KR102003466B1 - Method for swell effect correction of offshore 3d seismic survey data at shallow tratum and marine 3d seismic survey mehod using the same - Google Patents

Abstract

The present invention relates to a data processing method for correcting a swell effect from seismic survey data acquired from a marine 3D seismic survey. As a transmission time of a sound wave is affected by a change in a height between a sound source and a receiver in accordance with a swell in an actual marine survey, a water level of a survey area is measured on the basis of a sea level. Moreover, after a theoretical arrival time (standard arrival time) of a sea-bed reflection signal is calculated, difference between the standard arrival time and an actual arrival time is used to remove a swell effect of seismic survey data.

Description

TECHNICAL FIELD [0001] The present invention relates to a multi-channel three-dimensional (3D) seismic surveying method,

TECHNICAL FIELD The present invention relates to a seismic surveillance technique, and more particularly, to a multi-channel 3D seismic exploration technique for exploring a seabed area using a high frequency sound source.

Perform seismic surveys for the purpose of exploration of underwater resources such as oil, natural gas, and gas hydrates, or engineering for marine construction such as submarine cables, tunnels, bridges,

1, in the seismic wave survey, the probe 1 floats the sound source and the receiver while floating the seismic source 3 and the hydrophone 4 connected to the cable r, . As shown in Fig. 1, a sound wave is emitted and received at a point (A), and a probe sends and receives a sound wave again at a point (B) after moving the predetermined interval (I, time interval or distance interval). The sound waves are periodically generated in the negative (3) circle, and the sound waves pass through the water L and are reflected on the seafloor S, the deeper seam layer G or the seabed structure ). Through the data processing of the received reflected wave signal, the existence of the submarine stratum structure or the existence of the resource is detected.

The seismic survey can be divided into single-channel exploration when there is only one receiver and multi-channel method when there are multiple receivers. It can also be used for 2D and 3D exploration.

Will be described with reference to Figs. 2 and 3. Fig. 2D scanning can be performed by installing only one receiver (refer to FIG. 1, single channel) or by installing a plurality of receivers in a row of streamers (see FIG. 2, multi channel) along the traveling direction of the probe, (A straight line) along a vertical section (2D) of the lower part thereof. On the other hand, 3D exploration enumerates a plurality of receivers (multi-channels) along a direction perpendicular to the direction of the probe, and explores a stratum of a certain volume (3D) of the lower stratum when the probe travels. If you have a single vertical section as a result of 2D exploration, 3D exploration has the same principle as collecting a plurality of vertical sections obtained from each channel in parallel.

Seismic surveys can be divided into high frequency survey and low frequency survey according to frequency band of source. High-frequency exploration is mainly used for exploration of the underground stratum area, and air guns, sparkers, boomers and geologic explorers of hundreds to thousands of Hz are used as sound sources. The high-frequency sound source has a short wavelength, allowing precise exploration (high resolution exploration) in units of 1m or less. On the other hand, in case of low frequency surveying, the resolution is low because of the long wavelength of sound waves, but it is suitable for exploring the deep sea floor region by spreading to deep sea floor.

Since marine seismic surveys are carried out in the sea, consideration should be given to the specificity of the oceans, ie the difference in tides and the influence of the wings. During the high tide, the water level rises, so the time for the sound waves to reach and reflect on the strata (the two way travel time) becomes longer, Therefore, the arrival time is corrected based on the reference sea level. It is not difficult to calibrate the tidal car as it appears constantly, but the problem is swell. This is because the swell does not have the same pattern as the tidal car.

The deep ground survey using low frequency uses the sound source of long wavelength and the ground is very deep, so the influence of the woof is not relatively large. However, in the case of a shallow stratospheric survey, a short sound source with a wavelength of less than 1m is used, and the object to be surveyed is also located at a low level.

Previously, a method of compensating for the influence of the waviness in the single channel method has been proposed. However, this method is applicable only to a form in which a sound source and a receiver are placed next to each other in a single channel system, and sound waves transmitted vertically are reflected on the ground layer and received vertically. In the case of having such a vertical path, it is easy to correct the influence of the swell.

However, in the 3D multi-channel method, since the path of the sound wave is in the 'V' shape, the sound wave is propagated in the V-character even in the 2D multi-channel streamer method as shown in FIG.

In order to improve the reliability of the oceanographic seismic surveys in the form of V-shaped sound waves, a new method is required to remove the influence of the survey from the survey data.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new method for eliminating the influence of waviness in 3D seismic survey data using a high frequency sound source and a marine 3D seismic exploration method using the same.

On the other hand, other unspecified purposes of the present invention will be further considered within the scope of the following detailed description and easily deduced from the effects thereof.

In order to accomplish the above object, the present invention provides a method for correcting the influence of waveness of 3D oceanic seismic survey data, comprising the steps of: dividing a survey area into a plurality of bins (unit areas) and performing a 3D marine seepage survey using multi- A method for correcting a waviness effect in the seismic exploration data using exploration data consisting of a plurality of acquired traces and depth data from the sea surface to the sea floor of the exploration area,

(a) deriving an actual transmission time (Tr) of a bottom surface reflection signal by picking up a bottom surface reflection signal for each trace, which is seismic wave detection data for each of the plurality of bins;

(b) deriving a depth of water for each of the plurality of bins from the depth data and acquiring a propagation speed of the seawater under the seawater condition at the time of acquiring the survey data;

(c) calculating a standard transmission time (Ts) of the seabed reflection signal of the elastic wave with respect to each of the bins under the condition that there is no waveness in the survey area;

(d) calculating a time difference [Delta] T between the actual delivery time and the standard delivery time for each bin;

(e) reflecting the time difference obtained for each bin on the corresponding trace to correct a time difference caused by the waveness.

According to the present invention, the seismic exploration data and the depth data can be acquired by performing direct seismic exploration or utilize existing exploration data.

In one example of the present invention, the standard delivery time Ts is calculated by the following equation (1)

Ts = {h ² + (2 x d _midpoint ) ² } ^1/2 / V _w ... Equation 1

Where h is the horizontal distance between the sound source and the receiver, d _midpoint is the sea level reference depth at the midpoint between the sound source and the receiver, and V _w is the transmission rate of the sound wave in the sea water.

Also, in one embodiment of the present invention, the depth data can be acquired by a multi-beam echo sounder.

In addition, in one example of the present invention, the seismic survey data is obtained by performing a submarine meandering layer using a high frequency sound source.

It is another object of the present invention to provide a marine 3D seismic exploration method using the waveness influence correction method described above.

In the seismic wave exploration method according to the present invention,

(a) dividing an exploration area into a plurality of bins (unit areas), performing a 3D seismic wave survey to acquire seismic exploration data and a depth data of a plurality of traces;

(b) correcting the waviness effect on the seismic survey data using the method according to claim 1;

(c) a post-processing step of deriving a 3D cube, which is the final product for the exploration area, through post-processing on the probe data whose blade influence is corrected.

In an exemplary embodiment of the present invention, the post-processing step may include performing NMO (Normal Moveout) correction for correcting a delay time according to a distance difference between a sound source and a receiver for each trace in the probe data in which the influence of the waviness is corrected And polymerizing traces for the same bin after the NMO correction to improve the signal-to-noise ratio.

In the present invention, it is advantageous that accuracy and reliability of the survey data on the deep stratum are improved by removing the influence of the wav in the exploration data obtained from the ocean 3D seismic exploration using the high frequency sound source.

On the other hand, even if the effects are not explicitly mentioned here, the effect described in the following specification, which is expected by the technical features of the present invention, and its potential effects are treated as described in the specification of the present invention.

1 is a view for explaining the principle of seismic wave exploration.
FIGS. 2 and 3 are views for explaining a multi-channel method, and are a diagram for comparing a 2D method (FIG. 2, streamer type receiver) and a 3D method (FIG. 3).
4 is a schematic flowchart of a waveness impact correction method and a seismic wave exploration method of a marine 3D seismic survey data according to an exemplary embodiment of the present invention.
Fig. 5 shows an example in which the probe region is divided into a plurality of unit regions (bins, bins).
Figure 6 is intended to illustrate seismic exploration for individual beans in the exploration area.
FIG. 7 is a vertical section including line (C) in FIG. 6, and a process in which a reflection signal is recorded in a receiver.
Figure 8 is an example of?
Fig. 9 is for explaining the NMO correction.
Fig. 10 is intended to explain the principle of eliminating the influence of the waviness.
Fig. 11 compares the case where the influence of the woof is removed and the case where the woof effect is not removed.
* The accompanying drawings illustrate examples of the present invention in order to facilitate understanding of the technical idea of the present invention, and thus the scope of the present invention is not limited thereto.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.

The present invention relates to a multi-channel 3D seismic exploration technique in marine seismic exploration. Also, it is applied mainly to exploration of a shallow ground layer using a high frequency sound source. Of course, we do not rule out application to deep earth exploration using low frequency sources.

Further, the present invention is also applicable to a case in which the transmission path of a sound wave is V-shaped, that is, the sound source and the receiver are spaced apart from each other by a considerable distance even in the single-channel method.

Hereinafter, a method for correcting a waveness effect of a 3D oceanic seismic survey data according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a schematic flowchart of a waveness influence correction method and a seismic wave exploration method of an acoustic wave surveying data according to an example of the present invention.

In the present invention, the seismic survey data is first collected. Seismic exploration data can be acquired by direct survey, but existing exploration data may be utilized.

A brief description will be given of the case where the direct survey is performed.

First prepare the exploration equipment. 3, a cable r is suspended at the rear of the probe 1 and a high frequency sound source 3 such as a boomer, an air gun, a sparker, Float. At the back of the sound source 3, a plurality of receivers 4 are suspended at a certain distance along the direction perpendicular to the traveling direction of the probe, A GPS device is mounted on the probe 1 and a GPS device can be mounted on the sound source 3 or the receiver 4. [ It is not necessary that the GPS equipment is installed in both the sound source and the receiver. It is only necessary to be able to grasp the precise position of the sound source 3 and each receiver 4 through the GPS equipment. Also, in the present invention, a water depth meter is installed to measure the water depth for each bin in the survey area. In particular, a multi-beam echo sounder (MBES) can be used in this example. (Vw) of the sound waves.

As described above, in the state where the probe, the sound source, the receiver, the water depth meter, and the GPS equipment are mounted, the probe is moved in the probe area and performs the seismic exploration.

At the time of the exploration, first, as shown in FIG. 5, the exploration area T is divided into a plurality of unit areas (the above-mentioned bin), and accurate location information about each bin is acquired and inputted to the controller.

The probe generates a sound wave at a predetermined time interval or a distance traveled by a certain distance while receiving the reflected wave and records the return wave while moving the probe region along the designed side line (the probe path).

FIG. 6 illustrates a process of transmitting and receiving a sound wave in the seismic wave survey, and FIG. 7 shows raw data (hereinafter referred to as 'survey data') obtained by the seismic wave survey.

6 shows one bin b and an example C in which the sound source 3 and one receiver 4 are arranged on both sides thereof. The sound waves are reflected at the intermediate point (m) between the sound source 3 and the receiver 4. Therefore, if the position of the sound source 3 and the receiver 4 is known precisely, it can be known which bin b in the exploration area T is reflected. In FIG. 6, an example (K) in which the sound source and the receiver are arranged diagonally with respect to the bin is shown. In this case, if the position of the midpoint 7 between the sound source and the receiver is known accurately, Or whether or not It does not matter where the reflection is from within the bin, and they are all treated as signals for the bin. Generally, since the length of one side of the bean is set at a distance of about half of the distance between the sound source and the sound receiver, considering the acoustic wave wavelength, regardless of the position of the sound wave in the bin, It is acceptable.

7 shows a vertical section below the straight line between the sound source and the receiver in the example of FIG. 6C. The sound waves from the sound source 3 pass through the seawater, And enters the receiver 4. The receiver 4 is then turned off. The right side of FIG. 7 is the data in which the reflection signal entered into the receiver is recorded. Sound waves are first reflected back from the ocean floor (s), and sound waves reflected from deep layers are received at time intervals. In other words, in the case of a data record (hereinafter referred to as trace (t)) which is elongated downward, the starting point is the time point at which the sound waves are transmitted and the lower side is the time axis. That is, the signal (A) is recorded first, followed by the data (B to D), the noise (p) is recorded in the middle, and the sound waves from the sound source It is recorded first, which is not a reflected signal from the ground layer, and is removed from the trace example of FIG.

8 is an exploration data in which all the traces in the seismic exploration are recorded. Referring to FIG. 8, the Y-axis is the time axis (time goes down), and the X-axis is the recorded trace number (called trace number). As shown in this example, when eight receivers are installed, traces are recorded in each of eight receivers for one sound wave transmission. For example, the first eight traces recorded traces received from eight receivers in the first shot (Shot No. 1). In FIG. 8, since 20 shots are transmitted and eight channels are received, 160 traces are recorded in all.

One trace is a record of one bin. For example, if the trace recorded at the receiver # 5 of the third shot and the trace recorded at the receiver # 1 of the eighth shot are signals reflected from the same bin, substantially the same signal pattern should be seen when the noise is removed. For example, according to the distribution of the depth of field of the bin, two traces must record the reflected signal from the ground layer at the same time point. However, in the two traces, a difference occurs at the time when the signal is recorded.

Referring to FIG. 9, a seismic ray path is shown according to the offset between the sound source Xn and the receiver Rn. Even if the reflected points are the same, the longer the distance between the sound source and the receiver (offset), the longer the time the signal arrives. In the case of operating the eight channels as in the present example, the signal arrives relatively late when the sound source is close to the receiver R1, and the signal arrives late when the sound source and the receiver R6 are far away. For example, in the example of (C) for the same bin in Fig. 6, the signal arrives later in the case of the longer (K) option.

The NMO (Normal Moveout) correction is performed to correct the distance delay (time delay) due to the offset. The trace on the left side of FIG. 9 is the actual trace, and the right side is the time delay corrected in consideration of the offset. That is, the trace is vertically shifted upward along the time axis in proportion to the length of the offset. By doing so, you can get a trace that excludes the effect of the offset. Since the position of the sound source and the position of the receiver are continuously acquired through the GPS, the distance between the sound source and each receiver is known and the NMO correction can be performed.

As described above, in the seismic exploration, the exploration area T is divided into a plurality of bins, and the seismic waves are surveyed along the designed line. In general, a plurality of traces are acquired for each bin by performing a probe search. After performing NMO correction on a trace-by-trace basis, traces for the same bin overlap each other. For example, the trace recorded by the receiver # 5 of the third shot and the trace recorded by the receiver # 1 of the eighth shot are overlapped with each other. This polymerization strengthens the amplitudes of the layered reflection signals, but random noise that does not show a specific pattern does not occur at the same time and is interspersed. That is, when the polymerization is carried out, the ground reflection signal and the noise are clearly distinguished. This is called signal-to-noise ratio, and noise can be removed by increasing the signal-to-noise ratio through polymerization. NMO can also be considered as a preliminary step for polymerization. Without NMO correction, the signal-to-noise ratio does not increase because the amplitudes of the ground reflection signals are not reinforced when the trace is polymerized.

After the polymerization, a three-dimensional cube is finally obtained for the stratum through subsequent treatment.

Referring to FIG. 4, once the seismic surveys are summarized, the seismic surveys are divided into a plurality of bins in the preparation of the survey equipment, a plurality of bins in the survey area, seismic waves along the designed line, NMO correction for the same bin, trace polymerization for the same bin, and 3D cube derivation.

The present invention relates to a process which has not been described so far, that is, a process indicated by a dotted line in FIG. This is performed before the NMO correction after acquiring the seismic survey data. As described in the prior art, in marine seismic surveys, especially in high frequency exploration, the arrival time of a sound wave (watch) is influenced by the waviness. For example, in the case of 1 m of wave height, there may be a difference between the transmission position of the sound wave or the reception position within the range of 2 m up and down from the sea water reference plane, and accordingly, the sight is also affected.

In the present invention, the water depth from the seawater reference plane to the sea floor is measured and data are obtained for the exploration area (each bean) to remove the influence of the swell in the survey data. In this example, a multi-beam echo sounder (MBES) is used. A multi-beam echo sounder emits more than 200 acoustic beams in a frequency band of approximately 30 kHz or more, receives it again, and measures the depth of the sea floor. It is mainly used to create an undersea map.

Also in this example, the depth of each mid point in the survey area is measured using a multi-beam echo sounder. Of course, in the present invention, it is not necessary to use a multi-load acoustic echo sounder in order to measure depth of water, and it is suggested that sounding is possible through various methods and equipment.

Meanwhile, in the present invention, the arrival time of the bottom of the sound wave (reception time of the first reflection signal) in all the traces is obtained from the seismic wave data. More specifically, the STA / LTA algorithm is widely used in the field to automatically determine the time of arrival (referred to as 'auto picking').

Of course, in the present invention, various methods such as the Energy Ratio (ER) model can be used in addition to the STA / LTA method as a method of picking up the sea bottom reaching time.

As described above, if the depth data for each bin of the exploration area is secured and the time of reaching the bottom of the seabed from all the traces of the seismic exploration data is secured, the influence of the waveness is removed for each trace. The elimination of the sweep effect is very simple but is done through a clear and reliable method.

Will be described with reference to FIG.

FIG. 10 shows the arrangement of the sound source and the receiver in the condition of a wav (w). The sound source 3 is positioned at the apex of the worm and the receiver 4 is placed at the bottom and the sea level o without influence of the swell is displayed.

The actual sound waves emitted from the sound source 3 propagate along the path indicated by a in the drawing. On the other hand, if there is no deformation, the sound source (3) is located at sea level (o) and will propagate along the path indicated by b in the figure. The path a is longer than b, so that the time for which the sound waves reflected at the bottom surface s in the path a are written to the receiver 4 is delayed. On the contrary, if both the sound source 3 and the receiver 4 are located below the sea surface o, the reception time of the reflected wave will be faster.

In the present invention, the following equation is used to eliminate the influence of the waviness.

Ts = {h ² + (2 x d _midpoint ) ² } ^1/2 / V _w ... Equation 1

Where h is the horizontal distance between the sound source 3 and the receiver 4 and d _midpoint is the sea level reference depth at the midpoint between the sound source 3 and the receiver 4 and V _w is the depth It is the delivery speed in seawater. Ts is the arrival time of the sound waves reflected from the seabed surface (hereinafter referred to as "standard transmission time") in the case where the sound waves and the receiver are both located on the sea surface.

The d _midpoint is measured by using a multi-beam echo sounder, and the effect of the waviness is removed. Since the path b and the offset h are isosceles triangles, the total length of the path b is obtained by adding the square value (h ² ) of the offset and the square value (2 × d _midpoint ) ² of twice the depth of the water (1/2). By dividing this distance by the sound wave propagation velocity (V _w ), it is possible to obtain the standard transmission time (Ts) of the sound wave when there is no influence of the swell as in the above equation.

The offset (h) is measured by a GPS device, and the depth and sound propagation velocity are measured by a multi-beam acoustic echo canceller, so the standard propagation time when there is no influence of the swell can be determined.

Then, a time difference? T between the actual delivery time Tr actually measured in the path a and the standard delivery time Ts is obtained.

ΔT = Tr - Ts ... Equation 2

Here, the time difference is the difference between the time of actual measurement of the bottom surface reflection signal measured in the actual resolution (waveness environment) (actual transmission time) and the standard transmission time of the bottom surface reflection signal measured using the above formula.

This difference value is due to the influence of the swell. After calculating the time difference for each bin in the exploration area, this time difference is reflected in each trace. For example, if there is a time delay of 0.01 seconds in a certain bin, correction is performed by pulling the entire trace for 0.01 second. For example, in FIG. 8, the trace is moved upward by 0.01 seconds. If the time difference is negative, reverse the trace downward by 0.01 second. In other words, although the time difference is calculated based on the sea floor, this time difference is also applied to the signals reflected from all the ground layers as well as the sea floor reflection signal, so the time difference is corrected with respect to the entire trace.

This correction can eliminate all of the effects of the sound wave propagation time by the wraps on all traces.

Once the influence of the propagation time by the swell is corrected, NMO correction can be performed as described above, and the traces can be superimposed to finally derive the 3D cube.

In the present invention, the final results are calculated and compared using the seismic survey data of the case where the effect of the waviness is removed and the case where the waviness is not removed. The result is shown in Fig.

Fig. 11 is a view of sampling four vertical cross-sections of (a) to (d) in the finally derived 3D cube Z. Fig. The upper part of the figure shows the case where the influence of the swell is not corrected, while the lower part shows the case where the influence of the swell is corrected. Referring to FIG. 11, in the case where the influence of the swath is not corrected, it is seen that the bottom surface of the sea floor appears to be continuously uneven like a toothed wheel, whereas when the influence of the swath is corrected, the sea bottom is relatively straightened. Correcting the influence of the swarf accurately reflects the actual seafloor environment.

According to the present invention, it is possible to eliminate the influence of the waviness of the exploration data acquired in the marine seismic exploration through a very simple method, thereby providing more accurate and reliable exploration data.

Particularly, in the present invention, correcting the influence of the swarf in a very simple manner can reduce the data processing time and the load on the computer, which is advantageous in that it is possible to rapidly process the survey data.

In the present invention, the post-processing method using NMO correction, trace polymerization and the like has been described in the present invention. However, the method of calculating the final result through post-processing of the probe data having the correction of the worm impact is not limited to the other methods I do not know.

The scope of protection of the present invention is not limited to the description and the expression of the embodiments explicitly described in the foregoing. It is again to be understood that the present invention is not limited by the modifications or substitutions that are obvious to those skilled in the art.

Claims (9)

A plurality of traces formed by a plurality of traces obtained by dividing the survey area into a plurality of bins (unit areas) and obtained through 3D oceanic seismic exploration using multi-channels with respect to the survey areas; and a water depth A method for correcting a waviness effect in the seismic exploration data using data,
(a) deriving an actual transmission time (Tr) of a bottom surface reflection signal by picking up a bottom surface reflection signal for each trace, which is seismic wave detection data for each of the plurality of bins;
(b) deriving a depth of water for each of the plurality of bins from the depth data and acquiring a propagation speed of the seawater under the seawater condition at the time of acquiring the survey data;
(c) calculating a standard transmission time (Ts) of the seabed reflection signal of the elastic wave with respect to each of the bins under the condition that there is no waveness in the survey area;
(d) calculating a time difference [Delta] T between the actual delivery time and the standard delivery time for each bin;
(e) reflecting the time difference obtained for each bin on a corresponding trace to correct a time difference caused by the waveness,
The standard delivery time Ts is calculated by the following equation 1,
Ts = {h ² + (2 x d _midpoint ) ² } ^1/2 / V _w ... Equation 1
Where h is the horizontal distance between the sound source and the receiver, d _midpoint is the sea level reference depth at the _midpoint between the sound source and the receiver, and V _w is the transmission speed in the sea water of the sound wave. Correction method of waveness impact of survey data. The method according to claim 1,
Wherein the seismic exploration data and the depth data are acquired by performing direct seismic exploration or using existing exploration data. delete The method according to claim 1,
Wherein the depth data is acquired by a multi-beam acoustic echo canceller. The method according to claim 1,
Wherein the seismic survey data is obtained by performing a submarine meandering layer using a high frequency sound source. (a) dividing an exploration area into a plurality of bins (unit areas), performing a 3D seismic wave survey to acquire seismic exploration data and a depth data of a plurality of traces;
(b) correcting the waviness effect on the seismic survey data using the method according to claim 1;
(c) a post-processing step of deriving a 3D cube, which is a final product for the exploration area, through post-processing on the exploration data whose blade influence is corrected. The method according to claim 6,
The post-
Performing NMO (Normal Moveout) correction to correct a delay time corresponding to a distance difference between a sound source and a receiver for each trace in the probe data in which the influence of the swath is corrected;
And polymerizing traces for the same bin after the NMO correction to improve the signal-to-noise ratio. delete The method according to claim 6,
Wherein the depth data is obtained by a multi-beam acoustic echo sounder.

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