A phase-controlled amplitude energy compensation method for seismic pre-stack gather data

Abstract

The invention relates to a phase-controlled amplitude energy compensation method suitable for seismic pre-stack gather data, belonging to the technical field of oil and gas field exploration. The method vertically divides a stratum into a plurality of layers for individual compensation processing, firstly performs spherical diffusion compensation on each small layer to eliminate the amplitude energy difference in the vertical direction, then integrates AVO forward modeling and waveform classification methods in the horizontal direction to calculate the amplitude compensation curves of different seismic phases, and finally performs energy compensation of seismic traces of different offset distances based on the amplitude compensation curves of the small layer, so as to realize the true amplitude energy compensation of seismic pre-stack gather data considering the difference characteristics of seismic phases.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploration, and in particular to a phase-controlled amplitude energy compensation method suitable for seismic pre-stack gather data. Background Art

[0002] In seismic exploration, the amplitude of seismic records is a very important information and has a significant impact on exploration accuracy. However, due to factors such as absorption and attenuation of underground media and spherical diffusion of seismic waves, the energy of seismic waves is often attenuated, causing the amplitude of seismic records to change. Therefore, when processing seismic data, it is often necessary to restore the amplitude of seismic records to the true level. This process is called true amplitude energy compensation of seismic records.

[0003] At present, the commonly used true amplitude energy compensation methods at home and abroad include surface consistency amplitude compensation and spherical diffusion compensation. Among them, surface consistency amplitude compensation is the most commonly used for energy compensation caused by offset distance differences.

[0004] 1. Principle of spherical diffusion method

[0005] When seismic waves propagate in underground strata, the wavefront is approximately a sphere, and expands as the wave propagates forward, but the total energy of the wave is constant, so when the wave propagates, as the wavefront becomes larger, the wave energy density becomes smaller, that is, the amplitude energy of the wave is inversely proportional to the propagation distance of the wave. Since seismic records are records of seismic waves traveling, speed and time are generally used instead of distance, so spherical diffusion loss is also a function of seismic wave speed and time. In seismic data processing, this functional relationship is generally simplified to a spherical diffusion compensation factor, and the spherical diffusion compensation factor is used to weight the seismic trace to compensate for the attenuation loss of seismic amplitude caused by spherical diffusion. The processing of this compensation method must be of good fidelity.

[0006] 2. Principle of surface consistency amplitude compensation method

[0007] Due to the different complexity of the surface in different regions, there are differences in the conditions of excitation and reception in different regions during seismic exploration, which leads to certain differences in the amplitude, energy and other aspects of the shot data in different regions. The purpose of surface consistency amplitude compensation is to eliminate the energy imbalance between shots and traces caused by excitation and reception factors. Its main principle is based on the surface consistency assumption, which believes that seismic traces can be decomposed into the convolution of several components such as source, receiver, shot offset and seismic pulse response; further, according to the compensation factors of different influencing factors decomposed from the seismic traces, the amplitude compensation of the seismic traces is performed to achieve the effect of eliminating the lateral inconsistency of seismic records (Meng Songling, 2010).

[0008] 3. Disadvantages of Existing Methods

[0009] The existing spherical diffusion compensation method only considers the kinematic characteristics of seismic waves and is suitable for simpler homogeneous media or isotropic formations. The compensation results generally have problems with fidelity and cannot achieve true amplitude compensation. The existing surface consistency amplitude compensation method generally applies a compensation factor to the entire seismic trace and cannot time-varyingly compensate for the energy attenuation in the time direction and the energy attenuation related to the frequency, and does not consider the anisotropy of the underground medium in different directions, and also has problems with fidelity.

[0010] Therefore, in order to address the common phenomenon that pre-stack gather data have obvious energy differences at different offset distances, that is, the seismic records have strong energy at close offset distances and weak energy at far offset distances, the present invention has invented a phase-controlled amplitude energy compensation method for seismic pre-stack gather data that takes into account the anisotropic characteristics of the formation, so as to compensate for the energy loss caused by different offset distances. Summary of the invention

[0011] The invention relates to a phase-controlled amplitude energy compensation method suitable for seismic pre-stack gather data, belonging to the technical field of oil and gas field exploration. The method vertically divides a stratum into a plurality of layers for individual compensation processing, firstly performs spherical diffusion compensation on each small layer segment to eliminate the amplitude energy difference in the vertical direction, then integrates AVO forward simulation and waveform classification methods in the horizontal direction to calculate the amplitude compensation curves of different seismic phases, and finally performs energy compensation of seismic traces of different offset distances based on the amplitude compensation curves of the small layer segment, thereby realizing true amplitude energy compensation of seismic pre-stack gather data considering the anisotropic characteristics of the stratum.

[0012] The specific steps of the present invention include:

[0013] (1) The 3D pre-stack seismic gather data of the study area are stacked to obtain a 3D post-stack data volume, and the seismic data are divided into multiple small segments vertically using a time window of 200 ms to 300 ms;

[0014] (2) For a single small layer segment, the seismic waveform classification method is used to divide the small layer segment into three types of seismic waveforms on the plane, and each type of waveform corresponds to a different seismic phase zone;

[0015] (3) Input the logging data of the completed wells in the study area. The number of completed wells is not less than 3. The completed wells are divided into 3 categories according to the different geological or seismic facies characteristics represented by the completed wells. According to the waveform characteristics of the seismic traces beside the wells of the 3 categories of completed wells, the 3 categories of completed wells are matched with the 3 categories of waveform characteristics in step 2;

[0016] (4) For a single CMP point within the small layer segment,

[0017] (4-1) According to the time of the layer segment, the spherical diffusion compensation method is used to perform longitudinal energy compensation on the prestack gather of the small layer segment.

[0018] (4-2) Extract the amplitude curve of the top interface of the CMP gather of the small layer at different offsets, the ordinate of the curve is the amplitude, and the abscissa is the offset. The amplitude-offset curve is normalized and fitted with a quadratic polynomial to obtain a fitting curve.

[0019] (4-3) Based on the plane coordinates of the CMP point and the waveform classification array in step 2, the completed well corresponding to the current CMP point is extracted, and the well logging curve of the well is used to perform AVO forward simulation to obtain the amplitude-offset simulation curve of the small layer at different offset distances.

[0020] (4-4) Calculate the difference between the amplitude-offset simulation curve of step 4-3 and the quadratic fitting curve of step 4-2, and record it as the amplitude-offset compensation factor curve.

[0021] (4-5) using the amplitude factor curve of step 4-4 to perform amplitude compensation on the gather data of the CMP point;

[0022] (5) Circularly calculate all CMP points in the current small layer segment;

[0023] (6) After cyclic calculation of all small layers, the amplitude-compensated pre-stack gather data volume is obtained.

[0024] A phase-controlled amplitude energy compensation method suitable for seismic pre-stack gather data has the following characteristics, mainly manifested as:

[0025] (1) The present invention introduces an "amplitude-offset compensation factor" to establish a quantitative relationship between the seismic amplitude of the target layer and the AVO forward modeling, retains the azimuthal anisotropy, and uses the idea of ​​phase control to improve the quality of seismic gathers and increase the reliability of subsequent inversion results, which is highly innovative.

[0026] (2) The core foundation of the present invention is whether amplitude energy compensation can be performed under the premise of retaining effective information of seismic fractures. After years of research, the inventors found that by combining AVO forward modeling with seismic prestack gathers using the idea of ​​phase control, amplitude compensation can be performed on seismic prestack gathers; and there is methodological theoretical support: ① Under the guidance of phase control, the corresponding relationship between seismic AVO forward modeling and prestack seismic data can be established; ② The AVO forward modeling "amplitude-offset curve" does not contain azimuthal anisotropy information, that is, it does not destroy the original seismic fracture information. Therefore, the present invention has a good methodological theoretical basis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a technical flow chart of the present invention;

[0028] Figure 2 and Figure 3 The CMP gathers before and after amplitude compensation of pre-stack gathers in a certain study area of ​​Sichuan Basin, China, obtained by the present invention, are shown in FIG. Figure 2 is the pre-stack gather before compensation of the CMP point (line 3646, trace 2300), Figure 3 This is the pre-stack gather after compensation of the CMP point (line 3646, trace 2300). DETAILED DESCRIPTION

[0029] Example 1

[0030] A phase-controlled amplitude energy compensation method applicable to seismic pre-stack gather data, comprising the following steps:

[0031] Step 1: Input the pre-stack seismic gather data Sq(x,y,h,t) of the study area and perform stacking processing. The post-stack seismic data is recorded as Sh(x,y,t), where x represents the horizontal survey line number, y represents the vertical survey line number, h represents the offset distance, and t represents the time. The seismic data is divided into multiple small layers in the vertical direction using a time window of 200ms to 300ms;

[0032] Step 2: Select a small layer segment in step 1, starting from time t0 to t1, and use seismic post-stack data to perform seismic waveform classification analysis on the small layer segment. The number of waveform classifications is set to 3, representing different seismic phase belts. The corresponding waveform classification array is recorded as B(x, y) = {B1, B2, B3};

[0033] Step 3: Input the logging data of the completed wells in the study area. The number of completed wells is not less than 3. According to the different geological or seismic phase characteristics represented by the completed wells, the completed wells are divided into 3 categories. According to the waveform characteristics of the seismic traces beside the wells of the 3 categories of completed wells, the 3 categories of completed wells are matched with the 3 categories of waveform characteristics in step 2. Well W1 corresponds to waveform B1, well W2 corresponds to waveform B2, and well W3 corresponds to waveform B3.

[0034] Step 4: For the seismic pre-stack gather of a CMP point in the current small layer segment, the plane coordinates of the CMP point are x and y, the vertical analysis time window is from t0 to t1, and its amplitude energy is recorded as Aq(h,t), where h is the offset distance and t is the time;

[0035] Step 4-1: In the longitudinal time window from t0 to t1, the spherical diffusion compensation method is used to perform longitudinal energy compensation on the seismic pre-stack gathers, and the compensated amplitude energy is recorded as Ah(h, t);

[0036] Step 4-2: Based on Ah(h, t) in step 4-1, extract the amplitude curves of the top interface of the small layer at different offset distances, record the relationship between amplitude and offset distance as A0(h), and perform normalization and quadratic polynomial fitting, record it as fitting array Anh(h), where h is the offset distance;

[0037] Step 4-3: Based on the plane coordinates of the CMP point and the waveform classification array in step 2, extract the completed well corresponding to the current CMP point. Assuming it is well W1, use the logging curve of well W1 to perform AVO forward simulation. The forward simulation formula is calculated using the simplified form of the Zoeppritz equation proposed by Aki and Richards in 1980 to obtain the amplitude-offset simulation array Amn(h) of the current CMP point at different offsets, where h is the offset;

[0038] Step 4-4: Calculate the difference curve between the value Amn(h) obtained in step 4-3 and Anh(h) in step 4-2, and record it as the amplitude-offset compensation factor array Abc(h).

[0039] Abc(h)=Amn(h)-Anh(h)(2)

[0040] Step 4-5: Use the amplitude-offset compensation factor array Abc(h) of step 4-4 to perform amplitude compensation on the seismic pre-stack gather data of the current CMP point.

[0041] Aq(h,t)=Aq(h,t)╳(1-Abc(h))(3)

[0042] Step 5: Change the CMP point number and repeat step 4 to cyclically calculate all CMP points in the current small layer segment;

[0043] Step 6: Replace the small layer segment, repeat steps 2 to 5, and cyclically calculate all the small layers to obtain the amplitude compensated pre-stack gather data volume Sqb (x, y, h, t).

[0044] Example 2

[0045] Figure 2 and Figure 3 They are respectively examples of pre-stack trace energy compensation analysis of a target layer segment in a certain study area in Sichuan Basin, China. Figure 2 This is a seismic profile of a CMP point in the pre-stack gather (line 3646, trace 2300) in the study area (before restoration). Figure 3 The amplitude recovery analysis profile (after recovery) of the seismic pre-stack gather (line 3646, trace 2300) is obtained by the present invention. It can be seen that the event axis is more continuous after recovery, and the effect is better.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A phase-controlled amplitude energy compensation method applicable to seismic pre-stack gather data, comprising the following steps: Step 1: Input the pre-stack seismic gather data Sq(x,y,h,t) of the study area and perform stacking processing. The post-stack seismic data is recorded as Sh(x,y,t), where x represents the horizontal survey line number, y represents the vertical survey line number, h represents the offset distance, and t represents the time. The seismic data is divided into multiple small segments in the vertical direction using a time window of 200ms~300ms; Step 2: Select a small layer segment in step 1, starting from time t0 to t1, and use seismic post-stack data to perform seismic waveform classification analysis on the small layer segment. The number of waveform classifications is set to 3, representing different seismic phase belts. The corresponding waveform classification array is recorded as B(x,y)={B1,B2,B3}; Step 3: Input the logging data of the completed wells in the study area. The number of completed wells is not less than 3. According to the different geological or seismic phase characteristics represented by the completed wells, the completed wells are divided into 3 categories. According to the waveform characteristics of the seismic traces beside the wells of the 3 categories of completed wells, the 3 categories of completed wells are matched with the 3 categories of waveform characteristics in step 2. Well W1 corresponds to waveform B1, well W2 corresponds to waveform B2, and well W3 corresponds to waveform B3. Step 4: For the seismic pre-stack gather of a CMP point in the current small layer segment, the plane coordinates of the CMP point are x and y, the vertical analysis time window is from t0 to t1, and its amplitude energy is recorded as Aq(h,t), where h is the offset distance and t is the time; Step 4-1: In the longitudinal time window from t0 to t1, the spherical diffusion compensation method is used to perform longitudinal energy compensation on the seismic pre-stack gathers, and the compensated amplitude energy is recorded as Ah(h, t); Step 4-2: Based on Ah(h, t) in step 4-1, extract the amplitude curves of the top interface of the small layer at different offset distances, record the relationship between amplitude and offset distance as A0(h), and perform normalization and quadratic polynomial fitting, record it as fitting array Anh(h), where h is the offset distance; Step 4-3: Based on the plane coordinates of the CMP point and the waveform classification array in step 2, extract the completed well corresponding to the current CMP point. Assuming it is well W1, use the well logging curve of well W1 to perform AVO forward simulation. The forward simulation formula is calculated using the simplified form of the Zoeppritz equation to obtain the amplitude-offset simulation array Amn(h) of the current CMP point at different offsets, where h is the offset; Step 4-4: Calculate the difference curve between the array Amn(h) obtained in step 4-3 and Anh(h) in step 4-2, and record it as the amplitude-offset compensation factor array Abc(h). ； Step 4-5: Use the amplitude-offset compensation factor array Abc(h) of step 4-4 to perform amplitude compensation on the seismic pre-stack gather data of the current CMP point. ； Step 5: Change the CMP point number and repeat step 4 to calculate all CMP points in the current small layer segment in a loop; Step 6: Replace the small layer segment, repeat steps 2 to 5, and cyclically calculate all the small layers to obtain the amplitude compensated pre-stack gather data volume Sqb (x, y, h, t).

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