Seismic image enhancement in post stack depth migration by finite offset CDS stack method

摘要

Seismic imaging in complex geological structures such as thrust belts and areas with complex geological structures is affected by several factors that often lead to poor-quality final result. Usually such structures produce locally very steep dips, strong lateral variations in velocity and abrupt truncation of the reflectors. Common reflection surface stack is a macro velocity model independent method that is introduced for seismic imaging in complex media. However, this method has some drawbacks in imaging of low-quality data from complex structures. Many improvements to this method have been introduced in several researches to overcome this drawback. However, the problem of conflicting dips situation is still a problematic issue in this method. In this study, a new method, called finite offset common diffraction surface (FO-CDS) stack, is introduced to overcome this problem and remove some geological interpretation ambiguities in seismic sections. This method is based on improving the CDS stack operator, with the idea of partial common reflection surface stack. This modification will enhance the quality of the final seismic image, where it suffers from conflicting dips problem and low signal to noise ratio. The new idea is to change the operator of the CDS equation into a finite offset mode in different steps for each sample. Subsequently, a time-variant linear function is designed for each sample to define the offset range using FO-CDS operator. The width of this function is designed according to the Fresnel zone. The new operator was applied on a synthetic and a real low fold land data. Results show the ability of the new method in enhancing the quality of the stacked section in the presence of faults and conflicting dips.