【摘要】 逆时偏移(RTM)采用双程波方程与相关成像条件会产生低频成像噪声,通过叠后Laplace滤波可以压制低频成像噪声,但会损失有效的低频成像信息,在实际资料处理中表现为低频高陡断面波成像受到严重影响。反射角道集切除的方法理论上能有效压制低频噪声,但不能保证低频信号不受损失,而且需要进行逆时偏移角度道集的提取,计算成本和周期大幅增加,同时传播角度的精度对成像效果影响较大,低频噪声残留问题突出。为此,提出一种基于复数域波场(或复数波场)分解的保幅成像方法,通过复数波场运算实现上下行波和左右行波的分解和成像,理论上能够避免低频噪声的产生。针对复数域波场分解在实现过程中需要进行高维希尔伯特变换、计算量和存储量成倍增加的问题,采用复数波场空间域褶积的方法避免了高维傅里叶变换与反变换的运算,在GPU上实现了高效成像,效果与效率得到兼顾。模型和实际数据的应用结果表明,该方法能够在计算量和存储量增加不超过20%的条件下,实现波场分解与逆时偏移,成像剖面保幅性高,噪声剖面无有效反射同相轴,低频高陡构造的成像效果优于传统的RTM成像方法,对于深部断层成像和落实有利圈闭具有实用价值。更多还原

【Abstract】 Reverse time migration(RTM) can easily generate low frequency imaging noise using the full wave equation and auto-correlation imaging conditions.Commonly used post stack Laplace filtering can attenuate the noise but cause loss of effective low frequency imaging information,which would affect the imaging of low frequency high steep events.Reflecting angle gather muting can theoretically suppress low frequency noise,but can not preserve the effective low frequency information.Extraction of angle gather of RTM is expensive and greatly prolongs the production period.In addition,the problem of low frequency noise remains due to the angle accuracy of the propagation wave.Herein,an amplitude-preserved imaging method based on wave field decomposition in complex domain(CWD)is proposed.The analytic solution of wave field decomposition is adopted to realize the decomposition imaging of waves moving down-up and left-right,theoretically avoiding the low frequency imaging noise.The wavefield decomposition in complex domain is difficult to implement,because high-dimensional Hilbert transform is required,and the computation and storage space needed are doubled.Therefore,a spatial domain convolution was used to avoid the high dimensional Fourier transformation.The method was implemented using a GPU,with both efficiency and effectiveness.Testing on both synthetic and field data showed that the method can realize wave field decomposition and reverse time migration,under the condition that the computation amount and the storage amount increase by no more than 20%.The CWD-RTM method can realize amplitude-preserved imaging with less loss of effective reflection,and the imaging for low frequency and steep structure is superior to that of the traditional RTM method,indicating the practicability for imaging of deep fault and discovery of favorable traps.更多还原