早至波速度反演技术研究

发布时间：2018-10-15 17:42

【摘要】：速度是反映地下构造和岩石物性的一个重要参数。地球物理问题归根到底是速度估计的问题。如何准确重建地下速度场信息就成了地震波勘探的核心问题,而近地表速度建模问题又是地球物理建模普遍存在的重点及难点问题。近地表速度的精度直接影响勘探区域的地震资料静校正、整个速度场的建模以及最终成像的效果。目前常用的近地表建模方法和技术,如折射波法、面波法以及常规的走时层析方法等多基于高频近似的射线理论,不能满足当前近地表精细建模的需求。因此更精确的近地表速度反演方法越来越为大家所关注。全波形反演是基于波动方程的非线性反演理论,利用了地震全波场信息,在理论上被认为是建模精度最高的手段,已经实现了海上实际资料应用,但陆上实际资料应用受低频数据缺失,观测系统限制,陆上随机干扰严重和近地表条件诸多因素的影响还存在诸多困难。论文联合初至走时层析与全波形反演的建模优势,引入早至波的概念,基于全波形反演思想,介绍了一种特征波波形反演方法—早至波波形反演。将速度建模问题转化为求解目标函数极值问题,即利用观测记录和模型正演记录之间的最佳匹配建立地下模型,仅使用早至波信息,避开基于射线理论高频假设的最短路径原理弊端和全波形反演对大偏移距和低频的要求,利用早至波的运动学和动力学信息,填补常规建模手段的‘盲区’,完成近地表及中浅层的高精度速度建模。论文从波形反演基本理论出发,引入早至波波形反演流程,通过模型测试,直观的展示了早至波波形反演处理精细速度建模的能力,反演结果的精度和分辨率比初至波走时层析反演的结果要高,该方法非线性程度较低,反演过程相对稳定,计算效率较高,收敛效果相对较好,即使在初始模型精度较低的情况下,仍然可以同时分辨低波数和高波数成分。最后,将早至波波行反演应用到实际资料,考虑整个反演过程需要关注的细节,根据处理理论模型与实际资料的经验,展示了方法的正确性,可行性和实用性。提出一套对于速度横向变化大和表层构造比较复杂的情况下的表层速度建模策略。与此同时,该方法与其他非地震方法的结合在近地表的矿产普查,工程物探,油气勘探等领域具有广泛的应用前景。
[Abstract]:Velocity is an important parameter reflecting underground structure and petrophysical properties. The problem of geophysics is, in the final analysis, the problem of velocity estimation. How to accurately reconstruct the information of underground velocity field has become the core problem of seismic wave exploration, and the problem of near-surface velocity modeling is an important and difficult problem in geophysical modeling. The accuracy of near-surface velocity directly affects the static correction of seismic data in exploration area, the modeling of the whole velocity field and the effect of final imaging. At present, the commonly used near-surface modeling methods and techniques, such as refraction wave method, surface wave method and conventional travel-time tomography method, are based on high-frequency approximation ray theory, which can not meet the needs of the current fine modeling near the surface. Therefore, more and more accurate near-surface velocity inversion method has attracted more and more attention. Full wave inversion is a nonlinear inversion theory based on wave equation, which uses seismic full wave field information. It is considered to be the most accurate method of modeling in theory, and has realized the application of practical data on the sea. However, there are still many difficulties in the application of practical data on land due to the lack of low frequency data, the limitation of observation system, the serious random disturbance on land and the near surface conditions. This paper combines the modeling advantages of first arrival time tomography and full waveform inversion, and introduces the concept of early arrival wave. Based on the idea of full wave inversion, this paper introduces a characteristic wave inversion method-early arrival wave inversion. The velocity modeling problem is transformed into solving the objective function extremum problem, that is, using the best match between the observation record and the model forward record, the underground model is established, and only the early wave information is used. Avoiding the defects of the principle of the shortest path based on the high frequency hypothesis of ray theory and the requirement of large offset and low frequency for full waveform inversion, and using the kinematics and dynamics information of the early arrival wave to fill the 'blind zone' of the conventional modeling methods, The high precision velocity modeling of near surface and medium shallow layer is completed. Based on the basic theory of waveform inversion, the paper introduces the inversion process of early to early wave waveform, and through model testing, shows the ability of precision velocity modeling of early to early wave inversion processing. The accuracy and resolution of the inversion results are higher than those of the first arrival wave travel time tomography inversion results. This method has lower nonlinearity, the inversion process is relatively stable, the computational efficiency is higher, and the convergence effect is relatively good. Even if the accuracy of the initial model is low, the low wavenumber and the high wavenumber components can still be distinguished at the same time. Finally, the early wave inversion is applied to the actual data, considering the details of the whole inversion process, the correctness, feasibility and practicability of the method are demonstrated according to the experience of processing the theoretical model and the actual data. A set of surface velocity modeling strategies for large lateral velocity variation and complex surface structure is proposed. At the same time, the combination of this method and other non-seismic methods has a broad application prospect in the near surface mineral survey, engineering geophysical exploration, oil and gas exploration and other fields.
【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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