炮检距域全局优化傅里叶有限差分偏移

Globally optimized Fourier finite-difference migration in offset domain

(洛斯阿拉莫斯国家实验室，美国圣菲市NM〖CD*2〗87547)

Los Alamos National Laboratory, Los Alamos, NM 87545, USA

将共炮集全局优化傅里叶有限差分(GOFFD)法扩展应用于炮检距域，其中，双平方根方程中的每一个单平方根项都由裂步傅里叶算子与有限差分算子之间的相互耦合来近似。由于该方法采用全局优化的有限差分系数，从而使得在对横向速度变化剧烈的介质进行成像时，能够更好地对陡倾构造进行成像。脉冲响应试验结果表明，炮检距域全局优化的傅里叶有限差分偏移方法较裂步傅里叶以及虚拟屏等偏移算法更为精确。SEG/EAGE盐丘模型试验结果也表明，该方法对盐丘边界和盐下弱反射层的成像也较裂步傅里叶算法更准确。

A globally optimized Fourier finite-difference operator was applied in offset-domain wave-equation migration. Each single-square-root term in the double-square-root equation is approximated by a split-step Fourier operator coupled with an optimized finite-difference operator. The optimization of the finite-difference coefficients is achieved by maximizing the maximum dip angle of the entire model, leading to better ability for the new method to handle steeply dipping events in a medium with strong lateral velocity variations. Numerical results with the impulse response show that the proposed method is more accurate than other approaches including the split-step Fourier and the pseudo-screen migration methods. Results with the SEG/EAGE salt model show that the proposed method resolves the salt boundary and the sub-salt weak reflectors more accurately than the split-step Fourier migration method does.