F. Lefeuvre, P. Desegaulx, H. Tabti
Nowadays, it is common knowledge that azimuthal anisotropy in a reservoir, and more precisely fracture induced anisotropy, is detectable and measurable with geophysical techniques using shear-waves (S waves).
We discuss through two new techniques how it might be possible to use P waves associated with S waves for fracture-related anisotropy detection and analysis. We show on two real data sets that P waves are sensitive to fractures using (1) a statistical approach based on seismic attributed through a learning and recognition process, and using (2) a new technique of amplitude versus offset (AVO) analysis in 3D. The latter technique is called AVO-AVAZ analysis (AVAZ stands for Amplitude Versus Azimuth). The P waves need to be calibrated with S waves to really identify fractures but we show on two real data applications their high potential to detect fracture effects and especially their high potential to extend local 1D or 2D S wave information to a larger 3D scale.
The resemblance of P wave seismic attribute prediction with the S wave prediction and the results of the AVO-AVAZ technique allow us to say confidently : (1) P waves are influenced by fractures, as expected, and (2) P waves can detect fracture effects. This should have a significant impact on the design of future seismic acquisition but we also suggest that most existing 3D P wave data should be analyzed and re-interpreted if anisotropy cannot be neglected.
AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France