Azimuthal Velocity Analysis (AZIM) and OVT PreSTM
Unless properly accounted for in seismic imaging, the effects of anisotropy can significantly degrade the seismic image. One form of anisotropy that is common in nearly all 3D WAZ data from land and hard rock marine basins is horizontal transverse isotropy (HTI). ION's approach to addressing HTI in wide azimuth seismic data is built on two foundational technologies: non-sectored azimuthal velocity analysis (AZIM) and offset vector tiling (OVT).
Azimuthal Velocity Analysis (AZIM)
The most commonly considered mechanism for HTI anisotropy is vertical aligned fractures embedded in an isotropic background medium. This type of anisotropy causes azimuthal travel time variations which can become apparent at near-to-mid offsets. Our AZIM technology was developed to account for these directional velocity variations. AZIM leverages an azimuthally-varying normal move out (NMO) function to improve the stacked image and provide a robust foundation for geologic interpretation of anisotropy. The result may be used to detect reservoir fracture patterns and to improve quantitative AVO.
Offset Vector Tiling (OVT) PreSTM
Similarly, geologic dip has an azimuthally-varying time shift signature in wide azimuth 3D seismic data as HTI. In order to obtain an accurate seismic image in areas with appreciable geologic dip (e.g. > 10 degrees), the dip effects must be decoupled from the HTI effects. Unlike conventional offset pre-stack time migration (PreSTM), offset vector tile (OVT) PreSTM preserves azimuth and offset information through migration, allowing post-migration azimuthal velocity analysis without the need for prior azimuthal sectoring of the data.
Benefits from Integrated AZIM and OVT PreSTM Imaging
- More accurate mapping of subsurface features
- More accurate identification of fault patterns
- Refined ability to optimize well locations
The combination of OVT PreSTM and AZIM results in more robust HTI analysis and azimuthal velocity anisotropy attributes, as well as a significant improvement in the seismic image from the incorporation of HTI into the PreSTM velocity field as can be seen in figures a and b below.
(mouse over image for figure b)