Quality factor extraction using instantaneous frequency at envelope peak of direct waves of VSP data

In the work, employing a function with four undetermined parameters to model the source wavelet, an analytical relation between Q-factor and envelope peak instantaneous frequency (EPIF) is derived from the theory of one-way waves propagating in an anelastic medium; at the same time, a method for extracting instantaneous frequency (IF) in wavelet domain is developed for improving the precision and anti-noise performance of IF estimation, and based on these, a method called EPIF in wavelet domain (WEPIF) is proposed for estimating Q-factor of VSP data. Test of synthetic zero-offset VSP data indicates that, comparing with logarithm spectral ratio method and centroid frequency shift method, WEPIF method is more stable and precise, and less sensitive to interface reflection waves. The Q-factors of single-shot zero-offset VSP data of 6-series from a certain gas field is estimated by WEPIF method, and the result shows that the extent of absorption corresponds well to the gas saturation of reservoirs.