复杂地表条件下TTI介质多波高斯束偏移成像方法研究

Multi-component seismic technology is an important means of detecting underground oil and gas resources. As the deepening of hydrocarbon exploration degree, seismic exploration faces increasingly complicated near-surface and subsurface conditions. How to obtain accurate migration imaging of multiwave seismic data in anisotropic media under complex surface condition has become a frontier subject urgently to be solved for seismic exploration. Compared with high computational cost of the wave equation, the Gaussian beam is derived from asymptotic ray theory, which can be flexibly and effectively applied to complex surface wavefield continuation. Meanwhile it retains dynamical features of wave equation, and solves the problems of multi-valued traveltime and caustics of traditional ray method. Therefore, this project will study multiwave Gaussian beam migration imaging method for anisotropic media under complex surface condition. By studying anisotropic kinematic and dynamic ray tracing of P-wave and S-wave, we will first develop multiwave Gaussian beam migration imaging method in 2D TTI media. Based on above, we will use Gaussian beams to directly calculate continuation wavefield in the complex surface, and adopt local slant stack and not to slant stack in two ways to derive the formula of downward-continued recorded wavefield under complex surface condition. Combining the anisotropic ray tracing theory and cross-correlation imaging condition, we will realize 2D multiwave Gaussian beam prestack depth migration in TTI media under complex surface condition. The research of this project will provide an effective migration method for accurate imaging of multi-component seismic data in anisotropic media under complex surface condition.

多分量地震技术是探测地下油气等资源的重要手段。随着勘探程度的不断深入，地震勘探面对的近地表和地下介质情况愈加复杂，如何对复杂地表各向异性介质中多波地震资料准确地偏移成像已成为地震勘探亟待解决的前沿课题。相比于高计算成本波动方程算法，高斯束发展于渐近射线理论，能灵活、高效地进行复杂地表波场延拓，并兼具波动方程的动力学特征，解决了传统射线方法多值走时、焦散等问题。因此，本项目拟开展复杂地表条件下各向异性多波高斯束偏移成像方法研究。通过各向异性P波和S波运动学和动力学射线追踪，发展二维TTI介质多波高斯束偏移成像方法；利用高斯束在复杂地表直接进行波场延拓，采用局部倾斜叠加和非倾斜叠加两种方式表示复杂地表波场反向延拓公式，结合各向异性射线追踪理论以及互相关成像条件，实现二维复杂地表条件下TTI介质多波高斯束叠前深度偏移，为复杂地表各向异性介质中多分量地震数据的准确成像提供一种有效的直接偏移方法。

随着油气勘探开发程度的不断深入，地震勘探所面对的地表和地下介质情况越来越复杂，地震勘探方法的研究也由各向同性介质的假设发展到各向异性介质，由传统的纵波勘探逐渐发展到多波地震勘探。对于更逼近真实地质情况的复杂地表条件下各向异性介质多分量地震资料，迫切地需求一种有效的多波地震偏移成像方法。高斯束偏移方法不仅具有接近于波动方程偏移的成像精度，同时还保留了Kirchhoff偏移方法灵活、高效的优点以及对复杂地表条件良好的适应性。因此，本项目在各向异性高斯束偏移方法研究的基础上，对复杂地表条件下TTI介质多波高斯束叠前深度偏移成像方法进行了系统的研究。项目研究过程中取得了如下进展和成果：（1）基于各向异性射线追踪理论，分别实现了二维TTI介质中PP波和PS波共炮域和角度域的高斯束叠前深度偏移成像方法；（2）利用高斯束直接在复杂地表进行波场延拓计算，采用局部倾斜叠加和非倾斜叠加两种方式表示复杂地表条件下的波场反向延拓公式；（3）在上述研究的基础上，分别给出了基于局部倾斜叠加和非倾斜叠加的二维复杂地表条件下TTI介质PP波和PS波高斯束叠前深度偏移成像方法。本项目研究为复杂地表条件下TTI介质中多分量地震数据的准确成像提供了准确有效的直接偏移成像方法，对于解决复杂地表条件下各向异性介质的地震偏移成像具有重要的理论和实用价值。