CN113189646A

CN113189646A - Method for removing dragging type shallow-section stratum abnormal fluctuation

Info

Publication number: CN113189646A
Application number: CN202110416825.1A
Authority: CN
Inventors: 刘菲菲
Original assignee: Binzhou University
Current assignee: Binzhou University
Priority date: 2021-04-19
Filing date: 2021-04-19
Publication date: 2021-07-30
Anticipated expiration: 2041-04-19
Also published as: CN115291280A; CN113189646B

Abstract

The invention discloses a method for removing dragging type shallow-section stratum abnormal fluctuation, which provides two different strategies aiming at the existence of the data of a depth finder, when the data of the depth finder exists, the real seabed time in the flat and static sea surface is defined by the data of the depth finder synchronously measured along with a ship, the seabed time of the shallow-section data is picked up by fusing the water depth data measured by the depth finder and the shallow-section data, and the picked-up seabed time of the shallow-section data is corrected to the real seabed time to realize the elimination of the stratum abnormal fluctuation phenomenon; if no depth finder data exists, the real seabed time when the sea bed is flat and quiet is approximated by calculating the average value of the abnormal fluctuation quantity of the seabed in a complete sea wave period, and the seabed time of the picked shallow profile data is corrected to the real seabed time to eliminate the abnormal fluctuation phenomenon of the stratum; the scheme of the invention has the advantages of high reliability, convenience, high efficiency, wide application range and higher practical application value.

Description

Method for removing dragging type shallow-section stratum abnormal fluctuation

Technical Field

The invention relates to the field of marine high-resolution shallow profile seismic data processing, in particular to a method for removing abnormal fluctuation of a dragging type shallow profile stratum.

Background

A shallow profiler (sub-bottom profiler) is an instrument for detecting a shallow profile structure by using sound waves; the shallow stratum profiler is an improved ultra-wideband submarine profiler, and is a device for profile display of the bottom strata of oceans, rivers and lakes, and can detect the geological structure condition below the water bottom by combining geological interpretation. The method is widely applied to marine geological survey, geophysical exploration and marine engineering, marine observation, submarine resource exploration and development, channel bay engineering and submarine pipeline laying.

The invention mainly aims at a dragging type shallow dissection system, namely a shallow dissection system with independent seismic source and receiver and dragged behind a ship body in the acquisition process. Its equipment manufacturers are, for example, AAE, Netherlands GEO, France SIG. The shallow profile of these companies generally obtains a better seismic profile during the acquisition process if the sea state is good, but the seismic profile is more affected when the sea state is poor, and particularly, the problem of abnormal stratigraphic fluctuation of the seismic profile is shown. As shown in fig. 1, it is obvious that there is significant formation abnormal fluctuation in the seabed and the formation below, which is not an actual geological phenomenon but is caused by poor sea state, so how to eliminate the "geological artifact" in the processing is very important for the later geological interpretation.

It is believed that under poor sea conditions, the distance between the source and the receivers changes, i.e., the offset changes, which in turn affects the seafloor reflection time. Therefore, the formation fluctuation is considered to be caused by the change of the offset distance, and the problem of the formation fluctuation can be solved by eliminating the influence of the offset distance. However, in actual processing, the influence of offset is only eliminated by eliminating the influence factor of the transverse space, but in poor sea conditions, besides the change of the left and right space distance between the seismic source and the wave detection point, the change of the up-and-down fluctuation along with the sea waves is also existed, and the up-and-down fluctuation of the sea waves is the main reason of the formation fluctuation, but the existing method can only 'relieve' the formation fluctuation problem, and is difficult to completely solve the problem.

Disclosure of Invention

The invention provides a method for removing dragging type shallow-section stratum abnormal fluctuation aiming at the defects in the prior art, and the method is mainly used for removing the stratum abnormal fluctuation by eliminating the influence of the fluctuation of sea waves on a seismic section.

The invention is realized by adopting the following technical scheme: a method for removing abnormal fluctuation of a drag-type shallow cut stratum comprises the following steps:

step A, if the data of the depth finder exists, fusing the water depth data measured by the depth finder with the shallow profile data, and then performing step B; if no depth finder data exists, directly executing the step B;

b, picking up shallow profile data seabed time;

step C, determining real seabed time;

and D, correcting the seabed time of the shallow profile data picked up in the step B to the real seabed time, and eliminating the abnormal fluctuation phenomenon of the stratum.

Further, in the step a, a spatial position matching method is adopted for data fusion, and the method specifically includes:

step A1, quality control of the data of the depth finder: eliminating zero interference and correcting the position of the depth finder;

step A2, repositioning the spatial position of the shallow profile data to obtain a corrected shallow profile position coordinate;

step a3, least squares spatial distance fitting: and matching the spatial positions of all the channels of the shallow profile data with the spatial position of the depth sounder water depth data to realize the matching of the depth sounder water depth data and the shallow profile data.

Further, in the step a3, when performing least-squares spatial distance fitting, the following method is specifically adopted:

(1) calculating the distance between each point of the shallow profile data and each point of the depth sounder to obtain a minimum distance point by taking the shallow profile data as a reference, arranging all the minimum distance points in a sequence from small to large after all the shallow profile data points are calculated, and calculating the average value of the distance points in the middle of 50%;

(2) setting a percentage cutoff value according to the size of the sample quantity, wherein the minimum distance point corresponding to the percentage cutoff value is a threshold value after the percentage cutoff value is determined, and adjusting the cutoff value by comparing the threshold value with the average value;

(3) reserving all minimum distance points within the threshold range and setting the minimum distance points as optimal matching points; and considering that the depth sounder is not matched with the shallow profile data when the minimum distance point within the threshold range is exceeded, setting the minimum distance point as a hollow track, interpolating the hollow track, completing the matching of the spatial positions of all tracks of the shallow profile data and the spatial position of the depth sounder water depth data, and then importing the depth sounder water depth data into the shallow profile data.

Further, in step a3, considering that the distance between the shallow profile and the positioning device is difficult to be accurately measured, and a distance difference exists between the depth data of the depth finder and the shallow profile in the horizontal direction of the seabed, the distance between the shallow profile and the positioning device is re-determined by measuring the distance difference between the depth data of the depth finder and the shallow profile in the horizontal direction of the seabed, and then the least square spatial distance fitting is performed again, so that more accurate matching is realized.

Further, the step B specifically includes the following steps:

step B1, eliminating the spherical diffusion effect: spherical diffusion compensation is carried out at the seawater speed of 1500 m/s;

step B2, determining the simple sea bottom surface:

(1) if the depth finder depth data exist, the depth finder depth data are smoothed and then used as a simple sea bottom surface;

(2) if no depth finder depth data exists, the sea bottom profile is outlined according to the sea bottom form, the distance between the picked point and the sea bottom is kept to be the same during picking, and then the points which are not picked are interpolated to determine the simple sea bottom surface;

step B3, determining the automatic picking seabed time according to the amplitude energy in the fixed time window by taking the simple seabed surface as the reference;

and B4, correcting the abnormal points picked up in the step B3, and further determining the seabed time of the shallow profile data.

Further, in the step C, when determining the real seafloor time:

if the depth finder depth data exists, determining the real seabed time by taking the depth finder depth data as a reference;

if no depth finder depth data exists, simulating real seabed time according to actual seismic data: and measuring the period of the abnormal fluctuation of the shallow profile data stratum, namely the number of samples in the transverse direction, and then calculating the average value of the seabed time within the period range to obtain the real seabed time.

Compared with the prior art, the invention has the advantages and positive effects that:

the scheme of the invention provides two different strategies aiming at the existence of the depth finder depth data, and when the depth finder depth data exists, the seabed time in the flat and static sea surface is defined by the depth finder depth data synchronously measured along with a ship; if no depth finder depth data exists, the seabed time when the sea bed is in a flat and static sea surface is approximated by calculating the average value of the seabed abnormal fluctuation in a complete period, and the seabed time of the picked shallow profile data is corrected to the real seabed time, so that the stratum abnormal fluctuation phenomenon is eliminated; the scheme is convenient, reliable, high in treatment efficiency and wide in application range.

Drawings

FIG. 1 is a schematic diagram of a formation abnormal fluctuation phenomenon in shallow profile survey caused by poor sea state;

FIG. 2 is a schematic diagram of the principle of abnormal fluctuation of a shallow section of a formation;

FIG. 3 is a schematic diagram of a significant wave cycle in accordance with an embodiment of the present invention;

FIG. 4 is a schematic diagram of a method of an embodiment of the present invention;

FIG. 5 is a schematic illustration of processing shallow profile data points outside of a threshold range in accordance with an embodiment of the present invention;

FIG. 6 is a schematic diagram illustrating a lateral difference between the depth of the water in the shallow section and the sea bottom of the depth finder when the distance difference D is inaccurate according to an embodiment of the present invention;

FIG. 7 is a schematic diagram illustrating an example of fusion of water depth data and shallow profile data of a depth finder according to an embodiment of the present invention;

FIG. 8 is a schematic diagram showing a comparison of shallow profile data before and after the abnormal formation heave phenomenon is eliminated in the embodiment of the present invention.

Detailed Description

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be further described with reference to the accompanying drawings and examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those described herein, and thus, the present invention is not limited to the specific embodiments disclosed below.

For a clearer understanding of the present solution, the principle of the formation abnormal undulation will be explained first: as shown in fig. 2, when the sea conditions are poor, the up-and-down fluctuation of sea waves causes the seismic source and the geophone to deviate from the calm sea, and the extreme cases are two: one is that the seismic source and the wave detecting point are both positioned at the wave crest of the sea wave, at this time, the seismic wave is excited from the seismic source and is received by the wave detecting point after being reflected by the sea bottom, the travel time of the seismic wave is obviously increased, and the wave trough of the abnormal undulating stratum is formed on the seismic section; one is that the seismic source and the wave detecting point are both positioned at the wave trough of the sea wave, at this time, the seismic wave is excited from the seismic source and is received by the wave detecting point after being reflected by the sea bottom, the travel time is obviously reduced, and the wave crest of the abnormal undulating stratum is formed on the seismic section.

In the case of a wave height of 3 meters, the increase of the state a travel relative to the calm surface in fig. 2 is about (1.5m +1.5m)/1.5m/ms is 2ms, and the decrease of the state B travel relative to the calm surface in fig. 2 is about (1.5m +1.5m)/1.5m/ms is 2 ms. Therefore, the abnormal fluctuation of the stratum on the seismic section can reach 4ms under poor sea conditions, which far exceeds the tolerance amount of the high-resolution shallow section, so that the influence of the fluctuation effect of the waves on the seismic section needs to be eliminated.

According to the analysis, when the seismic source and the demodulator probe are respectively corrected to the calm sea surface, the stratum fluctuation phenomenon can be eliminated when the travel time amount is consistent, so the key of the problem is how to find the seabed time when the optimum calm sea surface is obtained.

In the scheme of the invention, when the depth finder depth data exists, the seabed time in the flat and quiet sea surface is defined by the depth finder depth data synchronously measured along with the ship, because the depth finder is generally arranged at the most stable position of the center of gravity at the rear part of the ship body, the fluctuation amplitude along with the sea surface is smaller, and the measured depth data is more accurate; if no depth finder depth data exists, the sea bottom time in the flat sea surface can be approximated by calculating the average value of the abnormal sea bottom fluctuation in a complete sea wave period, and because the seismic source blasting time is a fixed value and the fluctuation of the sea waves has periodicity, the stratum fluctuation has certain regularity, namely the stratum fluctuation often fluctuates up and down around the sea bottom time in the flat sea surface and has certain periodicity (fig. 3), so the method has wider application range.

As shown in fig. 4, the present embodiment provides a method for removing an abnormal undulation of a drag-type shallow cut formation, which specifically includes the following steps:

step A, if the water depth data of the depth finder exists, fusing the water depth data measured by the depth finder with the shallow profile data:

the fusion is carried out for importing the water depth data of the depth sounder into the shallow profile data, and the traditional method generally adopts a time matching mode for fusion about data fusion; the water depth data of the depth sounder is recorded once in 1 second generally, and the water depth data of the shallow section is recorded once in 4-5 seconds generally, so that the water depth data recorded by the depth sounder necessarily contains the water depth data of all the shallow section positions theoretically. However, in practical application, the depth finder system and the shallow dissection system belong to two systems, and a synchronous controller is absent between the two systems, so that the two systems are not matched in time. In addition, the time scales adopted by the depth finder and the shallow profile data record may be different, that is, there is a conversion between the beijing time and the greenwich mean time, and if the time spans the day, the time may be disordered, and in addition, the processing is more troublesome when the record discontinuity occurs between the two, so that the two are relatively troublesome to unify.

The embodiment provides a spatial position matching method for data fusion, namely, the judgment is carried out according to the principle that the distance between two points of the position of the depth finder and the shallow profile data is shortest, the method is relatively simpler and more convenient, and the specific steps are as follows:

step A1, quality control of the depth finder water depth data:

in complex sea conditions, the depth finder has zero value of the depth finder water depth data due to the fact that the ship body shakes greatly and the situation that a reflected signal is difficult to receive sometimes occurs, and therefore zero value interference is firstly eliminated for the depth finder water depth data, namely, the zero value data is interpolated by adopting surrounding normal values.

In addition, in general, a certain distance exists between the depth finder and the positioning device, so that the GPS information recorded by the positioning device has a certain deviation from the actual depth finder position, and it is necessary to measure the relative position between the two according to the actual situation and perform position correction; in order to facilitate position calculation, a spherical coordinate needs to be converted into a planar coordinate, generally, mercator projection or UTM projection is commonly used for projection, and a real position coordinate of the depth finder needs to be calculated according to a ship navigation direction, as shown in formula 1:

wherein X1 is the abscissa of the depth finder before position correction, Y1 is the ordinate of the depth finder before position correction, X is the abscissa after position correction of the depth finder, Y is the ordinate after position correction of the depth finder, S is the distance between the depth finder and the positioning device, and alpha is the heading angle.

Step A2, shallow section data space position repositioning:

in accordance with the principle of correcting the position of the depth sounder in step a1, the shallow-profile seismic source is generally located several tens of meters behind the survey vessel, and has a distance difference with the positioning device, so that position correction is also required. The distance D between the shallow section and the positioning device is 40-80m, which is related to the field acquisition situation and is determined according to the actual situation. In this embodiment, the shallow section coordinate relocation is as shown in formula 2:

wherein X '1 is the abscissa of the shallow profile before position correction, Y'1 is the ordinate of the shallow profile before position correction, X 'is the abscissa of the shallow profile after position correction, Y' is the ordinate of the shallow profile after position correction, D is the distance between the shallow profile and the positioning equipment, and alpha is the course angle. It should be noted that the D value is generally determined by measuring the release length of the shallow-section seismic source, and the result is not necessarily reliable, and needs to be corrected by further matching with the shallow-section seabed.

Step a3, least squares spatial distance fitting:

(1) calculating the distance between each point of the shallow profile data and all spatial positions of the depth sounder by taking the shallow profile data as a reference to obtain a minimum distance point

Wherein D_mtnThe method comprises the steps that a shallow profile data point and minimum distance points of all space positions of a depth finder are taken as the minimum distance points, X is an abscissa after the position of the depth finder is corrected, Y is an ordinate after the position of the depth finder is corrected, X 'is an abscissa after the position of the shallow profile is corrected, Y' is an ordinate after the position of the shallow profile is corrected, all the minimum distance points are arranged from small to large after all shallow profile data points are calculated, the distance points in the middle 50% are selected, and an average value is obtained;

(2) and setting a percentage cutoff value, wherein the percentage cutoff value is generally set according to the sample size, and the larger the sample size is, the larger the percentage cutoff value is, the smaller the sample size is, the smaller the percentage cutoff value is, and the generally set percentage cutoff value is more suitable to be 90% -95%.

(3) And if the difference between the two values is too large, the percentage truncation value is indicated to be too large, and the percentage truncation value needs to be reduced until the deviation value of the two values is within a reasonable range.

(4) Reserving all minimum distance points within the threshold range, and considering the minimum distance points as optimal matching points; and considering that the depth sounder is not matched with the shallow profile data by exceeding the minimum distance point within the threshold range, setting the depth sounder as a hollow track (figure 5), interpolating the hollow track, completing the matching of the spatial positions of all tracks of the shallow profile data and the spatial position of the depth sounder water depth data, and then importing the depth sounder water depth data into the shallow profile data.

In addition, considering that the distance D between the shallow profile and the positioning device in the formula 2 is difficult to be accurately measured, there may be a distance difference between the imported depth finder water depth data and the shallow profile seabed in the transverse direction, the distance difference between the two is measured, an accurate D value (fig. 6) can be obtained again according to the distance difference between the two, and then least square spatial distance fitting is performed again, so that matching and fusion of the depth finder water depth data and the shallow profile data can be realized. When the D value is determined, re-measurement is not needed when the rest of the line coordinate in the project is corrected.

The depth finder and shallow profile seabed data fusion example is shown in fig. 7, and it can be seen that the depth finder depth data and the shallow profile data are well fused, and it is obvious that the seabed scarp really exists through the depth finder depth data detection, and other seabed topography fluctuations are false images and are all caused by surge. And if no depth finder depth data exists, directly skipping the step and directly executing the step B.

B, picking up shallow profile data seabed time:

because the conventional shallow profile data generally has large data volume and the efficiency of the method adopting manual picking is too low, and because the shallow profile has large difference in acquisition environment and more influence factors such as environmental noise and the like, the conventional method cannot realize complete automatic picking, and the optimal seabed picking method at the present stage adopts a method combining automatic picking and manual correction. The method comprises the following specific steps:

step B1, eliminating the spherical diffusion effect: the spherical diffusion compensation is carried out at the seawater speed of 1500m/s mainly for making the seabed energy consistent and avoiding the overlarge energy difference between deep water and shallow water.

Step B2, determining the simple sea bottom surface:

if the depth finder depth data exists, the depth finder depth data is smoothed and then used as a simple sea bottom surface;

if no depth finder depth data exists, the seabed contour is roughly drawn at a certain position above the seabed according to the seabed form, the distance between the pickup point and the seabed is kept to be roughly the same during pickup, and then the simple seabed surface can be realized by interpolating the points which are not picked.

Step B3, determining the automatically picked seabed time according to the amplitude energy in a fixed time window by taking the simple seabed surface as a reference:

the fixed time window takes a simple sea bottom surface as a starting point, and is fixed in length downward based on the sea bottom, and the length is generally 30-50 ms; and searching an amplitude energy point which reaches the set value firstly in the time window range, wherein the point position is the seabed time which is automatically picked up, the amplitude energy point generally needs to be set according to the actual shallow profile data condition, and the common amplitude energy is 2000.

Step B4, correcting abnormal pickup positions: when the environmental noise is large, the noise is often picked up, and in addition, when the sea bottom topography is large in fluctuation, the sea bottom energy is too large or too small, so that the sea bottom geology is not accurately picked up. Therefore, manual quality control is required after automatic picking, and picked abnormal points are corrected again by a manual method.

Step C, determining the real seabed time:

because the precision of the water depth data of the depth finder is far higher than that of the shallow profile, if the water depth data of the depth finder exists, the water depth data measured by the depth finder is the real seabed time;

if no depth finder depth data exists, actual seismic data are needed to approximate the real seabed time: because the wave motion of the sea wave is periodic, the sea floor stratum usually presents the periodic characteristic when abnormally fluctuating, which represents the periodic variation of the relative height difference of a seismic source and a wave detection point, and the variation basically makes periodic reciprocating motion around a calm sea surface, so the average sea floor time of one period is the sea floor time when the sea floor is calm, the period of the abnormally fluctuating of the shallow profile data stratum is measured, as shown in figure 4, namely the number of samples on the transverse direction, and the average value of the sea floor time in the range is calculated to obtain the real sea floor time.

Step D, correcting the picked shallow-section seabed time to the real seabed time, and eliminating the abnormal fluctuation phenomenon of the stratum can be realized:

the correction amount is calculated by

Δt＝T1-T2 (3)

Where Δ T is the correction amount, T1 is the real seafloor time, and T2 is the picked seafloor time.

Fig. 8 is shallow profile data in the Bohai Bay region, and no sounding data is acquired at this time, so that the smooth seabed time after picking up the seabed is adopted to approximate to the real seabed time. Because the acquisition quality is higher, the automatic pickup can almost completely and accurately pick up the seabed time, so the pickup efficiency is greatly improved, the seabed becomes smooth after the abnormal fluctuation phenomenon of the stratum is eliminated, the continuity of the underlying stratum becomes good, the integral section signal-to-noise ratio is also improved, and the stratum is easier to track and identify.

The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.

Claims

1. A method for removing abnormal fluctuation of a drag type shallow cut stratum is characterized by comprising the following steps:

b, picking up shallow profile data seabed time;

step C, determining real seabed time;

2. The method for removing abnormal undulations of a drag-type shallow cut formation as claimed in claim 1, wherein: in the step a, a spatial position matching method is adopted for data fusion, and the method specifically includes:

3. The method for removing abnormal undulations of a drag-type shallow cut formation as claimed in claim 2, wherein: in the step a3, when performing least-squares spatial distance fitting, the following method is specifically adopted:

4. The method for removing abnormal undulations of a drag-type shallow cut formation as claimed in claim 3, wherein: in the step a3, considering that the distance between the shallow profile and the positioning device is difficult to be accurately measured, and a distance difference exists between the depth data of the depth finder and the shallow profile in the transverse direction of the seabed, the distance between the shallow profile and the positioning device is re-determined by measuring the distance difference between the depth data of the depth finder and the shallow profile in the transverse direction of the seabed, and then the least square spatial distance fitting is performed again, so that more accurate matching is realized.

5. The method for removing abnormal undulations of a drag-type shallow cut formation as claimed in claim 1, wherein: the step B specifically comprises the following steps:

step B2, determining the simple sea bottom surface:

6. The method for removing abnormal undulations of a drag-type shallow cut formation as claimed in claim 1, wherein: in the step C, when the real seabed time is determined: