Full broadband processing including total Q compensation in the presence of gas

Abstract

Summary Recent efforts in marine broadband processing have largely been focused on source and receiver deghosting. To fully recover the frequency bandwidth of seismic data, the anelastic nature of the earth needs to be taken into account. In addition, in the presence of gas anomalies, attenuation of seismic waves will cause further degradation in the resolution of migrated images. By quantifying the attenuation of seismic energy using quality factor Q, we can model the intrinsic absorptive nature of the earth as background Q and the localized absorptive bodies, e.g. gas pockets, as anomalous Q. Using the frequency information and the amplitude information of the data to estimate the background Q (FS-QTomo) and anomalous Q (A-QTomo), respectively, the attenuation effects of the earth can be compensated by the application of Q-PSDM in the presence of gas with the resultant combined Q model. The accuracy of these processes is further enhanced by broadband processing with deghosting in terms of better estimation of the centroid frequency for FS-QTomo and deeper penetration of low frequency signal through the gas bodies for A-QTomo. Thus, the interplay of deghosting and Q tomography provides a full broadband processing workflow for restoring the distortion of amplitude, frequency and phase caused by the combined effects of the earth’s anelasticity and gas pockets. We applied our workflow on a field data example and demonstrated through this first case study that high resolution broadband seismic data with improved signal to noise ratio (S/N) can be obtained.