正交各向异性介质中多方位三维转换波叠前时间偏移

目前大多数转换波叠前时间偏移(PSTM)算法只考虑了VTI各向异性介质对转换波旅行时的影响，而具有垂直裂缝的HTI各向异性介质具有较强的速度方位各向异性特点,不同传播方向的速度按照椭圆规律变化,仅使用VTI各向异性参数而不考虑速度方位变化对旅行时的影响,将导致多方位三维转换波叠前偏移成像质量下降。针对上述问题,提出一种基于正交各向异性介质的多方位三维转换波PSTM偏移算法,其转换波旅行时计算公式同时考虑了VTI和HTI各向异性参数,更加接近于地层介质的实际情况。由于转换波还受到映射在水平径向分量(R)和切向分量(T)的快、慢横波影响,因此需要在转换波叠前时间偏移之前进行R,T分量的快、慢横波分离。在常规三维转换波资料处理的基础上,利用基于正交各向异性介质的多方位三维转换波PSTM偏移算法对西南地区某实际资料进行了测试处理,结果表明,转换波叠前时间偏移结果在构造解释上更加合理,地层特征更加清晰,证实了算法的合理性和实用性。

Most of the migration algorithms for converted wave prestack time migration (PSTM) only consider the VTI anisotropic medium effect.HTI anisotropic medium induced by vertical fractures has stronger azimuth velocity anisotropy,so velocity fields with different propagation directions will vary in the ellipse rule.Imaging quality of PSTM for multi-azimuth 3D converted wave data will reduce by using VTI anisotropy parameters without considering HTI anisotropy parameters in orthotropic medium.According to the above problem,we proposed a multi-azimuth 3D converted wave PSTM based on orthogonal anisotropic medium.The traveltime formula of the proposed PSTM algorithm simultaneously considers the VTI and HTI anisotropic parameters.This equation makes multi-azimuth 3D converted wave data processing closer to the actual formation medium.However,converted wave is also influenced by fast and slow shear waves mapping to R- and T-component unlike compression wave,therefore shear wave separation needs to be done for R- and T-component before converted wave PSTM in orthotropic medium.It is necessary to separate PS-wave into PS1-wave and PS2-wave from R- and T-component in orthotropic medium for multi-azimuth 3D converted wave data.The multi-azimuth 3D converted-wave PSTM based on orthotropic medium is applied on the seismic data in Southwest China,the structure interpretation is more reasonable and characteristics of events are clearer on the results of PSTM for multi-azimuth 3D converted wave after PS1 and PS2 wave separation,which demonstrates the rationality and practicability of our algorithm.

国家科技重大专项项目(2011ZX05005-005-006)资助。