A method for multiple wave post-stack identification and suppression

Abstract

The application provides a multiple wave post-stack identification and suppression method, comprising the following steps: (1) establishing a multiple wave mirror-source combination chart; (2) multiple wave mirror-source calibration and prediction, comprising: ① identification of abnormal reflection, ② multiple wave source-mirror identification; ③ multiple wave distribution prediction; (3) multiple wave post-stack suppression and effective wave field recombination, comprising: ① preliminary separation of multiple wave field, ② geological target feature frequency screening and recombination, ③ noise suppression on the feature frequency body, to obtain the final result data. The method of the application regards the free surface multiple wave and the interlayer multiple wave as the same type of interference wave, and fully utilizes the stability and predictability of the spatial distribution characteristics of the high-speed layer petrophysical parameters to realize the prediction of the key multiple wave field distribution range affecting the imaging of the geological target, and effectively improves the quality of the low signal-to-noise ratio seismic data through the effective combination of the local domain wavelet decomposition and the screening and recombination of the feature frequency information.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas seismic exploration technology, in particular to the multiple wave post-stack identification and suppression technology in the process of improving the imaging quality of seismic data in complex exploration area. BACKGROUND

[0002] The Ordovician carbonate fracture-cave type reservoir (fault control, karst) in Tarim Basin is the main oil and gas exploration area, and the typical seismic response feature combination of the reservoir of the same scale is strike-slip fault + "bead-like" strong amplitude abnormal reflection. The Ordovician system in the south of Tarim Basin also has the geological conditions for developing the same scale reservoir, but due to the serious absorption and attenuation effect of the huge sand dunes on the surface, the effective seismic signal of the Ordovician system is weak, and the signal-to-noise ratio is low. At the same time, multiple strong reflection interfaces formed by high-speed layers in the overlying strata cause multiple sets of multiple waves generated by the back and forth oscillation of seismic waves between them, and the difference between the energy and the effective wave is not obvious, which makes it difficult to identify in the velocity spectrum and pre-stack gather, and also brings great challenges to multiple wave suppression, seriously affecting the accurate imaging of Ordovician carbonate reservoirs, faults and structures, and bringing great uncertainty to the oil and gas exploration of the study area.

[0003] Multiple waves refer to seismic waves that are reflected more than once underground, which are divided into two types according to the combination of the interface, namely free surface multiple waves and interlayer multiple waves. At present, there are two main suppression techniques:

[0004] (1) Filtering method based on the geometric seismological characteristics of the difference in velocity, periodicity and separability of multiple waves, such as predictive deconvolution, Radon transform, principal component analysis and internal cutout, which is based on the premise that the statistical characteristics of multiple waves and effective waves are significantly different or separable or periodic in the transform domain. But this kind of method cannot completely suppress multiple waves, especially the interlayer multiple waves with small walk time, which cannot be distinguished in velocity spectrum, gather and other data, but it does affect the imaging of geological targets, and there is nothing we can do in this case, which cannot meet the imaging requirements of Ordovician carbonate fracture-cave type reservoirs, and the filtering method is mainly based on pre-stack gather data, which has a large amount of calculation.

[0005] (2) Based on the wavelet theory of multiple wave attenuation method. On the basis of obtaining the accurate multiple wave model, through the adaptive subtraction method to achieve the purpose of eliminating multiple wave, mainly wave equation extrapolation method, model fitting method, free interface multiple wave attenuation method, inverse scattering series method, etc. They are all in the constraint of strong reflection interface, using wave theory and other theoretical forward prediction of all possible multiple wave, and the actual data are matched in time, phase, amplitude, and adaptive subtraction, realizing the separation of multiple wave field. This method is under the premise of specifying a reflection interface, calculating all the multiple waves related to the reflection interface below, but it cannot simulate the real situation of absorption and attenuation of seismic wave in the propagation process under the real geological conditions. In actual seismic data, through the multiple wave field characteristic calibration, it is found that the key multiple waves that affect the imaging of the geological target are often mixed together with the low signal-to-noise ratio Ordovician effective waves, and it is difficult to separate them. If the above method is used for suppression, part of the effective wave field will be removed, making the wave field more complex, the effect of multiple wave suppression is not obvious, and even the signal-to-noise ratio and reflection characteristics of the seismic data are more chaotic. At the same time, the calculation amount of this method is also relatively large. SUMMARY

[0006] In order to solve the above problems of the prior art, the present application provides a multiple wave post-stack identification and suppression method.

[0007] The technical scheme of the present application is as follows:

[0008] A multiple wave post-stack identification and suppression method, characterized in that it comprises the following steps:

[0009] (1) On the basis of well seismic fine calibration, a multiple wave mirror-source combination chart is established;

[0010] (2) Multiple wave mirror-source calibration and prediction, including: ① identification of abnormal reflection, ② multiple wave source-mirror identification; ③ multiple wave distribution prediction;

[0011] (3) Multiple wave post-stack suppression and effective wave field reorganization, including: ① preliminary separation of multiple wave field, ② geological target characteristic frequency screening and reorganization, ③ noise suppression on the characteristic frequency body to obtain the final result data.

[0012] Preferably, step (1) comprises: identifying all possible free surfaces and / or high-speed layer interfaces in the overlying strata of the target layer by using acoustic logging data, and judging the multiple waves that can affect the imaging of the target layer according to the optimal combination of key interfaces that produce multiple waves, the double relative travel time of multiple waves and the time of the target layer, to establish a mirror-source combination chart.

[0013] Further preferably, in step (1), the well acoustic curve is converted into a layer velocity curve, the free surface and all high-velocity layers are calibrated, and the formula (1) of the relationship between the double travel time thickness of the multiple waves and the relative spatial position of the top interface of the target layer is used to combine all the upper negative and lower positive strong reflection interfaces two by two, and when t dcb > t o-top As the basis for identifying the source-mirror combination that generates the multiple waves capable of affecting the imaging of the Ordovician geological target of the target layer, the establishment of the multiple wave mirror-source combination chart is finally realized

[0014] t dcb = t i + (t i+1 -t i ) x 2 (1).

[0015] Preferably, step (2) comprises: ①under the guidance of regional geology and the understanding of drilled strata, judging the effectiveness of the seismic reflection of the main target layer from the aspects of frequency, strata occurrence, structure and / or strata contact relationship, and identifying abnormal seismic reflection events; ②judging the strong reflection interface corresponding to the main multiple waves affecting the imaging of the geological target according to the multiple wave mirror-source combination chart, and finally realizing mirror-source calibration and interpretation; ③based on the understanding and interpretation results of the multiple wave mirror-source-image, predicting the double travel time of the multiple waves as the bottom interface travel time plus the mirror-source time thickness, and then fine-tuning according to the degree of coincidence with the abnormal reflection, so that the best position of the coincidence is the predicted position of the multiple waves.

[0016] Further preferably, the abnormal seismic reflection events in step (2) have continuity or distribution in space.

[0017] Preferably, step (3) comprises: under the constraint of the spatial position of the multiple waves, first, determining the approximate time window range according to the waveform characteristics of the abnormal reflection, and realizing the preliminary controllable decomposition of the multiple waves by using the local domain wavelet decomposition or simulated attenuation technology to enhance the proportion of effective seismic wave field information; second, selecting a determined geological target as the basis, screening multiple characteristic frequency information conducive to the imaging of the geological target by frequency scanning, realizing the reorganization of the imaging characteristic frequency information of the geological body, highlighting the effective information of the target imaging, and finally realizing the suppression of the multiple waves after suppressing random noise.

[0018] Further preferably, the determined address target in step (3) comprises a fracture and / or a drilled well result.

[0019] The technical effects of the present application are as follows:

[0020] During the propagation of seismic wave field in the desert area of Tarim Basin, due to the absorption and attenuation of large sand dunes, strong reflection attenuation of high-speed layer and other effects, the effective signal of the main target layer of Ordovician is very weak, even the energy is similar to the multiple waves generated by the back and forth oscillation between the seismic waves in the overlying high-speed layer, and the difference and periodicity of the multiple waves on CMP, CRP gather and velocity spectrum are very small, and the effect of filtering method and multiple wave attenuation method based on wave equation is not good.

[0021] In order to effectively suppress multiple waves, improve the imaging quality of low signal-to-noise ratio seismic data, and highlight the seismic reflection characteristics of geological bodies such as structure, fracture and fracture-controlled reservoir, based on the understanding of the principle and mirror relationship of multiple wave generation, a multiple wave post-stack identification and suppression method is provided, which avoids the disadvantages caused by the small difference between multiple waves and effective waves or the multiple wave attenuation method based on wave theory, effectively improves the imaging quality of low signal-to-noise ratio seismic data, and lays a data foundation for the subsequent selection of favorable exploration targets.

[0022] Compared with the existing multiple wave suppression method, the method of the application regards the free surface multiple wave and the interlayer multiple wave as the same type of interference wave, and fully utilizes the stability and predictability of the spatial distribution characteristics of the high-speed layer rock physical parameters to realize the prediction of the distribution range of the key multiple wave field affecting the imaging of geological targets, and effectively improves the quality of low signal-to-noise ratio seismic data through the effective combination of local domain wavelet decomposition and screening and recombination of characteristic frequency information, and more importantly, effectively highlights the characteristic frequency information of the imaging of geological targets such as structure, fracture and reservoir, which improves the reliable data for comprehensive research and well deployment.

[0023] The multiple wave post-stack identification and suppression in the application has the following advantages:

[0024] (1) The multiple wave source-mirror combination chart is established, which provides a basis for clearly and accurately judging the key interface (source-mirror) generating multiple waves, and is beneficial to the accurate suppression of multiple waves and the protection of effective wave field.

[0025] (2) Based on the source-mirror combination multiple wave distribution prediction, the main multiple wave field distribution range affecting the imaging of geological target body is effectively and quickly predicted under the guidance of geological law, and the problem of multiple wave identification and prediction of low signal-to-noise ratio seismic data of target layer is well solved.

[0026] (3) The method of multiple wave post-stack suppression and effective wave field reorganization is to effectively utilize the stability and predictability of multiple wave distribution, to regard the free surface multiple wave and interlayer multiple wave as the same type of multiple interference, to realize the multiple wave post-stack suppression through the local wavelet decomposition under specific conditions and the effective characteristic frequency attribute screening reorganization. The method effectively avoids the problems such as the inapplicability of the small difference filtering method due to the difference with the effective wave and the multiple wave over-saturation attenuation caused by the multiple wave full wave field based on the wave motion theory. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a flow chart of the multiple wave post-stack suppression method of the embodiment of the present application.

[0028] Figure 2 It is a schematic diagram of the basic principle of identifying multiple waves.

[0029] Figure 3 It is a source mirror combination identification chart for generating multiple waves.

[0030] Figure 4 It is a schematic diagram of abnormal reflection identification.

[0031] Figure 5 It is a schematic diagram of abnormal reflection identification along the bottom boundary of the Bachu Formation.

[0032] Figure 6 It is a multiple wave distribution prediction (L1753) affecting the imaging of the Ordovician top carbonate rock fracture-vug reservoir.

[0033] Figure 7 It is a multiple wave post-stack suppression effect comparative analysis (L1753).

[0034] Figure 8 It is a multiple wave post-stack suppression effect comparative analysis (L1650).

[0035] Figure 9 It is a comparative chart of the planar distribution of the carbonate rock fracture-vug type reservoir after the multiple wave post-stack suppression.

[0036] Figure 10 It is the application of the multiple wave post-stack suppression technology in the LX work area. DETAILED DESCRIPTION

[0037] In order to better understand the present application, the present application will be further explained in combination with the drawings and specific embodiments.

[0038] EMBODIMENT

[0039] The present embodiment takes the Ordovician multiple wave suppression in the Yubei area of the Tarim Basin and the simulation reflection characteristics of the carbonate rock fracture-vug type reservoir as an example.

[0040] Figure 1The multiple wave post-stack suppression technical flow chart provided by the embodiment of the present application, Figure 2 is a basic principle diagram of identifying multiple waves of the present application. The multiple wave post-stack suppression technique comprises the following steps:

[0041] Step (1): Establishment of multiple wave mirror-source combination panel. On the basis of fine well-seismic calibration, the well logging acoustic curve of Y1 well is converted into a layer velocity curve, the free surface and the top and bottom interfaces of all high-speed layers (mainly the Paleogene gypsium layer, Permian igneous rock and Carboniferous limestone, etc.) are calibrated, and then according to the principle diagram shown in Figure 2 , the formula (1) of the relationship between the multiple wave double travel time thickness and the relative spatial position of the top interface of the target layer is used to combine all the strong reflection interfaces in pairs, when t dcb > t o-top As the basis for identifying the source-mirror combination that can generate multiple waves that can affect the imaging of the Ordovician geological target of the target layer, the establishment of the multiple wave mirror-source combination panel is finally realized, so that the longitudinal development position of the multiple wave image in the target layer can be predicted. In fact, the development position of the multiple wave is the "image" of its mirror relative to the source. As shown in Figure 3 , the development position of the multiple wave ① is the "image" of interface 2 relative to interface 3; the multiple wave ② is the same.

[0042] t dcb = t i + (t i+1 -t i ) × 2 (1)

[0043] Wherein, t o-top is the double travel time of the Ordovician top interface, t dcb is the final travel time of the multiple wave, and t i is the double travel time of the i-th strong reflection interface.

[0044] Step (2): Multiple wave mirror-source calibration and prediction.

[0045] ① Identification of abnormal reflection. According to the research on the strata and structural form of the research area, the abnormal reflection of the target layer is determined, such as Figure 4 the short overlap wave valley reflection of the top surface reflection of the Middle Ordovician, the contact relationship between the top surface of the structural belt and the overlying strata, the strata contact relationship, the strata dip angle and the reservoir body condition do not conform to the drilling conditions of Y1 well, etc. can be regarded as abnormal reflection. In Tarim Basin, the multiple wave is reflected as reflection different from normal strata or cutting through normal strata, and the frequency is obviously higher than that of normal strata.

[0046] ② Multiple wave source-mirror identification. The position of the normal reflection phase axis is calibrated by the multiple wave source-mirror combination template. In order to better compare with the source-mirror combination template, it can be as Figure 5The interface is flattened and then compared, and the top and bottom strong reflection interfaces that generate the multiple waves can be directly identified according to the source-mirror relationship of the multiple waves. Based on the identification of the source-mirror combination of the multiple waves, the corresponding strong reflection interface is finely interpreted.

[0047] ③Multiple wave distribution prediction. According to formula (1) and Figure 2 The source-mirror strong interface travel time is converted into the double-path travel time of the multiple waves, and the Figure 6 In the multiple wave distribution prediction, three groups of interlayer multiple wave mirror-source combinations that affect the imaging of the Ordovician target layer are predicted: the standard limestone bottom interface- bioclastic limestone top interface, the Xiaohaizi limestone bottom interface- standard limestone top interface, and the Xiaohaizi limestone bottom interface- bioclastic limestone top interface. In combination with the waveform characteristics of the abnormal reflection, the predicted structure is fine-tuned, and the finally predicted spatial distribution position is in good agreement with the abnormal reflection of the profile.

[0048] Step (3): Multiple wave post-stack suppression and effective wave field reorganization.

[0049] ①Multiple wave field preliminary separation. Local domain wavelet decomposition is carried out based on the constraint of the spatial distribution of the multiple waves until the influence of the abnormal reflection on the geological target is obviously improved, and the "bead-like" strong reflection anomaly of the carbonate fracture-vug type reservoir is effectively highlighted, but there is obvious noise, such as Figure 7 b、 Figure 8 b.

[0050] ②Geological target feature frequency screening and reorganization. Based on the faults, reservoirs, and drilled wells in the work area, the single frequency volume or partial frequency band information of the preliminary separation results of the multiple waves is screened by using the wavelet transform decomposition algorithm, all feature frequency data that can accurately reflect the imaging of the geological target are taken as a set, and are effectively fused out to highlight the seismic reflection characteristics of the geological target, and the feature frequency volume is generated.

[0051] ③Noise suppression is performed on the feature frequency volume to obtain the final result data, Figure 7 c、 Figure 8 c. It can be seen that the result data maintains a high signal-to-noise ratio while effectively highlighting the seismic abnormal reflection, and the amplitude variation ratio attribute of the target layer is more in line with the development law of the carbonate fracture-vug type reservoir, such as Figure 9 , the multiple wave occurrence of the Ordovician system in the LX three-dimensional seismic work area is obviously different from the top and bottom of the Ordovician system, and the energy is stronger than that of the effective wave, such as Figure 10 a, by using the technology, the multiple waves are well suppressed, and the fracture characteristics and the "strong amplitude" reflection characteristics of the carbonate fracture-vug type reservoir are more obvious, such as Figure 10 b.

[0052] In Tarim Basin area, especially in the south of Tarim Basin, due to low signal-to-noise ratio of seismic data and development of multiple waves, at present, based on filtering method and wave equation forward attenuation method, no effect is achieved, which seriously influences accurate imaging of faults, structures and reservoirs of Ordovician target layer, and this also increases multi-solution of zone evaluation, trap implementation and well site deployment in the research area. The multiple wave post-stack identification and suppression technology of the embodiment is based on post-stack result data body, does not need obvious difference and periodicity of multiple waves and effective waves, and does not need to consider all possibilities, but on the basis of fast identification of main multiple waves influencing geological target imaging based on multiple wave mirror-source combination chart, through local domain wavelet analysis and geological target characteristic frequency screening and recombination, the imaging precision of seismic data is effectively improved. It can be seen that the application provides better selection for effective suppression of multiple waves in seismic data processing, and provides technical support for accurate imaging of future seismic data, and has wide application background in the area with development characteristics of multiple waves in Tarim Basin or similar areas.

Claims

1. A method for multiple wave poststack identification and suppression, characterized by The method comprises the following steps: (1) on the basis of fine well-seismic calibration, a multiple mirror-source combination chart is established; Specifically, all possible free surfaces and / or high-speed layer interfaces in the overlying strata of the target layer are identified using acoustic logging data, and based on the optimal combination of key interfaces that generate multiple waves, the double relative travel time of multiple waves and the time of the target layer, multiple waves that can affect the imaging of the target layer are judged, and a mirror-source combination chart is established; the acoustic wave curve is converted into a layer velocity curve, the free surface and all high-speed layers are calibrated, and the relationship formula (1) of the double travel time thickness of multiple waves and the relative spatial position of the top interface of the target layer is used to combine all the strong reflection interfaces with negative above and positive below in pairs, and when As the basis for the identification of source-mirror combinations that generate multiple waves that can affect the imaging of the Ordovician geological targets in the target layer, the establishment of the multiple wave mirror-source combination chart is finally realized （1）， wherein, is the two-way travel time of the Ordovician top, is the final travel time of the multiple, is the two-way travel time of the first strong reflector interface; (2) multiple mirror-source calibration and prediction, including: ① identification of abnormal reflection, ② multiple mirror-source identification; ③ multiple wave distribution prediction; specifically, ① under the guidance of regional geology and drilled stratum understanding, the effectiveness of seismic reflection of the main target layer is judged from the aspects of frequency, stratum occurrence, structure and / or stratum contact relationship, and abnormal seismic reflection phase axis is identified; ② the main multiple wave corresponding to the strong reflection interface affecting the imaging of the geological target is judged by comparing the multiple mirror-source combination chart, and finally the mirror-source calibration and interpretation are realized; ③ based on the understanding and interpretation results of the multiple mirror-source image, the two-way travel time of the multiple wave is predicted as the bottom boundary travel time plus the mirror-source time thickness, and then the non-normal reflection is fine-tuned according to the degree of coincidence, so that the best position is the multiple wave prediction position; (3) multiple wave post-stack suppression and effective wave field recombination, including: ① preliminary separation of multiple wave field, ② frequency screening and recombination of geological target characteristics, ③ noise suppression is carried out on the characteristic frequency body to obtain the final result data.

2. The method of claim 1, wherein The abnormal seismic reflection phase axis has continuity or distribution in space.

3. The method of claim 1, wherein Step (3) comprises: under the constraint of the spatial position of the multiple wave distribution, firstly, the approximate time window range is determined according to the waveform characteristics of the abnormal reflection, and the local domain wavelet decomposition or simulated attenuation technology is used to realize the preliminary controllable decomposition of the multiple wave, and the proportion of effective seismic wave field information is enhanced; secondly, the determined geological target is selected as the basis, the multiple characteristic frequency information which is helpful to the imaging of the geological target is screened through frequency scanning, the imaging characteristic frequency information of the geological body is recombined, the effective information of the target imaging is highlighted, and finally the multiple wave suppression is realized after random noise suppression.

4. The method of claim 3, wherein The determined address target includes fracture and / or drilled well results.

Images