Scattering characteristics in heterogeneously fractured reservoirs from waveform estimation

Offset-dependent characteristics of seismic scattering are useful for chara cterizing fractured reservoirs. We use two models that have different backg round medium properties and different azimuthal AVO responses to study elas tic wave propagation and scattering in gas-saturated, heterogeneously fract ured reservoirs. Heterogeneous fracture density distributions are built thr ough stochastic modelling. Synthetic seismograms are generated by 3-D finit e difference modelling, and waveforms along crack-normal and strike directi ons are considered in this paper. The multiple signal classification (MUSIC ) frequency estimator is used in waveform estimation to provide frequency-d omain attributes related to seismic wave scattering by fracture heterogenei ty. Our results indicate that the strength of the scattering held is a func tion of the background medium. The strength also increases with increasing fracture scatterer density and with decreasing correlation length of spatia l variations of fracture density. The scattering field is weak at the top o f the fractured reservoir. The first-order results are dominated by velocit y anisotropy of the mean fracture density field. However, the base of the f ractured reservoir corresponds to a strong scattering held on which fractur e heterogeneity has a larger effect and is characterized by the loss of coh erence.