Orthorhombic PSTM improves results below fractured overburdens.
When vertically aligned fractures are embedded in VTI (vertical transverse isotropic) media, they cause seismic velocities and anisotropic coefficients to vary with azimuth. Velocities that vary with azimuth in addition to incident angle require an orthorhombic velocity model, which is the natural extension of VTI and HTI velocity models.
CGG has successfully developed a robust workflow that enables accurate orthorhombic velocity analysis and pre-stack time migration for imaging target areas below fractured overburdens.
It benefits AVO/AVAZ analysis for fracture characterization, stress estimation and lithology discrimination with improved gather flatness, larger reliable angles and better preservation of amplitudes.
|Isotropic velocity model||Orthorhombic velocity model|
|These PSTM stacks demonstrate the uplift orthorhombic velocity analysis (right) gives compared to isotropic velocity analysis (left), with more consistent amplitudes along coherent events.|