抛物线Radon变换方法在压制地震多次波中的应用

多次波的存在会降低地震资料的信噪比,影响地震资料处理效果和后续的地质解释精度,压制多次波干扰是地震资料处理中的一个重要环节。利用有限差分方法正演模拟几个典型地质模型的地震波场,之后进行动校正,再通过抛物线Radon变换方法把t-x域一次反射波和多次波变换到τ-q域,由于存在速度的差异,Radon域记录中的一次反射波和多次波的能量互相分开,在Radon域对多次波的能量切除,保留反射波的有效信息,达到压制多次波的效果,提高资料的信噪比。通过对实际地震数据进行抛物线Radon变换结果也进一步验证了该方法在压制多次波中的应用效果。      

基于波场传播方向的波动方程偏移有效去噪方法(英文)

本文研究分析了双程波波动方程偏移成像中广泛存在的三种主要噪声,特别是针对过去研究中没能很好解决的存在于高速盐丘悬垂边界附近的射线状噪声,提出了基于优化成像条件的有效去噪方法。射线状噪声主要来自于震源一侧波场的下行透射波分量和接收阵列一侧波场的上行散射波互相关成像。这一部分能量具有较强的互相关性,但并不携带真实的反射面信息。它广泛存在叠前偏移成像中,与信号在强度上同量级。多数情况下偏移成像中的相关噪声由方向性传播的波场能量产生。利用波场梯度得到的波场传播角度,可以分离出噪声对应的波场能量,并在成像条件中减去。采用这一方法可以有效地去除多种噪声,包括直达波噪声、散射波噪声和射线状噪声。该去噪方法不依赖波场外推算子,在需要时可以方便地运用到几乎所有的波动方程偏移中去。并且该去噪方法针对噪声的物理根源,对信号的损害很小。对去噪后的偏移成像结果额外地进行波数域滤波处理,可以进一步提高叠加图像的质量。这一去噪方法在超广角单程波偏移成像中取得良好效果,我们同时期待其在其他双程波波动方程偏移特别是逆时偏移(RTM)中的成功运用。     

塔河地区地震道距大小对去噪效果的分析

目前塔河地区开发地震采用了30m道距,中-近炮检距面波干扰较严重.本文对实际单炮的波场特征进行分析后,分别建立了该区5m、10m、20m和30m道距的单炮模型,然后对不同道距单炮模型进行了FK谱分析,发现采用30m道距时,由于干扰波的空间假频与反射波混叠在一起,FK滤波去噪效果有限;当采用20m道距时,虽然干扰波仍存在空间假频现象,但已能与反射波信号明显区分开,滤波去噪效果明显改善;当道距小于10m时,干扰波不存在空间假频现象,去噪效果最理想.结合实际单炮资料的FK谱及去噪效果分析,说明塔河地区通过减小检波器道距仍有改善地震资料品质的潜力.     

基于高斯束与高斯波包的Gabor框架散射波模拟方法

在给出真实模型和相应光滑背景模型的情况下,如何计算扰动模型(散射体)产生的散射波场是一个有实际意义的正演问题.在Gabor变换域描述散射体,且入射波场为短时宽带信号时,散射波场可以在频率域用高斯束或时间域用高斯波包描述.相对于波动方程方法,高斯束和高斯波包的计算效率更高;背景模型光滑时,高斯束和高斯波包方法的精度也接近波动方程方法.文中导出了声波假设下应用高斯束和高斯波包计算散射波的方法.测试分析了高斯波包的计算精度.给出了一般散射体的散射波模拟策略.同时针对一个理论模型完成了本文方法计算散射波的实验,实验结果表明高斯波包散射波计算方法是有效可行的.     

基于迭代去噪的多源地震混合采集数据分离

多源地震混合采集采用随机线性编码方式同时激发多个震源,检波器连续接收地震信号,获得波场混叠的炮记录.该采集技术能够显著提升采集效率和成像质量,其实现关键在于炮分离,即将相互混叠的多源波场数据彼此分离,获得传统采集的单炮记录.最小平方算法只能得到伪分离记录,不能去除混叠噪声.在高混合度的混叠数据中,混叠噪声的能量往往数倍于有效信号,炮分离难度倍增.但在伪分离记录中,该噪声在除共炮点道集以外的其它时域均为随机分布.本文研究提出了一种多时域组合迭代去噪的炮分离技术:通过运用多级中值滤波与Curvelet阈值迭代去噪算法,在不同时域根据混叠噪声特性采用相应的去噪手段,并设计迭代算法优化炮分离结果.实际资料处理结果证明:将本方法应用于高混合度的混叠数据,无论是分离质量还是计算效率,都有明显提升.     

地震散射波模拟成像方法在铜陵某矿区的应用

针对深部隐伏的金属矿床,以铜陵某矿区为例,应用散射波正演模拟技术,对金属矿地震数据野外采集中涉及的偏移距、覆盖次数、道间距等参数进行了不同炮记录的模拟对比,辅助指导非均匀地质体金属矿地震勘探野外数据采集的观测系统设计;针对该地区实际采集的地震数据,应用基于等效偏移距的共散射点成像方法,对金属矿地震数据进行了处理,通过与常规反射波法处理结果对比,散射成像效果较好,说明散射波技术在金属矿地震勘探中应用有一定的可行性和适用性.     

地震资料去噪方法技术综合评述

地震资料去噪，无论是叠前还是叠后，都是处理中非常重要的内容.随着勘探技术的进步，地球物理界积累和开发的去噪软件已越来越多.对各种去噪方法进行分门别类，阐述其基本原理、物理意义、适用条件、发展前景，既有理论价值又有实际指导意义.本文从噪声的特征出发，首先对地震资料噪声进行了分类；然后综合评述了目前实际生产中常用的几种去噪方法，包括频率域滤波、频率波数域滤波、频率空间域滤波、Radon变换、聚束滤波、基于小波分解和重建的去噪方法等；最后还简述了去噪技术的应用及发展情况.     

地震环境噪声成像中的地形影响校正

以传统地震环境噪声面波成像方法研究地壳速度结构时,在一些极端的地形条件下,结果与真实结构会存在较大偏差.我们以地震波场三维正演模拟为基础,提出了一种地形校正方法.我们保留了传统噪声面波成像简单的两步反演法,在面波层析成像和一维速度结构反演的基础上,通过地震波场三维模拟近似估计地形和散射波场的影响,并据此校正瑞利波频散曲线,最终反演得到校正地形影响的S波速度结构.理论测试与在实际观测数据上的应用都证明了校正方法的有效性,同时也显示了地形校正的必要性.     

地震资料去噪方法、技术综合评述

地震资料去噪，无论是叠前还是叠后，都是处理中非常重要的内容.随着勘探技术的进步，地球物理界积累和开发的去噪软件已越来越多.对各种去噪方法进行分门别类，阐述其基本原理、物理意义、适用条件、发展前景，既有理论价值又有实际指导意义.本文从噪声的特征出发，首先对地震资料噪声进行了分类；然后综合评述了目前实际生产中常用的几种去噪方法，包括频率域滤波、频率波数域滤波、频率空间域滤波、Radon变换、聚束滤波、基于小波分解和重建的去噪方法等；最后还简述了去噪技术的应用及发展情况.     

深水陡坡带地质模型波场正演模拟

近年来,全球海上油气勘探热点逐渐由浅水走向深水,而地震资料采集和处理是制约深水油气勘探的重要因素.以往资料表明,受采集观测系统的影响,深水盆地陡坡带的地震成像效果往往较差,对边界断层和下伏地层产状的认识造成严重影响.本文根据巴布亚盆地某深水工区实际数据,构建典型深水陡坡带地质模型,通过地震波场正演模拟方法对陡坡带地震采集的观测方式进行优化.结合基于波动方程的单炮照明和多炮照明组合等地震照明方法对目标层进行照明分析,探索影响陡坡带深大断层和上、下盘地层成像效果的原因.最后通过局部炮集数据进行叠前深度偏移处理,进一步验证波场正演模拟和照明分析指导观测系统优化设计的有效性.波场正演模拟和照明分析结果表明,对于拖缆式地震采集,采用左侧激发、长排列接收方式对深水陡坡带成像具有相对较好的效果.     

基于波动方程预测和双曲Radon变换联合压制表面多次波

基于波动方程预测的表面多次波压制方法可处理复杂地下介质的地震资料,但计算成本较高.基于滤波的多次波压制方法计算效率较高,但其成功应用仅局限于一次波和多次波有明显时差差别的地震数据,对来自速度逆转等复杂介质数据则较难获得满意的压制效果.本文将波动方程预测的反馈迭代法和滤波法有效结合,采用GPU(图形处理器)和CPU协同并行加速计算粗略预测表面多次波,随后在双曲Radon域比较分析原始数据和预测的多次波,设计合理有效的Butterworth型自适应滤波器,滤出原始数据Radon域中的多次波能量,进行Radon反变换后,在时空域将多次波从原始数据中减去,得多次波压制结果.文中对理论模拟的单炮数据、复杂的SMAART模型以及实际地震数据进行了计算,结果表明,结合基于波动方程预测和双曲Radon变换的方法有效突破了两种方法各自的局限性,可高效高精度地压制复杂地下介质的表面多次波.     

Fast hyperbolic deconvolutive Radon transform using generalized Fourier slice theorem

The hyperbolic Radon transform has a long history of applications in seismic data processing because of its ability to focus/sparsify the data in the transform domain. Recently, deconvolutive Radon transform has also been proposed with an improved time resolution which provides improved processing results. The basis functions of the (deconvolutive) Radon transform, however, are time-variant, making the classical Fourier based algorithms ineffective to carry out the required computations. A direct implementation of the associated summations in the time–space domain is also computationally expensive, thus limiting the application of the transform on large data sets. In this paper, we present a new method for fast computation of the hyperbolic (deconvolutive) Radon transform. The method is based on the recently proposed generalized Fourier slice theorem which establishes an analytic expression between the Fourier transforms associated with the data and Radon plane. This allows very fast computations of the forward and inverse transforms simply using fast Fourier transform and interpolation procedures. These canonical transforms are used within an efficient iterative method for sparse solution of (deconvolutive) Radon transform. Numerical examples from synthetic and field seismic data confirm high performance of the proposed fast algorithm for filling in the large gaps in seismic data, separating primaries from multiple reflections, and performing high-quality stretch-free stacking.     

Time-domain hyperbolic Radon transform for separation of P-P and P-SV wavefields

A time-domain hyperbolic Radon transform based method for separating multicomponent seismic data into P-P and P-SV wavefields is presented. This wavefield separation method isolates P-P and P-SV wavefields in the Radon panel due to their differences in slowness, and an inverse transform of only part of the data leads to separated wavefields. A problem of hyperbolic Radon transform is that it works in the time domain entailing the inversion of large operators which is prohibitively time-consuming. By applying the conjugate gradient algorithm during the inversion of hyperbolic Radon transform, the computational cost can be kept reasonably low for practical application. Synthetic data examples prove that P-P and P-SV wavefield separation by hyperbolic Radon transform produces more accurate separated wavefields compared with separation by high-resolution parabolic Radon transform, and the feasibility of the proposed separation scheme is also verified by a real field data example.     

High-resolution frequency-domain Radon transform and variable-depth streamer data deghosting

Receiver ghost reflections adversely affect variable-depth streamer (VDS) data acquisition. In addition, the frequency notches caused by the interference between receiver ghosts and primary waves strongly affect seismic data processing and imaging. We developed a high-resolution Radon transform algorithm and used it to predict receiver ghosts from VDS data. The receiver ghost reflections are subtracted and removed from the raw data. We propose a forward Radon transform operator of VDS data in the frequency domain and, based on the ray paths of the receiver ghosts, we propose an inverse Radon transform operator. We apply the proposed methodology to model and field data with good results. We use matching and subtracting modules of commercially available seismic data processing software to remove the receiver ghosts. The frequency notches are compensated and the effective frequency bandwidth of the seismic data broadens.     

High‐resolution Radon transforms for improved dipole acoustic imaging

Imaging using dipole acoustic logging reflections has become a research topic of increasing interest in recent years. Extracting reflections from the whole waveform is both important and extremely difficult because the reflections are obscured by large‐amplitude direct waves. A method of wavefield separation based on high‐resolution Radon transforms has been applied to separate the reflected waves. First, an analysis of the common offset gathers shows that the linear Radon transform can be used to separate the direct and reflected wave fields. However, traditional linear Radon transforms cannot focus the wave event using the least squares method. An improved high‐resolution linear Radon transform is achieved using the principles of maximum entropy and Bayesian methods based on previous studies. The separation method is tested using synthetic data for hard and soft formations, a void model, and a fault model. The high‐resolution Radon transform method is used to process a field dataset and exhibits improved results compared with those of the standard method.     

煤层陷落柱散射波数值模拟与成像

煤层陷落柱是煤田勘探开发中常见的一种典型的非均匀地质体.由于来自陷落柱的反射信号少、反射能量弱,使得基于反射波原理的常规地震成像方法难以有效识别陷落柱.本文以散射波理论为基础,采用数值模拟方法,研究了陷落柱的散射波场特征,研究表明地面接收的波场中含有来自陷落柱陡倾角界面的散射波场.通过共散射点道集波场的模拟,可以清晰地识别散射波,获得地下散射点和非均匀地质体的信息,判断散射点的位置,从而勾画出不均匀地质体的形态.采用等效偏移距假设抽取共散射点道集,在此基础上进行叠前偏移,对陷落柱成像;模拟与实际数据成像结果对比表明此方法能够合理地提取散射点的散射波场信息,对陷落柱形态及内部结构准确成像,是一种有效的煤田陷落柱成像方法.     

Radon变换在非规则观测系统中波场分离的应用

Radon变换是数据处理中广泛应用的一种方法技术.本文介绍了Radon变换在规则及其非规则观测系统中波场分离中应用,讨论了Radon变换的公式、实现方法和有关计算参数的选择.通过理论模型的试算,阐明了Radon变换在缺失道、道距变化情况下依然可以高精度的分离波场,并对线性、抛物Radon变换进行了比较,对隧道超前预报反射波资料进行了处理,给出了隧道超前预报处理流程中提取反射波的算例.     

各向异性Radon变换及其在多次波压制中的应用

即使采用分辨率很高的双曲Radon变换,对速度各向异性发育介质及长偏移距情况下的地震数据,其Radon域内能量仍不收敛.为了克服此难题,我们在Radon变换的积分路径中考虑了非双曲走时的影响,通过引入非双曲时差公式中的各向异性非椭圆率η参数,可以准确描述出长偏移距条件下来自同一层位的时距曲线,并推导了由偏移距、慢度、非椭圆率三参数控制的积分曲线正反变换公式,我们称之为各向异性Radon变换.离散化求解时,各向异性Radon变换是时变的,频率域快速算法已不适用,本文采用了最优相似系数加权Gauss-Seidel迭代算法,保持其计算精度的同时也有较高的计算效率.将此方法应用在模型数据以及实际长偏移距海上地震数据的多次波压制处理中,收到了较好的处理效果.     

Three-parameter Radon transform in layered transversely isotropic media

Radon transform is a powerful tool with many applications in different stages of seismic data processing, because of its capability to focus seismic events in the transform domain. Three-parameter Radon transform can optimally focus and separate different seismic events, if its basis functions accurately match the events. In anisotropic media, the conventional hyperbolic or shifted hyperbolic basis functions lose their accuracy and cannot preserve data fidelity, especially at large offsets. To address this issue, we propose an accurate traveltime approximation for transversely isotropic media with vertical symmetry axis, and derive two versions of Radon basis functions, time-variant and time-invariant. A time-variant basis function can be used in time domain Radon transform algorithms while a time-invariant version can be used in, generally more efficient, frequency domain algorithms. Comparing the time-variant and time-invariant Radon transform by the proposed basis functions, the time-invariant version can better focus different seismic events; it is also more accurate, especially in presence of vertical heterogeneity. However, the proposed time-invariant basis functions are suitable for a specific type of layered anisotropic media, known as factorized media. We test the proposed methods and illustrate successful applications of them for trace interpolation and coherent noise attenuation.