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Quick Search     Advanced Search OGP   2023 Vol.58 Issue.4 Published 2023-08-15 ACQUISITION TECHNIQUE PROCESSING TECHNIQUE SEISMIC SIMULATION MIGRATION AND IMAGING MICROSEISMIC PETROPHYSICS COMPREHENSIVE RESEARCH SEISMIC GEOLOGY NON-SEISMIC INTELLIGENT GEOPHYSICAL TECHNIQUE PERSONEGE 0 2023 Vol. 58 (4): 0-0 [Abstract] ( 113 ) [HTML 1KB] [ PDF 1013KB] ( 182 ) 1030 2023 Vol. 58 (4): 1030-1030 [Abstract] ( 60 ) [HTML 1KB] [ PDF 752KB] ( 192 ) INTELLIGENT GEOPHYSICAL TECHNIQUE 753 Space-varying wavelet extraction method by ConvGRU network with autoencoder-decoder architecture DAI Yongshou, LI Honghao, SUN Weifeng, SONG Jianguo, SUN Jiazhao The imaging and inversion quality of seismic exploration is inseparable from the accurate extraction of seismic wavelets. Meanwhile, the dominant frequency and phase of wavelets will change during propagation, causing changes in wavelet morphology. However, existing wavelet estimation methods still lack studies on wavelet spatial variability and rely on prior information such as well logging data. Therefore, this paper proposes a space-varying wavelet extraction method that combines the autoencoder-decoder architecture and ConvGRU network. The method combines convolution operation and gated calculation to extract the main frequency and phase features of wavelets in different traces. Then the features are encoded to obtain the feature variables which can more efficiently extract the features of different traces and different time by the decoder. Finite difference forward modeling and non-stationary convolution model are employed to build training data consistent with actual data distribution. The autoencoder-decoder network model is built and the training data is adopted to train the network and obtain a model for extracting space-varying seismic wavelets. Finally, this model is leveraged to extract multi-trace seismic wavelets. The numerical simulation results show that the proposed method is more accurate than traditional wavelet extraction methods. The processing of actual seismic data in western China proves that the method put forward in this paper is of certain practical application significance. 2023 Vol. 58 (4): 753-765 [Abstract] ( 122 ) [HTML 1KB] [ PDF 30347KB] ( 325 ) 766 Unsupervised seismic data random noise suppression method based on weighted total variation regularization and ADMM solution WANG Jing, CHEN Rui, MA Xiaoqin, WU Bangyu Noise suppression is a crucial step for seismic data processing. In recent years, with the rapid development of deep learning, its application in seismic data denoising has achieved significant effects. For practical application, since it is difficult to collect a large number of labeled seismic data(noise-free data), this paper proposes to suppress the random noise in two-dimensional(2D) seismic data based on the unsupervised deep image prior(DIP) framework. Firstly, the influence of skip connection on network denoising performance is explored, and the network architecture is determined. Secondly, the weighted total variation(WTV) regularization term is added to the loss function. Different from that of the traditional total variation(TV) regularization term, the weight coefficient of the WTV regularization term is no longer a fixed hyper parameter but a learnable parameter related to the spatial structure of data. Finally, the alternating direction method of multipliers(ADMM) is used to solve the optimization problem. Synthetic and real data experiments show that the DIP method combining WTV regularization term and ADMM can reduce the effective signal loss while suppressing random noise in seismic data and has better denoising stability than DIP;the peak signal-to-noise ratio fluctuation of adjacent iterations is small, and it is easier to develop early stopping criteria and applied. 2023 Vol. 58 (4): 766-779,800 [Abstract] ( 99 ) [HTML 1KB] [ PDF 19501KB] ( 272 ) 780 Abnormal amplitude suppression method based on denoising convolutional neural network FAN Chengxiang, GUO Hongwei, YUAN Yijun Abnormal amplitude of seismic data often leads to uneven spatial energy in seismic data, resulting in arc phenomenon during the prestack migration and interfering with seismic data interpretation. Therefore, suppressing abnormal amplitudes has become an important step in seismic data processing. Due to the limitation of application conditions, traditional methods fail to completely suppress abnormal amplitude while protecting effective signals. Therefore, a method for suppressing abnormal amplitude based on a denoising convolutional neural network (DnCNN) is proposed. Firstly, according to the distribution characteristics of seismic abnormal amplitude, this method builds a DnCNN structure suitable for suppressing abnormal amplitude through network improvement and optimization. Secondly, training sets with and without abnormal amplitude are produced by artificial synthesis and real data extraction. The network is trained with the training set, and a network training model that can suppress abnormal amplitude is obtained. Finally, tests on model data and real seismic data show that the proposed method can effectively suppress abnormal amplitude in seismic data, protect effective signals, and obtain better processing results than commonly used traditional methods. 2023 Vol. 58 (4): 780-788 [Abstract] ( 88 ) [HTML 1KB] [ PDF 17773KB] ( 243 ) ACQUISITION TECHNIQUE 789 Surface structure survey by microtremor based on F-J method ZHAO Rongrong, YANG Zhentao, REN Chenghao, ZHOU Xin, WANG Yi, CHEN Wei 3D seismic exploration is typically employed in areas where micro logging and other static correction methods cannot be implemented, such as towns and roads. Recently researchers have tried to replace existing static correction methods with microtremor surveys and yielded some achievements. At present, in petroleum exploration, microtremor survey mainly employs surface wave dispersion curves to invert formation velocity structures. This method is still in its infancy in petroleum exploration. As the core technology, dispersion imaging methods can be classfied into many types, such as the frequency-Bessel(F-J) transformation method proposed in 2019, which has attracted the attention of geophysicists. Compared with the spatial autocorrelation method(SPAC), the F-J method has great advantages in adopting ambient noise for higher-mode surface wave imaging. To better study the applicability of F-J method, this paper first analyzes the influence of different observation systems and acquisition param-eters on F-J imaging using synthetic data. Then, the effect of different observation systems and acquisition time on FJ dispersion imaging is analyzed through the field ambient noise data of an area in Sichuan. In practical application, the dispersion spectrum obtained by subsection optimization superposition can effectively improve the imaging quality of the dispersion spectrum and provide a data basis for the accurate extraction of dispersion curves. Finally, logging data comparison shows that multi-mode joint inversion using fundamental mode and higher-mode dispersion curves can accurately invert formation structures, thus making it possible to obtain surface structures economically and efficiently. 2023 Vol. 58 (4): 789-800 [Abstract] ( 91 ) [HTML 1KB] [ PDF 15148KB] ( 271 ) PROCESSING TECHNIQUE 801 CMP gather Q scanning based on relative entropy criterion LI Penghui, WANG Huazhong The geodetic filtering effects(mainly thin layer overlapping effect, scattering effect, and inelastic effect) of underground media will attenuate seismic signal amplitudes, narrow frequency bands, reduce the main frequency, and distort phases, and they can be represented by the effect caused by equivalent Q value. It is very important to estimate the equivalent Q value reasonably and make the corresponding Q compensation to improve the seismic data resolution. The absorption attenuation is a cumulative effect. When the Q value of the stratum is constant, the attenuation of seismic wavelet becomes more and more obvious with the increase in the propagation distance/time and frequency. In other words, the amplitude and high-frequency components of deep and far offset reflection wavelets are attenuated more seriously. In this paper, it is assumed that the stratum is horizontally layered, and the reflection events conform to the hyperbolic law;the underground root mean square velocity model is known, and a single attenuation wavelet can be extracted along the time window of the hyperbolic trajectory by using the CMP gather. Then a set of Q values is selected to compensate for the amplitude spectrum of the attenuation wavelet in the frequency domain by Q values. According to the principle of optimum consistency of amplitude spectrum of compensated seismic wavelet at different offsets, the equivalent Q value of horizontal strata is estimated. This method needs an excellent measurement criterion. Therefore, the measurement criteria, such as similarity coefficient, centroid frequency, KL divergence, and JS divergence are compared. Experimental results show that the JS divergence criterion is more sensitive to the normalized amplitude spectrum consistency measurement and has a stronger anti-noise ability when the appropriate frequency band range(e. g., 0~60 Hz) is selected. The quality factor estimation method by CMP gather scanning based on relative entropy criterion can obtain relatively stable equivalent Q value estimation results when the signal-to-noise ratio is suitable. 2023 Vol. 58 (4): 801-811 [Abstract] ( 53 ) [HTML 1KB] [ PDF 4910KB] ( 152 ) 812 Approximate equation for calculating P-wave traveltime in horizontally layered VTI media WEI Jian, SUN Xiang'e The calculation accuracy of P-wave traveltime equations based on the Taylor series is affected by the transverse isotropy medium with vertical symmetry axis(VTI). In order to improve this situation, a calculation method based on square processing and coefficient matching is proposed. In this method, the square processing is used to transform the traveltime equation of the non-square form based on the Taylor series into the square form containing high-order terms, and then the coefficient matching method is used to deal with the high-order terms of the traveltime square equation so that the highest order of the equation offset is the commonly used fourth order. Then, on the basis of simplifying the form of parameters and optimizing the traveltime square equation, a new coefficient y, which is related to the anisotropic parameter, is obtained. Finally, a fourth-order P-wave traveltime calculation method with y based on square processing and coefficient matching is formed. The experimental results based on the horizontally layered VTI medium model show that compared with the rational approximation method, the generalized moveout approximation method based on three rays, and the extended generalized moveout approximation method, this method has smaller errors, and the calculation ability at the far offset is improved to some extent, which provides more options for the applications based on traveltime equations. 2023 Vol. 58 (4): 812-817 [Abstract] ( 60 ) [HTML 1KB] [ PDF 1343KB] ( 139 ) 818 Simultaneous reconstruction and denoising of seismic data using multi-channel singular spectrum analysis based on hierarchical clustering CAO Jingjie, XU Changhao, ZHU Yuefei High signal-to-noise ratio, high fidelity, and high-resolution seismic data are prerequisites for clear imaging of subsurface structures. During seismic data acquisition, factors such as unfavorable topography and bad channels lead to the phenomenon that seismic data cannot satisfy the sampling theorem, and reconstruction is required to obtain complete seismic data. The multi-channel singular spectrum analysis method is a common seismic data reconstruction and denoising method, and its key is to determine the number of effective singular values for each divided data block. This parameter needs to be determined based on different data characteristics, but current manual selection methods require a lot of labor and computational resources. For each data block, based on the framework of multi-channel singular spectrum analysis in the frequency domain, the discrete point curves and spectral patterns of singular values are analyzed, and a hierarchical clustering method is proposed to automatically identify the number of singular values corresponding to the effective signals, which improves the denoising effect and reconstruction quality of seismic data. Then, the hierarchical clustering method is adopted to cluster the singular value sequence obtained by singular value decomposition of the block Hankel matrix and acquire the number of effective singular values of each frequency. Additionally, the number of singular values taken within the effective frequency is maximized to obtain the effective singular values for data blocks. In the framework of simultaneous reconstruction and denoising by damped multi-channel singular spectrum analysis, an improved multi-channel singular spectrum analysis (MSSA) method is put forward to realize simultaneous reconstruction and denoising of seismic data. Tests conducted on simulated and actual seismic data show that the MSSA method based on hierarchical clustering is superior in simultaneous reconstruction and denoising, and the accuracy of the obtained singular values is verified. The method can avoid the manual selection of the effective number of singular values and reduce the workload of seismic data processing, which is of practical significance for the reconstruction and denoising of large-scale seismic data. 2023 Vol. 58 (4): 818-829 [Abstract] ( 84 ) [HTML 1KB] [ PDF 10887KB] ( 192 ) 830 Inversion of multi-mode Rayleigh wave dispersion curves based on lightning attachment procedure optimization FU Yu, AI Hanbing, YAO Zhen'an, LI Hongxing, TIAN Xiao, ZHANG Xingmian In Rayleigh wave exploration, inversion of picked dispersion curves is the key to retrieving subsurface stratigraphic information, which is characterized by multiple parameters and optimal values. Traditional global optimization methods such as particle swarm optimization(PSO) algorithm and genetic algorithm(GA) feature slow convergence speed and low precision. To this end, this paper adopts a novel global optimization algorithm, lightning attachment procedure optimization(LAPO) for dispersion curve inversion. The LAPO algorithm is inspired by the natural lightning formation process involving the process of connecting downward and upward leader movements. This algorithm can find the optimal solution by simulating the lightning formation process in nature and has strong global search and local exploitation abilities without parameter tuning. Tests carried out through the theoretical geological model and actual data show that compared with PSO, LAPO yields faster convergence speed, higher solution accuracy, and more stable performance. Additionally, it can be applied to the inversion of both fundamental and multimode dispersion curves, and is a valuable tool for the quantitative interpretation of Rayleigh dispersion curves. 2023 Vol. 58 (4): 830-838 [Abstract] ( 79 ) [HTML 1KB] [ PDF 2501KB] ( 147 ) SEISMIC SIMULATION 839 Numerical simulation of seismic waves in viscoelastic media based on orthogonal body-fitted grid LIU Zhiqiang, HUANG Lei, LI Gangzhu, NIU Xingguo, ZHANG Xiaomeng Conventional finite difference numerical simulation of seismic waves employs regular grids in Cartesian coordinates to divide the calculated region. During simulating seismic wavefields under undulating surfaces, it is not only unfavorable to realize the free boundary conditions, but also prone to generate false scattered waves at the corners of the grid due to stepped grid approximation, thus affecting the simulation accuracy. To this end, the orthogonal body-fitted grid generation technique in computational fluid dynamics is introduced into the grid generation of viscoelastic media under undulating surfaces. The first-order velocity-stress equation in curvilinear coordinates is calculated by the optimized homologous grid finite difference method, and the point oscillation generated by the homologous grid difference is eliminated by the selective filtering method. The orthogonal body-fitted grid can accurately describe the undulating surface, and due to the orthogonality of the grid, free boundary conditions can be implemented without complicated coordinate transformation and interpolation operations. Numerical examples show that the numerical solutions obtained by this method are in good agreement with the analytical ones. By comparing the simulation results of the proposed method with those of the regular grid finite difference method, the proposed method can effectively eliminate the false scattered waves caused by the stepped grid in the condition of the same grid spacing, thus improving the numerical simulation accuracy. In addition, the simulation results of two-layers and three-layers viscoelastic medium models on undulating surfaces show that the proposed method is also applicable for complex models. 2023 Vol. 58 (4): 839-846 [Abstract] ( 73 ) [HTML 1KB] [ PDF 4416KB] ( 179 ) 847 Numerical simulation and dispersion curve verification of three-dimensional background noises HUO Keyu, SHAO Guangzhou, WANG Guoshun, BAI Shuai, WU Hua In recent years, background noise imaging technology using vibrations generated by human production activities and natural earthquakes as the source has gradually become a research hotspot. Whether it is to verify the effectiveness of the background noise imaging method and the dispersion curve extraction method based on the known model, or to optimize the parameters of the background noise data acquisition method, it is necessary to obtain the required theoretical synthetic data of background noises through wave field numerical simulation. Three-dimensional (3D) numerical simulation is an important research content in background noise imaging. In view of the randomness of background noises in time and space, this paper introduces the random source into the finite difference numerical simulation of the 3D Rayleigh wave field to effectively calculate background noise data. The dispersion curve of the noise recorded by simulation is extracted by the two-trace method based on Aki formula and compared with the theoretical dispersion curve, so as to verify the feasibility and effectiveness of noise simulation. The test results of the theoretical model show that when the source parameters are within a reasonable range, the dispersion curve of the synthetic background noise data and the theoretical dispersion curve are well fitted;at the same time, the dispersion curve extracted from the 3D simulation data is more accurate than that by the two-dimensional simulation data. 2023 Vol. 58 (4): 847-856 [Abstract] ( 84 ) [HTML 1KB] [ PDF 6750KB] ( 199 ) 857 Multi-phase seismic traveltime computation in 2D/3D undulated surface model using factored eikonal equation ZHANG Yun, LI Xihai, BAI Chaoying, NIU Chao, WANG Yiting, ZENG Xiaoniu The seismic traveltime computation scheme in undulating surface conditions is a basic tool to study the underground structures of such surface areas. The fast marching method (FMM) and the fast sweeping method (FSM) are both developed based on solving the eikonal equation with finite difference. They have the problem of source singularity due to the high curvature of the wavefront around the source. Previous studies show that the com-putational efficiency of FMM is higher than FSM for complex models. Thus, this paper employs the FMM to solve the factorization equation and avoid source singularity. Specifically, the original eikonal equation can be transformed into the factored eikonal equation, in which the seismic traveltime can be regarded as the product of a distance function T 0 and a correction factor T1 of traveltime. The correction factor T1 of traveltime can be solved by the FMM algorithm and then the distance function T0 is multiplied to obtain the traveltime(T). To address the problem that the upwind finite difference formula with even grid spacing is not applicable to surface/interface undulation, this paper constructs an upwind finite difference formula with uneven grid spacing. Finally, the multistage computational technique is adopted to propose a computation method for global multi-phase seismic traveltime. The simulation tests indicate that the new algorithm solves the source singularity of FMM, significantly improves the computational accuracy and efficiency of the original algorithm, and can accurately calculate the multi-phase seismic traveltime. 2023 Vol. 58 (4): 857-871 [Abstract] ( 65 ) [HTML 1KB] [ PDF 4094KB] ( 163 ) MIGRATION AND IMAGING 872 Viscoacoustic reverse-time migration imaging based on fractional Laplacian with up-going and down-going wave decomposition WANG Xipeng, ZHANG Qingchen, MAO Weijian The subsurface media typically exhibit viscosity, which causes energy attenuation and(phase) dispersion effects during seismic wave propagation and in turn reduces the illumination energy of migration imaging. The twoway wave equation reverse-time migration with cross-correlation imaging conditions may produce low-frequency noise and false images when there is no highly accurate velocity models or strong velocity gradients. To this end, this paper proposes a viscoacoustic reverse-time migration method based on decoupled fractional Laplacian with up and down-going wave decomposition(Q-compensated reverse-time migration method). The viscoacoustic wave equation based on decoupled fractional Laplacian is employed to separately extrapolate the source wavefield and receiver wavefield and correct the attenuation effects generated by subsurface media during the process. An adaptive stability factor is introduced to handle numerical instability arising from the attenuation compensation of seismic waves. The time-domain analytical wavefield extrapolation method is adopted to separately decompose the propagation directions of the source and receiver wavefields on each time slice. Finally, the cross-correlation imaging condition is utilized for imaging of the down-going source wavefield and up-going receiver wavefield. Numerical tests show that the Q-compensated reverse-time migration method can correct the amplitude attenuation and(phase) dispersion effects caused by the viscosity characteristics of subsurface media. This imaging method significantly reduces the low-frequency noise and false images in traditional reverse-time migration imaging. 2023 Vol. 58 (4): 872-882 [Abstract] ( 66 ) [HTML 1KB] [ PDF 4493KB] ( 175 ) 883 Variable “wavelet” simulated imaging method based on illumination compensation JIAO Junfeng, ZHAO Aiguo, LIAN Ximeng, CUI Qinghui, SUN Chengyu, WU Han Currently prestack depth migration is the key technology of high-precision seismic imaging. For a given velocity model, the traditional method is to solve the wave equation for wavefield forward modeling first, and then do prestack migration imaging for the forward wavefield. This method features low computational efficiency and high requirements for hardware. At present, the simulated prestack depth migration method based on an imaging operator does not need wavefield forward modeling and migration processing with high computational efficiency. However, there are some problems, such as inconsistency of the energy distribution with the actual situation, serious zonal reconstruction division, and incorrect imaging waveform. To improve the effect of simulated prestack migration imaging algorithms, a variable "wavelet" simulated prestack depth migration imaging method based on illumination com-pensation is proposed in this paper. This method first calculates the ray path according to the acquisition geometry, adopts the unit impulse instead of the point spread function to construct the direct imaging operator in the wavenum-ber domain, and acts as the imaging operator on the reflection coefficient model. Then, the imaging results in the simulated depth domain are obtained by unsteady convolution in the spatial domain, which solves the problem that the waveform cannot change spatially in the simulated depth imaging. Through the superposition of multi-point simulation imaging results under the action of unit impulse, the problems of spatial energy difference and illumination inability in individual areas are addressed. This method not only retains the advantage of the fast calculation speed of the original algorithm but also tackles the problems of energy distribution and "wavelet" space variation. Model test proves that the imaging results of this method are accurate, which can provide more accurate references for the selection of acquisition geometry and seismic imaging. 2023 Vol. 58 (4): 883-892 [Abstract] ( 69 ) [HTML 1KB] [ PDF 8459KB] ( 168 ) PETROPHYSICS 893 Rock physical modelling for deep shale reservoirs involving the influence of pressure WU Chenyue, YIN Xingyao, YIN Linjie, LI Kun Formation pressure affects the elasticity of shale reservoirs, and in deep high-pressure conditions, fracture structure is an important factor influencing the elasticity of shale reservoirs. At present, few seismic rock physical modeling methods for deep shale reservoirs consider the influence of pressure. Firstly, based on Toksöz inclusion theory, this paper considers the influence of effective pressure on the aspect ratio of cracks, establishes a quantitative relationship between effective pressure and the aspect ratio of cracks, and introduces the influence of effective pressure into the Eshelby Cheng model for pressure correction. Secondly, the corrected Eshelby Cheng model is em-ployed to couple the horizontal fractures affected by effective pressure into the background medium in the form of inclusions and build a seismic rock physics model of deep shale reservoirs considering pressure effects. Finally, the built seismic rock physics model is applied to the actual work area and compared with the non-pressure corrected Eshelby-Cheng model for estimating the P-wave and S-wave velocities. By analyzing the effects of effective pressure on the aspect ratio of fractures, Thomsen anisotropy parameters, and P-wave and S-wave velocities in the reservoir, the results show that in the early stages of effective pressure changes, the aspect ratio of fractures and Thomsen anisotropy parameters decrease with the increasing effective pressure. The P-wave and S-wave velocities of reservoirs increase with the rising effective pressure, and when the effective pressure increases to a certain limit, all three of the above tend to stabilize, which means that changes in effective pressure no longer affect the reservoir. The P-wave velocity and S-wave velocity prediction in deep shale reservoirs through this method is highly consistent with actual data, thus proving the applicability of this model for deep shale reservoirs. 2023 Vol. 58 (4): 893-901 [Abstract] ( 80 ) [HTML 1KB] [ PDF 2024KB] ( 171 ) 902 Analysis of seismic wave dispersion,attenuation and anisotropy of fractured media under anisotropic permeability JIANG Xiaomin, CHEN Xuehua, WU Haojie, LUO Xin, LIU Junjie Permeability anisotropy and seismic anisotropy are the key characteristics of fluid-bearing fracture-pore rock. In this paper, fracture parameters (dip angle, azimuth angle, radius, etc.) are used to characterize the permeability of fractured media and analyze the anisotropy variation of permeability. The seismic anisotropy and dispersion-attenuation characteristics of seismic waves of orthogonal media under permeability anisotropy are studied based on Chapman's multi-group fracture equivalent medium model. The numerical simulation results show that:① The permeability anisotropy changes with fracture parameters and is symmetrically influenced by fracture azimuth angle;the variation of fracture radius and dip angle affects the permeability anisotropy, especially the fracture radius. ②In the case of permeability anisotropy, there are two different relaxation time for the dispersion and attenuation of seismic waves, and the characteristic frequency decreases first and then increases with the increase in gas content in the fluid-bearing fractured medium. ③ The two different characteristic frequencies produced by different permeability are related to the frequency corresponding to the extreme value of the seismic anisotropy coefficient. This indicates that permeability anisotropy can cause anisotropy of seismic dispersion and attenuation. The numerical analysis results in this paper can provide a powerful theoretical basis for the prediction of reservoir permeability and fluid identification in fractured reservoirs. 2023 Vol. 58 (4): 902-912 [Abstract] ( 73 ) [HTML 1KB] [ PDF 3740KB] ( 159 ) MICROSEISMIC 913 Application of microseismic monitoring in evaluation of geological body integrity for UGS in oil-gas fields LIAO Wei, WEI Lulu, LUO Haitao, ZHANG Shijie, XU Gang, CHEN Long Underground gas storage(UGS) in oil-gas fields is an underground gas storage space reconstructed from depleted oil and gas reservoirs, and it is the most important type of gas storage. Compared with foreign UGS in oilgas fields, domestic UGS geological bodies are mostly complex fault blocks with deep burial, poor reservoir permeability, and strong heterogeneity. The unique and complicated geological conditions in China pose great challenges to the safe operation of UGS geological bodies. Microseismic monitoring technology can monitor the rock fracture in real time and is the most direct monitoring approach for the geological body activities of UGS. Therefore, based on the principle of microseismic monitoring and the definition of geological body integrity of UGS, this paper studies the data processing method according to the characteristics of microseismic monitoring data of UGS. Taking Hutubi UGS in Xinjiang as an example, this paper carries out microseismic monitoring data processing and interpretation and evaluates its UGS geological body integrity. The results are as follows:① Microseismic monitoring technology plays an important role in ensuring the geological body safety of UGS and can monitor rock fracture activities of faults, cap rocks, and bottom rock in real time. ② During the study period, the UGS geological body of Hutubi is relatively stable, and there is no obvious aggregation of microseismic events and the occurrence of large magnitude microseismic events near the reservoir depth, but it still needs long-term monitoring. ③Microseismic monitoring can realize three-dimensional monitoring and has a wider monitoring range and richer monitoring information than conventional monitoring methods. 2023 Vol. 58 (4): 913-921 [Abstract] ( 77 ) [HTML 1KB] [ PDF 5931KB] ( 164 ) COMPREHENSIVE RESEARCH 922 Prestack seismic inversion prediction method for hydrocarbon source rocks in few-well areas ZHANG Weiwei, LIN Heming, LUO Ming, XIAO Zhangbo, LUO Wei, GAO Dan It is difficult to extract accurate wavelets and build fine low-frequency models through well seismic calibration for hydrocarbon source rocks in few-well areas. Therefore, a prestack seismic inversion prediction method for hydrocarbon source rocks in few-well areas based on blind signal theory is proposed. First, according to the theory, the blind wavelets are extracted from the seismic data by higher-order statistics, and the low-frequency components of the model parameters are estimated in the complex frequency domain based on Bayesian theory. Then the blind wavelets and low-frequency model are further employed for elastic impedance inversion in the complex frequency domain. Finally, the relationship between the elastic impedance and physical parameters of hydrocarbon source rocks is established by the seismic petrophysics model of hydrocarbon source rocks. Physical parameters such as the shale content and indicator of hydrocarbon source rocks are obtained by elastic impedance inversion to predict the spatial distribution features of hydrocarbon source rocks in few-well areas and quantitatively evaluate hydrocarbon source rocks. In this method, the blind seismic wavelet extraction is a statistical method that does not require well data. The extracted blind seismic wavelet can provide priori constraints for the prestack seismic inversion of hydrocarbon source rocks in few-well areas. The proposed method solves the problem that deterministic wavelet extraction cannot be performed in the no-well or few-well areas. The reliability and accuracy of this method are proven by the test results. 2023 Vol. 58 (4): 922-932 [Abstract] ( 75 ) [HTML 1KB] [ PDF 7223KB] ( 207 ) 933 P-P wave reflection coefficient approximate expression and P- & S-wave impedance inversion based on normal impedance component WANG Shengrong, SUN Chengyu, CAI Ruiqian, DU Yijing The proposal of elastic impedance(EI) is based on the P-P wave reflection coefficient approximate expression for near-vertical incidence, which is related to the Zoeppritz equation. However, specific assumptions are required for the formation properties and geometry system, such as small differences between the impedance interfaces and small incidence angles, which limit the practical application of EI. Additionally, EI is different from acoustic impedance and does not have a definite dimension, which means that it is not a physical quantity and cannot be directly interpreted physically. Therefore, according to the physical definition of impedance, the two components of stress vectors and two components of velocity vectors are divided and inverted to form the impedance tensor, which has a definite dimension. For the case of P-wave incidence, the normal component(T) of the impedance tensor is used to approximately express the reflection coefficient, and a corresponding inversion method is developed. Numerical examples show that the results of T inversion and EI inversion are basically consistent and are in good agreement with the theoretical values. However, for the low-velocity layer, the S-wave impedance by T inversion is relatively stable and oscillates less compared with EI inversion. In addition, as the exponential operation is not included in the definition of T, the sensitivity of the inversion result to velocity, density, and angle is reduced, and the inversion result is relatively stable. The test results of actual seismic data show that the inversion result is in good agreement with the actual drilling data, and the impedance differences are evident in seismic events, indicating two sets of thin reservoirs with a clear low Poisson's ratio anomaly. Since the proposed method only uses data from two angles for inversion, it is particularly suitable for geometry systems with a narrow range of incidence angles. The normal impedance component extends the connotation of prestack seismic inversion and is a beneficial supplement to seismic impedance inversion. 2023 Vol. 58 (4): 933-941 [Abstract] ( 52 ) [HTML 1KB] [ PDF 4299KB] ( 144 ) 942 Bayesian inversion based on BISQ model for reservoir physical properties QU Zhipeng, WEN Jin, HAN Hongwei, BU Fan, WANG Xingmou, ZHU Jianbing For problems with multiple solutions such as the physical property inversion, common methods are usually difficult to obtain optimal solutions with high efficiency and accuracy. Therefore, according to the Bayesian statistics, we use the Gaussian prior model to introduce the constraints from well-log data and develop a Bayesian inversion method for reservoir physical properties to overcome the multi-solution problem. Next, a petrophysical forward model is developed based on the BISQ and effective fluid theories, which can reflect the multiple physical effects of solids and fluid in the porous medium and finely characterize the propagation process of seismic waves in the reservoir, thus enhancing the reliability of inversion results. In addition, because deterministic optimization algorithms usually have only local convergence capability and fail to converge to the global optimal solution of the inversion problem, hybrid genetic algorithms with global convergence capability are introduced to improve the accuracy and efficiency of the inversion method. Finally, the proposed inversion method is used to predict the porosity and water saturation in oil field A in eastern China, and positive results are obtained. 2023 Vol. 58 (4): 942-948 [Abstract] ( 71 ) [HTML 1KB] [ PDF 3979KB] ( 179 ) 949 Modeling of anisotropic parameters based on HTI medium travel-time inversion and AVAZ inversion ZHOU Cheng, YANG Yuyong, ZHOU Huailai, WANG Yuanjun, TAO Bocheng, YU Peilin Traditional methods for anisotropic inversion primarily rely on well logging data and layer information to construct initial models through interpolation, resulting in low model accuracy. To address this issue in establishing the initial model of seismic anisotropic inversion, under the assumption of horizontal transverse isotropy(HTI) medium, the travel-time information from offset vector tile(OVT) data is utilized to extract anisotropic parameters(ε and δ). Then, another anisotropic parameter γ is estimated based on the empirical relationship between the anisotropic parameters, so as to establish an initial anisotropic parameter model. Furthermore, an initial elastic parameter model is established by using the elastic parameters obtained from isotropic inversion. Finally, On the basis of the Rüger approximation formula for reflection coefficients, the elastic parameters and anisotropic parameters are retrieved by the Gauss-Newton method. Application of the proposed method to model and real data demonstrates its ability to achieve high-precision anisotropic parameter inversion without being constrained by well logging data, providing a basis for acquiring micro-fracture information in fractured reservoirs. 2023 Vol. 58 (4): 949-960,969 [Abstract] ( 77 ) [HTML 1KB] [ PDF 7998KB] ( 141 ) 961 Division of distributary sandbar-type shallow-water delta facies belts based on low-angle progradation seismic reflection characteristics ZHOU Kun The distribution of drilling in the Z6 block is non-uniform, and the target reservoir is composed of complex sandstone and mudstone with similar wave impedance characteristics. Therefore, for the region with few wells on the west side of the Z6 block, it is difficult to analyze the distribution characteristics of favorable sedimentary facies belts and accurately characterize the sand body boundaries. Relying solely on seismic reflection amplitude characteristics makes it challenging to distinguish sandstone from mudstone, and conventional post-stack seismic inversion techniques are ineffective in predicting reservoir distribution. Thus, a sedimentary model with its forward modeling suitable for the Z6 block is established based on three-dimensional(3D) seismic and drilling data, coupled with previous studies on the sedimentary characteristics of the shallow-water delta. Through analysis of the seismic response characteristics of sand bodies and seismic attribute optimization, the favorable reservoir distribution is predicted. The following findings are obtained:① The influence of low-angle progradation or lateral accretion on the seismic waveform of the underlying strata is the key to determining the boundary of sand bodies. This approach is suitable for delineating the sedimentary facies belts of the distributary sandbar-type shallow-water delta, and it is critical for predicting the extension range of the favorable reservoir during the exploration phase. ②Instantaneous phase and instantaneous frequency attributes more clearly depict the distributary sandbar and the boundary between the distributary channel bays compared with traditional amplitude-type attributes, especially the instantaneous phase attribute, which is not affected by amplitude and is sensitive to phase changes in geological bodies such as lithologic pinchout. ③ Near the source direction, the sand bodies are significantly controlled by distributary channels, exhibiting a linear feature, while near the center of the lake, the sand bodies are obviously affected by the lake wave, exhibiting lump-shaped and lobeshaped features. This study shows that under the guidance of the sedimentary model, the distribution of the distributary sandbar predicted by seismic attribute analysis and the characteristics of sandstone and mudstone revealed by drilling data match well in the case of few wells. Furthermore, the sand body boundaries of the distributary sandbartype shallow-water delta can be reasonably depicted through effective seismic attribute analysis. 2023 Vol. 58 (4): 961-969 [Abstract] ( 66 ) [HTML 1KB] [ PDF 6710KB] ( 145 ) 970 Compaction-centrifugal flow percolation and hydrocarbon enrichment of T/C-P unconformable double stratigraphic structure: A case study of Triassic T1b Formation in Madong slope area, Junggar Basin MENG Xiangchao, QI Hongyan, CHEN Yang, DOU Yang, GUO Huajun, PENG Bo To discuss the percolation effect of atmospheric fresh water on overlying strata above the unconformable surface, this paper uses data such as seismic-geology comprehensive profile, reservoir physical property, fluid(oil and water) geochemical parameters, formation testing, and pilot production to comprehensive analyze the stratum structure and compaction-centrifugal flow distribution characteristics related to the unconformable surface. It reveals that under the control of the T/C-P unconformable double stratigraphic structure, the vertical percolation of atmospheric fresh water to the overlying strata above the T/P unconformable surface by compaction-centrifugal flow leads to the low oil & gas charging degree of Triassic Baikouquan(T1b) Formation in Madong slope area. The results show that the direction of the fluid potential in the compaction-centrifugal flow percolation zone of T1b Formation above the T/P unconformable surface in the Madong slope area is opposite to that of the gravity potential, which is closely related to the capillary self-imbibition of the mud-rich conglomerate facies at the bottom of T1b Formation and the associated wetting water phase. The atmospheric fresh water percolates upward mainly along the micro-pore throat in the mud-rich conglomerate of the T1b Formation above the T/P unconformable surface, forming a bottom-up compactioncentrifugal flow. The vertical percolation depth of compaction-centrifugal flow is about 45 m, and the plane extension distance is about 28 km. The compaction-centrifugal flow against gravity potential leads to a low degree of oil & gas charging in the T1b Formation, and oil & gas mainly accumulate in the mud-poor conglomerate reservoir with excellent physical properties in the middle and upper part of the sand formation. According to compaction-centrifugal flow percolation and hydrocarbon enrichment characteristics of T/C-P unconformable double stratigraphic structure, logging quantitative identification criteria of the T1b Formation reservoir are lgRT > 1.4 Ω·m(RT > 25 Ω·m) and IMP < 9000 g·cm-3·m·s-1. The RT-IMP joint-constrained oil reservoir quantitative prediction map is used to predict two oil and gas enrichment areas, namely the east wing of Xiazijie Fan(with an area of 98 km2) and the north wing of Madong-Xiayan Fan(with an area of 104 km2). 2023 Vol. 58 (4): 970-982 [Abstract] ( 52 ) [HTML 1KB] [ PDF 8589KB] ( 122 ) SEISMIC GEOLOGY 983 Characteristics of brush structures in No. 1 structural belt and their geological significance in Nanpu Sag SUN Yonghe, LIU Lu, MENG Lingjian, MA Yan The main and secondary associated fault configuration of brush structures controlling the Nanpu No. 1 structure belt is different from the common brush structure fault configuration. For this reason, the evolution process of brush structures is complicated due to the reactivity of pre-existing basement faults and the interaction between late and new faults under the background of multi-stage superimposed deformation in Nanpu Sag, and it is difficult to understand the genesis of brush structures and their control law on oil and gas. Therefore, based on three-dimensional(3D) contiguous seismic data, structural analysis theory and related techniques are applied to systematically study the structural pattern of the No. 1 structural belt in Nanpu Sag and restore its evolution process, and the genesis of brush structures and its internal relationship with oil and gas accumulation are highlighted, so as to provide a theoretical basis for oil and gas exploration in the brush structure of Bohai Bay Basin. The results show that:①The brush structure of the No. 1 structural belt in Nanpu Sag is controlled by main faults F1 and FN and secondary faults. F1 started to be active in the Mesozoic and then reactivated in the Cenozoic. It propagated and grew from south to north. The southern boundary fault FN started to be active in the Ed3 deposition period, and the secondary fault held by F1 and FN started to be active in the Nm deposition period. ②The brush structure has experienced three stages of evolution:Paleogene rifting Ⅰ and Ⅱ, as well as post-Neogene rifting. The segmented growth of main faults in the Paleogene Es deposition period provides the background for the formation of the brush structure, and the stress field in the Paleogene Ed deposition period provides the stress mechanism for the development of the brush structure;the oblique extension of F1 and the orthogonal extension of FN in the Ng-Nm deposition period of the Neogene control the secondary faults, and the brush structure is established. ③ On the one hand, the development of brush structures in the Nanpu No. 1 structural belt indicates the stress regime transition in the Cenozoic. On the other hand, the main and secondary faults controlling brush structures as oil source faults control not only the vertical migration of oil and gas but also the formation of synchronous and reverse fault traps, indicating the location of oil and gas enrichment. 2023 Vol. 58 (4): 983-992 [Abstract] ( 53 ) [HTML 1KB] [ PDF 11200KB] ( 206 ) NON-SEISMIC 993 Three-dimensional inversion of gravity/magnetic anomalies based on curvelet compression and its applications ZHANG Henglei, GENG Meixia, HU Xiangyun The three-dimensional(3D) inversion of gravity/magnetic anomalies plays an important role in constructing the 3D fine structure of underground space. However, the matrix of the kernel function in 3D inversion is large, and it requires huge computer memory, which limits its wide application. In order to reduce the memory required by the kernel function, a 3D inversion method of gravity/magnetic anomalies based on curvelet compression is proposed in this paper. In other words, through curvelet transform, the energy of the kernel matrix is mainly retained in a small part of sparse curvelet coefficients, which can achieve efficient compression inversion. Compared with wavelet transform, curvelet transform has superior signal sparse representation ability, so it can obtain higher compression accuracy under the same compression rate. In this paper, the application effects of wavelet compression and curvelet compression in the 3D inversion of gravity/magnetic anomalies are compared. Under the same calculation accuracy, curvelet compression can improve the kernel compression rate by 100% and reduce the memory requirement by 50%. In the model test, the kernel function has a size of(100×100)×(100×100×50), with a storage capacity of 37 GB in double precision, and the proposed method adopting a compression ratio of 4%(the kernel's memory is only 1.48 GB) obtains the inversion results similar to the wavelet compression adopting a compression ratio of 10%. The proposed method is applied to the 3D inversion of magnetic anomalies in the Galinge mining area in western China, in which the 3D magnetization model obtained from compression and inversion reveals the buried depth, spatial distribution, and magnetic strength of the ore body, which provides a reliable basis for later drilling verification, reserve evaluation, and concealed ore detection. 2023 Vol. 58 (4): 993-1001 [Abstract] ( 71 ) [HTML 1KB] [ PDF 3183KB] ( 171 ) 1002 2.5D DC resistivity forward modeling based on a local weak form element-free method MA Changying, YAN Lingling, YAO Zhen'an, LIU Jianxin, ZHAO Wenxue, ZHOU Cong The traditional numerical simulation method relies on elements based on nodal connection information, so its application is limited. Although the element-free Galerkin method(EFGM) based on the global weak form does not require the division of elements based on nodal connection information, it still relies on the background quadrature elements divided in the global domain. In this paper, the partition of unity quadrature method is used to transform the global local integration into nodal local domain integration based on EFGM. Therefore, the background quadrature element divided in the global domain is not needed, and the dependence on the element is further reduced. As a result, 2.5-dimensional direct current(DC) resistivity forward modeling based on a local weak form elementfree method is realized with higher flexibility and accuracy. The proposed method, the EFGM, and the finite element method(FEM) are respectively used to simulate different geoelectric models, and the results are compared, which prove the correctness and effectiveness of the proposed method for the forward modeling of DC resistivity. In addition, the flexibility and adaptability of the proposed method are better than those of EFGM and FEM, with higher accuracy and low computational efficiency. In order to improve the accuracy of this method in simulating the undulating terrain, node encryption is carried out in the undulating terrain, and Gaussian points outside the terrain are not calculated. The results are basically consistent with those obtained by the EFGM and FEM. 2023 Vol. 58 (4): 1002-1016 [Abstract] ( 58 ) [HTML 1KB] [ PDF 7189KB] ( 161 ) 1017 Adaptive finite element forward modeling for three-dimensional wide-field electromagnetic method ZHOU Feng, XU Jintong, ZHANG Zhiyong, LAN Zeluan, CHEN Hui, TANG Hongzhi In order to improve the solving accuracy of wide-field electromagnetic method forward modeling, an adaptive finite element technique of a posterior error estimation strategy based on normal continuity of current density is used to realize three-dimensional(3D) wide-field electromagnetic method forward modeling. Firstly, based on Maxwell's equations, the electric field equations satisfied by the controlled field source are derived. The vector finite element technique with unstructured tetrahedral meshes is used to discretize the electric field equations, which results in large and sparse complex linear equations. Then, a posterior error estimation strategy based on normal continuity of current density is designed and incorporated into large and sparse complex linear finite element equations, and a high-precision 3D wide-field electromagnetic method forward calculation is achieved. Finally, an optimized Brent-Dekker root-finding algorithm is used to improve the stability of wide-field apparent resistivity, and the correctness of the adaptive algorithm is verified by using a layered media model. At the same time, typical terrain and spherical geo-electric models are designed to analyze the response characteristics of the wide-field electromagnetic method. The results show that the adaptive finite element method can reduce the low efficiency caused by artificial mesh design and improve the accuracy of forward modeling by mesh refinement in key regions. In addition, compared with CSAMT (controlled source audiofrequency magnetotellurics), the wide-field electromagnetic method has a larger exploration depth and range and is less affected by non-plane waves under the same transmit/receive distance. 2023 Vol. 58 (4): 1017-1029 [Abstract] ( 69 ) [HTML 1KB] [ PDF 7348KB] ( 179 ) PERSONEGE 1031 Geophysicist YONG Xueshan 2023 Vol. 58 (4): 1031-1031 [Abstract] ( 73 ) [HTML 1KB] [ PDF 811KB] ( 228 )

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