为了模拟碳酸盐岩储层中不同横向尺度溶洞的地震响应特征，设计了具有不同横向尺度但高度和充填物相同的溶洞地质模型，分别采用数值模拟技术和物理模拟技术进行了正演模拟，分析研究了由溶洞宽度变化引起的地震响应变化的特征。研究结果表明，溶洞宽度的变化会引起溶洞反射特征“串珠”中“珠”的数目发生改变，溶洞顶、底位置与溶洞绕射波的相位有对应关系，在偏移剖面中“串珠”尺度与实际溶洞尺度之间存在较大差异。对比同一模型的数值模拟和物理模拟正演结果发现，所得的不同横向尺度溶洞的地震响应特征总的趋势是一致的，但在细节上有所差异，这表明两种正演方法具有互补性，为研究溶洞的“串珠状”地震波反射特征提供了更好的手段。

<FONT face=Verdana>In order to simulate the seismic responses of caverns with different lateral scale in carbonate reservoirs,we designed cavern geologic models with same height and fillings but different lateral scale,adopted numerical simulation and physical modeling for forward simulation,and analyzed the variation features of seismic responses via the changes of cave width.The results indicate that the changes of cave width will cause the number of“pill”varying in the“string”reflection characteristic,the top and bottom of cave has corresponding relationship with cave diffracted wave.On migration section,the scale of“string”has large contrast with actual cave width.The comparison on forward simulation results of the same model by numerical simulation and physical modeling methods shows that the overall trend of seismic response of different lateralscale caverns is uniform,but difference exists in detail,which indicates that the two methods are complementary and provides better means for study the“string”reflection characteristic of caverns.</FONT>

针对塔河油田碳酸盐岩的地质特点,设计和制作了裂缝、孔洞和洞-缝3种典型物理模型,并采用超声波测试方法进行了模型正演模拟,以分析当地下存在溶洞、裂缝时的地震波传播的能量和反射结构的变化。给出了模型的制作原理和制作材料,对模拟结果进行了分析。结果表明,地层中存在较大的溶洞时,叠加剖面上溶洞的上方会出现弱反射,但溶洞内部往往形成强绕射波,经偏移归位后成为强短反射,并连续出现;地层中存在裂缝时,在叠加剖面上表现为杂乱反射地震相;地层中存在不规则的缝-洞组合时,叠加剖面上以杂乱反射相为主。

反射波地震采集设计基于层状介质假设,信号分析过程压制了绕射波、散射波等弱信号,反射波地震成像处理后频带狭窄,这些均限制了原始宽频数据的充分利用。从均衡利用反射波、绕射波、散射波信息入手,重新定义全波场地震勘探的内涵,明确其特点和适应条件,提出一套适用于全波场地震勘探的关键技术。在地震采集阶段,需要采用多套观测系统或一次性部署分期采集设计,即要在常规观测系统中镶嵌小面元、小偏移距、小道间距数据,利用共中心点道集离散化、小偏移距高覆盖等方法,增强原始地震数据中绕射波、散射波等弱信号的能量。在地震处理过程中,原始地震数据中的信号与噪音需要重新定义,通过多观测系统数据融合处理,实现地震数据有效信号的增强;通过不同面元、不同排列方式数据的差异化应用,使不同态式地震波能被有效分解和分别成像。在地震解释过程中,充分利用全波场地震资料,依靠多尺度、多维度井-震标定,实现多态式、多域地震属性解释,揭示复杂岩性体的内幕结构,提高非层状储集层横向分辨能力。

尽管高精度三维地震采集取得了巨大的成功, 但面对更复杂地质体时, 探索能同时进行连续界面反射及随机介质散射的全波场地震采集的方法依然十分重要。地震采集面临两大困难, 一个是不存在同时满足大倾角界面反射波与小尺度介质散射波的单一观测系统, 即现有野外排列并不能对散射波充分采样; 另一个是面对小尺度介质产生的地震波散射, 不能同时满足横向分辨率与最小介质尺度对空间采样的要求, 认为对小尺度介质进行充分采样无效。在引入量子力学概念后, 地下非均质体与地震波的传播构成量子系统, 散射波被视为概率波, 空间采样密度便不再受限制。全波场地震采集是均衡获取多态式地震波的过程, 由于不能靠稀疏、规则的采样方式获取, 概率波采集需要满足遍历性, 宜采用共中心点道集离散化技术, 基于多观测系统设计和炮道密度控制的细分面元方法实现。考虑到地震散射波信号弱, 存在局域性和不确定性, 应选择小面元、小道距、小偏移距、近偏高覆盖和炮点与检波点局部随机布设等采集参数。全波场地震采集方式灵活, 支持同期、多期镶嵌或井场连续地震采集, 有效信号更丰富, 背景噪声更低, 地震波信号的频率范围更宽, 而且经济上可以接受且物理可实现。

High-precision 3D seismic acquisition has achieved considerable success.However, for complex geological bodies, it is important to develop full-wave field seismic acquisition methods that can adapt to both continuous interface reflection and random medium scattering.There are two difficulties in seismic acquisition.First, there is no single seismic layout that satisfies both the reflection of large dip interfaces and the scattering of small-scale media; thus, the existing field arrays cannot adequately sample the scattered waves.Second, for the scattering of seismic waves generated by small-scale media, existing observation systems cannot satisfy both the lateral resolution and spatial sampling requirements of the minimum medium size; thus, it is impossible to completely sample small-scale media.According to the concept of quantum mechanics, the propagation of underground heterogeneous bodies and seismic waves is considered to constitute a quantum system, and scattered waves are considered probability waves, so that the spatial sampling density is no longer limited.Full-wave field seismic acquisition is a process of obtaining multi-state seismic waves in a balanced manner.Because probability waves cannot be obtained through sparse and regular sampling, probability-wave acquisition must satisfy the ergodicity requirement.It is advisable to adopt common-midpoint gather discretization technology, which is achieved through multiple observation system design and bin subdivision controlled by the trace density.Owing to the weak seismic scattered wave signal and the characteristics of localization and uncertainty, acquisition parameters should be selected, such as a small bin, a small trace spacing, a small spread, high coverage at near-offset, and a local random layout of the shot and receiver.The full-wave field seismic acquisition method is more flexible and can support simultaneous acquisition, multi-phase embedded acquisition, or well site continuous acquisition.The data have richer effective signals, less background noise, and wider frequency bands.This technology is economically acceptable and physically achievable.

为了充分利用地下小尺度不连续地质体如断层、裂缝、河道、粗糙岩丘边缘等携带的高分辨率信息,利用倾角域共成像点道集(CIGs)中反射波同相轴表现为具有稳相顶点的凹形曲线,绕射波同相轴表现为拟线性的明显差异,发展了一种基于稀疏约束预条件共轭梯度法的混合域高分辨率Radon变换绕射波分离成像方法。该方法首先在传统混合域Radon变换算法中引入预条件算子,然后构造了新的时变稀疏模型权,最后实现了倾角域CIGs绕射波分离与成像。与最小二乘Radon变换方法、频率域高分辨率Radon变换方法相比,该方法的分辨率和精度都明显提高。模型数据和实际地震资料的测试结果表明,基于混合域高分辨率Radon变换的绕射波分离成像方法去除反射波更为干净彻底,并且与常规反射波成像方法相比,该方法能有效改善断层等小尺度地质体的成像质量。

实现绕射波分离成像,要利用反射波和绕射波的特征差异,不同方法所利用的特征差异不尽相同。在地下反射层位水平连续的假设条件下,基于反射波和绕射波在相干性方面的差异,提出一种基于奇异值分解的绕射波分离成像方法。首先通过炮域动校正拉平反射波,使其相干性增强,而绕射波呈现非线性形态,相干性较弱,两者在相干性方面差异明显。基于此,再利用奇异值分解重构出反射波,并将其从地震数据中减去,从而分离出绕射波。为了在有效压制反射波的同时,尽可能地保护绕射波能量,在重构反射波时采用了一种迭代的方式。最后对数据进行反动校,得到绕射波单炮记录,继而实现绕射波成像。数值模型和实际资料应用结果表明,该方法能够有效压制强反射,提高小尺度非均质体的识别精度,有良好的应用价值。

The difference between the characteristics of reflected waves and those of diffracted waves is utilized in current methods for separating and imaging of seismic diffractions.Under the assumption that the reflective horizons in the subsurface are horizontal and continuous,an approach based on singular value decomposition and using the coherence difference is proposed in this study.First,the NMO corrections in shot gathers were used to flatten the reflections and enhance lateral coherence;the diffractions showed weaker coherence due to their nonlinearity.Subsequently,singular value decomposition was applied to construct the reflections,which were then subtracted from the data to obtain the diffractions.In order to effectively suppress the reflections and better preserve the diffractions,an iterative method was utilized.Finally,after reversing the NMO corrections,the shot gathers that approximately contained the diffractions were obtained;subsequently,the information was used to produce diffraction images.The results obtained by processing both synthetic and actual data showed that the proposed method can effectively suppress strong reflections and improve the identification of small-scale non-homogeneous objects.

地震勘探中的绕射体如断层、裂缝、地层尖灭、孔洞、盐体等地质异常体是常见的油气运移通道和(或)储集体,对它们的刻画和描述在油气资源勘探中具有重要意义。在常规地震数据处理中,绕射体往往被能量更强的反射体所掩盖,为更好地识别这些小尺度地质异常体,可对绕射体进行单独成像。为此,发展了基于行波分解的绕射波逆时偏移成像方法,得到了高分辨率的绕射体成像结果。其关键在于利用绕射波和反射波传播方向的差异,单独提取绕射体成像结果。主要步骤如下:构建解析波场,对源检端地震波场分别进行分解得到下左和下右行波;修改逆时偏移成像条件,利用分解得到的下左行波和下右行波对所有入射角度的绕射体和满足Snell定律的正、负倾角的反射层分别进行成像;得到&ldquo;正倾角反射层+绕射体&rdquo;和&ldquo;负倾角反射层+绕射体&rdquo;两种成像结果,并将两种成像结果进行相关,从而达到了压制反射波,提取绕射波的目的。模拟数据和实际数据应用结果表明:该方法得到的绕射波成像结果可以有效压制反射层能量,精准定位地下介质中存在的绕射体。

Diffractors such as faults,fractures,pinch-outs,and karsts are typical migration channels or reservoirs for oil and gas.The quantitative characterization of subsurface diffractors is crucial for oil exploration.In traditional processing,diffractors are often obscured by reflectors with large impedance contrast or contaminated by imaging noises.To better locate and quantitatively characterize these small-scale anomalies,it is necessary to develop a target-oriented method to image the diffraction separately.We herein proposed a diffraction-wave reverse time migration (RTM) method based on directional wavefield decomposition.The key for separation of reflection and diffraction lies in the behavior of wavefield direction,as the reflections obey Snells law while scattering-waves have multiple emergence directions.In this method,the directional wavefield decomposition method was utilized to decompose the seismic wavefields into the downward-left and downward-right propagation waves.Moreover,the conventional RTM imaging condition was modified to produce two directional imaging results,i.e.the imaging for positive dip reflections with diffractions,and the imaging for negative dip reflections with diffractions.By correlating these two results,the reflection images were cancelled out,whereas the diffraction images were enhanced.Tests on both synthetic and real data demonstrated that the proposed method can efficiently suppress the imaging of reflectors,and accurately locate the subsurface diffractors.

地震资料中的绕射波携带了小尺度地质异常体信息,可以更加清晰地刻画断层、边界以及缝洞储集体等非均质体构造,但在常规地震资料处理中,绕射波往往作为噪声被压制掉。对分离地震绕射波和反射波的方法以及绕射体单独成像方法进行了研究。首先,从理论上阐 述了地震绕射波的产生机制及地震特征;然后,从绕射波与反射波分离的角度出发,利用两者在不同域的形态差异,通过平面波分解技术、多聚焦叠加技术和聚焦切除反聚焦技术对绕射波与反射波进行分离;最后,应用高精度偏移方法对分离后的绕射波进行偏移成像。基于剖 析和总结典型地区的应用实例,发现绕射目标单独成像可以实现小尺度异常体的识别,非均质地质体的成像精度显著提高,对高精度地震解释具有重要意义。由于绕射波本质上是三维现象,在三维情况下实现绕射波与反射波的分离并成像具有重要意义,也是未来研究与应用的 发展方向。

The diffracted wave in seismic data carries the information of small-scale geological anomalies,which can assist in enhancing the accuracy of describing heterogeneous structures,such as faults,boundaries,and fracture cave reservoirs.However,in conventional seismic data processing,the diffraction wave is often suppressed as noise.In this study,the seismic diffraction and reflection waves separation method and the separate imaging method of diffractor are studied.First,the generation mechanism and seismic characteristics of seismic diffracted wave were developed theoretically.Then,from the perspective of the separation of diffracted wave and reflected wave using their morphological differences in different domains diffracted and reflected waves were separated using plane wave decomposition technology,multi-focus superposition technology,and focusing-mute-defocusing technology.Finally,the high-precision migration method was used to migrate and image the separated diffracted wave.By dissecting and summarizing the application examples in typical areas,results showed that the diffraction target imaging alone can achieve the identification of small-scale abnormal bodies.Additionally,the imaging accuracy of heterogeneous geological bodies significantly improved,which is critical for accurate high-precision seismic interpretation.