粘声波保幅逆时偏移方法研究

发布时间：2019-04-27 04:22

【摘要】：叠前逆时偏移以双程波理论为基础,具有使地下复杂的速度场开展成像的能力,不仅对剧烈变化的速度场具有很好的适应性,而且还能对复杂地形和陡倾角进行成像,对复杂地质目标介质(尤其是大倾角地区)勘探有着重大的作用。目前地震勘探所使用的逆时偏移成像算子大部分都是在理想弹性各向同性介质假设的条件下推导的,然而,地震勘探中面临的实际地下介质其实普遍存在着粘滞性,地震波经过地下地层中,地下介质并非是完全弹性介质,即使对透射损失、几何扩散等因素引起的衰减进行进行补偿后,地震剖面里面中,深层的能量仍要弱于浅层。说明地震波在实际传播经过的路径里存在能量的耗损,使得地震波的振幅发生衰减,相位产生畸变,使得地震资料信噪比低,深部变得模糊。因此,有必要研究基于粘声介质双程波动方程理论,发展粘声介质逆时深度偏移方法,校正子波的空变特征,补偿振幅衰减,以适应实际地层地震勘探的要求。地震波成像是地震学的关键中间环节,它前面与野外地震数据采集紧密相关,后面为叠后波阻抗反演、叠前AVA/AVO反演等提供扎实的基础数据,对地震处理和成像的要求,不仅是把地表上记录的反射波归位到地下的正确位置上去,对于深度域成像,目标是使反射系数直接归位到它的正确深度和位置上去。还要求波的“振幅”大小与局部反射点的反射系数呈正相关关系;然后是估计地下岩石介质的物性参数,主要是速度和密度参数,最终描述含油气储层。然而,常规逆时偏移成像往往存在低频噪音,以及没有补偿地震波在传播过程中透射与反射产生的能量损失,还有,观测系统的往往不规则,地震数据存在有限的频带,这都对制约着真振幅偏移成像。为了改善成像效果,实现保幅偏移成像,发展根据需要成像的介质参数,在反演的理论框架下建立最小二乘偏移的目标函数,并借助伴随状态法推导迭代反演算法,利用局部寻优算子,构建最小二乘逆时偏移的迭代反演方法,将有效提高复杂介质条件下地质体的成像精度,合理消除由于地层吸收、透射及几何扩散等作用对振幅、频率及相位的影响作用,提高成像分辨率,改善振幅属性,实现保幅、保真、高精度成像剖面。基于以上理论分析的基础上,本文基于标准线性固体粘弹性机制模型的粘声介质理论,实现粘声介质逆时深度偏移,并将粘声介质逆时偏移与最小二乘思路相结合,发展了带有振幅补偿的粘声介质最小二乘LSRTM。模型数据试算结果较好,验证了粘声介质逆时偏移与最小二乘偏移能够补偿粘声介质对地震波吸收衰减,可以进行保幅成像。
[Abstract]:Based on the two-way wave theory, the prestack inverse time migration has the ability of imaging the complex underground velocity field, which not only has good adaptability to the rapidly changing velocity field, but also can image the complex terrain and steep dip angle. It plays an important role in the exploration of complex geological target medium (especially in the area of large dip angle). At present, most of the inverse time migration imaging operators used in seismic exploration are derived under the assumption of ideal elastic isotropic medium. However, the actual underground medium faced by seismic exploration is generally viscous. After the seismic wave passes through the underground strata, the underground medium is not completely elastic. Even after compensating the attenuation caused by transmission loss and geometric diffusion, the energy in the deep layer of the seismic section is still weaker than that in the shallow layer. It is shown that there is energy loss in the path through which seismic wave propagates, which causes the amplitude of seismic wave to attenuate and the phase distorts, which makes the signal-to-noise ratio of seismic data low and the depth blurred. Therefore, it is necessary to develop the inverse time-depth migration method based on the two-way wave equation theory of the viscoelastic medium, to correct the spatial variation characteristics of the wavelet and compensate the amplitude attenuation in order to meet the requirements of seismic exploration in the actual formation. Seismic wave imaging is a key intermediate link in seismology, which is closely related to field seismic data acquisition in front of it, and provides solid basic data for post-stack impedance inversion, prestack AVA/AVO inversion and so on, which requires seismic processing and imaging. It is not only to relocate the reflected wave recorded on the surface to the correct position underground, but also to relocate the reflection coefficient directly to its correct depth and position for depth-domain imaging. It is also required that the amplitude of the wave is positively correlated with the reflection coefficient of the local reflection point, and then the physical parameters of the underground rock medium, mainly the velocity and density parameters, are estimated, and finally the oil-bearing reservoir is described. However, the conventional inverse time migration imaging often has low frequency noise and does not compensate for the energy loss caused by transmission and reflection of seismic waves in the process of propagation. Moreover, the observation system is often irregular and the seismic data have a limited frequency band. This is all restricted to true amplitude migration imaging. In order to improve the imaging effect and realize the amplitude-preserving migration imaging, according to the need of imaging medium parameters, the objective function of least square migration is established in the framework of inversion theory, and the iterative inversion algorithm is deduced by means of adjoint state method. By using the local optimization operator, the iterative inversion method of least square inverse time migration is constructed, which will effectively improve the imaging accuracy of geological bodies under complex medium conditions, and reasonably eliminate the amplitude due to the action of stratum absorption, transmission and geometric diffusion, etc. The influence of frequency and phase can improve imaging resolution and amplitude attribute, and realize preserving, fidelity and high precision imaging profile. Based on the above theoretical analysis, based on the viscoelastic mechanism model of standard linear solid, this paper realizes the inverse time depth migration of the viscoelastic medium, and combines the inverse time migration of the viscoelastic medium with the least square method. The least squares LSRTM. with amplitude compensation for viscoelastic media is developed. The experimental results show that the inverse time migration and least square migration of the viscoelastic medium can compensate the absorption and attenuation of seismic waves and can be used for amplitude-preserving imaging.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4

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