CN107402404B - VSP data wave field separation method - Google Patents

Abstract

A method of wavefield separation of VSP material, comprising the steps of: step 1: carrying out wave field pickup on VSP data to be processed to obtain information of a plurality of wave fields, and recording the position of a same-phase axis of each wave field; step 2: for each in-phase axis, for each point on the in-phase axis, drawing a timing window for the point according to the position of the point; and step 3: and for each in-phase axis, aiming at each point on the in-phase axis, carrying out one-dimensional median filtering processing on the point according to a time window defined for the point. The method omits the leveling and reverse-pulling processes of the existing method, and can simultaneously process a plurality of groups of wave field information, thereby improving the efficiency of wave field separation.

Description

VSP data wave field separation method

Technical Field

the invention relates to a wave field separation technology, in particular to a method for separating a wave field of VSP data.

background

The wave field separation is an important link step in VSP data processing, for VSP data, accurate and efficient wave field separation is the basis of data processing, because the VSP data contains a lot of wave field information, and various wave fields are mutually interlaced, the complex clutter field needs to be subjected to efficient and accurate wave field separation, so that the relatively accurate single wave field is obtained, the next processing of the data is facilitated, and the utilization rate of the VSP data is improved.

the accurate and efficient separation of the wave field information such as the upgoing wave, the downgoing wave and the converted wave in the VSP data channel set is beneficial to obtaining better underground medium attribute information, provides good precondition for obtaining a good imaging section for the following migration, and provides great help for well-ground combined interpretation and inversion so as to improve the resolution of seismic data. The existing median filtering wave field separation technology needs to firstly flatten the in-phase axis of the wave field to be separated in the data, then eliminate the wave field by applying the median filtering principle, and finally perform the reverse drawing treatment to recover the separated trace gather. The method has the defects of complicated flattening and back-drawing processes, greatly reduced separation efficiency and capability of removing only one wave field information at a time.

Disclosure of Invention

the invention aims to provide a method for separating a wave field of VSP data, which omits the flattening and back-drawing processes of the existing method, can process multi-layer wave field information simultaneously and improves the efficiency of wave field separation.

The invention adopts the following solution:

A method of wavefield separation of VSP material, comprising the steps of:

Step 1: carrying out wave field pickup on VSP data to be processed to obtain information of a plurality of wave fields, and recording the position of a same-phase axis of each wave field;

Step 2: for each in-phase axis, for each point on the in-phase axis, drawing a time window for the point according to the position of the point;

and step 3: and for each in-phase axis, aiming at each point on the in-phase axis, carrying out one-dimensional median filtering processing on the point according to a time window defined for the point.

Preferably, the one-dimensional median filtering process is performed according to the following formula (1):

g(x)＝med{f(x-k),...,f(x),...,f(x+k),k∈N} (1)

Wherein g (x) is the output of one-dimensional median filtering, f (x) is the original signal which needs to be subjected to one-dimensional median filtering, med represents the sorted median, and N is a positive integer and represents the number of points in the time window.

Preferably, N is equal to 5, 7 or 9.

Preferably, for each in-phase axis, for each point on the in-phase axis, a time window is defined by taking the position of the point as the center and choosing the same number of points above and below the point.

Compared with the prior art, the method has the advantages that a median filtering processing method in the existing wave field separation method is improved, and the multi-layer complex VSP wave field can be accurately and efficiently separated at the same time.

drawings

the above and other objects, features and advantages of the present disclosure will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings.

fig. 1a to 1c show examples of one-dimensional median filtering methods;

FIG. 2 shows an example of a two-dimensional median filtering method;

FIGS. 3a and 3b show a circular template and a cross-shaped template, respectively, of a two-dimensional median filtering method;

FIGS. 4a and 4b are diagrams illustrating wavefield separation of VSP data using a conventional one-dimensional median filtering method, before and after flattening of the in-phase axis, respectively;

FIG. 5 shows a flow chart of a method of wavefield separation of VSP data in accordance with an illustrative embodiment;

FIG. 6 illustrates the in-phase axes picked up in the wavefield separation method of VSP data according to an exemplary embodiment;

FIG. 7 illustrates a time window chosen for one in-phase axis in a wavefield separation method of VSP data according to an exemplary embodiment;

FIG. 8 illustrates wavefield-separated data resulting from applying a method of wavefield separation of VSP data according to an exemplary embodiment.

Detailed Description

preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

In order to make the present invention more comprehensible to those skilled in the art, a conventional median filtering-based wavefield separation technique will first be described in detail.

Median filtering is a non-linear signal processing technique based on the ordering statistical theory, and is capable of suppressing and eliminating noise. The basic principle of median filtering is to replace the value of a point in a digital image or digital sequence with the median of the values of the points in a neighborhood of the point, so that the surrounding values are relatively close to each other, thereby eliminating the isolated noise point and further achieving the purpose of smoothing.

The median filtering method includes one-dimensional median filtering and two-dimensional median filtering. The one-dimensional median filtering is generally to take the same number of points before and after the point to be processed is adjacent, then to sequence the odd number of values from small to large, to replace the value of the point to be processed with the middle value after sequencing, and then to perform the one-dimensional median filtering in sequence.

An example of one-dimensional median filtering is shown in fig. 1a-1 c. In this example, two values are selected before and after the value 25 (fig. 1a), fig. 1b shows the sorted data table, where the intermediate value is changed to 13, and then the value 25 to be filtered is replaced with 13, resulting in a median filtered data table (fig. 1 c).

The output of the one-dimensional median filtering is shown in equation (1) below:

g(x)＝med{f(x-k),...,f(x),...,f(x+k),k∈N} (1)

Wherein g (x) is the output of one-dimensional median filtering, f (x) is the original signal which needs to be subjected to one-dimensional median filtering, med represents the sorted median, and N is a positive integer and represents the number of points in a time window.

The two-dimensional median filtering needs to select a two-dimensional sliding template with a certain structure, the template can be a square, a cross (see fig. 3b) or a circle (see fig. 3a), and the like, and the values in the template are sorted according to the size of the values to generate a monotonically increasing (or decreasing) value sequence (see fig. 2).

the output of the two-dimensional median filtering is shown in equation (2) below:

g(x,y)＝med{f(x-k,y-l),k,l∈W} (2)

where g (X, y) is the output of the two-dimensional median filtering, f (X, y) is the original signal to be subjected to the two-dimensional median filtering, W is a two-dimensional template, usually a 5X 5, 3X 3 region, which may be in different shapes, such as a line, a circle (see fig. 3a), a cross (see fig. 3b), a circular ring, etc., and med represents the sorted median.

A one-dimensional median filtering method is used in the wavefield separation of VSP data. Using the traditional median filtering method requires that the same phase axis of the picked wavefield is pulled to the horizontal (fig. 4a and fig. 4b show schematic diagrams before and after the same phase axis is flattened respectively), then median filtering processing is performed on the flattened same phase axis one by one to eliminate the selected same phase axis, and finally the same phase axis is pulled back to the original state, thus completing one-step wavefield separation. As can be seen from this process, the conventional median filtering method is relatively complicated and introduces unnecessary errors in the artificial flattening and inverse-pulling processes. In addition, the method can only eliminate one wave field and then another wave field, and under the conditions of complex wavelength, rich information received in data and serious mutual interleaving of the wave fields, the separation efficiency is greatly reduced by using the traditional median filtering method, and the processing progress is influenced.

Aiming at the defects of the VSP data wave field separation by using the traditional median filtering method, the invention provides a novel VSP data wave field separation method, which improves the traditional median filtering method, processes each seismic signal and can simultaneously filter a plurality of groups of wave fields along the direction of a same phase axis.

A wavefield separation method of VSP data according to an exemplary embodiment is described below with reference to fig. 5, which includes the steps of:

Step 1: and carrying out wave field pickup on VSP data to be subjected to wave field separation to obtain information of a plurality of wave fields, and recording the position of a same-phase axis of each wave field.

FIG. 6 shows an example of performing wavefield picking for VSP data to be performed wavefield separation, where the solid black lines in FIG. 6 represent the in-phase axes of the multiple sets of wavefields picked, each set of wavefields comprising one in-phase axis, and where in FIG. 6, 6 sets of wavefields are picked, correspondingly comprising 6 in-phase axes.

step 2: for each in-phase axis, for each point on the in-phase axis, a time window is demarcated for the point according to the position of the point.

Wavefield information picked from VSP data is represented by discrete data points, for each in-phase axis, for each point on the in-phase axis, a time window (also referred to in some literature as a filter window) is drawn for that point based on its position.

And the time window determines the selection range of the points adjacent to the points to be processed in the one-dimensional median filtering, sorts the numerical values of the points in the time window, and takes the sorted middle numerical value to replace the numerical value of the points to be processed.

Preferably, in this step, for any point on the in-phase axis, the same number of points are selected above and below the point as the center, and the time windows are divided for one-dimensional median filtering in the next step.

Preferably, the timing window is defined by including the point above and below the point by taking the position of the point as a center and taking 5 points, 7 points, 9 points, 11 points or 13 points.

fig. 7 shows the selection of a time window for each point on the in-phase axis in the direction of the in-phase axis for one of the in-phase axes shown in fig. 6 (the in-phase axis indicated by an arrow in fig. 7), resulting in a set of time windows as indicated by the black parallelogram-shaped line box indicated by an arrow in fig. 7 (only one time window for the in-phase axis is shown here, and the other in-phase axes are similar thereto).

And step 3: and for each in-phase axis, aiming at each point on the in-phase axis, carrying out one-dimensional median filtering processing on the point according to a time window defined for the point.

and for each in-phase axis, aiming at each point on the in-phase axis, carrying out one-dimensional median filtering processing on the point according to a time window defined for the point. The one-dimensional median filtering process can be implemented using the above equation (1), i.e.:

g(x)＝med{f(x-k),...,f(x),...,f(x+k),k∈N} (1)

Wherein g (x) is the output of the one-dimensional median filtering, f (x) is the original signal which needs to be subjected to the one-dimensional median filtering, med represents the sorted median, and N is a positive integer and represents the number of points in the time window defined in the step 2.

and sequentially carrying out one-dimensional median filtering processing on a plurality of in-phase axes of the wave fields, thereby achieving the purposes of simultaneously eliminating a plurality of wave fields and retaining a single wave field and obtaining data after wave field separation.

FIG. 8 illustrates wavefield-separated data resulting from applying a method of wavefield separation of VSP data according to an exemplary embodiment. As can be seen from figure 8, the wavefield separation results in a single up-going reflected wavefield with the inphase axes representing the remaining wavefield interleaved with the single up-going reflected wavefield being simultaneously cancelled. The method can efficiently separate the wave fields, and the effect meets the requirement of the next processing.

in a traditional wave field separation method based on median filtering, the in-phase axis direction of a wave field needs to be picked up first, then the in-phase axis is pulled to be horizontal, then median filtering processing is carried out, and finally back pulling processing is carried out to recover a separated gather.

According to the method for wave field separation of the VSP data, the multiple wave fields of the VSP data are subjected to median filtering along the direction respectively, wave field separation can be performed along multiple directions simultaneously in the same gather, the fact that the in-phase axis is subjected to flattening and reverse-drawing processing is avoided, the precision and the efficiency of wave field separation are improved, a good data base is provided for subsequent processing, and good effects can be obtained through the subsequent processing.

The above-described embodiment is only one embodiment of the present invention, and various modifications or changes based on the principles disclosed in the present invention will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described embodiment of the present invention, and therefore, the foregoing description is only preferred and not limiting.

Claims (3)

1. A method of wavefield separation of VSP material, comprising the steps of:

Step 1: carrying out wave field pickup on VSP data to be processed to obtain information of a plurality of wave fields, and recording the position of a same-phase axis of each wave field;

Step 2: for each in-phase axis, for each point on the in-phase axis, drawing a time window for the point according to the position of the point;

And step 3: for each in-phase axis, aiming at each point on the in-phase axis, carrying out one-dimensional median filtering processing on the point according to a time window defined for the point;

And for each in-phase axis, selecting the same number of points above and below the point to divide a time window by taking the position of the point as the center for each point on the in-phase axis.

2. The method of wavefield separation of VSP data of claim 1, wherein the one-dimensional median filtering process is performed according to the following equation (1):

g(x)＝med{f(x-k),...,f(x),...,f(x+k),k∈N} (1)

Wherein g (x) is the output of one-dimensional median filtering, f (x) is the original signal which needs to be subjected to one-dimensional median filtering, med represents the sorted median, and N is a positive integer and represents the number of points in the time window.

3. the method of wavefield separation of VSP data of claim 2, wherein N is equal to 5, 7, or 9.