多方位多时刻三维最小二乘逆时偏移方法研究

The least-squares reverse time migration method can accurately image the underground structure, the results have definite physical significance, but are susceptible to the disturbance of the stability of the wave field algorithm, the influence of low-frequency noise and the deviation illusion. At the same time, because of the large amount of computation and the demand of data storage, this method is often limited by the two-dimensional space hypothesis and does not conform to the actual situation of underground media. Based on the three-dimensional computational space, this project aims to improve the stability of the wave field simulation of the least-square reverse time migration algorithm by means of the method of integral wave field simulation and polynomial approximation strategy. Using omni-directional traveling wave separation method based on the Hilbert transform, the problem of low-frequency noise and migration interference in imaging gradients could be solved; the problem of excessive storage could be solved by using multi-directional multi-time excitation amplitude imaging algorithm; multithreading multi-GPU parallel technology guarantees the principle research and the efficient implementation of the numerical test. This project can form an efficient and stable three-dimensional least-squares reverse time migration method to describe three-dimensional subsurface media with high accuracy and reservoir properties, and guide the subsequent three-dimensional reservoir structure interpretation and inversion.

最小二乘逆时偏移方法可以精确地成像地下构造，成像结果物理意义明确，但易受波场算法稳定性不强、低频噪声影响严重、偏移假象等问题的干扰。同时，由于计算量和数据存储需求巨大，目前该方法还受限于二维空间假设，不符合地下介质的实际情况。针对以上问题，本项目以三维计算空间为基础，通过对积分法波场模拟方法和多种多项式近似策略的研究，改善最小二乘逆时偏移方法中波场模拟的稳定性；采用基于Hilbert变换的全方位行波分离方法，解决成像梯度中低频噪声和偏移干扰问题；利用多方位多时刻激发振幅成像思路，解决存储量过大的问题；利用多线程多GPU并行技术，保证算法的高效性。通过本项目的研究，形成高效稳定的三维最小二乘逆时偏移技术，实现对地下介质的三维高精度成像，为后续的储层构造解释、储层性质描述和储层反演提供高质量的地震成像数据体。

最小二乘逆时偏移是目前较为精确的地下构造成像方法，所得结果具有明确的物理意义，利于指导后期解释、反演等工作。但该方法受波场算法稳定性不强、低频噪声影响严重、偏移假象等问题的干扰。三维地震资料成像方法更符合地震勘探客观实际，但受数据量巨大、算法复杂等问题的困扰。为此，本项目重点开展了基于积分法波场模拟方法的三维地震资料最小二乘逆时偏移方法研究。研究实现了一步法波场延拓的地震波场模拟方法，分别采用了切比雪夫多项式和多倍角公式等多种多项式近似策略，对比分析了不同多项式近似策略的计算效率和稳定性关系，实现了地震波场的稳定模拟；结合多GPU协同技术，实现了对三维地震波场模拟的多GPU联合运算，改善了GPU技术对大尺寸三维数据的适应性；基于时空域Hilbert变换，将地震波行波分离由二维空间扩展至三维空间，实现了三维地震波场的上下左右前后全方位波场分离；并行对比研究了激发振幅和互相关成像策略，并采用后者作为最小二乘逆时偏移成像条件，保障成像精度；项目最终实现了基于稳定波场模拟方法的三维最小二乘逆时偏移方法。本项目研究对推动三维空间下地震波场的高稳定性模拟具有重要意义，对三维空间认识地震波传播规律，提高复杂油气目标的识别精度有重要的理论指导和推广借鉴意义，对推动油气勘探取得突破进展和保障国家能源安全有重要作用。