高效层间多次波压制技术在四川页岩气勘探中的应用

Application of efficient internal multiple suppression technique in Shale gas exploration of Sichuan Basin

四川盆地是当前中国页岩气资源最丰富的重点勘探开发区域,该区域大量发育的层间多次波严重影响了地震偏移成像结果,降低了地震解释的精度,因此层间多次波压制技术的研究与应用在该地区具有建设性意义.拉冬变换层间多次波压制方法在业界使用比较广泛,但其难以区分中深层的层间多次波.基于反射界面的层间多次波预测方法则需要识别和拾取多次波的下行反射界面,当产生多次波的界面较多且地下构造复杂时,层位解释与识别就会非常困难,应用成本大大提高,实现难度系数增大.本文介绍了一种只需定义一个虚拟反射界面就可以进行层间多次波预测的新方法,文中详述了该方法的基本原理,并利用实际测井数据正演,了解工区内的多次波产生机制与发育情况,最后将此方法应用到四川盆地页岩气地震勘探资料处理中.该方法避免了拾取所有产生层间多次波反射界面所带来的巨大工作量,克服了以往实现多层层间多次波压制的复杂性,使得层间多次波处理更加便捷和高效.通过对层间多次波压制前后的道集、速度谱、叠前时间偏移剖面以及井震匹配相关系数的对比可以发现,本方法在保真保幅的基础之上有效的压制了层间多次波,为后期的反演与解释工作奠定了坚实的基础.

The Sichuan Basin is currently the key exploration and development area with the richest shale gas resources in China. The extensive internal multiples generated in this area seriously affects the seismic imaging results and reduces the accuracy of seismic interpretation. Therefore, it’s necessary to develop the research and application of internal multiples suppression technology in this area. Radon transform is widely used in the industry, but it is difficult to distinguish the interbed multiples at mid-deep area. The prediction method of internal multiple based on boundary-related method needs to identify and pick up the downward reflectors of multiple. When there are many reflectors producing multiple and the subsurface structure is complex, the horizon identification and interpretation will be very difficult, the cost of internal multiple suppression will be greatly increased, and the difficulty of de-multiple will be increased. This paper introduces a new method to predict internal multiples by defining a fictitious horizon. The principle of this method is described in detail. The generation mechanism and development of multiples in current seismic survey are known by forward modeling using actual logging data. Finally, this method is applied to seismic data processing in shale gas exploration of Sichuan basin. This method avoids the huge workload caused by picking up all the reflectors of internal multiples, overcomes the complexity of multi-layer internal multiples suppression in the past, and makes the processing of internal multiples more convenient and efficient. Through the comparison of gathers, velocity spectrum, pre-stack time migration section and well seismic matching correlation coefficient before and after suppression of internal multiples, it can be found that this method effectively suppresses internal multiples on the basis of fidelity and amplitude preservation, which lays a solid foundation for later inversion and interpretation.