Physical Modeling Supports Testing of Seismic Techniques for Porous–fractured Reservoir Characterization

The possibility of detecting azimuthally aligned fractures and estimating fracture density, orientation and saturation type is investigated by measuring ultrasonic offset-and-azimuth-dependent reflection and transmission amplitudes of elastic waves in a large (160x160x30cm) physical model. The model is represented by three layers of Plexiglas, with the middle layer consisting of four or five replaceable fragments of “reservoir rock” with controlled matrix (“equant”) porosity penetrated by plane, rough face, azimuthally aligned fractures of controlled density and opening. The pores and fractures are hydraulically connected and filled with a replaceable fluid; then controlled uniaxial stress is applied. On the whole, the model imitates the East Siberia carbonate fractured reservoir. The 2D observations with diverse acquisition parameters imitated at the model surface have shown that (a) the most reliable information on the fracture localization and parameters is provided by converted P-S waves; (b) fracture-induced azimuthal anisotropy of P-P waves attenuation exceeds azimuthal anisotropy of the P-P velocity by an order of magnitude; (c) fracture orientation can be defined quite reliably at fracture density > 0.01; (d) the observed dependence of seismic wave field parameters on fracture face roughness and fracture density and orientation is consistent with effective model predictions.