地震资料波阻抗多尺度融合反演

本文依据最佳约束反演策略,应用波动方程多尺度反演方法反演中频段波阻抗.利用神经网络技术实现对中频段波阻抗的标定及高、中、低频波阻抗的融合,避免了因高、中、低频波阻抗频段重叠及中频段波阻抗精度低所造成的反演结果的误差.这种方法具有对初始模型依赖性低、收敛速度快、反演结果稳定、抗噪能力强等特点.     

井中相控声源激发的声场

用不同的声源激发,可以得到不同的声波测井波形.根据唯一性定理和叠加定理,由多个位于不同位置且发射时间有一定差别的声源构成的相控声源激发的声场是叠加声场.本文先用一些实验结果肯定了相控声源激发声场的指向性随相控参数改变,而后用数值模拟的方法计算了井中相控声源激发的声场.发现井内相控声源在地层中激发的声场能够在一个确定的方向形成声束.改变相控参数,该声束的方向和能量均发生改变.     

Convolutional neural networks for automated microseismic detection in downhole distributed acoustic sensing data and comparison to a surface geophone array

Distributed acoustic sensing is a growing technology that enables affordable downhole recording of strain wavefields from microseismic events with spatial sampling down to ∼1 m. Exploiting this high spatial information density motivates different detection approaches than typically used for downhole geophones. A new machine learning method using convolutional neural networks is described that operates on the full strain wavefield. The method is tested using data recorded in a horizontal observation well during hydraulic fracturing in the Eagle Ford Shale, Texas, and the results are compared to a surface geophone array that simultaneously recorded microseismic activity. The neural network was trained using synthetic microseismic events injected into real ambient noise, and it was applied to detect events in the remaining data. There were 535 detections found and no false positives. In general, the signal-to-noise ratio of events recorded by distributed acoustic sensing was lower than the surface array and 368 of 933 surface array events were found. Despite this, 167 new events were found in distributed acoustic sensing data that had no detected counterpart in the surface array. These differences can be attributed to the different detection threshold that depends on both magnitude and distance to the optical fibre. As distributed acoustic sensing data quality continues to improve, neural networks offer many advantages for automated, real-time microseismic event detection, including low computational cost, minimal data pre-processing, low false trigger rates and continuous performance improvement as more training data are acquired.     

稠油蒸汽热采区声波资料异常现象的物理解释及应用

针对稠油蒸汽热采区常见的声波资料异常现象, 根据双相多孔介质声波传播理论及相关实验结果,对于这一特殊的声波测井响应特征进行了解释,认为注入蒸汽的影响导致了纵波速度的低异常及幅度的强衰减, 而使声波测井资料显现出异常高时差值或出现“跳变”现象.据此总结了利用声波资料评价蒸汽波及范围与蒸汽前缘的解释方法,并进行了多井评价实验, 取得了满意结果.同时,也为利用孔隙介质弹性波动理论评价地下蒸汽分布范围的适用性提供了新的现场实际例证.     

基于孪生网络的人工震源分布式光纤传感数据噪声压制

受耦合效应和其他诸多因素的影响,野外实际采集的分布式光纤声波传感(Distributed Fiber-optic Acoustic Sensing,DAS)数据的信噪比通常较低.因此,在后续处理之前,需要首先对DAS数据进行去噪处理.传统的基于人工智能监督学习的去噪方法能够对DAS数据中的噪声进行压制,但它需要大量含噪声和无噪声数据进行成组标记,人工标记工作量巨大.为此,本文提出了基于自监督学习孪生网络的DAS地震数据去噪方法.该方法基于自监督学习中的孪生网络结构,采用U-Net网络建立深度学习框架.所提框架通过对输入的含噪声数据进行数据自我特征学习,迭代获取去噪目标函数的最优解,从而实现自监督高精度深度学习去噪网络构建.合成数据和实际资料处理结果表明,本文方法可以有效抑制人工震源DAS采集数据中的随机噪声,显著提高去噪结果的信噪比和同相轴的连续性.此外,本文方法能够避免常规监督学习方法需要进行数据标记的人工工作量,有效提高实际地震数据去噪处理效率.

     

相控声源与声束的形成

用多个声源,按照一定的规律排列,分别用不同的时间激发,使每个声源激发的声波在介质中传播时有一定的相位差,这种产生声波的方法叫相控方法,这多个声源统称为相控声源．用相控声源的主要目的之一是产生一个可以控制其方向的声束．相对于点声源激发的球面波来讲,声束的能量比较集中,在介质中传播的比较远,对小的障碍物散射比较强．这样可以使声波传播的比较远,对那些声衰减比较大的介质进行一些精度比较高的探测．本文讨论相控声源在固体中激发的声束．     

岩石声波差异衰减特征及工程应用前景探讨

声波在岩石材料中传播时会发生差异衰减现象.由于岩石强度、完整性不同，造成其频率响应不同，声波通过不同强度的岩石时，对不同频率的声波信号滤除状况也就有所不同.通过力学强度高的岩石时，声波基本能够保持其原有频率成分，相反，当通过低强度岩石时，高频分量会迅速衰减而缺失，主要保留低频分量.通过实例研究，分析了声谱衰减特征与岩样矿物组成、密度及结构完整性的关系，验证了声谱衰减特征与岩体强度具有很好相关性的结论.通过分析研究声波信号在不同岩体中传播的衰减变化，指出声波衰减在一定程度上能够反映出岩体的风化程度、破碎状态、强度及各向异性等特征.可以发展成为岩体工程地质勘测、试验和施工中的常规实验方法.     

Effects of boundary conditions on vibrating mode of acoustic logging dipole transducer

Acoustic transducer is an important part of acoustic well logging tool. In this paper,ANSYS software package is used to design acoustic dipole transducer and simulate vibrating mode of the dipole transducer in different mechanical boundary conditions. The results show that boundary conditions influence the number of vibrating mode in the same frequency band and the frequency value of the same vibrating mode. Several acoustic dipole transducers are designed according to the results of numerical simulation and laboratory measurements. The basic frequency of vibrating mode of experi-ment has good agreement with that of simulation. The numerical simulation plays a good guidance role in designing,producing and correctly installing the acoustic dipole transducer.     

淮南深地实验室分布式光纤地震立体台阵观测数据分析

在淮南深地实验室布设了水泥固结的传感光缆,结合竖井中已有通信光缆,利用分布式光纤地震传感技术(DAS)构建了高密度的三分量立体台阵,开展了为期一年的连续观测.通过分析地下870 m的背景噪声记录,发现其日间变化幅度较小,这表明深地实验室受气压、温度和人类活动等的影响较小.然而,在低频段观测到明显增强的噪声,这给低频信号研究带来了一定困难.在连续记录中,识别出了多个地方震和区域震信号,尤其是获得了高质量的玛多地震P波信号.与共址地震仪数据的一致性表明DAS波形记录的可靠性.通过三分量DAS记录识别了Rayleigh面波信号,并利用多重滤波技术测量得到其群速度频散曲线;利用DAS应变率记录与共址宽频带地震仪的速度记录比值获得了相速度信息.两种方法测得的面波频散数据可用于研究速度结构.这些初步结果展现了深地实验室提供的超静环境以及三分量立体DAS台阵观测的优势,为后续进一步研究提供参考.

     

基于超级混合虚折射干涉法的阵列声波处理方法及其在套管井中的应用

在声学测井勘探时,复杂多变的测井条件（如胶结不好的套管井和随钻测井等）下的强直达干扰信号会导致地层信号的信噪比降低,使得地层有用信号的提取十分困难.本文在超级虚折射法的基础上,利用声源与接收器的互易原理,对原始波场信号进行互相关和褶积重建,并对所有可能的位形产生的信号进行叠加,将该叠加波场与超级虚折射波场进行叠加,重构出超级混合虚折射波场,使不同接收器上的折射波信噪比在超级虚折射的基础上进一步得到提高,显著提高了有用信号的信噪比,同时解决了超级虚折射近场能量不足的问题.套管井测井的理论模拟及实际处理表明,该方法可以很好地压制套管波信号、提高地层信号的信噪比.

     

Numerical analysis of one-dimensional nonlinear acoustic wave

Numerical investigations on one-dimensional nonlinear acoustic wave with third and fourth order nonlinearities are presented using high-order finite-difference (HFD) operators with a simple flux-limiter (SFL) algorithm. As shown by our numerical tests, the HFDSFL method is able to produce more stable, accurate and conservative solutions to the nonlinear acoustic waves than those computed by finite-difference combined with the flux-corrected-transport algorithm. Unlike the linear acoustic waves, the nonlinear acoustic waves have variable phase velocity and waveform both in time-space (t-x) domain and frequency-wavenumber (f-k) domain; of our special interest is the behaviour during the propagation of nonlinear acoustic waves: the waveforms are strongly linked to the type of medium nonlinearities, generation of harmonics, frequency and wavenumber peak shifts. In seismic sense, these characteristics of nonlinear wave will introduce new issues during such seismic processing as Normal Moveout and f-k filter. Moreover, as shown by our numerical experiment for a four-layer model, the nonlinearities of media will introduce extra velocity errors in seismic velocity inversion.     

Tutorial: unified 1D inversion of the acoustic reflection response

Acoustic inversion in one-dimension gives impedance as a function of travel time. Inverting the reflection response is a linear problem. Recursive methods, from top to bottom or vice versa, are known and use a fundamental wave field that is computed from the reflection response. An integral over the solution to the Marchenko equation, on the other hand, retrieves the impedance at any vertical travel time instant. It is a non-recursive method, but requires the zero-frequency value of the reflection response. These methods use the same fundamental wave field in different ways. Combining the two methods leads to a non-recursive scheme that works with finite-frequency bandwidth. This can be used for target-oriented inversion. When a reflection response is available along a line over a horizontally layered medium, the thickness and wave velocity of any layer can be obtained together with the velocity of an adjacent layer and the density ratio of the two layers. Statistical analysis over 1000 noise realizations shows that the forward recursive method and the Marchenko-type method perform well on computed noisy data.     

贴井壁声波测井仪的有限差分模拟研究

贴井壁声波测井仪在石油勘探开发中具有广泛的应用.它能够避开泥浆的影响而直接检测井壁附近的地层性质.但目前对此进行的数值模拟研究还仅局限于比较简单的模型.有限差分法可以模拟比较复杂的井眼模型,然而贴井壁声源的频率较高（80kHz左右）,使有限差分法计算量过大.本文应用局部加密交错网格有限差分方法解决了这类数值模拟中计算精度和计算量之间的矛盾.用这种算法模拟了井中有仪器时贴井壁声源激发的声场,并将其与无仪器时的声场作了比较.对模拟结果的验证和分析显示,该有限差分方法能够正确模拟贴井壁声源激发的声场.通过考察井中仪器本体对贴井壁声源激发声场的影响发现,测井仪器本体能够对直达波进行衰减而对环绕井壁传播的面波影响不大.     

Seismic data analysis using local time‐frequency decomposition

Many natural phenomena, including geologic events and geophysical data, are fundamentally nonstationary ‐ exhibiting statistical variation that changes in space and time. Time‐frequency characterization is useful for analysing such data, seismic traces in particular. We present a novel time‐frequency decomposition, which aims at depicting the nonstationary character of seismic data. The proposed decomposition uses a Fourier basis to match the target signal using regularized least‐squares inversion. The decomposition is invertible, which makes it suitable for analysing nonstationary data. The proposed method can provide more flexible time‐frequency representation than the classical S transform. Results of applying the method to both synthetic and field data examples demonstrate that the local time‐frequency decomposition can characterize nonstationary variation of seismic data and be used in practical applications, such as seismic ground‐roll noise attenuation and multicomponent data registration.     

Axisymmetric wave propagation in multilayered poroelastic grounds due to a transient acoustic point source

This paper deals with the study of axisymmetric wave propagation in various acoustic/porous stratified media coupling configurations. It presents the theoretical developments of a semi-analytical method, its validation for a limit test-case half-space ground, and an extension to a realistic multilayered seabed, when spherical waves are emitted from a transient point source in water.     

Time domain scattering of acoustic plane waves by vertical faults

Acoustic plane wave scattering at a vertical fault structure represents the simplest two-dimensional model of geophysical exploration that can be investigated by analytical techniques. The exact and complete solution, in the time domain, for the scattering of the pressure field of an acoustic plane wave normally incident on a vertical fault structure is determined adapting previous results given for the frequency domain. The wave form of the pressure field of the incident plane wave is expressed by a causal time function that decays exponentially with time at every point above the fault (z<0). The zero-order term of the scattered pressure field has been computed above the fault. This zero-order term consists of an inverse Fourier transform which reduces to a closed expression forx=0, and contains an integral of a Hankel function forx#0. The high frequency part of the inverse Fourier transform forx#0 is computed employing asymptotic expressions for the Hankel function. The integral of the asymptotic expression of the Hankel function reduces to: (i) a Fresnel integral which contains a plane wave term for |x||z|; and (ii) a stationary point plane wave term plus an upper limit term for |x|=O(|z|). For the latter case the plane wave term cancels, leaving a cylindrical wave emanated from the edge of the fault. The wave front is well defined in shape, in phase and in amplitude. The amplitude of the scattered field is discontinuous atx=0, presents a jump and is well defined for |x| small and is rather smooth for |x| large.     

A case study:cross-well acoustic tomography in Fuyu oil-field

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声频谱测井方法研究进展

主要介绍声频谱测井方法的理论基础和解释应用．声频谱测井作为一种新的声波测井方法，它是利用多个频率实现对井壁附近不同径向深度处地层的探测．首先介绍了声频谱测井方法的理论基础，在此基础上在声频谱声系中设计了10K、20K、40K三种不同主频的声波探头组合，结合声频谱参数与岩石储集参数的关系，设计了声频谱测井的基本解释方案，探讨了声频谱测井解释方法在确定孔隙度、渗透率、识别油气、裂缝，以及岩石力学参数计算及过套管测井等方面的应用．     

奇异性分析方法在地震资料解释及反演研究中的应用

本文引入启动函数拓展传统的地层转换模型,在该模型中利用奇异性信息量化地层速度的突变特征,并基于传统的褶积模型研究奇异性信息在波阻抗到合成地震记录之间的传递性.研究结果表明,地震记录中较好地保留了地层介质的奇异性特征,因而从地震记录中提取的奇异性信息除了可以帮助进行地震解释外,还可以作为介质波阻抗反演的有力的支持工具.     

Seismic resonances of spherical acoustic cavities

We study the interaction of a seismic wavefield with a spherical acoustic gas‐ or fluid‐filled cavity. The intention of this study is to clarify whether seismic resonances can be expected, a characteristic feature that may help in detecting cavities in the subsurface. This is important for many applications, in particular the detection of underground nuclear explosions, which are to be prohibited by the Comprehensive Test Ban Treaty. To calculate the full seismic wavefield from an incident plane wave that interacts with the cavity, we considered an analytic formulation of the problem. The wavefield interaction consists of elastic scattering and the wavefield interaction between the acoustic and elastic media. Acoustic resonant modes caused by internal reflections in the acoustic cavity show up as spectral peaks in the frequency domain. The resonant peaks coincide with the eigenfrequencies of the un‐damped system described by the particular acoustic medium bounded in a sphere with stiff walls. The filling of the cavity could thus be determined by the observation of spectral peaks from acoustic resonances. By energy transmission from the internal oscillations back into the elastic domain, the oscillations experience damping, resulting in a frequency shift and a limitation of the resonance amplitudes. In case of a gas‐filled cavity, the impedance contrast is still high, which means low damping of the internal oscillations resulting in very narrow resonances of high amplitude. In synthetic seismograms calculated in the surrounding elastic domain, the acoustic resonances of gas‐filled cavities show up as persisting oscillations. However, due to the weak acoustic–elastic coupling in this case, the amplitudes of the oscillations are very low. Due to a lower impedance contrast, a fluid‐filled cavity has a stronger acoustic–elastic coupling, which results in wide spectral peaks of lower amplitudes. In the synthetic seismograms derived in the surrounding medium of fluid‐filled cavities, acoustic resonances show up as strong but fast decaying reverberations.