Interpreting seismic anisotropy in fractured reservoirs

An upper limit to the compliance of individual fractures within a reservoir can be determined, given estimates of the effective confining pressure at reservoir depths and the mean aperture of open fractures which is usually obtained from core and well log analysis. The value can then be used with elastic wave numerical modelling to determine an upper limit to the seismic velocity anisotropy that would result from any specified reservoir discrete fracture model. This provides a level of confidence when using seismic anisotropy as an indicator of the presence of fractures that could contribute significantly to reservoir permeability. The least certain aspect of the proposed methodology is the estimate of the ratio of normal to shear fracture compliance.