CN114488285A - Seismic data interference wave identification method based on VSP observation mode - Google Patents

Abstract

The invention relates to a seismic data interference wave identification method based on a VSP observation mode, and belongs to the technical field of seismic data processing in seismic exploration. According to the method, the downward propagation process can be recorded by utilizing the VSP data, the changes and differences of the kinematics and dynamics characteristics of various waves can be observed, the VSP observation data at the same position as the ground seismic observation data are obtained to identify interference waves in the ground seismic data, the obtained VSP observation data are converted into P, R, T sections, and corresponding P, R, T component data are obtained; the identification of the interference wave is performed based on the principle that the energy of the interference wave is totally attenuated in the P component and is intensified in the R, T component. Through the process, the interference waves can be accurately identified based on the energy distribution condition of the VSP observation data in the P, R, T component, and the problem of poor identification effect caused by direct identification of the ground earthquake observation data is solved.

Description

Seismic data interference wave identification method based on VSP observation mode

Technical Field

The invention relates to a seismic data interference wave identification method based on a VSP observation mode, and belongs to the technical field of seismic data processing in seismic exploration.

Background

The loess plateau seismic data contains a special interference wave, commonly called 'Bazi Hu', which is in the form of the left half part in the figure 1 in the near arrangement and in the form of the right half part in the figure 1 in the far arrangement; the near arrangement refers to that a plurality of detectors are placed on a survey line segment, excitation points are arranged at the middle point of the survey line segment, each detector receives and obtains a seismic record, and the far arrangement refers to that the excitation points in the near arrangement are shifted to a certain distance along the vertical direction of the survey line to obtain the seismic record. The interference wave has strong energy and has great influence on the quality of seismic data in an effective wave frequency range. Therefore, there is a need to be able to accurately identify such interference waves, and at present, there are two main identification methods.

One of the main methods of interference wave investigation (identification) currently used is: cross arrangement or L arrangement shot-point chasing survey method. The method includes the steps that excitation points are arranged to continuously track interference waves in two mutually perpendicular directions, characteristic parameters such as apparent speed, wavelength, frequency and energy intensity of the interference waves in the line measuring direction and the perpendicular line measuring direction are obtained, then, a plurality of combined noise pressing graphs for field collection are designed, and the optimal combination form is selected through an excitation and receiving noise pressing comparison test. The interference wave investigation method can only obtain parameters of two directions of the interference wave, cannot analyze the combined noise suppression effect indoors, and is suitable for areas where the interference wave is relatively simple or the interference wave is clearly known.

The second main method comprises: a square array interference wave investigation (identification) method (similar to the box wave investigation method). The method is characterized in that dozens of hundreds of excitation points are distributed in two mutually perpendicular directions, and multi-azimuth characteristic parameters of interference waves are obtained through intensive observation of square wave detection points. The method has the advantages that: not only can parameters such as speed, wavelength, energy intensity and the like of different directions of the interference wave be observed. Due to the same excitation receiving condition, errors caused by time, surface anisotropy and the like are avoided; and can carry out combination pressure through indoor processing and make an uproar and space wave field false frequency analysis, both can carry out the analysis to interference wave, also can carry out the analysis to the effect wave, provide powerful tool for the design and the demonstration of acquisition parameter.

The interference wave investigation (identification) scheme adopts a single-component vertical detector to receive the seismic wave signals in a linear or area arrangement mode in a horizontal plane, so that the interference wave investigation (identification) scheme has the following characteristics: (1) because of the area combination, the seismic wave receiving device can receive seismic waves from different underground directions; (2) the detectors are arranged in the horizontal direction and can only receive the upgoing wave (which propagates from bottom to top); (3) the vertical detector is only sensitive to seismic signals of mass point vertical vibration and cannot receive seismic waves of mass point vibration in the horizontal direction. (4) Single component reception, failure to analyze the polarization characteristics of the seismic wave, failure to accurately identify the type of interference waves,

therefore, the two methods can only determine partial dynamic and kinematic characteristics of the seismic waves, and cannot identify the polarization characteristics of the seismic waves. Therefore, when the type of the interference wave is judged by mistake, effective measures can not be taken to suppress the seismic data when the seismic data are collected, the quality of the seismic data is reduced, and meanwhile, a technical means of pertinence can not be taken to eliminate the interference when the seismic data are processed, so that the subsequent seismic interpretation precision is influenced.

Disclosure of Invention

The invention aims to provide a seismic data interference wave identification method based on a VSP observation mode, and the method is used for solving the problem that special interference waves in the existing loess tableland seismic data cannot be identified according to polarization characteristics of the special interference waves.

The invention provides a seismic data interference wave identification method based on a VSP observation mode for solving the technical problems, which comprises the following steps:

1) acquiring surface seismic data in a work area and VSP observation data corresponding to the same position, establishing a forward model according to the VSP observation data to obtain shallow VSP data of the well section in a simulated mode, and supplementing the shallow VSP data into the VSP observation data to obtain non-zero offset VSP data of the whole well section;

2) preprocessing the obtained full-interval non-zero-offset VSP data to obtain corresponding Z, X, Y component records; x, Y, Z refers to three components of the downhole detector which are vertical to each other, wherein Z is a vertical component and the direction is fixed, X, Y is a horizontal component and the direction is random;

3) converting the preprocessed full-interval non-zero-offset VSP data from Z, Y, X coordinate system data to P, R, T coordinate system data to obtain corresponding R component, P component and T component; wherein P is the shot-geophone direction in the ray plane, namely the connecting line direction from the excitation point to the downhole geophone, R is the direction vertical to P in the ray plane, and T is the direction vertical to P, T in the horizontal plane;

4) the polarization characteristics of the VSP data are determined according to the sizes of the components from the VSP data to P, R, T, and the identification of interference waves is carried out on the basis of the principle that the energy in the P component is totally attenuated and the interference waves in the R, T component are strengthened.

According to the method, the downward propagation process can be recorded by utilizing the VSP data, the changes and differences of the kinematics and dynamics characteristics of various waves can be observed, the VSP observation data at the same position as the ground seismic observation data are obtained to identify interference waves in the ground seismic data, the obtained VSP observation data are converted into P, R, T sections, and corresponding P, R, T component data are obtained; the identification of the interference wave is performed based on the principle that the interference wave is attenuated in the P component and is amplified in the R, T component. Through the process, the interference waves can be accurately identified based on the energy distribution condition of the VSP observation data in the P, R, T component, and the problem of poor identification effect caused by direct identification of the ground earthquake observation data is solved.

Further, in order to learn the interference waves kinematically, the method further comprises the step of judging the wave field kinematic type according to the time distance, the speed and the amplitude characteristics of the identified interference waves in the ground earthquake observation.

Further, in order to accurately confirm the mechanism of the interference wave, the method comprises the step of determining the mechanism type of the interference wave according to the interference wave identified in the step 4) and the wave field kinematic type.

Further, in order to improve the accuracy of interference wave identification, the preprocessing refers to data editing, gather band-pass filtering and geometric diffusion compensation of the full-interval non-zero-bias VSP data.

Further, the non-zero offset VSP means that the excitation point is offset from the wellhead of the observation well by a set distance.

Further, in order to realize fast coordinate conversion, the coordinate conversion process in step 3) is as follows:

a. determining a horizontal polarization angle by using an energy relation of a first arrival part of a direct wave;

b. converting X, Y horizontal coordinate system into component and T of standard coordinate system through coordinate rotation according to the obtained horizontal polarization angle;

c. and converting the component and the vertical component of the standard coordinate system into a P component along the direction of the longitudinal wave ray between the seismic source and the detector and an R component orthogonal to the P component by using the horizontal polarization angle and taking the T as an axis.

Further, the conversion formula adopted in the step b is as follows:

where X, Y is the horizontal component, H₀And theta is a component of the standard coordinate system and is a horizontal polarization angle.

Further, the conversion formula of the P component and the R component in step c is:

wherein Z is a vertical component, H₀And theta is a component of the standard coordinate system and is a horizontal polarization angle.

Drawings

FIG. 1 is a schematic diagram of a comparison between near-array and far-array single-shot records of seismic data in loess tablelands;

FIG. 2 is a schematic representation of actual recordings and simulated recordings of VSP shot-shared gathers in an embodiment of the present invention;

FIG. 3-a is a full interval non-zero offset VSP record (upper simulation + lower actual) taken in an embodiment of the present invention;

FIG. 3-b is a schematic diagram of ray paths of interference waves in horizontal and vertical directions according to an embodiment of the present invention;

FIG. 3-c is a schematic diagram of the time-distance curve of the interference wave in the embodiment of the present invention displayed on the near-alignment record;

FIG. 4 is a schematic diagram of P-wave and S-wave propagation and polarization in P, R, T coordinate system according to the present invention;

FIG. 5-a is a P component recording after polarization rotation in an embodiment of the present invention;

FIG. 5-b is a record of the R component after polarization rotation in an embodiment of the present invention;

FIG. 5-c is a T component record after polarization rotation in an embodiment of the present invention;

FIG. 6-a is a diagram of an elastic wave simulated ground level observation single shot record in an embodiment of the invention;

FIG. 6-b is a single shot record of a sonic simulated ground level observation in an embodiment of the present invention;

FIG. 7 is a ground two-dimensional horizontal observation single shot record in an embodiment of the invention;

FIG. 8-a is the actual recording of WalkawayVSP in an embodiment of the present invention;

fig. 8-b is a far-ranging single shot record in an embodiment of the present invention.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings.

The loess tableland seismic data is provided with a special interference wave, commonly called 'eight-character-hu', which is arranged in a hyperbolic line, the regular interference wave has strong energy, and the ground seismic level observation can only receive the uplink propagation process of the loess tableland seismic data and cannot know the downlink propagation process of the loess tableland seismic data. The VSP is observed along the vertical direction underground, and the downlink propagation process of the VSP can be recorded; when the detector is positioned near the interface, the changes and differences of the kinematic and dynamic characteristics of various waves can be observed more obviously, and the changes of corresponding wave fields related to various interfaces can be received and researched better; the geophone can avoid or reduce natural interference above the ground in a relatively 'quiet' environment underground, and facilitates wave recording and identification. Therefore, the invention provides a seismic data interference wave identification method based on a VSP observation mode, and the specific implementation process of the method is as follows.

1. And acquiring non-zero offset VSP data of the work area, and obtaining a non-zero offset VSP simulation record of the whole well section through forward modeling.

Taking a certain well in a work area as an example, a plurality of detectors are arranged at a certain distance under the well, excitation points (consistent with shot points of horizontal observation) are arranged on the ground at a certain interval, therefore, each excitation point (shot point) is equivalent to a non-zero offset VSP gather, and the gather of all the excitation points corresponding to one detection point can be extracted for shot-inspection interchange, which is equivalent to ground earthquake single shot record of horizontal observation. With the above arrangement, the non-zero-offset VSP data obtained in this embodiment is shown on the left side in fig. 2, where the non-zero-offset VSP refers to the excitation point (shot point) being offset from the wellhead of the observation well by a distance, generally around 2/3 of the observation depth. The detector in the embodiment adopts X, Y, Z three-component detector, X, Y, Z refers to three components of the three-component detector which are perpendicular to each other, wherein Z is a vertical component, the direction is fixed, X, Y is a horizontal component, and the direction is random.

Because the multilayer casing is adopted during drilling, namely, a drill bit with large diameter is used for drilling an upper stratum (generally more than 300 meters), the casing with large diameter is put in to prevent the stratum from collapsing and stepping, and according to the designed well depth and the rock hardness of the stratum, the second, third and other multilayer casings are put in from the ground well mouth to the depth, so that the multilayer casing is arranged at the shallow well section; when cement is used for cementing wells, a multi-layer casing cannot be well cemented with a stratum, interference is formed on seismic waves, shallow VSP data cannot be obtained, only velocity data obtained by VSP data in a work area can be used for building a forward model, VSP records of the whole well section of the well are simulated, namely, a velocity model is built by using corresponding stratum depth and velocity obtained by the obtained non-zero deviation VSP data, the process that the seismic waves are transmitted underground and received by a downhole detector when explosives are shot off is simulated by using a wave equation method, and seismic records observed in the vertical direction in the well are obtained, and the process is shown on the right side of a graph 2. Superposing the simulated shallow VSP data to the actual observation record of the well to obtain a ground detector (R) for vertical observation in the well_C) As shown in fig. 3-a.

2. And acquiring ground seismic observation data, and determining that the interference waves are the same wave field when the ground observation and the well observation are carried out.

The ground earthquake observation mode refers to horizontal direction observation, and the excitation point and the receiving point are both on the ground; the vertical observation is the observation mode of the VSP, the excitation point is on the ground, and the receiving point is in the well and is arranged along the vertical direction. When obtaining seismic records observed in the vertical direction in the well, the seismic records (R) at the same position are recorded during horizontal observation of seismic exploration_C) And when in-well and ground earthquake observation is compared, the wave group characteristics of the same seismic channel are established, and the corresponding relation between the wave group characteristics and the ground earthquake observation is established, so that the type of the interference wave during ground level observation is determined by analyzing the VSP record observed in the well, and the wave group characteristics refer to the arrival time, frequency, amplitude and the like of the seismic wave.

For the present embodiment, the time differences between the horizontal and vertical measurements of the special wavefield and the first wave are compared to establish a corresponding relationship (460 ms and 463ms are shown in fig. 3-b and 3-c, respectively, and are basically the same, which is illustrated as the same wave group), where the first wave is the first arriving seismic wave. The type of such interference waves at surface level observation is thus determined by analyzing VSP recordings observed in the well.

3. Three component VSP data is conventionally processed to obtain Z, X, Y three component records.

The conventional processing in this embodiment refers to seismic data processing modes such as data editing, gather extraction, band-pass filtering, geometric diffusion compensation, and the like.

4. And carrying out polarization rotation processing on the three-component data after the conventional processing to obtain corresponding P, R, T-component data.

VSP data was transformed from the Z, Y, X coordinate system to the P, R, T coordinate system to yield corresponding P, R, T component data, where P is the shot-in-ray plane direction, R is the direction perpendicular to P in the ray plane, and T is the direction perpendicular to P, T in the horizontal plane (as shown in FIG. 4). The specific treatment process is as follows:

1) x, Y horizontal coordinate system conversion is carried out, the vector of X, Y coordinate system is converted into the component H of the standard coordinate system through coordinate rotation₀And T, the conversion formula is:

2) h is converted by the rotation of the coordinate of the vertical plane, taking T as an axis₀And Z is converted into a P component along the longitudinal wave ray direction between the seismic source and the wave detector and an R component orthogonal to the P component, and the conversion formula is as follows:

wherein theta is a horizontal polarization angle, and the adopted calculation formula is as follows:

wherein y and x are Y, X vectors of X, Y coordinate systems respectively.

5. The polarization characteristics of the VSP data are determined according to the sizes of the components from the VSP data to P, R, T, and the identification of interference waves is carried out on the basis of the principle that energy in the P component is totally attenuated and the interference waves are strengthened in the R, T component.

Since the P-wave propagation direction coincides with the polarization direction, the S-wave (including SV and SH waves) propagation direction is perpendicular to the polarization direction (as shown in fig. 5-a, 5-b, and 5-c). Therefore, the P component mainly includes a downlink direct wave and an uplink SV wave; the R component comprises a downlink SV converted transverse wave and an uplink P wave; the T component is in the horizontal plane and perpendicular to the ray plane, and is only SH waves.

Energy allocation refers to the down-going wave of this particular wave in the non-zero offset VSP vertical component recordings in the boxes in fig. 5-a, 5-b and 5-c, almost totally attenuated in the P component and enhanced in the R, T component. As shown in fig. 5-a, the polarization direction of the downlink S wave is almost perpendicular to the P component, and the downlink S wave is not contained in the P component; as shown in fig. 5-b, the polarization direction of the downlink S wave is parallel to the direction of the R component, and the downlink S wave is mainly in the R component. Therefore, it is determined to be a transversal wave, SV wave in R component and SH wave in T component according to its aforementioned energy distribution in P, R component. Since the T component is in the horizontal plane, and perpendicular to the ray plane, it can only be an SH wave. Theoretically, a P wave is an SH-untranslatable wave, and if this particular wave is a P-SV shear wave, there should be substantial attenuation in the T component, but the SH wave energy in the T component is strong. Therefore, it can be determined that it is a pure shear wave (including SV and SH).

6. And judging the wave field kinematics type according to the time interval, the speed and the amplitude characteristics of the identified interference waves during the ground earthquake observation.

The wave field kinematics type refers to the change characteristic of the seismic wave propagation path of the wave field along with time, and as can be seen from the near-array record of fig. 7, the time distance curve of the "yahu" is a straight line, so that only the direct waves and the refracted waves are possible, but the energy attenuation of the direct waves is fast, and the energy of the "yahu" is strong, and only the refracted waves are possible.

7. And finally determining the mechanism type of the interference wave by integrating the analysis results of the VSP and the seismic data observed at the ground level.

The mechanism type refers to the pure transverse wave determined in combination with the step 5 and the refraction wave determined in the step 6. Therefore, the present invention can accurately confirm the mechanism type of the refraction wave of the pure transverse wave.

The demonstration result of the invention is verified by using simulation record (near arrangement) of horizontal observation and actual data of WalkawayVSP (far arrangement) so as to determine the reliability of the identification method of the invention.

The simulation record of horizontal observation refers to that the velocity model obtained by VSP of a work area is utilized to respectively simulate the seismic record of horizontal observation by the wave equation and the acoustic ray tracing method, as shown in figure 6-a and figure 6-b. The difference between the two is that the former is a full wave field, the latter only has longitudinal waves, and the wave field characteristics of the former are better consistent with the actual record (as shown in figure 7), so that the effectiveness of the method is demonstrated.

The observation system of WalkawayVSP is characterized in that a wave detection point is fixed at a certain observation well section, and a shot point moves along a well mouth at a certain distance, so that common wave detection point gather records with different offset distances can be obtained (as shown in figure 8-a). According to the principle of shot-to-shot interchange, the same shot-to-shot relationship is formed with the ground three-dimensional far arrangement (as shown in fig. 8-b). Therefore, the WalkawayVSP can be regarded as a bridge between the well observation and the ground observation, so that a direct corresponding relation is established. Two groups of obvious downward transverse waves can be seen in the WalkawayVSP record. The wave group I is converted transverse wave, and the wave group II is pure transverse wave. The source point, energy, frequency and other wave group characteristics of the two groups of transverse waves correspond to the converted transverse waves and the pure transverse waves in the VSP. The first arrival recorded by the WalkawayVSP is a down direct wave, and the wave group II is also a direct wave. Since the frequency of the wave group I is high, the attenuation is fast, the energy is weak, and the detection cannot be carried out. The first record of the ground is the uplink refracted wave, and the eight-character Chinese fiddle is also the uplink refracted wave, so that the correspondence relationship between the eight-character Chinese fiddle and the wave group II is consistent. The similarity of the wave group characteristics of the special wave field and the Chinese character 'ba-hu' in the wave group II and the VSP explains the corresponding relation, and the viewpoint that the Chinese character 'ba-hu' is a pure transverse wave refracted wave is verified.

Therefore, the interference wave of the Chinese character 'ba hu' can be accurately identified by the identification method, and a reliable basis is provided for the subsequent processing of seismic data.

Claims (8)

1. A seismic data interference wave identification method based on a VSP observation mode is characterized by comprising the following steps:

1) acquiring surface seismic data in a work area and VSP observation data corresponding to the same position, establishing a forward model according to the VSP observation data to obtain shallow VSP data of the well section in a simulated mode, and supplementing the shallow VSP data into the VSP observation data to obtain non-zero offset VSP data of the whole well section;

2) preprocessing the obtained full-well-section non-zero offset VSP data to obtain corresponding Z, X, Y component records; x, Y, Z refers to three components of the downhole detector which are vertical to each other, wherein Z is a vertical component and the direction is fixed, X, Y is a horizontal component and the direction is random;

3) converting the preprocessed full-interval non-zero-offset VSP data from Z, Y, X coordinate system data to P, R, T coordinate system data to obtain corresponding R component, P component and T component; wherein P is shot-examination direction in the ray plane, namely the connecting line direction from the excitation point to the underground detector, R is the direction vertical to P in the ray plane, and T is the direction vertical to P, T in the horizontal plane;

4) the polarization characteristics of the VSP data are determined according to the sizes of the components from the VSP data to P, R, T, and the identification of interference waves is carried out on the basis of the principle that energy in the P component is totally attenuated and the interference waves are strengthened in the R, T component.

2. The method of claim 1, further comprising determining the wave field kinematics type according to the time interval, velocity and amplitude characteristics of the identified interference waves during the ground seismic observation.

3. The method of identifying interference waves in seismic data based on VSP observation according to claim 2, wherein the method includes determining the mechanism type of the interference waves according to the interference waves identified in step 4) and the wave field kinematics type.

4. The method of claim 1 or 3, wherein the preprocessing comprises data editing, gather band pass filtering and geometric diffusion compensation of the full interval non-zero offset VSP data.

5. The method for identifying seismic data interference waves based on the VSP observation mode according to claim 4, wherein the non-zero offset VSP means that an excitation point is deviated from a well head of an observation well by a set distance.

6. The method for identifying seismic data interference waves based on VSP observation according to claim 1, wherein the coordinate transformation process in step 3) is as follows:

a. determining a horizontal polarization angle by using an energy relation of a first arrival part of a direct wave;

b. converting X, Y horizontal coordinate system into component and T of standard coordinate system through coordinate rotation according to the obtained horizontal polarization angle;

c. the components of the standard coordinate system and the vertical component are converted into a P component along the direction of the longitudinal wave ray between the source and the detector and an R component orthogonal to the P component by using the horizontal polarization angle and taking T as an axis.

7. The method of claim 6, wherein the step b uses a conversion formula as follows:

where X, Y is the horizontal component, H₀And theta is a component of the standard coordinate system and is a horizontal polarization angle.

8. The method of claim 6, wherein the conversion formula of the P component and the R component in step c is as follows:

wherein Z is a vertical component, H₀And theta is a component of the standard coordinate system and is a horizontal polarization angle.

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