Optimizing the wavefield storage strategy in reflection-acoustic logging reverse-time migration

反射声波测井逆时偏移中的波场存储策略优化方法（英文）

In this paper,wavefield storage optimization strategies are discussed with respect to reverse-time migration(RTM)imaging in reflection-acoustic logging,considering the problem of massive wavefield data storage in RTM itself.In doing so,two optimization methods are proposed and implemented to avoid wavefield storage.Firstly,the RTM based on the excitation-amplitude imaging condition uses the excitation time to judge the imaging time,and accordingly,we only need to store a small part of wavefield,such as the wavefield data of dozens of time points,the instances prove that they can even be imaged by only two time points.The traditional RTM usually needs to store the wavefield data of thousands of time points,compared with which the data storage can be reduced by tens or even thousands of times.Secondly,the RTM based on the random boundary uses the idea that the wavefield scatters rather than reflects in a random medium to reconstruct the wavefield source and thereby directly avoid storing the forward wavefield data.Numerical examples show that compared with other migration algorithms and the traditional RTM,both methods can effectively reduce wavefield data storage as well as improve data-processing efficiency while ensuring imaging accuracy,thereby providing the means for high-efficiency and highprecision imaging of fractures and caves by boreholes.

本文从反射声波测井逆时偏移成像方法出发,考虑逆时偏移本身存在海量波场数据存储问题,探讨了波场存储优化策略,提出并实现了激发振幅成像条件逆时偏移和随机边界法逆时偏移两种避免波场数据存储的优化方法。首先,激发振幅成像条件方法利用计算激发时间作为成像时间判断,只需存储小部分波场,如几十个时间点的波场数据,通过实例证明甚至仅需两个时间点波场即可完成成像。传统逆时偏移通常需存储数千时间点的波场数据,与之相比数据存储和读写量可缩小几十倍甚至数千倍;其次,随机边界方法利用波场在随机介质中发生散射而非反射进行震源声场反传重构,从而避免正传波场数据的存储。数值计算表明两种方法均可有效减少反射声波逆时偏移的波场数据存储,与其它偏移算法和常规逆时偏移相比,在保证成像精度的同时提高了数据处理效率,为井旁缝洞体高效、高精度成像提供了重要的技术手段。