Numerical Modeling of Responses from Fluid-filled Macrofractures with Boundary Conditions Specified on Fracture Surfaces

Modeled were oriented vertical macro-fracture systems (potential fluid conduits), with fractures being the length of seismic wave and fracture thicknesses by a factor of 104–5 smaller than the wave length. The numerical 2D-modeling was performed using grid characteristic method with boundary conditions (contact conditions) accurately specified on the surface of each fracture, and with the results displayed as seismograms of vertical and horizontal components on the day surface. It was established that the principal elements of seismic response were fronts of scattered P-, S- and converted waves on Z and on X components respectively. The scattered converted wave front was noticed to be the dominant element of seismic response when the macro-fracture system is fluid-saturated, as it is much stronger on horizontal X component than the scattered P-wave front on vertical Z component. In widely-spread multi-layered sections with horizontal boundaries and fluid-saturated fractures, the identification of scattered converted wave front becomes far more advantageous as an indicator of macro-fracture system presence in productive formations. The article shows that these wave fronts are formed with sufficient robustness to realistic seismic acquisition conditions. Amplitude anomalies produced by scattered converted wave fronts on X-component seismograms can be used for detecting such fracture systems.