山前带联合层析反演地震成像

由于地表地形和地下构造的复杂性，山前带地震成像一直是地球物理勘探的难题，其中的难点之一是速度建模。为了改进山前带的地震成像，提出了一个以联合层析速度建模为关键技术的处理流程，包括：①利用复数域小波变换（CWT）的抗假频和高保真优点，在压制噪声的同时保护有效信号，尤其是低频信号；②拾取全炮检距初至，采用回转波层析反演得到可靠的浅层速度模型；③优化初始速度模型，通过浅、中、深联合层析速度反演和井约束建立全层速度模型；④通过基于真地表的TTI各向异性叠前深度偏移进行高陡构造成像，刻画复杂断块。将该方法应用于准噶尔盆地南缘山前带米泉三维实际资料的处理，结果表明：线性和含假频噪声得到了有效压制，低频信号得到保留；偏移剖面整体上归位更加合理，同相轴连续性明显提高，井震吻合度较高，地质目标的构造形态和断裂展布规律更加清晰，更有利于后续解释。该方法的成功应用不仅为准噶尔盆地山前带地震成像带来了希望，而且可以推广到世界上其他地区的山前带地震成像中。

Joint tomography for foothills seismic imaging

Foothills seismic imaging has been a challenging problem for oil and gas exploration for many decades due to the complexity of both near-surface and subsurface conditions. The key issue is velocity model building. This paper illustrates a workflow with joint tomography as a key component for improved foothills seismic imaging, including the following four steps:①complex wavelet transform (CWT) for noise attenuation, which is with the robust for aliased noise suppression with fidelity of keeping signal, especially low-frequency signals, while removing noise; ②turning-ray tomography for near-surface velocity estimation using picked full-offset first arrivals; ③joint tomography starting from a robust and seamless initial velocity model, constrained by well logs and geologic interpretation, for velocity model building; and ④TTI anisotropic prestack depth migration from true topography for imaging steep-dip faulting structures. The application of the proposed methodologies and workflow to Miquan foothills 3D seismic survey from the south rim of Junggar Basin, northwestern China, has demonstrated that linear and scattering noise has been effectively suppressed; low-frequency signal has been preserved, which is important for reservoir characterization. More accurate velocity model has resulted in better focusing and more continuity of seismic images after migration, and better tie with wells. Images in target zones have been improved, starting to show meaningful faulting structures with a regional anticline. This is significant for seismic exploration in foothills regions not only in China, but also elsewhere around the world.