Sensitivity Analysis Of Amplitude Variation With Offset (Avo) In Fractured Media

Abstract

The variation in seismic P to P reflection amplitude with offset (AVO) caused by a system of fractures embedded in an isotropic background is investigated. Additionally. a sensitivity analysis of AVO parameters with respect to the fracture system parameters is made. The fracture system is assumed to be aligned vertically or horizontally and can be gas filled or fluid filled. Elastic constants are calculated by using formulations of Schoenberg (1988). From the elastic constants, the reflection amplitude as a function of angle is calculated using equations from Ruger (1997). Theoretical results for a single interface between fractured and unfractured media, both with and without lithology change, show opportunities for extraction of crack density information from seismic P-wave data collected in fractured geothermal or hydrocarbon reservoirs. For vertically oriented fractures, wide angle data (> 30°) is crucial for the estimation of fracture parameters.