Detection of Fracture Orientation Using Azimuthal Variation of P-wave Avo Responses

Azimuthally-dependent P-wave AVO (amplitude variation with offset) responses can be related to open fracture orientation and have been suggested as a geophysical tool to identify fracture orientation in fractured oil and gas reservoirs. A field experiment recently conducted over a fractured reservoir in the Barinas Basin (Venezuela) provides data for an excellent test of this approach. Three lines of data were collected in three different azimuths, and three component receivers were used. The distribution of fractures in this reservoir was previously obtained using measurements of shear wave splitting from P-S converted waves from the same dataset (Ata and Michelena, 1995). In this work, we use P-wave data to see if the data can yield the same information using azimuthal variation of P-wave AVO responses. Results obtained from the azimuthal P-wave AVO analysis corroborate the results previously obtained using P-S converted waves. This analysis with field data is an example of the high potential of P-waves to detect fracture effects on seismic wave propagation. INTRODUCTION The detection of fractured zones and determining their orientation is an important part of reservoir development and enhanced oil recovery (EaR) projects. S-waves have been shown to be very effective in detecting azimuthal anisotropy and, more precisely, of fracture induced anisotropy. They are considered more reliable than P-waves for two main reasons. First, an anisotropic medium allows propagation of two quasi-shear waves with different polarizations. Measurements of travel times of these waves in a single propagation direction (vertical, for example) allow a definitive identification of