高斯束层析偏移速度建模方法及应用

A method of migration velocity analysis based on Gaussian Beam tomography and its application

常规地震层析反演分为射线层析和波动方程层析两类,基于射线类的常规层析方法由于理论假设的限制难以对复杂地区进行准确的速度建模;波动方程层析需要建立高精度的初始模型,其应用受到实际资料品质的限制。为此,开展了高斯束层析偏移速度建模方法研究,利用高斯束核函数构建病态性更小的灵敏度矩阵以提高层析反演的稳定性;采用高斯束叠前深度偏移进行高陡构造成像,并直接提取高分辨率的角度域共成像点道集(ADCIGs)用于高斯束层析反演,进而获得精确的偏移速度模型。为了避免在高陡构造地区人工拾取的繁杂,采用自动拾取技术获取反射点坐标与地层局部构造倾角。模型测试和实际资料应用结果显示,该方法具有较高的反演精度和稳定性。

Conventional seismic tomography includes ray tomography and wave-equation tomography. As a result of the limi- tation of theoretical assumptions, the conventional tomographic methods based on raypath are unable to build accurate veloci- ty model in area with complicated geological conditions. Moreover, wave-equation tomography fails to get a good application result, because it needs to establish the initial model with high precision. The method of migration velocity analysis based on Gaussian beam tomography （GBT） depends on the alternately iterative of migration and tomography to achieve velocity up- date, by which we can obtain the relatively correct velocity model. This method can improve the stability of inversion by con- structing less ill-posed Frechet matrix using Gaussian beams~ kernels. The pre-stack Gaussian beam depth migration not only has great advantages in high and steep structure zones, but also can extract angle-domain common imaging gathers （ADCIGs） with high resolution directly. By inputting the ADCIGs to Gaussian beam tomography, we will be able to obtain accurate ve- locity model. In order to avoid complex artificial pickup in the high-steep structure area, we proposed automatic picking tech- nique to pick up reflection points and the local stratigraphic structural dip. The model test and field data prove that the Gaussian beam tomographic method has high inversion accuracy and stability.