Aligned Vertical Factures, HTI Symmetry, and Thomsen Parameters

The Sayers and Kachanov (1991) crack-influence parameters are shown to be directly related to Thomsen (1986) weak-anisotropy parameters for fractured reservoirs when the fracture density is small enough. These results are then applied to seismic wave propagation in reservoirs having HTI symmetry due to aligned vertical fractures. The approach suggests a method of inverting for fracture density from wave speed data.