Abstract: Complex shallow gas anomalies will severely complicate and distort wave fields and degrade seismic bandwidth, which destroys the imaging of subsurface layers and causes the diapir fuzzy area. The quality factor Q is the attenuation attribute of rocks during the travel of seismic waves, and Q pre-stack depth migration is an imaging technique considering absorption and attenuation of seismic waves, which is proved to be an effective method to improve the image of gas clouds. Successful gas cloud imaging requires both accurate velocity model and accurate Q model, however, when the distribution of gas-bearing sand bodies and the diapir structures becomes more complex, common Q tomography often fails to provide the necessary resolution to build an accurate Q model. In this paper, we propose a method, by which a high accuracy absorption model can be obtained through the ray-based Q tomographic inversion guided by the highly detailed velocity information from FWI (full wave inversion). The iteration flow of velocity tomography, FWI velocity inversion, and Q tomography is called FWI guided Q model building technique. Through the application of the Q PSDM (pre-stack depth migration) imaging project in Baiyun sag, the FWI guided Q model building technique and the Q PSDM flow are proved successful and essential to improve the imaging of gas cloud areas and reduce the multiplicity of seismic exploration in the presence of complex gas clouds.

Key words: full wave inversion, Q pre-stack , depth migration, gas cloud area, diapir fuzzy area, Baiyun sag