PML边界条件下孔隙介质弹性波可变网格正演模拟方法研究

孔隙介质弹性波正演模拟对于储层预测和油气检测具有重要的指导意义。为提高孔隙介质波场正演模拟的精度,将可变网格方法应用于基于Biot理论的双相介质弹性波高阶有限差分正演模拟方法中,有效解决了二阶混合偏导数差分近似的可变网格过渡问题,推导了基于PML边界条件的可变网格差分格式,实现了空间与时间步长任意整数倍变化的双相介质弹性波可变网格正演模拟。对于细微地质结构或横向变化剧烈的介质区域,利用可变网格对区域精细重采样可有效提高正演的模拟精度;对于介质相对稳定的区域,采用大步长采样可保证正演计算效率。数值试验结果表明,与常规正演模拟方法相比,双相介质可变网格正演模拟方法的精度、效率有明显提高,对精细研究孔隙介质地震响应有着重要意义。

In order to improve the accuracy of forward modeling in porous media,a grid variation finite-difference simulation method is applied to Biots two-phase elastic wave equation.The difference approximation schemes in grid-variation zone for second-order mixed partial derivative are solved and the variable-grid finite difference scheme with PML boundary is derived,which realizes the two-phase media elastic wave variable-grid forward modeling with integral-multiple variable spatial and time grid steps.Numerical tests show that the grid step variation method would improve the simulation accuracy by using smaller gird step to resample the subtle geological structure and the area with rapid change of geological conditions.Moreover,the algorithm can also ensure the computational efficiency by suppressing the sampling rate to the region with relatively stable model parameters.Compared with conventional forward modeling method,the numerical testing result indicates that the two-phase variable-grid forward modeling method obviously improves the simulation accuracy and efficiency.

国家科技重大专项“海洋深水区油气勘探关键技术”项目(2011ZX05025-001)资助。