VTI介质qSV-qSV波高精度非双曲时距曲线方程近似形式研究

The high-precision approximation for non-hyperbolic traveltime equations of qSV-qSV wave in VTI media

1.中国石油大学(北京)理学院,北京102249;
2.中国石油大学(北京)地球物理学院,北京102249

1. College of Science,China University of Petroleum (Beijing),Beijing 102249,China;
2. College of Geophysics,China University of Petroleum (Beijing),Beijing 102249,China

近年来,宽频、大吨位的横波可控震源在油气勘探中的应用日益广泛,横波地震在气云区成像和地质构造解释等方面展现了显著优势。横波对各向异性尤为敏感,然而即使在较为简单的VTI(具有垂直对称轴的横向各向同性)介质中,qSV波的传播特征也相当复杂,例如在较强各向异性条件下(各向异性参数σ > 0.3),qSV-qSV波的时距曲线在中远偏移距 (x/z=1.7~2.0) 出现“横波三重波”(shear wave triplication)现象,导致近偏移距与中远偏移距的时距曲线特征差异显著。现有的qSV-qSV波时距曲线近似方程通常基于小偏移距(x/z=0)处的一阶近似,因而在中远偏移距范围内精度较低。针对这一问题,本文从qSV波相、群速度表示的精确时距曲线方程出发,结合相、群速度的二阶近似式,以及在x/z=2位置,相、群速度以及相、群角相等的特征,推导出了一种包含改进收敛因子的高精度的时距曲线方程。对比分析表明,在较强各向异性条件下,与现有的近似方程相比,新方程能够在远偏移距更好地收敛至实际时距曲线。本研究为地震横波资料处理提供了更加精确的非双曲时距曲线近似方程,有助于在地震资料处理中保留更多的远偏移距信息,对横波速度和各向异性参数的建模、横波反演等提供了重要的理论支撑。

In recent years,broadband shear wave vibrator with high energy has been developed for oil and gas exploration,and seismic shear waves (qSV-qSV waves) have shown good capability in gas-cloud imaging and geological interpretation.However,shear waves are particularly sensitive to anisotropy,the propagation characteristics of qSV waves are quite complex for the relatively simple VTI (vertically transversely isotropic) media.For example,under strongly anisotropic conditions (σ>0.3),the traveltime curve of qSV waves in VTI media exhibits a “shear wave triplication” phenomenon at intermediate to far offsets (x/z = 1.7~2.0),resulting in a significant difference in the traveltime curve characteristics between near-to-intermediate offsets (less than the offset corresponding to the “shear wave triplication”) and intermediate-to-far offsets (greater than the offset corresponding to the “shear wave triplication”).The existing approximate equations for the traveltime curve of qSV-qSV waves are typically based on a first-order approximation at small offsets (x/z=0),resulting in lower accuracy in the intermediate-to-far offset range.To solve this problem,starting from the precise traveltime equation expressed by the phase and group velocity of qSV waves,combined with the second-order approximation of phase and group velocity,and the characteristics that the phase velocity is equal to the group velocity,phase angle is equal to the group angle at the position x/z=2.Based on this,a high-precision time-distance curve equation with an improved convergence factor is derived.Under strongly anisotropic conditions,the new equation converges better to the real traveltime curve at far offsets compared to the existing approximate equations.This equation can help to retain more far offset seismic information,which is important for studying the inversion methods to obtain the seismic velocity parameters and anisotropy parameters,and analyzing the impact of anisotropy on kinematic characteristics.

国家自然科学基金项目(42122029)、中国石油集团地球物理勘探应用基础实验与先进理论方法研究项目(2022DQ0604-02)和中石油重大基础研究项目(2023ZZ05-02) 共同资助。

10.12431/issn.1000-1441.2025.64.01.004