基于f-x域时频非凸正则化低秩矩阵近似的共偏移距道集去噪方法

随机噪声压制是地震数据处理的关键环节,而时频稀疏低秩近似算法逐道处理地震数据过程中无法利用信号的道间相干性。为此,将时频稀疏低秩近似与f-x域去噪结合,提出一种f-x域时频非凸正则化低秩矩阵近似算法。该算法对f-x域中每一单频分量作时频分解后,再对时频系数矩阵作低秩矩阵近似计算,能够利用信号和噪声的时频谱差异实现非平稳信号去噪处理。与共炮点道集和共中心点道集相比,共偏移距道集具有平缓甚至接近水平的同相轴结构,基本满足f-x域去噪的线性同相轴假设前提,建议将所提算法应用于共偏移距道集去噪处理。通过数值模拟和实际地震数据试算,证明本文方法能够有效压制随机噪声,同时保持有效信号不被损害。     

偏移距域/角度域共成像点道集与偏移速度的关系

为了得到波动方程偏移距域共成像点道集(ODCIGs) 和角度域共成像点道集(ADCIGs) 与偏移速度的关系, 在匀速单层水平反射情况下, 对ODCIGs和ADCIGs随偏移速度的变化进行了定量的推导, 得到偏移速度偏小时ODCIGs与半偏移距成双曲关系, 反之成椭圆关系; 结合深度聚焦分析, 得到偏移速度偏大时, ADCIGs中视入射角大于真入射角, 反之, 小于真入射角; 在速度偏小时, ADCIGs上剩余时差(RMO) 与视入射角的正切值成椭圆关系, 反之成双曲关系.在地震有效入射角度范围内, ADCIGs对于偏大的偏移速度更加敏感.在偏移速度分析(MVA) 中, 从稍大的速度开始分析会对速度分析更加有利.      

基于IR—ADMM组合技术对地震随机噪声的压制

稀疏表示是一种现行有效的随机噪声压制方法,常采用交替方向乘子法逐道分解地震信号,但实际应用中交替方向乘子法计算效率高但精度不足,难以满足高保真地震数据处理的要求。通过结合迭代重加权和交替方向乘子法2种算法,提出了一种新的基于迭代重加权交替方向乘子法的联合稀疏表示方法,兼具收敛速度快和重建精度高的优点。共偏移距道集地震数据具有水平同相轴结构,满足共稀疏性条件,将联合稀疏表示算法应用于共偏移距道集就能够利用信号的空间相干性,提高去噪算法性能。理论和实际资料试算结果表明,所提算法具有较好的应用效果。     

基于等效偏移距的偏移成像方法

等效偏移距偏移(EOM)成像方法将克希霍夫时间偏移的双平方根方程转化为一个单平方根方程,使输入采样在没有发生时移的情况下映射到以等效偏移距为变量的共散射点道集上,使散射能量按照双曲线规律分布。然后通过克希霍夫动校正和适用在共散射点道集上的叠加来完成偏移成像。基于等效偏移距叠前地震偏移(EOM)的基本理论,对CSP道集的抽取过程进行模拟实现,并对模型进行速度分析,实现偏移成像。     

一种角度域叠前时间偏移方法

提出的角度域叠前时间偏移方法,能够在偏移成像过程中直接生成倾角域成像道集,在倾角成像道集上确定真地层倾角与倾角成像区,获得的最终叠加剖面在保证构造正确成像的同时避免了过大偏移孔径带来偏移噪声的弊端,提高了剖面的信噪比.应用本文方法在南堡凹陷马头营凸起地区取得了较好的应用效果,表明该方法对于信噪比较低、偏移噪声大的地区具有较大的工业应用价值.     

共聚焦点道集偏移速度建模

偏移速度建模可在多种道集实现.基于等时原理和差异时移分析,提出了共聚焦点道集偏移速度建模方法.偏移速度的更新是利用约束参数迭代反演实现,模型的参数化主要依据实际情况而定.为适应横向变速,选用了垂直速度梯度参数.模型试算表明:偏移速度相对误差在0.25%范围内,反射层深度误差小于10m.     

基于G-D波场分解的角度域共成像点道集提取及成像

通常的叠前深度偏移都是通过偏移距域共成像道集和炮域共成像道集来实现的,这里则通过对G-D波场局部平面波的分解,提出了局部角度域共成像点道集方法,从而改善了偏移成像速度及效果,为研究地下构造,岩性分析以及偏移速度分析提供新的途径。     

基于角度域共成像点道集的微分相似优化法偏移速度分析

微分相似优化(Differential Semblance Optimization,DSO)法是一种可以有效避免非线性最小二乘反演过程中不聚焦问题的速度反演方法.基于DSO原理的波动方程偏移速度分析将成像道集的聚焦或者拉平程度作为速度判定的准则,其目标泛函具有良好的凸性,可以有效避免局部极值问题,目标泛函的梯度较为光滑,并且对地震数据中低频成分的要求较低,对速度模型中背景速度的估计较为准确.一般情况下,DSO方法利用偏移距域共成像点道集建立目标泛函,文中利用角度域共成像点道集建立目标泛函对速度的准确性进行判定.模型试算结果表明,通过角道集可以更加直观地对速度的准确性进行判定,并且准确反映速度与深度的对应关系.     

波动方程角度域共成像道集

针对基于波场深度递推的波动方程叠前深度偏移成像方法难以准确地给出如Kirchhoff积分叠前深度偏移成像方法的偏移距域共成像道集的不足,在分析研究现有的各种波动方程偏移成像共成像道集方法的基础上,利用波场外推的单平方根算子和波场的窗口Fourier框架展开与重构方法,提出一种局部角度域共成像道集方法——成像点处反射角共成像道集方法.把这种角度域共成像道集方法应用于国际标准的Marmousi模型数据和一条实际二维地震数据都取得了理想的结果.提出的波动方程反射角度域共成像道集方法可为进一步的叠前偏移数据振幅随角度变化分析和偏移速度分析工作提供基础.     

叠前时间偏移成像技术及其应用

零炮检距剖面是地震反射成像过程中的重要成果.通过弯曲反射界面模型,分析了共中心点(CMP)道集与共反射点(CRP)道集的差别,认为当反射界面倾斜时,常规处理中的CMP叠加不能得到准确的零偏移距剖面,而沿CRP道集叠加的叠前时间偏移能得到准确的零偏移距剖面,另外,还介绍了叠前时间偏移的实现方法和步骤,包括预处理、偏移速度场的建立和偏移后CRP道集的处理等,并结合实际资料进行了效果分析.     

Random seismic noise attenuation data using the discrete and the continuous wavelet transforms

In this paper, we propose a technique of random noise attenuation from seismic data using discrete and continuous wavelet transforms. Firstly, the discrete wavelet transform (DWT) is applied to denoise seismic data using the threshold method. After, we calculate the continuous wavelet transform of the denoised seismic seismogram, the final denoised seismic seismogram is the continuous wavelet transform coefficients at the lower scale. Application to a synthetic seismogram shows the robustness of the proposed tool for random noise attenuation. Application to real vertical seismic profile recorded in Algeria clearly shows the efficiency of the proposed tool for random noise attenuation.     

Seismic random noise attenuation and signal-preserving by multiple directional time-frequency peak filtering

Time-frequency peak filtering (TFPF) is an effective method for seismic random noise attenuation. The linearity of the signal has a significant influence on the accuracy of the TFPF method. The higher the linearity of the signal to be filtered is, the better the denoising result is. With this in mind, and taking the lateral coherence of reflected events into account, we do TFPF along the reflected events to improve the degree of linearity and enhance the continuity of these events. The key factor to realize this idea is to find the traces of the reflected events. However, the traces of the events are too hard to obtain in the complicated field seismic data. In this paper, we propose a Multiple Directional TFPF (MD–TFPF), in which the filtering is performed in certain direction components of the seismic data. These components are obtained by a directional filter bank. In each direction component, we do TFPF along these decomposed reflected events (the local direction of the events) instead of the channel direction. The final result is achieved by adding up the filtering results of all decomposition directions of seismic data. In this way, filtering along the reflected events is implemented without accurately finding the directions. The effectiveness of the proposed method is tested on synthetic and field seismic data. The experimental results demonstrate that MD–TFPF can more effectively eliminate random noise and enhance the continuity of the reflected events with better preservation than the conventional TFPF, curvelet denoising method and F–X deconvolution method.     

随采地震噪声衰减研究

鉴于煤矿井下环境的封闭性及对安全生产的高要求特点,炸药震源在煤矿井下地震勘探施工中存在众多局限性,而以采煤机作为震源可以规避炸药震源的许多固有缺陷,具有可以在不影响回采工作面正常作业的情况下对工作面内部构造及应力开展实时探测的优势。但由于采煤机产生的能量远小于炸药震源,因此采集到信号的质量通常受到环境噪声影响,通过分析大量实际数据发现噪声中能量占比较多的为单频噪声和随机噪声,严重影响探测精度。为提高随采地震数据信噪比,提出了同时衰减单频噪声和随机噪声的方法,首先基于互相关技术在构建常规炮集记录的同时衰减单频噪声,然后通过小波变换衰减随机和残余单频噪声,通过模拟数据和实际数据证实,该方法可以在很大程度上提高信号的信噪比。     

Seismic random noise attenuation by time-frequency peak filtering based on joint time-frequency distribution

Time-Frequency Peak Filtering (TFPF) is an effective method to eliminate pervasive random noise when seismic signals are analyzed. In conventional TFPF, the pseudo Wigner–Ville distribution (PWVD) is used for estimating instantaneous frequency (IF), but is sensitive to noise interferences that mask the borderline between signal and noise and detract the energy concentration on the IF curve. This leads to the deviation of the peaks of the pseudo Wigner–Ville distribution from the instantaneous frequency, which is the cause of undesirable lateral oscillations as well as of amplitude attenuation of the highly varying seismic signal, and ultimately of the biased seismic signal. With the purpose to overcome greatly these drawbacks and increase the signal-to-noise ratio, we propose in this paper a TFPF refinement that is based upon the joint time-frequency distribution (JTFD). The joint time-frequency distribution is obtained by the combination of the PWVD and smooth PWVD (SPWVD). First we use SPWVD to generate a broad time-frequency area of the signal. Then this area is filtered with a step function to remove some divergent time-frequency points. Finally, the joint time-frequency distribution JTFD is obtained from PWVD weighted by this filtered distribution. The objective pursued with all these operations is to reduce the effects of the interferences and enhance the energy concentration around the IF of the signal in the time-frequency domain. Experiments with synthetic and real seismic data demonstrate that TFPF based on the joint time-frequency distribution can effectively suppress strong random noise and preserve events of interest.     

Whitney gathers in the solar atmosphere

The structures called Whitney gathers in the catastrophe theory are not unusual among the various types of chromospheric Hα filaments and coronal helmets. They result from a projection of smooth surfaces onto a plane of the sky. The apices of the helmets can be described as gathers of the surface B _r = 0 in the corona (where B _r is the magnetic field). Near the limb, Hα filaments are frequently observed as similar types of structures. A model of the B _r = 0 surface with sources located inside the Sun (∫ Bds = 0) is constructed here in this context. Gathers and folds of this surface are shown to be possible in relatively simple fields. Our model computations are supported by the available observational data.     

基于方位—反射角度道集的高斯束层析速度建模方法及实现

层析反演是速度建模中最重要的方法之一,结合偏移成像在成像域进行波动方程线性化走时层析速度建模是当前比较实用有效且精度较高的技术组合.文中首先给出了高斯束偏移提取方位—反射角度道集的方法,之后从高斯束偏移角度道集出发,在波动方程的一阶Born近似和Rytov近似下,推导了成像域波动方程线性化走时层析方程及其显式表达的层析核函数,并利用高斯束传播算子计算该核函数.基于高斯束传播算子的偏移成像与层析成像相结合进行深度域速度建模迭代及偏移成像,体现了速度建模与成像一体化的思想.数值计算及实际数据应用证明了基于高斯束传播算子的层析成像与偏移成像方法的有效性.     

海底电缆陆检噪音衰减方法及其在乌石地区的应用

海底电缆采集方式不同于传统的海洋托缆地震资料采集,检波器放在海底进行地震信号接收,一般是多分量检波器。检波器由于和海底的耦合性不好,一般信噪比较低,接收到的有效信号很弱,而地滚波和转换横波等噪音能量很强;其中转换横波对信号的干扰较大,也较难衰减。通过对乌石工区海底电缆资料进行统计分析,发现数据在共检波点域转换横波噪音相干性较好,于是在共检波点域使用τ-p变换方法将转换横波从数据中分离出来,分离转换横波后的陆检分量数据信噪比获得了极大的提高。     

裂隙-管道介质泉水流量衰减过程中的有色噪声辨识与消减

文章在实验室模拟岩溶地下水系统泉流量衰减过程的基础上,针对建模过程中存在的有色噪声问题,提出利用Cochrane-Orcutt迭代法与自相关相容协方差识别和消减建模过程中有色噪声,确定裂隙-管道介质岩溶泉衰减流量具有三阶自相关特征,并成功建立裂隙-管道介质中岩溶泉流量的向量自回归(VAR)方程,提高了模型精度。