3D geometry for demultiple and noise cancellation

Abstract

The simple process of CMP stack can act as a powerful mechanism for suppression of multiples and attenuation of many types of linear shot noise (air waves, ground roll, backscatter). In any 3D acquisition geometry, each CMP bin will have a variety of traces that have different shot-receiver offsets and azimuths. These recorded traces will be processed through various algorithms such as scaling, NMO, statics corrections, and so forth prior to summing them into CMP stack traces. The act of summing or stacking will increase coherent signal content and reduce incoherent (uncorrelated) noise—noise such as linear shot noise and multiples (whether surface or interbed). The offset and azimuth distribution of the traces in a CMP bin plays a critical role in determining the effectiveness of attenuating multiples and other noise. Thus, the CMP stack of the noise component of the recorded seismic data varies from bin to bin according to the offset distribution. Different geometries lead to different attenuation characteristics. It is instructive to investigate some key factors in 3D geometries to see their effect on noise attenuation in general. These key factors are: aspect ratio (width versus length of the recording patch), ratio of shot line interval to receiver line interval, and angle of shot lines to receiver lines (slanted geometries). Synthetic linear noise and multiples can be generated to investigate the effects of these key factors. By knowing the levels of input noise, the level of output noise can be established (through CMP stacking) at various points throughout the CMP bins of a particular 3D geometry. Hence, a range of noise attenuation may be assigned to a 3D geometry. In creating different geometries for analysis, it is important that the main parameters should be the same. In other words the geometries will have: different aspect ratio, same fold, …