass filtering the original signal;
removing multiple reflections from the pass-pass filtered signal;
performing delay compensation according to a difference between a side line of an oscillator and a side line of a receiver with respect to a signal from which multiple reflected waves are removed; and
A signal processing method using a land seismic exploration system, comprising: classifying a signal for which delay compensation has been performed according to a distance between an oscillator and a receiver to configure a proximity trace collection. delete delete delete delete delete

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