Inversion of AVAZ for Characterizing Fractured Reservoirs with Multiple Fracture Sets

Natural fractures in reservoirs play an important role in determining fluid flow, and knowledge of the orientation and density of fractures is required to optimize production. Variations in reflection amplitude as a function of azimuth and incidence angle are sensitive to the presence of fractures, but current models used to invert the seismic response often make simplified assumptions that prevent fractured reservoirs from being characterized correctly. For example, many models assume a single set of perfectly aligned fractures, whereas most reservoirs contain several fracture sets. In this presentation, the variation in the reflection coefficient of seismic P-waves as a function of azimuth and offset is used to determine the components of a second-rank fracture compliance tensor. The variation in the trace of this tensor as a function of position in the reservoir can be used to estimate the variation in fracture density and permeability of the fracture network, and may be used to choose the location of infill wells in the field. The use of this tensor to estimate the anisotropy of the permeability tensor, the orientation of deviated wells, and the relative orientation of neighboring infill wells to ensure adequate drainage will be discussed.