Advances in Fracture Characterization Accuracy Using the EarthStudy 360 VVAZ/AVAZ Workflow
The azimuthal analysis of seismic data is becoming increasingly important due to the growing interest in unconventional plays, especially in the analysis of vertical fractures/differential stress. The breakthrough EarthStudy 360™ technology is used to generate and visualize full-angle, full-azimuth gathers to enable a richer, more accurate view and analysis of the fracture and stress information sampled by the seismic method. This approach yields high-resolution fracture density and orientation maps and volumes from geologic formations that exhibit horizontal transverse anisotropy (HTI) using two independent full-azimuth inversion methods – full-azimuth residual velocity move out (RMOZ/VVAZ) and full-azimuth amplitude verses angle (AVAZ).
In Azimuthally-Dependent Kinematic Variation Analysis (VVAZ), we extract the global effective parameters from the azimuthal moveout for the bottom and top horizons of the orthorhombic layer. The eight effective parameters needed for the inversion are extracted by fitting the picked azimuthally-dependent moveout curve to an analytically calculated curve. It is possible to calculate local effective parameters within a single layer and continue to a fracture/stress characterization workflow, or invert for interval parameters and proceed to orthorhombic imaging.
In the presence of vertical fractures, the reflection amplitude is maximum recoded along the fracture azimuth and minimum perpendicular to the fracture plane, thus giving rise to an amplitude ellipse. AVO inversion is performed on each data point on the full azimuth gather (AVAZ).
This presentation covers the VVAZ/AVAZ workflow in Paradigm 19 for analyzing pre-stack seismic data (EarthStudy 360 Full Azimuth Reflection Gathers) that was migrated using a VTI background model.
Pramod Kumar is a geophysicist and Senior Technology Specialist – Customer Support. His main interests are seismic data processing and imaging, shallow velocity model building using diving wave tomography, geologically consistent velocity depth model building from seismic and borehole data, estimation of anisotropic parameters to create VTI/TTI velocity models, full-azimuth tomography, full-azimuth imaging, and fracture characterization using VVAZ and AVAZ attributes. Pramod holds a Master of Technology (M.Tech.) degree in Applied Geophysics from the Indian Institute of Technology Roorkee, in Roorkee, India. He has co-authored papers on depth-velocity modeling and fracture characterization.