基于波场分离的逆时偏移成像条件研究及在准噶尔盆地的应用

Wave Field Separation Based Reverse Time Migration Imaging Condition and It′s Application in Junggar Basin

与传统深度偏移成像方法相比,基于双程波的逆时偏移方法针对地下陡倾角地区和复杂地下地质条件地区的成像有着无可比拟的优势。逆时偏移方法的实现通常有3个步骤:①在时间域实现震源波场的正向外推;②在时间域实现检波点波场的反向外推;③应用合理的成像条件构建成像结果。在实际应用过程中,通常是采用互相关成像条件来构建成像,然而,互相关成像条件构建的逆时偏移成像结果会产生强振幅的低频噪音,这些噪音会极大地降低资料的信噪比,容易导致浅层构造被噪音掩盖而无法识别,仅采用单纯的带通滤波并不能很好地滤除这种噪音。提供了一种新的基于波场分离理论的逆时偏移成像条件,此方法能有效地消除这些特定的噪音,其核心思路就是将震源及检波点波场分离成它们的单程波传播分量,然后仅在反射点处利用互相关的成像条件构建成像结果,从而实现逆时偏移成像。Marm-ousi模型数据验证了该方法的准确性;同时,采用文中提到的成像条件在准噶尔盆地百口泉地区进行了逆时偏移测试,测试结果充分证明新成像条件对野外资料的适应性。

Two-way wave field based reverse-time migration（RTM） has advantage to form the image in the steeply dipping structures and complex geological background,compared with the depth migration imaging.Generally,three steps are required for the reverse-time migration as follows：①Forward extrapolation of earthquake source wavefields in time domain;②Backward extrapolation of receiver wavefields in time domain;③Using the effective imaging condition to construct image.The cross correlation imaging conditions are used to construct image in practical application.The low-frequency and high-amplitude noises occurs in the reverse-time migration imaging by using the cross correlation imaging conditions,the noises can usually contaminate the signals so that the shallow structure overridden by noses can not be identified.The bandpass filtering does not filtrate the noses effectively.In this paper,a new image condition of wave field separation based reverse time migration imaging condition is used to remove the noises effectively.We use the synthetic seismic data from Marmousi velocity model to verify the accuracy of this method.The reverse-time migration imaging is tested in the Junggar basin and the tested results show that the wave field separation based reverse time migration imaging method is reliable.