多尺度高阶FDTD逆时偏移在煤田地震勘探中的应用

目前煤田地震勘探的主要难点是深部复杂构造的成像。随着逆时偏移技术的发展，针对煤田地震勘探，如何在保证偏移成像精度的前提下，提高成像计算效率是急需解决的问题之一。从成像区域网格离散化的角度出发，针对高速层过采样和低速夹层采样不足问题，提出赋予研究对象多尺度网格的概念，具有较好的灵活性，能够对同一个地质模型采用疏密结合的方式成像。首先，根据速度模型设计多尺度网格模型，低速区域采用小尺度网格覆盖，高速区域采用大尺度网格覆盖;其次，采用高阶FDTD方法计算多尺度模型内各点的波场值，尤其过渡带内的点;最后，根据成像条件完成地下介质的逆时偏移成像。实验结果表明在保证模拟相同阶数精度条件下，多尺度逆时偏移方法比传统方法计算效率平均提升25.05%。

Application of multi scale high order FDTD inverse time migration in the coalfield seismic exploration

Currently the main difficulties in the coalfield seismic exploration are the image generation on the deep and complex geological structure.With the development of Reverse Time Migration (RTM),it is one of the urgent problem how to improve its efficiency at the same accuracy.From the point of view of imaging regional grid discretization,in the premise of ensuring the accuracy of migration imaging,to overcome the problem of over sampling for high speed layer and under sampling for low speed layer,this study puts forward the concept of multi scale grid for RTM.The algorithm has a good flexibility which can image the geological model in the way of sparse and dense.Firstly,the multi scale grid model is developed according to the velocity model,the small scale grid for the low speed area and large scale grid for high speed area are used.Secondly,the wave field value of each point is calculated based on the high order FDTD,especially the points in transition zone.Finally,the underground media is imaged based on the imaging condition.The experimental results show that under the condition of guaranteeing the accuracy of the same simulation order,the multi scale RTM computational efficiency can be promoted by 25.05% average compared with the traditional method.