叠前深度偏移在复杂构造成像研究中的应用——以川东三岔坪高陡构造为例

Application of prestack depth migration to complex structure imaging: A case study from the Sanchaping high-steep structure in the eastern Sichuan Basin

四川盆地东部三岔坪高陡构造由于经历复杂构造运动,地表出露岩性变化大,激发接收条件差,造成地震资料信噪比低,成像效果较差。针对以上问题,将叠前深度偏移方法应用于该复杂构造成像研究。在叠前常规处理和叠前时间偏移的基础上,利用已有测井、地质等资料,建立实体模型,并通过区域层速度填充该实体模型,从而建立起了高精度的速度模型;得到的叠前深度偏移结果,其剖面断点更清晰,绕射归位合理,信噪比较高,构造形态清楚,成像效果较好;进一步与某实钻井位数据进行比对,误差较小,说明处理结果真实可靠。结论认为:当速度存在剧烈的横向变化、速度分界面非水平层状时,只有叠前深度偏移能够实现共反射点的叠加和绕射点的归位,使地震资料正确成像;在叠前深度偏移过程中,建立高精度的速度模型非常关键。

The signal to noise ratio is low and the imaging quality is low in the Sanchaping structure of the eastern Sichuan Basin due to the complexity of tectonic movements, large variations of lithologies in outcrops and poor conditions of shooting and receiving. To solve these problems, the prestaek depth migration technique was applied to study the imaging of this complex structure. Based on conventional prestack seismic processing and prestack time migration, the logging and geologic data were used to establish a solid model. Regional interval velocities were filled into the solid model to establish a high-resolution velocity model. The prestack depth migration results obtained are characterized by clear breakpoint on profile, rational migration of diffracted waves, high signal-to noise ratio, well defined structure geometry, and high imaging quality. A comparative analysis with the drilled well data reveals that the processing results are low in error, thus reliable. The following conclusions were drawn. When lateral variation of velocity is strong and the velocity interface is not a horizontal layer, only the prestack depth migration can realize common reflection point stack and the regression of diffraction points, thus correct the imaging of the subsurface structure. It is critical to establish a high resolution veloc ity model in prestack depth migration.