Fracture filling fluids identification using azimuthally elastic impedance based on rock physics

• We derive a new azimuthal EI equation which contains fracture weaknesses.
• We propose a method of seismic inversion for elastic parameters and fracture weaknesses.
• Fracture fluid factor can be efficiently estimated by using azimuthal EI inversion.
• Azimuthal EI inversion is more stable than AVAZ inversion because it minimizes the effect of noise.

Fracture filling fluids identification is an important aspect of fractured reservoirs description. It is well known that fracture weaknesses parameters (the normal and tangential weaknesses) are closely related to fracture parameters (fracture density, fracture aspect ratio and fracture fillings). Hence, the fracture filling fluids can be identified after the fracture weaknesses parameters being obtained. The efficient method, which is presented to estimate the fracture weaknesses parameters in this paper, is azimuthally elastic impedance (EI) inversion. We first derive a new azimuthal EI equation which contains fracture weaknesses parameters. Using the formula, we propose a method of seismic inversion for elastic parameters (P-wave and S-wave impedances) and fracture weaknesses parameters. The fluid factor, which is introduced to identify the fluids in fractures, can be estimated after the calculation of elastic and fracture weaknesses parameters. Tests on real data show that the method is more stable and reasonable by reducing the uncertainty for the estimation of elastic parameters and fracture weaknesses parameters. The inverted results are in good agreement with the results of well log data.