面向高陡断层及小尺度缝洞体的黏声各向异性最小二乘逆时偏移方法研究

Prismatic and diffracted waves have special abilities to image high steep faults and small scale fracture-cavity bodies, so based on the theory of least-squares reverse time migration (LSRTM), we intend to develop a prismatic and diffracted viscoacoustic anisotropic LSRTM method for high steep faults and small scale fracture-cavity bodies. In this method, adaptive mesh generation and coordinate system transformation technologies are applied to improve the resolution of small scale target bodies by mapping them to large scale ones in the auxiliary coordinate system. In this project, we will mainly research the following issues: 1. Constructing demigration operators of prismatic and diffracted LSRTM, and developing prismatic and diffracted LSRTM imaging methods for high steep faults and small scale fracture-cavity bodies. 2. Introducing an adaptive nonuniform grid scheme and correcting the influence of extreme irregular surface topography by deriving wavefield extrapolation operator in the auxiliary coordinate system. 3. To compensate the amplitude attenuation from viscous media and correct the influence of anisotropy on traveltime and waveform, deriving the demigration and adjoint operator for viscoacoustic anisotropic LSRTM to establish a set of efficient viscoacoustic anisotropic prismatic and diffracted LSRTM theoretical methods, optimized algorithms and technical processes for high steep faults and small scale fracture-cavity bodies, which is suitable for complex carbonate rocks land data.

从最小二乘逆时偏移理论框架出发，结合棱柱波对高陡断层及绕射波对小尺度缝洞体独特的识别能力，实现面向高陡断层及小尺度缝洞体的棱柱波和绕射波黏声各向异性最小二乘逆时偏移方法，并采用自适应非规则网格剖分及坐标变换技术，将小尺度目标体等效地变换为辅助坐标系下的大尺度目标体，提高对小尺度目标体的分辨率。研究内容主要包括：1）构建棱柱波和绕射波最小二乘反偏移算子，研发面向高陡断层和小尺度缝洞体的棱柱波及绕射波最小二乘逆时偏移方法；2）引入自适应非规则网格机制，校正剧烈起伏地表对地震波传播的影响，推导辅助坐标系下的波场延拓算子；3）补偿黏滞性对振幅衰减的影响，校正各向异性对走时和波形的影响，推导黏声各向异性最小二乘反偏移算子和伴随算子，形成一套适用于复杂碳酸盐岩缝洞地震资料的面向高陡断层及小尺度缝洞体的黏声各向异性最小二乘逆时偏移理论方法、优化算法及技术流程。

从最小二乘逆时偏移理论框架出发，结合了棱柱波对高陡断层及绕射波对小尺度缝洞体独特的识别能力，实现了面向高陡断层及小尺度缝洞体的棱柱波和绕射波黏声各向异性最小二乘逆时偏移方法，并采用了自适应非规则网格剖分及坐标变换技术，将小尺度目标体等效地变换为辅助坐标系下的大尺度目标体，提高了对小尺度目标体的分辨率。研究内容主要包括：1）通过对曲坐标系下Q衰减的反偏移算子、Q补偿的正向传播算子、棱柱波FI和IF的逆向传播伴随算子分别进行求导，得到了起伏地表棱柱波Q-LSRTM方法；2）基于平面波道集的绕射波分离方法，随后系统地推导了绕射波PLSRTM成像方法和面向目标的PLSRTM成像方法；3）基于传统最小二乘逆时偏移，推导了黏声各向异性最小二乘反偏移算子和伴随算子，压制了低频噪音、增加了保幅性、提高了信噪比、振幅均衡性和补偿了深部能量。