Gather Conditioning for Inversion
The graph at right compares VP to VS sonic data for a huge number of worldwide rock samples. WIT's Dr. Joe Higginbotham realized that a hyperbola fit the data better than the straight line (Castagna's "mudrock line"). WIT's hyperbolic mudrock line (patent application filed) is described by only one parameter, which is a function of AVA slope over intercept. Thus, we can obtain a VS trend directly from the seismic amplitudes. We condition gathers (PSTM or PSDM gathers) as follows: 1) compute a VS curve from the unconditioned slope/intercept volumes; 2) Compute a survey-wide slope scaling parameter that brings the computed VS curve in line with empirical data; 3) calibrate the gathers accordingly. In addition to delivering conditioned gathers, we deliver background VS and density volumes for inversion.
Azimuthal Anisotropy ("Fracture") Analysis
Here we show a typical fracture map produced by WIT Angle. The "hot" colors like yellow and pink illustrate fractured zones, while the green arrows indicate implied fracture orientation. Faults and well spots are shown. The fracture orientation agreed with FMI information in one well.
Experience tells us that we can detect variations in azimuthal anisotropy of 0.5% or greater with wide azimuth P-wave data. In most cases, the magnitude azimuthal anisotropy varies from 0 to 1.5%, but we have seen isolated zones with 3%.
WIT Angle attributes (AVA and fractures) are offered at a reasonable incremental price beyond a typical WIT Depth project.
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