Constraining the interpretation of AVOA for fracture characterisation

This paper investigates the use of seismic anisotropy and amplitude variation with offset and azimuth (AVOA) for fracture characterisation. Specifically the aim of this work is to provide links between rock and fracture properties, elastic modelling and the interpretation of seismic signatures to reduce the potential ambiguity when interpreting AVOA data. Analytical expressions and numerical modelling are used to highlight the sensitivity of AVOA to fracture properties. Furthermore, little prior attention has been paid to wave propagation in media with multiple fracture alignments or fractured media with a permeable matrix therefore an investigation of AVOA for these cases is included. P-wave AVOA is of obvious interest since there are more of these data. However converted wave and shear-wave AVOA are also investigated as these may provide additional insight into fracture characteristics. It is shown that P-P and P-S AVOA hold significant information about fracturing but potential ambiguity in the interpretation of these data is observed that could lead to incorrect determination of fracture orientation. This highlights the need for forward modelling with rock properties data to constrain the interpretation. Additionally, shear-wave (S-S) AVOA is shown to exhibit significant azimuthal variations which provide strong indications of fracture orientation but only at near offsets and little insight can be gained into other fracture properties.