Forward modeling of ocean-bottom cable data and wave-mode separation in fluid–solid elastic media with irregular seabed

In marine seismic exploration, ocean-bottom cable techniques accurately record the multicomponent seismic wavefield; however, the seismic wave propagation in fluid–solid media cannot be simulated by a single wave equation. In addition, when the seabed interface is irregular, traditional finite-difference schemes cannot simulate the seismic wave propagation across the irregular seabed interface. Therefore, an acoustic–elastic forward modeling and vector-based P-and S-wave separation method is proposed. In this method, we divide the fluid–solid elastic media with irregular interface into orthogonal grids and map the irregular interface in the Cartesian coordinates system into a horizontal interface in the curvilinear coordinates system of the computational domain using coordinates transformation. The acoustic and elastic wave equations in the curvilinear coordinates system are applied to the fluid and solid medium, respectively. At the irregular interface, the two equations are combined into an acoustic–elastic equation in the curvilinear coordinates system. We next introduce a full staggered-grid scheme to improve the stability of the numerical simulation. Thus, separate P-and S-wave equations in the curvilinear coordinates system are derived to realize the P-and S-wave separation method.

The stability problem of reverse time migration for viscoacoustic VTI media

In real strata anisotropy and viscosity extensively exists. They degraded waveforms in amplitude, resulting in which reducing of image resolution. To obtain high-precision imaging of deep reservoirs, we extended the separated viscous and anisotropic reverse time migration （RTM） to a stable viscoacoustic anisotropic RTM for vertical transverse isotropic （VTI） media, based on single generalized standard and linear solid （GSLS） media theory.. We used a pseudo-spectral method to develop the numerical simulation. By introducing a regularization operator to eliminate the high-frequency instability problem, we built a stable inverse propagator and achieved viscoacoustic VTI media RTM. High-resolution imaging results were obtained after correcting for the effects of anisotropy and viscosity. Synthetic tests verify the validity and accuracy of algorithm.

Multiparameter least-squares reverse time migration for acoustic–elastic coupling media based on ocean bottom cable data

In marine seismic exploration,ocean bottom cable technology can record multicomponent seismic data for multiparameter inversion and imaging.This study proposes an elastic multiparameter lease-squares reverse time migration based on the ocean bottom cable technology.Herein,the wavefield continuation operators are mixed equations:the acoustic wave equations are used to calculate seismic wave propagation in the seawater medium,whereas in the solid media below the seabed,the wavefields are obtained by P-and S-wave separated vector elastic wave equations.At the seabed interface,acoustic–elastic coupling control equations are used to combine the two types of equations.P-and S-wave separated elastic migration operators,demigration operators,and gradient equations are derived to realize the elastic least-squares reverse time migration based on the P-and S-wave mode separation.The model tests verify that the proposed method can obtain high-quality images in both the P-and S-velocity components.In comparison with the traditional elastic least-squares reverse time migration method,the proposed method can readily suppress imaging crosstalk noise from multiparameter coupling.

多瞬时属性联合全波形反演方法研究

全波形反演(FWI)在实际中难以得到精度较高的深层速度模型,作者提出了一种基于一阶近似指数频率的时间域声波FWI方法来提高深层反演结果,但依然存在部分低频成分的缺失的问题。为此,本文利用瞬时振幅低频和保幅的优势为一阶近似指数频率的时间域声波FWI方法解决部分低频成分的缺失的问题,并形成了一套多瞬时属性联合反演流程。模型测试证明了该方法的可行性和有效性。

Pure q P-wave least-squares reverse time migration invertically transverse isotropic media and its application to field data

The anisotropic properties of subsurface media cause waveform distortions in seismic wave propagation,resulting in a negative infl uence on seismic imaging.In addition,wavefields simulated by the conventional coupled pseudo-acoustic equation are not only aff ected by SV-wave artifacts but are also limited by anisotropic parameters.We propose a least-squares reverse time migration(LSRTM)method based on the pure q P-wave equation in vertically transverse isotropic media.A fi nite diff erence and fast Fourier transform method,which can improve the effi ciency of the numerical simulation compared to a pseudo-spectral method,is used to solve the pure q P-wave equation.We derive the corresponding demigration operator,migration operator,and gradient updating formula to implement the LSRTM.Numerical tests on the Hess model and field data confirm that the proposed method has a good correction eff ect for the travel time deviation caused by underground anisotropic media.Further,it signifi cantly suppresses the migration noise,balances the imaging amplitude,and improves the imaging resolution.

三维黏声最小二乘逆时偏移方法模型研究

针对黏介质成像存在的问题及最小二乘逆时偏移方法的优势,通过广义标准线性固体(GSLS)的三维黏声波动方程,基于三维黏声波动方程的伴随算子及最小二乘逆时偏移框架,实现了三维黏声最小二乘逆时偏移方法。采用极性编码技术大幅度降低黏声最小二乘逆时偏移算法的计算量与内存,使三维黏声最小二乘逆时偏移算法的实用化成为可能。在模型试算部分,首先通过Marmousi模型验证了该方法对传统声波最小二乘逆时偏移方法的优势,最后对三维含Q平层模型及盐丘模型进行试算,证明了三维黏声最小二乘逆时偏移算法的正确性。

地震层析成像方法综述

地震层析成像作为一种有效还原地下介质速度模型的方法,为全波形反演提供了可靠的初始速度模型,从原始的射线层析到相移旅行时层析和瞬时旅行时层析,实现了地震波传播的有限频特性;从声波方程到弹性波方程,从各向同性介质到VTI,TTI介质,实现了对真实地下介质情况的模拟。减缓层析反演的病态性也一直是研究热点,常用的方法有正则化,用高斯束层析的敏感核代替传统的射线层析敏感核等。此外,为了避免使成像结果的精度依赖于共成像道集上反射位的真实深度,角度域双差分反射层析可以稳定有效地收敛到精确的偏移速度模型。如今,层析成像逐步向各向异性介质过渡,使用的数据从VSP到WVSP,从单一波形到多种波形联合反演发展,然而,分辨率和计算效率的相关问题仍然需要得到关注。

大学物理实验综合改革示范:数字示波器的原理与使用

在桂林电子科技大学电子信息特色的办学理念与大学物理综合实验改革的双重驱动下,以示波器的原理与使用实验为综合改革对象,在大学物理实验中构建了实践与应用能力培养较强的综合改革示范项目,取得了较好的教学效果。为电子信息类工程应用型人才培养,以及为当前新工科建设作出了积极的探索。

PID温控实验平台的设计与应用

本文设计了基于STC89C52单片机的温度控制系统。开发了PC机测控软件,通过串口通信实时对实验平台发送PID参数、PID控量、PWM周期、目标温度等控制参数,实时采集并保存来自实验平台的温度数据,并做出温度曲线。该平台经过实验验证取得了较为满意的控制效果,可以帮助学生更好地理解和灵活掌握PID控制理论,提高学生的综合能力和创新能力。

基于Python的物理实验数据实时检测分析系统

借助雨课堂在实验教学的扩展功能,开发了基于Python的实验数据实时检测分析系统.该系统教师可以实时从雨课堂的Web端获取学生的实验数据,检测分析学生实验数据存在的问题,对学生的实验操作成绩给出客观的评定,通过电子邮件的方式把每个学生实验数据处理结果推送给学生,提高了教师指导效率及课堂教学质量.

数字电位器调节特性和调节灵敏度测量仪

本文针对传统电位器调节特性和调节灵敏度测量装置的缺点,对其进行了数字化设计与改进。在原有实验仪器的基础上,将机械式电位器用数字电位器替代,并利用单片机结合键盘和数码管对数字电位器滑动端位置进行了控制和显示。数字电位器的使用有效解决了机械电位器滑动端位置读数误差大的问题,改进后的装置不仅可精确地控制和显示数字电位器的滑动端位置,而且操作方便,测定的调节特性曲线和调节灵敏度曲线与理论相一致。

基于行波分离的VTI介质逆时偏移

现阶段,各向同性介质假设已经不能满足复杂地质构造条件下的成像需求,忽略介质各向异性影响会使速度估计不准确,成像精度降低。为此,笔者从VTI介质一阶速度—应力方程出发,利用Poynting矢量特性对地震波进行方向行波分离,得出了基于上下行波分离的互相关成像条件,并将其应用在复杂VTI介质中。通过层状模型和SEG/EAGE岩丘模型测试验证了该算法的有效性以及在成像上的优越性;另外,当偏移速度不准确时,本文方法仍能够有效压制偏移噪声,成像质量更佳。

基于反馈迭代模型的多次波压制方法综述

在油气勘探中,多次波通常被视为影响地震数据处理和解释结果准确性的相干噪声,因此,多次波压制方法研究一直是地球物理勘探领域中的重要研究方向。鉴于自由表面多次波是地震勘探尤其是海上地震勘探资料中最为发育的多次波类型,因此,对自由表面多次波压制方法的研究是十分必要的。目前国内外精度较高且应用广泛的自由表面多次波压制方法即为基于波动方程的反馈迭代法,该方法以地震原始数据为预测因子,不需要其他先验条件,可以在数据驱动下实现高精度的自由表面多次波压制。在该方法理论基础上,近年来发展了一系列更为先进的方法技术。本文首先简要介绍了反馈迭代法的理论基础——反馈迭代模型;然后阐述了基于反馈迭代模型发展的SRME、反数据域法、EPSI、CL-SRME四种方法压制自由表面多次波的机理;最后对比了四种方法各自的优缺点,展望了基于反馈迭代模型的多次波压制方法的研究前景。

Improving the resolution of seismic traces based on the secondary time-frequency spectrum

The resolution of seismic data is critical to seismic data processing and the subsequent interpretation of fine structures. In conventional resolution improvement methods, the seismic data is assumed stationary and the noise level not changes with space, whereas the actual situation does not satisfy this assumption, so that results after resolution improvement processing is not up to the expected effect. To solve these problems, we propose a seismic resolution improvement method based on the secondary time-frequency spectrum. First, we propose the secondary time-frequency spectrum based on S transform （ST） and discuss the reflection coefficient sequence and time-dependent wavelet in the secondary time frequency spectrum. Second, using the secondary time frequency spectrum, we design a two- dimensional filter to extract the amplitude spectrum of the time-dependent wavelet. Then, we discuss the improvement of the resolution operator in noisy environments and propose a novel approach for determining the broad frequency range of the resolution operator in the time- fi＇equency-space domain. Finally, we apply the proposed method to synthetic and real data and compare the results of the traditional spectrum-modeling deconvolution and Q compensation method. The results suggest that the proposed method does not need to estimate the Q value and the resolution is not limited by the bandwidth of the source. Thus, the resolution of the seismic data is improved sufficiently based on the signal-to-noise ratio （SNR）.

Variable-grid reverse-time migration of different seismic survey data

With an increasing demand for high-resolution imaging of complex subsurface structures, thin layers and hidden reservoirs, borehole and cross-well seismic migration methods have become important. However, large differences are observed in the frequency bandwidth between the surface, borehole, and cross-well surveys. Thus, variable-grid- based algorithms have been adapted to reverse-time migration. Further, we introduce Lanczos filtering to ensure the stability of wavefield calculations as well as to decrease the artificial reflections that are caused due to the variable grid size. Finally, we observe that the application of this method to surface survey, borehole, and cross-well seismic data suggests improvements in the delineation of minor fractures and steeply dipping faults.

Prismatic and full-waveform joint inversion

Prismatic wave is that it has three of which is located at the reflection interface reflection paths and two reflection points, one and the other is located at the steep dip angle reflection layer, so that contains a lot of the high and steep reflection interface information that primary cannot reach. Prismatic wave field information can be separated by applying Born approximation to traditional reverse time migration profile, and then the prismatic wave is used to update velocity to improve the inversion efficiency for the salt dame flanks and some other high and steep structure. Under the guidance of this idea, a prismatic waveform inversion method is proposed （abbreviated as PWI）. PWI has a significant drawback that an iteration time of PWI is more than twice as that of FWI, meanwhile, the full wave field information cannot all be used, for this problem, we propose a joint inversion method to combine prismatic waveform inversion with full waveform inversion. In this method, FWI and PWI are applied alternately to invert the velocity. Model tests suggest that the joint inversion method is less dependence on the high and steep structure information in the initial model and improve high inversion efficiency and accuracy for the model with steep dip angle structure.

Multisource least-squares reverse-time migration with structure-oriented filtering

The technology of simultaneous-source acquisition of seismic data excited by several sources can significantly improve the data collection efficiency. However, direct imaging of simultaneous-source data or blended data may introduce crosstalk noise and affect the imaging quality. To address this problem, we introduce a structure-oriented filtering operator as preconditioner into the multisource least-squares reverse-time migration （LSRTM）. The structure-oriented filtering operator is a nonstationary filter along structural trends that suppresses crosstalk noise while maintaining structural information. The proposed method uses the conjugate-gradient method to minimize the mismatch between predicted and observed data, while effectively attenuating the interference noise caused by exciting several sources simultaneously. Numerical experiments using synthetic data suggest that the proposed method can suppress the crosstalk noise and produce highly accurate images.

Least squares reverse-time migration in the pseudodepth domain and reservoir exploration

Least squares reverse-time migration （LSRTM） is an inversion method that removes artificial images and preserves the amplitude of reflectivity sections. LSRTM has been used in reservoir exploration and processing of 4D seismic data. LSRTM is, however, a computationally costly and memory-intensive method. In this study, LSRTM in the pseudodepth domain was combined with the conjugate gradient method to reduce the computational cost while maintaining precision. The velocity field in the depth domain was transformed to the velocity field in the pseudodepth domain; thus, the total number of vertical sampling points was reduced and oversampling was avoided. Synthetic and field data were used to validate the proposed method. LSRTM in the pseudodepth domain in conjunction with the conjugate gradient method shows potential in treating field data.

基于分段采样和MCA的地震数据重建

数据重建是地震资料处理中一项重要的前期工作。压缩感知(compress sensing,CS)已经在数据重建领域取得了很好的应用。CS的关键是采样的随机性,随机采样将常规欠采样引起的互相干假频转化为较低能量的不相干噪声。一方面,传统的随机采样方法缺乏对采样点的约束,导致产生过多的噪声干扰,分段随机采样可有效地控制采样点之间的距离。另一方面,单一的数学变换会导致信号的不完全稀疏表达,影响数据重建效果,形态分量分析(morphological component analysis,MCA)将信号分解成几个具有显著特征的成分以逼近数据复杂的内部结构。本文在MCA框架下找到了一个新的字典组合(Shearlet+DCT),并使用块坐标松弛(block coordinate relaxation,BCR)算法得到最优解,从而获得理想重构结果。对实际资料的实验表明,该方法在重建分段随机采样数据时具有较好效果。

Separating and imaging diffractions in dip domain on the basis of slope analysis

Fracture-cave reservoirs in carbonate rocks are characterized by a large difference in fracture and cavity size,and a sharp variation in lithology and velocity,thereby resulting in complex diffraction responses.Some small-scale fractures and caves cause weak diffraction energy and would be obscured by the continuous reflection layer in the imaging section,thereby making them difficult to identify.This paper develops a diffraction wave imaging method in the dip domain,which can improve the resolution of small-scale diffractors in the imaging section.Common imaging gathers(CIGs)in the dip domain are extracted by Gaussian beam migration.In accordance with the geometric differences of the diffraction being quasilinear and the reflection being quasiparabolic in the dip-domain CIGs,we use slope analysis technique to filter waves and use Hanning window function to improve the diffraction wave separation level.The diffraction dip-domain CIGs are stacked horizontally to obtain diffraction imaging results.Wavefield separation analysis and numerical modeling results show that the slope analysis method,together with Hanning window filtering,can better suppress noise to obtain the diffraction dip-domain CIGs,thereby improving the clarity of the diffractors in the diffraction imaging section.